JP4138199B2 - Image information reading method and apparatus - Google Patents

Description

但し、ｋ＝１〜Ｎ（Ｎは主走査方向の画素数（画素位置又は画素番号））
ｌ＝１〜Ｍ（Ｍは副走査方向の画素数（画素位置又は画素番号））
同様にしき（１）の演算を副走査方向にも行なうことにより、画素密度変換がなされた画像信号Ｓ１′が得られる。
【００９７】
一方、このような１次元フィルタを用いたマスク演算においては、デジタル画像信号Ｓ１の縁部分においては、マスク演算を行うためのデータが不足する。したがってそのような縁部分の画素に対してフィルタリング処理を施す場合は、その画素の外側に、仮想的な画素位置を定め、この仮想的な画素位置の画素にそれぞれ適切な画素値を与えたうえでフィルタリング処理を行えばよい。
【００９８】
なお、画素密度変換手段３７ａにおける画素密度変換は、上記１次元フィルタを用いたマスク演算に限定されるものではなく、画素を間引く処理や補間演算により画素密度変換を行ってもよい。ここで補間演算としては、線形補間の他、滑らかさを重視したＢスプライン補間演算、鮮鋭度を重視したCubic スプライン補間演算等の高次の補間演算を適用することもできる。
【００９９】
そして、このように画素密度変換手段３７ａにおいて得られた画像信号Ｓ１′は、「低密度」が選択された場合には「高密度」が選択された場合と比較して１／１６の画素密度の信号となり、画像処理装置等に出力される。
【０１００】
このように本実施形態の画像情報読取装置によれば、レーザー光の主走査速度を変えることなく、高密度読取りの場合に比して、レーザー光Ｌの主走査方向について１／２、副走査方向について１／２の画素数である１／４の画素密度の低密度画像信号を得、さらにこの画像信号に対して主走査方向について１／２、副走査方向について１／２の画素数となるように画素密度変換処理を施すことで、全体として１／１６の画素密度の低密度画像信号を得ることができる。しかも、特性変更手段６０が、画素密度を規定するパラメータに応じて、走査レンズ２１の位置、電圧印加手段３９ａへの制御信号、Ｄ／Ａ変換器４２ａのサンプリングクロック、対数増幅器１６ａの周波数特性、アンチエリアジングフィルター３５ａおよび画素密度変換手段３７ａのパラメータをそれぞれ変更するため、読取り画素密度に適した、画素当たりのエネルギー付与、光電検出感度の設定、シェーディング補正、エリアジングノイズの抑制等が施された画像信号を得ることができる。
【０１０１】
なお、本実施形態の画像情報読取装置においては、高密度読取りが初期設定として設定されているものとしたが、本発明の画像情報読取方法および装置は、この態様に限られるものではなく、初期設定として「標準密度読取り」が設定されており、「高密度読取り」、「低密度読取り」にそれぞれ選択的に切り換えられるものとしてもよい。
【０１０２】
例えば、主走査周波数（主走査速度）を１６０Ｈｚ、画素密度１０pix ／ｍｍを標準密度読取りとしたときの、主走査サンプリング間隔、副走査画素ピッチ、副走査速度、アンチエリアジングフィルターカットオフ周波数を以下に示す。
【０１０３】
主走査サンプリング間隔：１００μｍ 副走査画素ピッチ：１００μｍ
主走査サンプリング周期：１．０μsec 副走査速度：１６ｍｍ／sec
アンチエリアジングフィルターカットオフ周波数：５００ｋＨｚ
（アナログフィルタのため、５００ｋＨｚ以下、例えば４００ｋＨｚなどを適用するのが望ましい。）
これに対して、画素密度２０pix ／ｍｍである高密度読取りのときは、主走査周波数を１６０Ｈｚ不変として、
主走査サンプリング間隔：５０μｍ 副走査画素ピッチ：５０μｍ
主走査サンプリング周期：０．５μsec 副走査速度：８ｍｍ／sec
アンチエリアジングフィルターカットオフ周波数：１０００ｋＨｚ
となり、一方、画素密度５pix ／ｍｍである低密度読取りのときは、主走査周波数を１６０Ｈｚ不変として、
主走査サンプリング間隔：２００μｍ 副走査画素ピッチ：２００μｍ
主走査サンプリング周期：２．０μsec 副走査速度：３２ｍｍ／sec
アンチエリアジングフィルターカットオフ周波数：２５０ｋＨｚ
となる。
【０１０４】
なお、上述したような「高密度読取り」、「低密度読取り」等、の読取り密度が段階的に予め設定されたものに限らず、読取り密度を規定するパラメータ（ｍ，ｎ）を任意に選択できるものとしてもよい。
【０１０５】
また特性変更手段６０による、メモリ４１ａに記憶されているシェーディング補正用データの変更方法の詳細について、図４を参照して説明する。
【０１０６】
図４に示すように、メモリ４１ａが、選択されうるｍ，ｎに応じたシェーディング補正データＤ１がこれらのｍ，ｎに対応付けられてそれぞれ記憶されている大容量のハードディスク４１ｃと、ハードディスク４１ｃから読み出されたシェーディング補正データをシェーディング補正を行なうシェーディング回路（ＳＨＤ回路）に受け渡すための一時的メモリであるシェーディングメモリ（ＳＨＤメモリ）４１ｄとから構成されており、特性変更手段６０は、これら２つのメモリ（ハードディスク４１ｃおよびＳＨＤメモリ４１ｄ）に対してメモリ制御を行なうものとすればよい。ここでメモリ制御としては例えば、ｍ，ｎの値ごとに予め設定されたシェーディング補正データをハードディスク４１ｃに予め記憶させておき、選択されたｍ，ｎの値に対応するシェーディング補正データを、選択の都度、ハードディスク４１ｃからＳＨＤメモリ４１ｄに転送し、この転送されたシェーディング補正データをＳＨＤメモリ４１ｄから読み出してＳＨＤ回路に送るようにする方法や、ｍ，ｎの値ごとに予め設定されたシェーディング補正データをハードディスク４１ｃに予め記憶させておき、起動時など所望とするときに、これらのシェーディング補正データの全てを、ハードディスク４１ｃから、ｍ，ｎの値ごとに互いに異なるアドレスに対応した記憶領域を有するＳＨＤメモリ４１ｄにｍ，ｎの値に対応させて転送し、選択されたｍ，ｎの値に対応するシェーディング補正データを、選択されたｍ，ｎの値に対応するＳＨＤメモリのアドレスから読み出してＳＨＤ回路に送るようにする方法などを適用することができる。
【０１０７】
ここでシェーディング補正の都度、特定のシェーディング補正データのみをＳＨＤメモリ４１ｄに転送する方法によれば、ＳＨＤメモリ４１ｄの容量を少なくすることができ、ハードウェア構成を簡単にすることができる。一方、全てのシェーディング補正データをハードディスク４１ｃからＳＨＤメモリ４１ｄに読み込む方法によれば、ソフトウェア構成を簡単にすることができ、ＳＨＤメモリ４１ｄからの補正データの読出し速度を高速化することができる。
【０１０８】
図５は本発明の第２の画像情報読取装置の一実施形態を示す図である。図５に示すように、本実施形態の画像情報読取装置は、被写体の放射線画像が蓄積記録された蓄積性蛍光体シートの両面から放射線画像を表す画像信号を得るものである。蓄積性蛍光体シート１が、モータ８により回転せしめられるエンドレスベルト９ａ，９ｂ上に配置される。このシート１の上方には、励起光としてのレーザ光１１を発するレーザ光源１０と、レーザ光１１を反射偏向してシート１を主走査する、モータ２０により回転される回転多面鏡１２と、レーザ光１１をシート１に結像するための走査レンズ２１とが配されている。さらに、レーザ光１１が走査される位置の上方には、そのレーザ光１１の走査により発せられる輝尽発光光を上方より集光する集光ガイド１４ａがシート１に近接して配置され、その位置の下方には、輝尽発光光を下方より集光する集光ガイド１４ｂがシート１と略垂直に配置されている。各集光ガイド１４ａ，１４ｂは、それぞれ輝尽発光光を光電的に検出するＰＭＴ１５ａ，１５ｂが接続されている。このＰＭＴ１５ａ，１５ｂは対数増幅器１６ａ，１６ｂに接続されており、ＰＭＴ１５ａ，１５ｂにより検出されたアナログ画像信号ＱＡ，ＱＢを予め設定されている周波数特性にしたがって対数的に増幅し、対数化画像信号ＱＡ′，ＱＢ′を出力する。
【０１０９】
一方、メモリ４１ａ，４１ｂには、予め設定されているサンプリング間隔に応じたシェーディング補正用データＤ１，Ｄ２が記憶されており、メモリ４１ａ，４１ｂにはこの補正用データＤ１，Ｄ２を予め設定されている基準クロックでアナログ信号Ｄ１′，Ｄ２′に変換するＤ／Ａ変換器４２ａ，４２ｂが接続されており、Ｄ／Ａ変換器４２ａ，４２ｂには、対数増幅器１６ａ，１６ｂから出力された対数化画像信号ＱＡ′，ＱＢ′にこの補正用アナログ信号Ｄ１′、Ｄ２′を加算して、シェーディング補正が施された画像信号Ｑ１，Ｑ２を出力する加算器４３ａ，４３ｂが接続されている。
【０１１０】
さらに加算器４３ａ，４３ｂには、後述するＡ／Ｄ変換によるエリアジングノイズ（折り返しノイズ）を除去するアンチエリアジングフィルタ３５ａ，３５ｂが接続されており、その後段には、このフィルタリングされた後の画像信号Ｑ１′，Ｑ２′を予め設定されている基準クロックでデジタル画像信号Ｓ１，Ｓ２に変換するＡ／Ｄ変換器３６ａ，３６ｂが設けられている。なお、アンチエリアジングフィルタ３５ａ，３５ｂは高密度用フィルタと低密度用フィルタとからなり、初期的には高密度用フィルタが選択されているが、後述する特性変更手段６０からの入力信号に応じて低密度用フィルタにも切り換えられるものである。
【０１１１】
さらにまた、Ａ／Ｄ変換器３６ａ，３６ｂには、デジタル画像信号Ｓ１，Ｓ２の画素密度を変換して、画像信号Ｓ１′，Ｓ２′を得る画素密度変換手段３７ａ，３７ｂが接続されている。そして、画素密度変換された画像信号Ｓ１′，Ｓ２′は加算手段３８において加算されて加算画像信号Ｓ３が得られる。
【０１１２】
また、本実施形態の画像情報読取装置は、図６に示すように、画像情報の読取り画素密度として、予め初期的に設定されている「高密度」（10pix／mm）と、この高密度よりも低密度である「低密度」（５pix／mm）とのうち、オペレーターが選択した密度の入力を受け、「高密度」のときはパラメータ（ｍ，ｎ）をｍ＝ｎ＝１とし、「低密度」のときはパラメータ（ｍ，ｎ）をｍ＝ｎ＝２として出力する入力手段７０と、この入力手段７０から出力されたパラメータ（ｍ，ｎ）が入力されて、これらのパラメータ（ｍ，ｎ）に応じて、エンドレスベルト９ａ，９ｂを駆動するモータ６１の回転速度を変更し、レーザ光源１０の出力を変更してレーザ光１１のパワーを変更し、走査レンズ２１を光軸方向に移動させてシート１を走査するレーザ光１１のビーム径を変更し、電圧印加手段３９ａ，３９ｂを制御してＰＭＴ１５ａ，１５ｂの感度を変更し、Ｄ／Ａ変換器４２ａ，４２ｂのサンプリングクロックを変更してメモリ４１ａ，４１ｂに記憶されているシェーディング補正用データＤ１，Ｄ２を変更して出力させ、Ｄ／Ａ変換器４２ａ，４２ｂがシェーディング補正用データをメモリ４１ａ，４１ｂから読み出すタイミングを変更し、Ａ／Ｄ変換器３６ａ，３６ｂのサンプリングクロックを変更し、対数増幅器１６ａ，１６ｂの周波数特性を変更し、アンチエリアジングフィルタ３５ａ，３５ｂの高密度用と低密度用とを切り換え、画素密度変換手段３７ａ，３７ｂにおいて画素密度変換を行う際のパラメータを変更する特性変更手段６０とを備えている。
【０１１３】
ここで、画素密度変換手段３７ａ，３７ｂにおいては、パラメータ（ｍ，ｎ）に応じて、デジタル画像信号Ｓ１，Ｓ２の主走査方向について１／ｍ倍、副走査方向について１／ｎ倍とする画素密度変換処理を行って、ｍ＝ｎ＝１の場合よりも、１／（ｍ×ｎ）^２ 倍の画素密度を有する画像信号Ｓ１′，Ｓ２′を得るものである。具体的には、デジタル画像信号Ｓ１，Ｓ２の主副両走査方向に対して１次元マスク演算を施すことによる方法、画素密度に応じて画素を間引く方法、Ｂスプライン補間演算、Cubic スプライン補間演算等の高次の補間演算による方法、線形補間演算による方法等により画素密度変換が行われる。また、この際、パラメータ（ｍ，ｎ）に応じて画素密度変換のパラメータが変更される。例えば１次元マスク演算を行う場合にはマスク係数が、間引き処理を行う場合には間引きの間隔が、補間演算を行う場合にはデジタル画像信号Ｓ１，Ｓ２に施す補間演算の種類が変更される。
【０１１４】
なお、加算手段３８においては、上記特開平7-287330号に記載されたように、加算画像信号Ｓ３のＳ／Ｎを高くするような周波数応答特性を有するフィルタによるフィルタリング処理を画像信号Ｓ１′，Ｓ２′に対して施した後に、加算画像信号Ｓ３を得る方法を採用することが好ましいが、単純に画像信号Ｓ１′，Ｓ２′を加算するものであってもよい。なお、フィルタリング処理を行う場合には、画素密度変換手段３７ａ，３７ｂにおいて行うようにしてもよい。
【０１１５】
次に本実施形態の放射線画像情報読取装置の作用について説明する。
【０１１６】
まず、オペレーターにより選択された「高密度」を表す信号が入力手段７０に入力される。「高密度」はこの画像情報読取装置の初期的設定であり、「高密度」に対応するパラメータ（ｍ，ｎ）＝（１，１）が入力手段７０から出力されて特性変更手段６０に入力される。
【０１１７】
特性変更手段６０は、入力されたパラメータ（ｍ，ｎ）＝（１，１）により、エンドレスベルト９ａ，９ｂを駆動するモータ８の回転速度、レーザ光源１０の出力、走査レンズ２１の位置、電圧印加手段３９ａ，３９ｂへの制御信号、Ｄ／Ａ変換器４２ａ，４２ｂのサンプリングクロック、Ｄ／Ａ変換器４２ａ，４２ｂがシェーディング補正用データＤ１，Ｄ２をメモリ４１ａ，４１ｂから読み出すタイミング、Ａ／Ｄ変換器３６ａ，３６ｂのサンプリングクロック、対数増幅器１６ａ，１６ｂの周波数特性、アンチエリアジングフィルタ３５ａ，３５ｂ、および画素密度変換手段３７ａ，３７ｂを、それぞれ初期設定（高密度用）のものとなるようにセットする。
【０１１８】
被写体の放射線画像が蓄積記録された蓄積性蛍光体シート１がエンドレスベルト９ａ，９ｂに配置されると、エンドレスベルト９ａ，９ｂにより矢印Ｙ方向に搬送（副走査）される。一方、レーザ光源１０から発せられたレーザ光１１はモータ２０により駆動され矢印方向に高速回転する回転多面鏡１２によって反射偏向され、走査レンズ２１を通ってシート１に入射し副走査の方向（矢印Ｙ方向）と略垂直な矢印Ｘ方向に主走査する。このレーザ光１１が照射されたシート１の箇所からは、蓄積記録されている放射線画像情報に応じた光量の輝尽発光光１３ａ，１３ｂ（ここで、輝尽発光光１３ａ，１３ｂはそれぞれシート１の上方（表面）、下方（裏面）から発散されたものを示す）が発散される。この輝尽発光光１３ａは集光ガイド１４ａによって導かれ、ＰＭＴ１５ａによって光電的に検出される。入射端面１８ａから集光ガイド１４ａ内に入射した輝尽発光光１３ａは、集光ガイド１４ａの内部を全反射を繰り返して進み、出射端面から出射してＰＭＴ１５ａに受光され、放射線画像を表す輝尽発光光１３ａの光量がＰＭＴ１５ａによってアナログ画像信号ＱＡに変換される。同様に、輝尽発光光１３ｂは集光ガイド１４ｂによって導かれ、ＰＭＴ１５ｂによって光電的に検出されてアナログ画像信号ＱＢに変換される。
【０１１９】
これらのアナログ画像信号ＱＡ，ＱＢは対数増幅器１６ａ，１６ｂに入力され、高密度用の周波数特性にセットされた対数増幅器34により対数化画像信号ＱＡ′，ＱＢ′に変換されて加算器４３ａ，４３ｂに入力される。
【０１２０】
一方、メモリ４１ａ，４１ｂに記憶されている高密度用のシェーディング補正用データＤ１，Ｄ２は、Ｄ／Ａ変換器４２ａ，４２ｂにより、高密度用のタイミングで読み出されるとともに、高密度用のクロックである基準クロックでのサンプリングレートでアナログ信号Ｄ１′，Ｄ２′に変換される。
【０１２１】
ここで、Ｄ／Ａ変換器４２ａ，４２ｂに入力されるクロックは、図７に示すように、特性変更手段６０に設けられたセレクター６２により切り換えられて出力される基準クロックである。
【０１２２】
シェーディング補正用のアナログ信号Ｄ１′，Ｄ２′は加算器４３ａ，４３ｂに入力され、対数増幅器１６ａ，１６ｂから入力された対数化画像信号ＱＡ′，ＱＢ′に加算され、これにより対数化画像信号ＱＡ′，ＱＢ′はシェーディング補正がなされた画像信号Ｑ１，Ｑ２に変換されてアンチエリアジングフィルタ３５ａ，３５ｂに入力される。
【０１２３】
アンチエリアジングフィルタ３５ａ，３５ｂは、特性変更手段６０により高密度用フィルタに切り換えられており、入力された画像信号Ｑ１，Ｑ２はこの高密度用フィルタによりエリアジングノイズが適切に除去されてＡ／Ｄ変換器３６ａ，３６ｂに入力される。
【０１２４】
Ａ／Ｄ変換器３６ａ，３６ｂは、特性変更手段６０のセレクター６２により切り換えられた基準クロックによるサンプリングレートで、入力された画像信号Ｑ１′，Ｑ２′をそれぞれデジタル画像信号Ｓ１，Ｓ２に変換する。
【０１２５】
画素密度変換手段３７ａ，３７ｂは、デジタル画像信号Ｓ１，Ｓ２の主走査方向について１／ｍ倍、副走査方向について１／ｎ倍とする画素密度変換を行うものであるが、ここではｍ＝ｎ＝１であるため、何ら画素密度変換処理を施すことなく、画像信号Ｓ１′，Ｓ２′を得る。
【０１２６】
加算手段３８は、画像信号Ｓ１′，Ｓ２′に対して、上記特開平7-287330号に記載されたような、加算画像信号Ｓ３のＳ／Ｎを高くするような周波数応答特性を有するフィルタによるフィルタリング処理を施し、このフィルタリング処理を施した画像信号Ｓ１′，Ｓ２′を相対応する画素同士で加算して加算画像信号Ｓ３を得て、画像処理装置等に出力する。
【０１２７】
次に、オペレーターにより「低密度」が選択された場合の作用について説明する。
【０１２８】
オペレーターにより「低密度」を表す信号が入力手段７０に入力されると、入力手段７０は「低密度」に対応するパラメータ（ｍ，ｎ）＝（２，２）を特性変更手段６０に出力する。
【０１２９】
特性変更手段６０は、入力されたパラメータ（ｍ，ｎ）＝（２，２）により、エンドレスベルト９ａ，９ｂを駆動するモータ８の回転速度、レーザ光源１０の出力、走査レンズ２１の位置、電圧印加手段３９ａ，３９ｂへの制御信号、Ｄ／Ａ変換器４２ａ，４２ｂのサンプリングクロック、Ｄ／Ａ変換器４２ａ，４２ｂがシェーディング補正用データＤ１，Ｄ２をメモリ４１ａ，４１ｂから読み出すタイミング、Ａ／Ｄ変換器３６ａ，３６ｂのサンプリングクロック、対数増幅器１６ａ，１６ｂの周波数特性、アンチエリアジングフィルタ３５ａ，３５ｂ、および画素密度変換手段３７ａ，３７ｂを、それぞれ低密度用のものとなるようにセットする。
【０１３０】
具体的には、エンドレスベルト９ａ，９ｂを駆動するモータ８の回転速度を２倍の速度に変更し、レーザ光源１０の出力を略２倍とし、走査レンズ２１の位置をレーザ光１１のビーム径がシート１上で略２倍となる位置まで移動し、電圧印加手段３９ａ，３９ｂへの制御信号をフォトマルチプライヤ１５ａ，１５ｂの感度を下げるような信号とし、Ｄ／Ａ変換器４２ａ，４２ｂがシェーディング補正用データＤ１，Ｄ２をメモリ４１ａ，４１ｂから読み出すタイミングを変更し、セレクター６２（図７参照）を分周回路６１から出力されるクロック（基準クロックを分周して得られたクロックであって、基準クロックの２倍の周期のクロック）に切り換えて、Ｄ／Ａ変換器４２ａ，４２ｂおよびＡ／Ｄ変換器３６ａ，３６ｂに入力されるサンプリングクロックを変更し、対数増幅器１６ａ，１６ｂの周波数特性を変更し、アンチエリアジングフィルタ３５ａ，３５ｂを低密度用フィルタに切り換え、画素密度変換手段３７ａ，３７ｂのパラメータを変更する。
【０１３１】
このように各部の特性が変更されて、前述した高密度読取りの場合と同様に画像情報の読取りがなされる。
【０１３２】
すなわち、エンドレスベルト９ａ，９ｂ上の所定の位置にセットされた蓄積性蛍光体シート１は、エンドレスベルト９ａ，９ｂにより、矢印Ｙ方向に上記高密度用の速度の２倍の速度で搬送（副走査）され、一方、レーザ光源１０から発せられた高密度用の２倍のパワーのレーザ光１１は、高密度読取りのときと同一の回転速度で高速回転する回転多面鏡１２によって反射偏向され、この偏向されたレーザ光１１は走査レンズ２１により、エンドレスベルト９ａ，９ｂ上を搬送されるシート１で収束され、かつ等速度で走査されて、このシート１を矢印Ｘ方向に主走査する。このときシート１上におけるビーム径は高密度読取りのときの２倍の大きさで収束される。
【０１３３】
シート１の、レーザ光１１で走査された部分から発光した輝尽発光光１３ａ，１３ｂは、集光ガイド１４ａ，１４ｂを介してＰＭＴ１５ａ，１５ｂまで導光される。ＰＭＴ１５ａ，１５ｂは、電圧印加手段３９ａ，３９ｂにより、高密度読取り用よりも低い感度となるような電圧が印加されており、入射した輝尽発光光１３ａ，１３ｂをこの低密度用の感度で検出し、アナログ画像信号ＱＡ，ＱＢに光電変換して出力する。このアナログ画像信号ＱＡ，ＱＢは対数増幅器１６ａ，１６ｂに入力され、低密度用の周波数特性にセットされた対数増幅器１６ａ，１６ｂにより対数化画像信号ＱＡ′，ＱＢ′に変換されて加算器４３ａ，４３ｂに入力される。
【０１３４】
一方、メモリ４１ａ，４１ｂに記憶されている高密度用のシェーディング補正用データＤ１，Ｄ２は、Ｄ／Ａ変換器４２ａ，４２ｂにより、低密度用のタイミングで読み出されるとともに、低密度用のクロックである２分周のクロックでのサンプリングレートでアナログ信号Ｄ１′，Ｄ２′に変換される。すなわち、特性変更手段６０に設けられた分周回路６１が、基準クロックを２分周して基準クロックの２倍の周期のクロックを発生し、セレクター６２はこの２分周のクロックを出力するように切り換えられている。この結果、シェーディング補正用のアナログ信号Ｄ１′，Ｄ２′は高密度用のシェーディング補正用データＤ１，Ｄ２に対して、主走査方向についてその画素数が１／２とされている。
【０１３５】
シェーディング補正用のアナログ信号Ｄ１′，Ｄ２′は加算器４３ａ，４３ｂに入力され、対数増幅器１６ａ，１６ｂから入力された対数化画像信号ＱＡ′，ＱＢ′に加算され、これにより対数化画像信号ＱＡ′，ＱＢ′はシェーディング補正がなされた画像信号Ｑ１，Ｑ２に変換されてアンチエリアジングフィルタ３５ａ，３５ｂに入力される。
【０１３６】
アンチエリアジングフィルタ３５ａ，３５ｂは、特性変更手段６０により低密度用フィルタに切り換えられており、入力された画像信号Ｑ１，Ｑ２はこの低密度用フィルタによりエリアジングノイズが適切に除去されてＡ／Ｄ変換器３６ａ，３６ｂに入力される。
【０１３７】
Ａ／Ｄ変換器３６ａ，３６ｂは、特性変更手段６０のセレクター６２により切り換えられた２分周のクロックによるサンプリングレートで、入力された画像信号ＱＡ′，ＱＢ′をデジタル画像信号Ｓ１，Ｓ２に変換する。
【０１３８】
画素密度変換手段３７ａ，３７ｂは、デジタル画像信号Ｓ１，Ｓ２の主走査方向について１／ｍ倍、副走査方向について１／ｎ倍とする画素密度変換を行う。ここで、ｍ＝ｎ＝２であるため、デジタル画像信号Ｓ１，Ｓ２の主走査方向および副走査方向についてそれぞれ画素数を１／２とする画素密度変換処理を施す。この画素密度変換処理として、ここでは１次元マスク演算について説明する。この１次元マスク演算に使用する１次元フィルタの例を下記に示す。
【０１３９】
ａ（ｘ，１）＝（-8/105,-5/105,34/105,63/105,34/105,-5/105,-8/105）
そしてこのフィルタａ（ｘ，１）を用いてデジタル画像信号Ｓ１，Ｓ２の主走査方向について１画素間隔でフィルタリング処理を行った後、副走査方向について１画素間隔でフィルタリング処理を行うことにより画素密度変換が行われる。具体的には、デジタル画像信号Ｓ１（Ｓ２についても同様であるため、ここではＳ１についてのみ説明する）の画素値をＳ１（ｘ，ｙ）、主走査方向における画素密度変換後の画素値をＳ１Ａ（ｘ／２，ｙ）とすると、画素値Ｓ１Ａ（ｘ／２，ｙ）は下記の式（１）により算出される。
【０１４０】

但し、ｋ＝１〜Ｎ（Ｎは主走査方向の画素数（画素位置又は画素番号））
ｌ＝１〜Ｍ（Ｍは副走査方向の画素数（画素位置又は画素番号））
同様に式（１）の演算を副走査方向にも行うことにより、画素密度変換がなされた画像信号Ｓ１′，Ｓ２′が得られる。
【０１４１】
一方、このような１次元フィルタを用いたマスク演算においては、デジタル画像信号Ｓ１，Ｓ２の縁部分においては、マスク演算を行うためのデータが不足する。例えば、図８に示す画像信号において、Ｓ１（１，１）およびＳ１（Ｎ，１）（斜線部）の画素に対してフィルタリング処理を施す場合は、３画素分のデータが不足する。この場合、仮想的な画素位置Ｓ１（−１，１），Ｓ１（−２，１），Ｓ１（−３，１）およびＳ１（Ｎ＋１，１），Ｓ１（Ｎ＋２，１），Ｓ１（Ｎ＋３，１）を定め、この仮想的な画素位置に画素位置Ｓ１（１，１）およびＳ１（Ｎ，１）のデータ値をコピーして、仮想的な画素位置においてデータ値が存在するものとしてフィルタリング処理を行えばよい。
【０１４２】
なお、画素密度変換手段３７ａ，３７ｂにおける画素密度変換は、上記１次元フィルタを用いたマスク演算に限定されるものではなく、画素を間引く処理や補間演算により画素密度変換を行ってもよい。
【０１４３】
ここで補間演算としては、線形補間の他、滑らかさを重視したＢスプライン補間演算、鮮鋭度を重視したCubic スプライン補間演算等の高次の補間演算を適用することができる。
【０１４４】
ここで、Cubic スプライン補間演算およびＢスプライン補間演算について説明する。本実施形態において使用される画像信号Ｓ１，Ｓ２は、等間隔の周期でサンプリングされた一方向に配列されたサンプリング点（画素）Ｘ_k-2 ，Ｘ_k-1 ，Ｘ_k ，Ｘ_k+1 ，Ｘ_k+2 ，…にそれぞれ対応した信号値（Ｓ_k-2 ，Ｓ_k-1 ，Ｓ_k ，Ｓ_k+1 ，Ｓ_k+2 ，…）を有するものする。Cubic スプライン補間演算は、オリジナルのサンプリング点（画素）Ｘ_k 〜Ｘ_k+1 間に設けられた補間点Ｘ_p の補間データＹ′を表す３次のCubic スプライン補間演算式（２）における補間データＹ_k-1 ，Ｙ_k ，Ｙ_k+1 ，Ｙ_k+2 にそれぞれ対応する補間係数ｃ_k-1 ，ｃ_k ，ｃ_k+1 ，ｃ_k+2 を、下記にそれぞれ示す演算により求めるものである。
【０１４５】
Ｙ′＝ｃ_k-1 Ｙ_k-1 ＋ｃ_k Ｙ_k ＋ｃ_k+1 Ｙ_k+1 ＋ｃ_k+2 Ｙ_k+2 （２）
ｃ_k-1 ＝（−ｔ³ ＋２ｔ² −ｔ）／２
ｃ_k ＝（３ｔ³ −５ｔ² ＋２）／２
ｃ_k+1 ＝（−３ｔ³ ＋４ｔ² ＋ｔ）／２
ｃ_k+2 ＝（ｔ³ −ｔ² ）／２
（但し、ｔ（０≦ｔ≦１）は格子間隔を１とし、画素Ｘ_k を基準としたときの補間点Ｘ_p の画素Ｘ_k+1 方向への位置を示す。）
Ｂスプライン補間演算は、オリジナルのサンプリング点Ｘ_k 〜Ｘ_k+1 間に設けられた補間点Ｘ_p の補間データＹ′を表す３次のＢスプライン補間演算式（３）における補間データＹ_k-1 ，Ｙ_k ，Ｙ_k+1 ，Ｙ_k+2 にそれぞれ対応する補間係数ｂ_k-1 ，ｂ_k ，ｂ_k+1 ，ｂ_k+2 を、下記にそれぞれ示す演算により求めるものである。
【０１４６】
Ｙ′＝ｂ_k-1 Ｙ_k-1 ＋ｂ_k Ｙ_k ＋ｂ_k+1 Ｙ_k+1 ＋ｂ_k+2 Ｙ_k+2 （３）
ｂ_k-1 ＝（−ｔ³ ＋３ｔ² −３ｔ＋１）／６
ｂ_k ＝（３ｔ³ −６ｔ² ＋４）／６
ｂ_k+1 ＝（−３ｔ³ ＋３ｔ² ＋３ｔ＋１）／６
ｂ_k+2 ＝ｔ³ ／６
（但し、ｔ（０≦ｔ≦１）は格子間隔を１とし、画素Ｘ_k を基準としたときの補間点Ｘ_p の画素Ｘ_k+1 方向への位置を示す。）
本実施形態においては、ｍ，ｎの値に応じて線形補間演算も含めて、補間演算の種類を選択すればよい。
【０１４７】
そして、このように画素密度変換手段３７ａ，３７ｂにおいて得られた画像信号Ｓ１′，Ｓ２′は加算手段３８に入力される。ここで、「低密度」が選択された場合には「高密度」が選択された場合と比較して、画素密度は１／１６となる。
【０１４８】
加算手段３８は、画像信号Ｓ１′，Ｓ２′に対して、上記特開平7-287330号に記載されたような、加算画像信号Ｓ３のＳ／Ｎを高くするような周波数応答特性を有するフィルタによるフィルタリング処理を施し、このフィルタリング処理を施した画像信号Ｓ１′，Ｓ２′を相対応する画素同士で加算して加算画像信号Ｓ３を得て、画像処理装置等に出力する。
【０１４９】
このように本実施形態の画像情報読取装置によれば、レーザ光１１の主走査速度を変えることなく、高密度読取りの場合に比して、レーザ光１１の主走査方向について１／２、副走査方向について１／２の画素数である、１／４の画素密度の画像信号を得、さらにこの画像信号に対して主走査方向について１／２、副走査方向について１／２の画素数となるように画素密度変換処理を施して、１／１６の画素密度の低密度画像信号を得ることができる。しかも、特性変更手段６０が、画素密度を規定するパラメータに応じて、走査レンズ２１の位置、電圧印加手段３９ａ，３９ｂへの制御信号、Ｄ／Ａ変換器４２ａ，４２ｂのサンプリングクロック、対数増幅器１６ａ，１６ｂの周波数特性、アンチエリアジングフィルタ３５ａ，３５ｂ、および画素密度変換手段３７ａ，３７ｂのパラメータをそれぞれ変更するため、読取り画素密度に適した、画素当たりのエネルギー付与、光電検出感度の設定、シェーディング補正、エリアジングノイズの抑制等が施された画像信号を得ることができる。
【０１５０】
とくに、本実施形態のように両面読取りを行う場合には、レーザ光１１によるエネルギーをシート１の裏面側まで十分に付与するために、片面側からのみ読取る方式に比して走査速度を遅くする必要があるが、その場合においても画素密度を粗くすることが許容されるときは副走査速度を速めることができ、これにより１つのシート当たりの走査時間を短縮することができる。
【０１５１】
また、２つのデジタル画像信号Ｓ１，Ｓ２に対して画素密度変換処理を施すことにより、加算画像信号に対して画素密度変換を施す場合と比較して、加算画像信号を得る際の加算マスク処理を行うための演算量を低減することができ、これにより加算演算の演算時間を短縮して処理を高速に行うことができる。
【０１５２】
なお、本実施形態の画像情報読取装置においては、高密度読取りが初期設定として設定されているものとしたが、本発明の画像情報読取方法および装置は、この態様に限られるものではなく、初期設定として「標準密度読取り」が、設定されており、「高密度読取り」、「低密度読取り」に切り換えられるものとしてもよい。
【０１５３】
例えば、主走査周波数（主走査速度）を１６０Ｈｚ、画素密度１０pix ／mmを標準密度読取りとしたときの、主走査サンプリング間隔、副走査画素ピッチ、副走査速度、アンチエリアジングフィルタカットオフ周波数を以下に示す。
【０１５４】
主走査サンプリング間隔：１００μｍ 副走査画素ピッチ：１００μｍ
主走査サンプリング周期：１．０μsec 副走査速度：１６ｍｍ／sec
アンチエリアジングフィルタカットオフ周波数：５００ｋＨｚ
（アナログフィルタのため、カットオフ周波数は５００ｋＨｚ以下であることが好ましく、例えば４００ｋＨｚなどを適用するのが望ましい。）
これに対して、画素密度２０pix ／mmである高密度読取りのときは、主走査周波数を１６０Ｈｚ不変として、
主走査サンプリング間隔：５０μｍ 副走査画素ピッチ：５０μｍ
主走査サンプリング周期：０．５μsec 副走査速度：８ｍｍ／sec
アンチエリアジングフィルタカットオフ周波数：１０００ｋＨｚ
となり、一方、画素密度５pix ／mmである低密度読取りのときは、主走査周波数を１６０Ｈｚ不変として、
主走査サンプリング間隔：２００μｍ 副走査画素ピッチ：２００μｍ
主走査サンプリング周期：２．０μsec 副走査速度：３２ｍｍ／sec
アンチエリアジングフィルタカットオフ周波数：２５０ｋＨｚ
となる。
【０１５５】
なお、上述したような「高密度読取り」、「低密度読取り」等、の読取り密度が段階的に予め設定されたものに限らず、読取り密度を規定するパラメータ（ｍ，ｎ）を任意に選択できるものとしてもよい。
【０１５６】
また、上記実施形態においては、デジタル画像信号Ｓ１，Ｓ２に対して画素密度変換処理を施してるが、デジタル画像信号Ｓ１，Ｓ２を先に加算して加算画像信号Ｓ３を得、この加算画像信号Ｓ３に対して画素密度変換処理を施してもよい。
【０１５７】
さらに、上記実施形態においては、画素密度変換手段３７ａ，３７ｂにおいて、デジタル画像信号Ｓ１，Ｓ２の主走査方向について１／ｍ倍、副走査方向について１／ｎ倍となるように画素密度変換をしているが、主走査方向についてａ／ｍ（ａ＞０）倍、副走査方向についてａ／ｎ倍となるように画素密度変換を行うようにしてもよい。この場合、加算画像信号Ｓ３の画素密度は（ａ／（ｍ×ｎ））^２ 倍となる。
【０１５８】
図９は本発明の第３の画像情報読取装置の一実施形態を示す図である。図示の画像情報読取装置は、モータ８により回転せしめられるエンドレスベルト９ａ上に放射線画像情報が蓄積記録された蓄積性蛍光体シート１が配置され、シート１の上方には、シート１を励起するレーザー光１１を発するレーザー光源１０と、モーター１２により回転され、レーザー光１１を反射偏向する回転多面鏡２０（主走査周波数１６０Ｈｚに相当）と、回転多面鏡２０で反射偏向されたレーザー光１１をシート１上に収束し、かつ等速度で主走査させる走査レンズ２１が配されている。
【０１５９】
さらに、前記レーザー光１１が走査されるシート１の直上には、そのレーザー光１１による励起で、シート１の上面から発せられる、蓄積記録されている画像情報に応じた輝尽発光光１３ａを上方より集光する光ガイド１４ａが近接して配置されている。光ガイド１４ａには集光した輝尽発光光１３ａを光電的に検出してアナログ画像信号ＱＡに変換するフォトマルチプライヤ（光電子増倍管）１５ａが接続されている。このフォトマルチプライヤ１５ａは、電圧印加手段３９ａにより印加される電圧に応じた感度で輝尽発光光１３ａを検出するものである。
【０１６０】
また、フォトマルチプライヤ１５ａには対数増幅器１６ａが接続されており、フォトマルチプライヤ１５ａにより検出されたアナログ画像信号ＱＡを予め設定されている周波数特性にしたがって対数的に増幅し、対数化画像信号ＱＡ′を出力する。
【０１６１】
一方、メモリー４１ａには、予め設定されているサンプリング間隔に応じたシェーディング補正用データＤ１が記憶されており、メモリー４１ａにはこの補正用データＤ１を予め設定されている基準クロックでアナログ信号Ｄ１′に変換するＤ／Ａ変換器４１ａが接続されており、Ｄ／Ａ変換器４２ａには、対数増幅器１６ａから出力された対数化画像信号ＱＡ′にこの補正用アナログ信号Ｄ１′を加算して、シェーディング補正が施された画像信号Ｑ１を出力する加算器４３ａが接続されている。
【０１６２】
さらに加算器４３ａには、後述するＡ／Ｄ変換によるエリアジングノイズ（折り返しノイズ）を除去するアンチエリアジングフィルター３５ａが接続されており、その後段には、このフィルタリングされた後の画像信号Ｑ１′を予め設定されている基準クロックでデジタル画像信号Ｓ１に変換するＡ／Ｄ変換器３６ａが設けられている。なお、アンチエリアジングフィルター３５ａは高密度用フィルターと低密度用フィルターとからなり、初期的には高密度用フィルターが選択されているが、後述する特性変更手段６０からの入力信号に応じて低密度用フィルターにも切り換えられるものである。
【０１６３】
さらにまた、本実施形態の画像情報読取装置は、画像情報の読取り画素密度として、予め初期的に設定されている「高密度」（10 pix／mm）と、この高密度よりも低密度である「低密度」（５ pix／mm）とのうち、オペレーターが選択した密度の入力を受け、「高密度」のときはパラメータ（ｍ，ｎ）をｍ＝ｎ＝１とし、「低密度」のときはパラメータ（ｍ，ｎ）をｍ＝ｎ＝２として出力する入力手段７０と、この入力手段７０から出力されたパラメータ（ｍ，ｎ）が入力されて、これらのパラメーター（ｍ，ｎ）に応じて、エンドレスベルト９ａを駆動するモータ８の回転速度を変更し、走査レンズ２１を光軸方向に移動させてシート１を走査するレーザー光１１のビーム径を変更し、電圧印加手段３９ａを制御してフォトマルチプライヤ１５ａの感度を変更し、Ｄ／Ａ変換器４２ａのサンプリングクロックを変更してメモリー４１ａに記憶されているシェーディング補正用データを変更して出力させ、Ａ／Ｄ変換器３６ａのサンプリングクロックを変更し、対数増幅器１６ａの周波数特性を変更し、アンチエリアジングフィルター３５ａの高密度用と低密度用とを切り換える特性変更手段６０とを備えている。
【０１６４】
次に本実施形態の放射線画像情報読取装置の作用について説明する。
【０１６５】
まず、オペレーターにより選択された「高密度」を表す信号が入力手段７０に入力される。「高密度」はこの画像情報読取装置の初期的設定であり、「高密度」に対応するパラメータ（ｍ，ｎ）＝（１，１）が入力手段７０から出力されて特性変更手段６０に入力される。
【０１６６】
特性変更手段７０は、入力されたパラメータ（ｍ，ｎ）＝（１，１）により、エンドレスベルト９ａを駆動するモータ８の回転速度、走査レンズ２１の位置、電圧印加手段３９ａへの制御信号、Ｄ／Ａ変換器４２ａのサンプリングクロック、Ａ／Ｄ変換器36のサンプリングクロック、対数増幅器１６ａの周波数特性、およびアンチエリアジングフィルター３５ａを、それぞれ初期設定（高密度用）のものとなるようにセットする。
【０１６７】
次いで、エンドレスベルト９ａ上の所定の位置にセットされた蓄積性蛍光体シート１は、エンドレスベルト９ａにより、矢印Ｙ方向に上記高密度用の速度で搬送（副走査）される。
【０１６８】
一方、レーザ光源１０から発せられたレーザー光１１は、モータ１２により駆動され矢印方向に高速回転する回転多面鏡２０によって反射偏向され、この偏向されたレーザー光１１は走査レンズ２１により、エンドレスベルト９ａ上を搬送されるシート１で収束され、かつ等速度で走査されて、このシート１を矢印Ｘ方向に主走査する。
【０１６９】
シート１の、レーザー光１１で走査された部分からは、そこに蓄積記録されている画像情報に応じた光量の輝尽発光光１３ａが発光し、輝尽発光光１３ａはレーザー光１１の主走査線に沿って配された光ガイド１４ａの入射端面１８ａからこの光ガイド１４ａ内に入射し、光ガイド１４ａの内部を全反射を繰り返しつつ、レーザ光カットフィルタ１７ａを介してフォトマルチプライヤ１５ａまで導光される。
【０１７０】
フォトマルチプライヤ１５ａは、電圧印加手段３９ａにより、高密度用の感度に対応した高圧が印加されており、入射した輝尽発光光１３ａを高密度用の感度で検出し、アナログ画像信号ＱＡに光電変換して出力する。
【０１７１】
このアナログ画像信号ＱＡは対数増幅器１６ａに入力され、高密度用の周波数特性にセットされた対数増幅器１６ａにより対数化画像信号ＱＡ′に変換されて加算器４３ａに入力される。
【０１７２】
一方、メモリー４１ａに記憶されている高密度用のシェーディング補正用データＤ１は、Ｄ／Ａ変換器４２ａにより、高密度用のクロックである基準クロックでのサンプリングレートでアナログ信号Ｄ１′に変換される。
【０１７３】
ここで、Ｄ／Ａ変換器４２ａに入力されるクロックは、図２に示すように、特性変更手段６０に設けられたセレクター６２により切り換えられて出力される基準クロックである。
【０１７４】
シェーディング補正用のアナログ信号Ｄ１′は加算器４３ａに入力され、対数増幅器１６ａから入力された対数化画像信号ＱＡ′に加算され、これにより対数化画像信号ＱＡ′はシェーディング補正がなされた画像信号Ｑ１に変換されてアンチエリアジングフィルター３５ａに入力される。
【０１７５】
アンチエリアジングフィルター３５ａは、特性変更手段６０により高密度用フィルターに切り換えられており、入力された画像信号Ｑ１はこの高密度用フィルターによりエリアジングノイズが適切に除去された信号Ｑ１′に変換されてＡ／Ｄ変換器３６ａに入力される。
【０１７６】
Ａ／Ｄ変換器３６ａは、特性変更手段６０のセレクター６２により切り換えられた基準クロックによるサンプリングレートで、入力された画像信号Ｑ１′をデジタル画像信号Ｓ１に変換して、画像処理装置等に出力する。
【０１７７】
次に、オペレーターにより「低密度」が選択された場合の作用について説明する。
【０１７８】
オペレーターにより「低密度」を表す信号が入力手段７０に入力されると、入力手段７０は「低密度」に対応するパラメータ（ｍ，ｎ）＝（２，２）を特性変更手段６０に出力する。
【０１７９】
特性変更手段７０は、入力されたパラメータ（ｍ，ｎ）＝（２，２）により、エンドレスベルト９ａを駆動するモータの回転速度、走査レンズ２１の位置、電圧印加手段３９ａへの制御信号、Ｄ／Ａ変換器４２ａのサンプリングクロック、Ａ／Ｄ変換器３６ａのサンプリングクロック、対数増幅器１６ａの周波数特性、およびアンチエリアジングフィルター３５ａを、それぞれ低密度用のものとなるようにセットする。具体的には、エンドレスベルト９ａを駆動するモータの回転速度を２倍の速度に変更し、走査レンズ２１の位置を、レーザー光１１のビーム径がシート１上で略２倍となる位置まで移動し、電圧印加手段３９ａへの制御信号を、フォトマルチプライヤ１５ａの感度を下げるような信号とし、セレクター６２（図２参照）を分周回路６１から出力されるクロック（基準クロックを分周し手得られたクロックであって、基準クロックの２倍の周期のクロック）に切り換えて、Ｄ／Ａ変換器４２ａおよびＡ／Ｄ変換器３６ａに入力されるサンプリングクロックを変更し、対数増幅器１６ａの周波数特性を変更し、アンチエリアジングフィルター３５ａを低密度用フィルターに切り換える。
【０１８０】
このように各部の特性が変更されて、前述した高密度読取りの場合と同様に画像情報の読取りがなされる。
【０１８１】
すなわち、エンドレスベルト９ａ上の所定の位置にセットされた蓄積性蛍光体シート１は、エンドレスベルト９ａにより、矢印Ｙ方向に上記高密度用の速度の２倍の速度で搬送（副走査）され、一方、レーザ光源１０から発せられたレーザー光１１は、高密度読取りのときと同一の回転速度で高速回転する回転多面鏡２０によって反射偏向され、この偏向されたレーザー光１１は走査レンズ２１により、エンドレスベルト９ａ上を搬送されるシート１で収束され、かつ等速度で走査されて、このシート１を矢印Ｘ方向に主走査する。このときシート１上におけるビーム径は高密度読取りのときの２倍の大きさで収束される。
【０１８２】
シート１の、レーザー光１１で走査された部分から発光した輝尽発光光１３ａは、光ガイド１４ａを通じてレーザ光カットフィルタ１７ａを介し、フォトマルチプライヤ１５ａまで導光される。
【０１８３】
フォトマルチプライヤ１５ａは、電圧印加手段３９ａにより、高密度読取り用よりも低い感度となるような電圧が印加されており、入射した輝尽発光光１３ａをこの低密度用の感度で検出し、アナログ画像信号ＱＡに光電変換して出力する。
【０１８４】
このアナログ画像信号ＱＡは対数増幅器１６ａに入力され、低密度用の周波数特性にセットされた対数増幅器１６ａにより対数化画像信号ＱＡ′に変換されて加算器４３ａに入力される。
【０１８５】
一方、メモリー４１ａに記憶されている高密度用のシェーディング補正用データＤ１は、Ｄ／Ａ変換器４２ａにより、低密度用のクロックである２分周のクロックでのサンプリングレートでアナログ信号Ｄ１′に変換される。すなわち、特性変更手段６０に設けられた分周回路６１が、基準クロックを２分周して基準クロックの２倍の周期のクロックを発生し、セレクター６２はこの２分周のクロックを出力するように切り換えられている。この結果、シェーディング補正用のアナログ信号Ｄ１′は高密度用のシェーディング補正用データＱＡ′に対して、主走査方向についてその画素数が１／２とされている。
【０１８６】
シェーディング補正用のアナログ信号Ｄ１′は加算器４３ａに入力され、対数増幅器１６ａから入力された対数化画像信号ＱＡ′に加算され、これにより対数化画像信号ＱＡ′はシェーディング補正がなされた画像信号Ｑ１に変換されてアンチエリアジングフィルター３５ａに入力される。
【０１８７】
アンチエリアジングフィルター３５ａは、特性変更手段６０により低密度用フィルターに切り換えられており、入力された画像信号Ｑ１はこの低密度用フィルターによりエリアジングノイズが適切に除去された信号Ｑ１′に変換されてＡ／Ｄ変換器３６ａに入力される。
【０１８８】
Ａ／Ｄ変換器３６ａは、特性変更手段６０のセレクター６２により切り換えられた２分周のクロックによるサンプリングレートで、入力された画像信号Ｑ１′をデジタル画像信号Ｓ１に変換する。
【０１８９】
このように本実施形態の画像情報読取装置によれば、レーザー光の主走査速度を変えることなく、高密度読取りの場合に比して、レーザー光Ｌの主走査方向について１／２、副走査方向について１／２の画素数である、全体として１／４の画素密度の低密度画像信号を得ることができる。しかも、特性変更手段６０が、画素密度を規定するパラメータに応じて、走査レンズ２１の位置、電圧印加手段３９ａへの制御信号、Ｄ／Ａ変換器４２ａのサンプリングクロック、対数増幅器１６ａの周波数特性、およびアンチエリアジングフィルター３５ａをそれぞれ変更するため、読取り画素密度に適した、画素当たりのエネルギー付与、光電検出感度の設定、シェーディング補正、エリアジングノイズの抑制等が施された画像信号を得ることができる。
【０１９０】
なお、本実施形態の画像情報読取装置においては、高密度読取りが初期設定として設定されているものとしたが、本発明の画像情報読取方法および装置は、この態様に限られるものではなく、初期設定として「標準密度読取り」が、設定されており、「高密度読取り」、「低密度読取り」に切り換えられるものとしてもよい。
【０１９１】
例えば、主走査周波数（主走査速度）を１６０Ｈｚ、画素密度１０pix ／mmを標準密度読取りとしたときの、主走査サンプリング間隔、副走査画素ピッチ、副走査速度、アンチエリアジングフィルターカットオフ周波数を以下に示す。
【０１９２】
主走査サンプリング間隔： 100μｍ 副走査画素ピッチ： 100μｍ
主走査サンプリング周期：１．０μsec 副走査速度：１６ｍｍ／sec
アンチエリアジングフィルターカットオフ周波数：５００ｋＨｚ
（アナログフィルタのため、正確には５００ｋＨｚ以下であることが好ましく、例えば４００ｋＨｚなどを適用するのが望ましい。）
これに対して、画素密度２０pix ／mmである高密度読取りのときは、主走査周波数を１６０Ｈｚ不変として、
主走査サンプリング間隔：５０μｍ 副走査画素ピッチ：５０μｍ
主走査サンプリング周期：０．５μsec 副走査速度：８ｍｍ／sec
アンチエリアジングフィルターカットオフ周波数：１０００ｋＨｚ
となり、一方、画素密度５pix ／mmである低密度読取りのときは、主走査周波数を１６０Ｈｚ不変として、
主走査サンプリング間隔： 200μｍ 副走査画素ピッチ： 200μｍ
主走査サンプリング周期：２．０μsec 副走査速度：３２ｍｍ／sec
アンチエリアジングフィルターカットオフ周波数：２５０ｋＨｚ
となる。
【０１９３】
なお、上述したような「高密度読取り」、「低密度読取り」等、の読取り密度が段階的に予め設定されたものに限らず、読取り密度を規定するパラメータ（ｍ，ｎ）を任意に選択できるものとしてもよい。
【図面の簡単な説明】
【図１】本発明の第１の画像情報読取装置の一実施形態の構成を示す図
【図２】クロックを変更する構成の一実施形態を示す図
【図３】図１に示した実施形態における特性変更手段の構成を示す図
【図４】図１に示した実施形態におけるメモリ管理の詳細を説明する図
【図５】本発明の第２の画像情報読取装置の一実施形態を示す図
【図６】図５に示した実施形態における特性変更手段の構成を示す図
【図７】クロックを変更する構成の一実施形態を示す図
【図８】フィルタリング処理を説明するための図
【図９】本発明の第３の画像情報読取装置の一実施形態を示す図
【符号の説明】
１ 蓄積性蛍光体シート
８ モータ
９ａ，９ｂ エンドレスベルト
１０ レーザ光源
１１ レーザ光
１２ 回転多面鏡
１４ａ，１４ｂ 光ガイド
１５ａ，１５ｂ フォトマルチプレイヤ
１６ａ，１６ｂ 対数増幅器
１７ａ，１７ｂ レーザ光カットフィルタ
２０ モータ
２１ 走査レンズ
３５ａ，３５ｂ アンチエリアジングフィルタ
３６ａ，３６ｂ Ａ／Ｄ変換器
３７ａ，３７ｂ 画素密度変換手段
３８ 加算手段
３９ａ，３９ｂ 電圧印加手段
４１ａ，４１ｂ メモリ
４２ａ，４２ｂ Ａ／Ｄ変換器
４３ａ，４３ｂ 加算器
６０ 特性変更手段
７０ 入力手段[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image information reading method and apparatus, and more particularly to an image information reading method and apparatus that can change the pixel density of a read image signal.
[0002]
[Prior art]
When irradiated with radiation (X-rays, α-rays, β-rays, γ-rays, electron beams, ultraviolet rays, etc.), a part of this radiation energy is accumulated, and when irradiated with excitation light such as visible light after that, depending on the accumulated energy Using a stimulable phosphor (stimulable phosphor) exhibiting stimulating luminescence, radiation image information of a subject such as a human body is temporarily recorded on a sheet-like stimulable phosphor (storable phosphor sheet), The stimulable phosphor sheet is scanned with a light beam such as a laser beam to generate stimulated emission light according to image information as signal light, and the obtained stimulated emission light is photoelectrically read by a photoelectric reading means. An analog image signal is obtained, a digital image signal having a predetermined pixel density can be obtained by sampling and quantizing the analog image signal at a predetermined interval, and a photographic photosensitive material based on the digital image signal. A radiation image information recording / reproducing system for outputting a radiation image of a subject as a visible image on a display device such as a recording medium or a CRT is already known (Japanese Patent Laid-Open Nos. 55-12429, 56-11395, 56). -11397 etc.).
[0003]
This system has a practical advantage that an image can be recorded over a very wide radiation exposure range as compared with a radiographic system using a conventional silver salt photograph.
[0004]
In addition, as a method of photoelectrically reading the above-mentioned stimulated emission light, photoelectric reading means are separately provided on both sides of the stimulable phosphor sheet, and excitation light is irradiated only on both sides or one side of the stimulable phosphor sheet. In addition, a radiation image reading apparatus has been proposed in which the stimulated emission light emitted from both sides of the stimulable phosphor sheet by the irradiation of the excitation light is photoelectrically detected by each photoelectric reading means (for example, JP-A-55). -87970). Such a radiation image reading apparatus has photoelectric reading means arranged so that one radiation image is accumulated and recorded on the stimulable phosphor sheet, and reading is performed from both sides of the stimulable phosphor sheet, and thereby, the light emission is stimulated. Light detection improves light collection efficiency, and by adding the two obtained image signals at a predetermined addition ratio, the detection position of the noise component is dispersed on the front and back of the sheet, so it can be obtained from only one side. Thus, it is possible to obtain an added image signal having a relatively improved S / N compared to the image signal.
[0005]
Furthermore, the S / N of the image signal (including the added image signal) is increased with respect to a single image signal obtained from one side of the sheet or two image signals obtained from both sides of the sheet. An image superposition method has been proposed in which an added image signal is obtained after filtering processing using a filter having a proper frequency response characteristic (Japanese Patent Laid-Open No. 7-287330). According to this method, the amount of radiation applied to the subject at the time of imaging is obtained, and the parameters (filter coefficients) for performing filtering processing on the image signal are obtained based on the amount of radiation, so that the subject is irradiated. An image signal representing an image with an optimum image quality or an added image signal representing a superimposed image can be obtained according to the radiation dose. Furthermore, in this method, since processing for changing the frequency characteristics is performed on the entire image signal, it is not necessary to perform frequency conversion such as Fourier transform, and the amount of calculation can be reduced.
[0006]
[Problems to be solved by the invention]
By the way, in the image reading unit of the radiation image information recording / reproducing system or in the radiation image information reading apparatus in which the image reading unit is configured alone, the pixel density of the obtained single image signal or the added image signal is described above. There is a demand to make the pixel density different from the predetermined pixel density.
[0007]
This is because, for example, when a large amount of radiographic images are taken, such as in a mass screening, it is required to improve the reading speed of the radiographic images taken, while the image quality required for the reproduced image is required. The reason is that it is sufficient to determine whether or not re-examination is necessary, and it is because there is no need to read image information at an excessively high pixel density. Of course, on the contrary, there is a case where it is required to read image information at a high pixel density so that a high-quality image can be reproduced even if the reading speed is lowered.
[0008]
In order to perform reading at other pixel densities in addition to reading at a predetermined pixel density set in advance as described above, the main scanning speed and the sub-scanning speed of the light beam can be simply changed. Conceivable. When changing the main scanning speed of the light beam, it is necessary to change the driving speed of a scanning optical system (for example, a polygon mirror or a galvanometer mirror) that performs the main scanning of the light beam.
[0009]
However, when the drive speed of the scanning optical system is changed, a certain time is required until the drive speed is stabilized due to the influence of the inertial force, and stable drive may not be guaranteed in all speed ranges. . For this reason, it is desirable that the pixel density can be changed without changing the main scanning speed of the light beam. Further, when the pixel density is changed in this way, the pixel densities in the main scanning direction and the sub-scanning direction need to be changed at the same rate.
[0010]
In addition, when changing the pixel density, it is desired to perform the pixel density conversion process as fast as possible.
[0011]
Furthermore, the following problems may occur when the pixel density is simply changed.
[0012]
That is,
(I) Since the energy of the signal light per pixel emitted from the sheet by changing the pixel density is different from the energy of the signal light per pixel at the original pixel density, the pixels before and after the change If the density ratio is large, the density (or luminance) of the entire reproduced image may change, which may affect the diagnostic performance.
[0013]
(II) When shading correction is performed on an analog image signal, there may be a case where the shading characteristics to be corrected are changed before and after the pixel density change, and the shading cannot be corrected appropriately.
[0014]
(III) When the analog image signal is logarithmically amplified, the frequency transfer characteristics may change before and after the pixel density is changed.
[0015]
(IV) When performing filtering that removes aliasing noise prior to sampling the analog image signal, the Nyquist frequency changes before and after the pixel density change, so the aliasing noise may not be cut properly. is there.
[0016]
These problems do not arise only in the reading of radiation image information from the stimulable phosphor sheet on which the radiation image information is recorded by the above-described radiation image information recording / reproducing system. The same may occur in a method or apparatus that scans with a beam and reads reflected light emitted as a signal light according to an image printed on the medium.
[0017]
The present invention has been made in view of the above circumstances, and a first object thereof is to provide an image information reading method and apparatus capable of changing the pixel density without changing the main scanning speed of the light beam. Is.
[0018]
A second object of the present invention is to provide an image information reading method and apparatus for double-sided reading that can change the pixel density without changing the main scanning speed of the light beam.
[0019]
[Means for Solving the Problems]
The image information reading method and apparatus of the present invention obtains a digital image signal having an arbitrary pixel density by changing the sub-scanning speed and sampling interval without changing the main scanning speed.
[0020]
That is, according to the first image information reading method of the present invention, a light beam is repeatedly main-scanned at a constant speed in a constant direction on a scanned sheet on which image information is recorded, and substantially orthogonal to the main-scanning direction. By sub-scanning in the direction, the light beam is scanned over substantially the entire surface of the scanned sheet, and the signal light emitted from the scanned sheet is photoelectrically detected by scanning the light beam, and the obtained analog image In an image information reading method for obtaining a digital image signal having a predetermined pixel density by sampling and quantizing a signal,
The sub-scanning speed is multiplied by m (m> 0), and the sampling interval is multiplied by n (n> 0).
[0021]
Here, it is preferable to further perform a pixel density conversion process for a / m (a> 0) times the number of pixels in the main scanning direction and a / n times the number of pixels in the sub-scanning direction. This is because the aspect ratio of the image can be made the same as that of the original image.
[0022]
The second image information reading method of the present invention relates to an added image signal of two image signals obtained by reading from both sides of the sheet, and a constant light beam is applied to the scanned sheet on which the image information is recorded. The light beam is scanned over substantially the entire surface of the scanned sheet by performing sub-scanning in a direction substantially perpendicular to the main scanning direction while repeatedly performing main scanning at a constant speed in the direction of. The signal light emitted from both sides of the scanned sheet is detected photoelectrically, the two analog image signals obtained are sampled and quantized to obtain two digital image signals, and the two digital image signals are added In an image information reading method for obtaining an added image signal having a predetermined pixel density,
The sub-scanning speed is multiplied by m (m> 0), the sampling interval is multiplied by n (n> 0), and the number of pixels in the main scanning direction is a / m (a> 0) times. The pixel density conversion process is performed to increase the number of pixels in the scanning direction by a / n times.
[0023]
Here, in the first and second inventions, the scanned sheet includes not only the stimulable phosphor sheet on which the radiation image is stored and recorded, but also a photographic print or the like used in the radiation image information recording / reproducing system described above. Also includes transparent originals such as reflective originals and films. Therefore, the signal light emitted from the scanned sheet includes reflected light emitted from the reflective original and transmitted light emitted from the transparent original, in addition to the stimulated light emitted from the storage phosphor sheet by being excited by the light beam. Including.
[0024]
Further, as a method of changing the sampling interval, a clock divided by a frequency dividing circuit is created with respect to the reference clock, and sampling is performed with this divided clock, or the period is different depending on the PLL with respect to the reference clock. It is possible to apply a method such as creating a clock and sampling with the new clock, or switching and applying a plurality of sampling clocks having different periods.
[0025]
Further, as a method of obtaining the added image signal, not only a method of simply adding pixels corresponding to each other of two digital image signals but also two digital images as described in the above-mentioned Japanese Patent Application Laid-Open No. 7-287330. It is possible to employ a method of performing addition after performing a filtering process with a filter having a frequency response characteristic that increases the S / N of the added image signal with respect to the signal.
[0026]
On the other hand, as the pixel density conversion processing, a method by performing a one-dimensional mask operation in the main scanning direction of an image signal, a method of thinning out pixels according to the pixel density, a B-spline interpolation operation, a Cubic spline interpolation operation, and the like The following interpolation calculation methods (for example, JP-A-8-16767 and 9-321981) and linear interpolation calculation methods (for example, JP-A-9-50516) can be employed.
[0027]
When performing this pixel density conversion, it is preferable to change parameters for one-dimensional mask calculation, parameters for thinning out pixels, and parameters for calculation formulas for interpolation calculation according to m and n. Here, the parameter for the one-dimensional mask calculation is a mask coefficient, and the parameter for thinning out pixels is the thinning-out interval of pixels. The parameter of the calculation formula of the interpolation calculation represents what type of interpolation calculation (for example, B-spline interpolation calculation, Cubic spline interpolation calculation, linear interpolation calculation) is used when performing the interpolation calculation.
[0028]
In the second image information reading method of the present invention, it is preferable to perform the pixel density conversion process on the two digital image signals. Here, performing pixel density conversion processing on two digital image signals means performing pixel density conversion before adding two digital image signals to obtain an added image signal.
[0029]
In each image information reading method of the present invention, it is preferable to change at least one of the following characteristics (1) to (8) according to m and n.
[0030]
(1) Diameter of a light beam that scans the scanned sheet
(2) Power of a light beam for scanning the scanned sheet
(3) Sensitivity to detect the signal light
(4) Shading correction data set in advance when shading correction is performed on the analog image signal
(5) Timing of outputting the shading correction data from the memory storing the shading correction data
(6) Frequency transfer characteristics when the analog image signal is logarithmically amplified
(7) Cut-off frequency when performing filtering to remove aliasing noise prior to sampling the analog image signal
(8) Parameters for filtering processing in the pixel density conversion processing (including thinning parameters when performing thinning processing as filtering processing)
Here, the changed items (1) to (8) are applied to at least one applicable item, and it is not always necessary to provide all the items (1) to (8) as configuration requirements. That is, for example, in an image information reading method that does not perform shading correction, it is not necessary to provide the configurations (4) and (5).
[0031]
Furthermore, it is only necessary to change at least one of the items (1) to (8), and only one of them may be included as a configuration requirement, or two or more of these may be included. .
[0032]
The items (1) to (3) are changed when the above-mentioned problem (I), that is, when the energy of the signal light per pixel emitted from the sheet by changing the pixel density is the original pixel density. Therefore, if the pixel density ratio before and after the change is large, the density (or brightness) of the entire image to be reproduced will change, affecting the diagnostic performance. Specifically, when the pixel density is changed to the high density side, (1) the light beam diameter is reduced, (2) the light beam power is reduced, and / or ( 3) When the sensitivity for detecting the signal light is increased while the pixel density is changed to the lower density side, (1) the light beam diameter is enlarged, (2) the power of the light beam is increased, and / or ( 3) Reduce the sensitivity to detect signal light Just do it.
[0033]
Similarly, when the pixel density is changed to the high density side, the item (6) is changed so that the frequency response characteristic is expanded to a higher frequency band, and the item (7) is also set to increase the cutoff frequency. When the pixel density is changed to the lower density side, the item (6) is changed so that the cutoff frequency is set to the lower frequency side, and the item (7) is similarly applied. The cut-off frequency may be changed to the low frequency side.
[0034]
The above item (8) is such that, for example, the filtering frequency (coefficient for mask calculation) is set so that the cutoff frequency when the mask calculation is performed at the low density side is lower than that at the high density side. Change it. Note that, when applying the thinning process parameter, it may be changed in a direction opposite to the change direction with respect to the pixel density level when the filtering process parameter is applied.
[0035]
Since item (4) above is not a characteristic that varies qualitatively according to the pixel density, shading correction data is prepared in advance for each representative pixel density, and shading corresponding to the changed pixel density. Data for correction is selected from these prepared data, or when data having a matching pixel density is not prepared, data corresponding to at least two types of pixel densities is prepared from the prepared data. The shading correction data corresponding to the changed pixel density may be obtained and applied by the interpolation processing used.
[0036]
The above item (5) is applied when shading correction is performed in real time on a digital image signal, and is obtained by outputting shading correction data prepared in advance at a timing according to the pixel density. The digital image signal is subjected to shading correction. Specifically, when the pixel density is changed to the high density side, the sampling speed increases, so the timing for outputting the shading correction data may be advanced according to the sampling speed. On the other hand, when the pixel density is changed to the low density side, the sampling speed is slowed down. Therefore, the timing for outputting the shading correction data may be delayed according to the sampling speed.
[0037]
Here, shading refers to light caused by unevenness in the intensity of the scanning beam due to uneven reflectance on the reflecting surface of an optical deflector (polygon mirror, galvanometer mirror, etc.) for scanning the light beam, and variations in the deflection speed of the optical deflector. Variations in the analog image signal obtained from the photoelectric reading means (part of the light detection efficiency) due to unevenness in the scanning speed of the beam or detection unevenness due to sensitivity unevenness in the main scanning direction of the photoelectric detecting means arranged along the main scanning direction. Mean decrease). The shading correction data refers to shading characteristics obtained in advance using, for example, a reference scanned sheet (for example, a stimulable phosphor sheet that is uniformly irradiated with radiation). (See JP 61-189763, 62-47259, 62-47261, 64-86759, JP-A-2-58973, etc.).
[0038]
In addition, in the above-mentioned changes (1), (2), (3), (6), (7), and (8), the characteristics for each pixel density (the beam diameter, Beam power in (2), sensitivity in (3), frequency response characteristics in (6), frequency response characteristics with different cutoff frequencies in (7), (8) In this case, the parameter may be changed by preparing a filtering parameter) and selecting a characteristic corresponding to the changed pixel density.
[0039]
Further, (4) as a method for changing the shading correction data, a method of selecting from a plurality of correction data prepared in advance as described above, and a method corresponding to a preset pixel density are prepared. One shading correction data may be obtained by sampling according to the changed pixel density, and the newly obtained shading correction data may be used.
[0040]
For each value of m and n, for example, “high density” (for example, when m = n = 0.5), “standard density” (original predetermined pixel density (corresponding to m = n = 1)), A correspondence relationship of “low density” (when m = n = 2) may be set.
[0041]
Further, the shading correction data is changed by selecting the shading correction data corresponding to the selected values of m and n from the shading correction data set in advance for each value of m and n that can be selected. In this case, it is preferable to apply one of the following two methods [I] and [II]. That is,
[I] Shading correction data set in advance for each value of m, n is stored in the first storage medium in advance, and shading correction data corresponding to the selected value of m, n is selected each time. The shading correction data is selected by transferring the shading correction data from the first storage medium to the second storage medium and reading the transferred shading correction data from the second storage medium.
[II] Pre-set shading correction data for each value of m and n is stored in advance in the first storage medium, and when desired, such as at the time of startup, all of these shading correction data are Transfer from the storage medium to the second storage medium having a storage area corresponding to a different address for each value of m, n, corresponding to the value of m, n, and corresponding to the selected value of m, n The shading correction data is selected by reading the shading correction data to be read from the address corresponding to the selected values of m and n.
[0042]
According to the method [I], the capacity of the second storage medium (memory) can be reduced, and the hardware configuration can be simplified. On the other hand, according to the method [II], the software configuration can be simplified and the reading speed of the correction data from the second storage medium can be increased.
[0043]
According to the third image information reading method of the present invention, a light beam is repeatedly main-scanned at a constant speed in a constant direction on a scanned sheet on which image information is recorded, in a direction substantially perpendicular to the main scanning direction. By sub-scanning, the light beam is scanned over substantially the entire surface of the scanned sheet, signal light emitted from the scanned sheet is detected photoelectrically by scanning the light beam, and the resulting analog image signal is In an image information reading method for obtaining a digital image signal having a predetermined pixel density by sampling and quantization,
The sub-scanning speed is multiplied by m (m> 0), the sampling interval is multiplied by n (n> 0), and depending on these m and n, the following characteristics (1) to (5) At least one of them is changed to obtain a digital image signal having a pixel density 1 / (m × n) times the predetermined pixel density.
[0044]
(1) Diameter of a light beam that scans the scanned sheet
(2) Sensitivity to detect the signal light
(3) Shading correction data set in advance when shading correction is performed on the analog image signal
(4) Frequency transfer characteristics when the analog image signal is logarithmically amplified
(5) Cutoff frequency when performing filtering to remove aliasing noise prior to sampling the analog image signal
Items (1) to (5) are the same as described above.
[0045]
A first image information reading apparatus of the present invention is an apparatus for carrying out the first image information reading method of the present invention, and is a light beam emitted from a light source on a scanned sheet on which image information is recorded. Main scanning means for repeatedly performing main scanning repeatedly in a constant direction at a constant speed, and the sheet or the sheet or the sheet so that the sheet is relatively sub-scanned in a direction substantially perpendicular to the main scanning direction of the light beam. Sub-scanning means for sub-scanning the light beam, photoelectric detection means for photoelectrically detecting signal light emitted from the scanned sheet by scanning the light beam, and sampling and quantizing the detected analog image signal In an image information reading apparatus provided with an A / D conversion means for obtaining a digital image signal having a predetermined pixel density,
The sub-scanning speed changing means for changing the sub-scanning speed by the sub-scanning means to m times according to the inputted m, and the sampling interval by the A / D converting means according to the inputted n And a sampling interval changing means for changing the sampling interval to n times.
[0046]
Here, it is preferable to further include a pixel density conversion processing unit that performs a pixel density conversion process in which the number of pixels in the main scanning direction is a / m times and the number of pixels in the sub-scanning direction is a / n times.
[0047]
A second image information reading apparatus of the present invention is an apparatus for carrying out the second image information reading method of the present invention, and is emitted from a light source onto a scanned sheet on which image information is recorded. Main scanning means for repeatedly scanning the light beam at a constant speed in a constant direction, and the sheet so that the sheet is relatively sub-scanned in a direction substantially perpendicular to the main scanning direction of the light beam. Alternatively, sub-scanning means for sub-scanning the light beam, photoelectric detection means for photoelectrically detecting signal light emitted from both sides of the scanned sheet by scanning the light beam, and two detected analog image signals Image information reading comprising: A / D conversion means for obtaining two digital image signals by sampling and quantization; and addition means for obtaining an added image signal having a predetermined pixel density by adding the two digital image signals In the location,
Sub-scanning speed changing means for changing the sub-scanning speed by the sub-scanning means to m times according to the input m;
Sampling interval changing means for changing the sampling interval by the A / D conversion means to n times according to the input n;
Pixel density conversion processing means for performing pixel density conversion processing for increasing the number of pixels in the main scanning direction by a / m (a> 0) times and setting the number of pixels in the sub-scanning direction by a / n times. It is what.
[0048]
In the second image information reading apparatus of the present invention, it is preferable that the pixel density conversion processing means is a means for performing pixel density conversion processing on the two digital image signals.
[0049]
Each image information reading apparatus of the present invention preferably further includes a characteristic changing unit that changes at least one of the following characteristics (1) to (8) according to m and n.
[0050]
(1) Diameter of a light beam that scans the scanned sheet
(2) Power of a light beam for scanning the scanned sheet
(3) Sensitivity to detect the signal light
(4) Shading correction data set in advance when shading correction is performed on the analog image signal
(5) Timing of outputting the shading correction data from the memory storing the shading correction data
(6) Frequency transfer characteristics when the analog image signal is logarithmically amplified
(7) Cut-off frequency when performing filtering to remove aliasing noise prior to sampling the analog image signal
(8) Parameters for filtering processing in the pixel density conversion processing (including thinning parameters when performing thinning processing as filtering processing)
The sub-scanning speed changing unit and the sampling interval changing unit may be part of the characteristic changing unit.
[0051]
When the characteristic changing means includes one that changes the shading correction data, among the shading correction data set in advance for each m and n value that can be selected, the shading correction according to the selected m and n values. The shading correction data may be changed by selecting data. In this case, it is preferable to apply one of the following two methods [I] and [II]. That is,
[I] Shading correction data set in advance for each value of m, n is stored in the first storage medium in advance, and shading correction data corresponding to the selected value of m, n is selected each time. The shading correction data is selected by transferring the shading correction data from the first storage medium to the second storage medium and reading the transferred shading correction data from the second storage medium.
[II] Pre-set shading correction data for each value of m and n is stored in advance in the first storage medium, and when desired, such as at the time of startup, all of these shading correction data are Transfer from the storage medium to the second storage medium having a storage area corresponding to a different address for each value of m, n, corresponding to the value of m, n, and corresponding to the selected value of m, n The shading correction data is selected by reading the shading correction data to be read from the address corresponding to the selected values of m and n.
[0052]
According to the method [I], the capacity of the second storage medium (memory) can be reduced, and the hardware configuration can be simplified. On the other hand, according to the method [II], the software configuration can be simplified and the reading speed of the correction data from the second storage medium can be increased.
[0053]
The third image information reading apparatus of the present invention comprises a main scanning unit that repeatedly scans a light beam emitted from a light source on a scanned sheet on which image information is recorded at a constant speed in a constant direction; Sub-scanning means for sub-scanning the sheet or the light beam so that the sheet is relatively sub-scanned in a direction substantially perpendicular to the main scanning direction of the beam; Image information comprising photoelectric detection means for photoelectrically detecting signal light emitted from the sheet, and A / D conversion means for sampling and quantizing the detected analog image signal to obtain a digital image signal having a predetermined pixel density In the reading device,
Pixel density input means for receiving inputs of values m and n corresponding to a pixel density of 1 / m times in the main scanning direction and 1 / n times in the sub scanning direction with respect to the predetermined pixel density;
Sub-scanning speed changing means for changing the sub-scanning speed by the sub-scanning means to m (m> 0) times;
Sampling interval changing means for changing the sampling interval by the A / D converter to n (n> 0) times;
It is characterized by comprising characteristic changing means for changing at least one of the following (1) to (5) according to m and n.
[0054]
(1) Diameter of a light beam that scans the scanned sheet
(2) Sensitivity to detect the signal light
(3) Shading correction data set in advance when shading correction is performed on the analog image signal
(4) Frequency transfer characteristics when the analog image signal is logarithmically amplified
(5) Cutoff frequency when performing filtering to remove aliasing noise prior to sampling the analog image signal
[0055]
【The invention's effect】
According to the image information reading method and apparatus of the present invention, the number of scanning lines (main scanning lines) of a light beam for scanning a scanned sheet is increased by multiplying the sub-scanning speed by m (m> 0)) times. The pixel density in the sub-scanning direction can be increased to 1 / m times because it increases or decreases to m times, and the pixel density in the main scanning direction is increased to 1 / n times by increasing the sampling interval by n (n> 0) times. Therefore, it is possible to obtain an image signal having a pixel density that is 1 / (m × n) 2 times the finally obtained image signal (added image signal in the case of double-sided reading). Further, since it is not necessary to change the main scanning speed of the light beam even when the pixel density is changed, it is not necessary to change the driving speed of a scanning optical system (for example, a polygon mirror or a galvanometer mirror) that scans the light beam. Therefore, it is possible to eliminate the unreadable time until the drive speed is stabilized, which occurs when the drive speed of the scanning optical system is changed.
[0056]
Further, in the invention in which the pixel density conversion processing is performed in which the number of pixels in the main scanning direction is a / m (a> 0) times and the number of pixels in the sub-scanning direction is a / n times, the pixel density conversion process is finally obtained. The pixel density in the main scanning direction of the image signal (added image signal in the case of double-sided reading) can be a / (m × n) times, and the pixel density in the sub-scanning direction can also be a / (m × n) times. The change rate of the pixel density in the main scanning direction and the sub-scanning direction is the same, and it is set in advance without changing the main scanning speed of the light beam while maintaining the aspect ratio (main / sub ratio) of the image size. (A / (m × n)) of this pixel density ² An image signal having a double pixel density can also be obtained.
[0057]
In particular, when performing double-sided reading for reading signals from both sides of the scanned sheet (the second image information reading method and apparatus of the present invention), in order to sufficiently apply energy by the light beam to the back side of the sheet. However, it is necessary to slow down the scanning speed as compared with the method of reading only from one side, but even in this case, if it is allowed to reduce the pixel density, the sub-scanning speed can be increased. The scanning time per sheet can be further shortened.
[0058]
In the case of double-sided reading, by performing pixel density conversion processing on two digital image signals, the image signals subjected to pixel density conversion processing can be added to obtain an added image signal. For this reason, it is possible to reduce the amount of addition calculation when adding digital image signals, thereby shortening the calculation time of the addition calculation and performing processing at high speed.
[0059]
Furthermore, according to the image information reading method and apparatus of the present invention, it is possible to solve various problems that occur when the reading pixel density is changed.
[0060]
That is, (I) Since the energy of signal light per pixel emitted from the sheet by changing the pixel density is different from the energy of signal light per pixel at the original pixel density, before and after the change When the pixel density ratio is large, the density (or luminance) of the entire image to be reproduced may change and affect the diagnostic performance. According to the image information reading method and apparatus of the present invention, Depending on the pixel density, (1) the energy applied to the unit area of the sheet can be changed by changing the diameter of the light beam that scans the scanned sheet, and (2) the light beam according to the pixel density. By changing the power, the energy applied to the unit area of the sheet can be changed, and (3) by changing the sensitivity for detecting the signal light according to the pixel density. It can be the level of the image signal is energy of the signal light obtained be varied to suppress a change.
[0061]
(II) When shading correction is performed on an analog image signal, the shading characteristics to be corrected may change before and after the pixel density change, and the shading may not be corrected appropriately. According to this image information reading method and apparatus, (4) by changing the shading correction data according to the pixel density, it is possible to perform the shading correction corresponding to the change in the shading characteristics, and according to the pixel density. (5) By changing the timing of output of the shading correction data from the memory, the shading correction corresponding to the change in the sampling rate can be performed.
[0062]
Furthermore, (III) when the analog image signal is logarithmically amplified, there may be a change in the frequency transfer characteristic before and after the pixel density change, but according to the image information reading method and apparatus of the present invention, the pixel density (6) By changing the frequency transfer characteristic when the analog image signal is logarithmically amplified, it is possible to suppress the change in the frequency characteristic of the obtained image signal.
[0063]
In addition, (IV) When performing filtering to remove aliasing noise prior to sampling the analog image signal, the Nyquist frequency changes before and after the pixel density change, so the aliasing noise cannot be cut properly. In some cases, according to the image information reading method and apparatus of the present invention, the frequency of the image signal obtained by changing the cutoff frequency of (7) filtering to remove aliasing noise according to the pixel density. It can suppress that a characteristic changes.
[0064]
Further, when performing the pixel density conversion process, (8) the aliasing noise at the time of the pixel density conversion is suppressed to a certain level or less by changing the parameter of the filtering process (masking coefficient) in the pixel density conversion process. Can do. In addition, errors that can occur due to interpolation processing such as spline interpolation calculation can be reduced.
[0065]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, specific embodiments of the image information reading apparatus of the present invention will be described with reference to the drawings.
[0066]
FIG. 1 is a diagram showing an embodiment of an image information reading apparatus according to the present invention. In the illustrated image information reading device, a stimulable phosphor sheet (hereinafter referred to as a sheet) 1 on which radiation image information is accumulated and recorded is disposed on an endless belt 9 a rotated by a motor (not shown). , A laser light source 10 that emits a laser beam 11 that excites the sheet 1, a rotary polygon mirror 12 (corresponding to a main scanning frequency of 160 Hz) that is rotated by a motor 20 to reflect and deflect the laser beam 11, and is reflected and deflected by the rotary polygon mirror 12 A scanning lens 21 that converges the laser beam L on the sheet 1 and performs main scanning at a constant speed is disposed.
[0067]
Further, immediately above the sheet 1 to which the laser beam 11 is scanned, the stimulated emission light 13a emitted from the upper surface of the sheet 1 is excited by the laser beam 11 and corresponding to the stored and recorded image information. A light guide 14a that collects light more closely is disposed. Connected to the light guide 14a is a photomultiplier (photomultiplier tube, hereinafter referred to as PMT) 15a that photoelectrically detects the condensed photostimulated light 13a and converts it into an analog image signal QA. The photomultiplier 15a detects the stimulated emission light 13a with a sensitivity corresponding to the voltage applied by the voltage applying means 39a.
[0068]
Further, a logarithmic amplifier 16a is connected to the photomultiplier 15a, and the analog image signal QA detected by the photomultiplier 15a is logarithmically amplified according to a preset frequency characteristic to obtain a logarithmic image signal QA. ′ Is output.
[0069]
On the other hand, shading correction data D1 corresponding to a preset sampling interval is stored in the memory 41a, and the correction data D1 is stored in the memory 41a with an analog signal D1 ′ using a preset reference clock. Is connected to the D / A converter 42a. The D / A converter 42a adds the correction analog signal D1 'to the logarithmic image signal QA' output from the logarithmic amplifier 16a. An adder 43a for outputting the image signal Q1 subjected to the shading correction is connected.
[0070]
Further, an anti-aliasing filter 35a that removes aliasing noise (folding noise) caused by A / D conversion, which will be described later, is connected to the adder 43a, and the filtered image signal Q1 'is connected to the subsequent stage. Is converted to a digital image signal S1 with a preset reference clock. The anti-aliasing filter 35a includes a high-density filter and a low-density filter. The high-density filter is initially selected. However, the anti-aliasing filter 35a has a low density according to an input signal from the characteristic changing unit 60 described later. It can also be switched to a filter.
[0071]
The A / D converter 36a is connected to pixel density conversion means 37a for converting the pixel density of the digital image signal S1 to obtain the image signal S1 ′.
[0072]
Furthermore, the image information reading apparatus of the present embodiment has a “high density” (10 pix / mm) that is initially set as a pixel density for reading image information, and a lower density than this high density. It receives the density selected by the operator from “Low Density” (5 pix / mm). When “High Density”, the parameter (m, n) is set to m = n = 1, and “Low Density” In some cases, the input means 70 outputs the parameter (m, n) as m = n = 2, and the parameter (m, n) output from the input means 70 is input to these parameters (m, n). Accordingly, the rotational speed of the motor 8 that drives the endless belt 9a is changed, the scanning lens 21 is moved in the optical axis direction, the beam diameter of the laser light 11 that scans the sheet 1 is changed, and the voltage applying means 39a is controlled. Photo multiplier 1 The sensitivity of a is changed, the sampling clock of the D / A converter 42a is changed, the shading correction data stored in the memory 41a is changed and output, and the sampling clock of the A / D converter 36a is changed. A characteristic changing unit 60 that changes the frequency characteristics of the logarithmic amplifier 16a, switches between high density and low density of the anti-aliasing filter 35a, and changes parameters when the pixel density conversion unit 37a performs pixel density conversion. It has.
[0073]
Here, the pixel density conversion unit 37a performs a pixel density conversion process for 1 / m times in the main scanning direction and 1 / n times in the sub scanning direction of the digital image signal S1 in accordance with the parameter (m, n). As a result, an image signal S1 ′ having a pixel density 1 / (m × n) 2 times that in the case of m = n = 1 is obtained. Specifically, a method by performing a one-dimensional mask operation in both the main and sub scanning directions of the digital image signal S1, a method of thinning out pixels according to the pixel density, a B spline interpolation operation, a Cubic spline interpolation operation, and the like. Pixel density conversion is performed by the following interpolation calculation method (for example, JP-A-8-16767 and 9-321981), linear interpolation calculation method (for example, JP-A-9-50516), or the like. At this time, the pixel density conversion parameter is changed according to the parameter (m, n). For example, the mask coefficient is changed when a one-dimensional mask calculation is performed, the interval between thinnings is performed when a thinning process is performed, and the type of interpolation calculation performed on the digital image signal S1 when an interpolation calculation is performed.
[0074]
Next, the operation of the radiation image information reading apparatus of this embodiment will be described.
[0075]
First, a signal representing “high density” selected by the operator is input to the input means 70. “High density” is an initial setting of the image information reading apparatus, and a parameter (m, n) = (1, 1) corresponding to “high density” is output from the input means 70 and input to the characteristic changing means 60. Is done.
[0076]
The characteristic changing means 60, according to the input parameter (m, n) = (1, 1), the rotational speed of the motor 8 that drives the endless belt 9a, the position of the scanning lens 21a, the control signal to the voltage applying means 39a, The sampling clock of the D / A converter 42a, the sampling clock of the A / D converter 36a, the frequency characteristics of the logarithmic amplifier 16a, the anti-aliasing filter 35a and the pixel density conversion means 37a are each initially set (for high density). Set to be.
[0077]
Next, the stimulable phosphor sheet 1 set at a predetermined position on the endless belt 9a is conveyed (sub-scanned) by the endless belt 9a in the arrow Y direction at the high density speed.
[0078]
On the other hand, the laser light 11 emitted from the laser light source 10 is reflected and deflected by a rotating polygon mirror 12 driven by a motor 20 and rotated at high speed in the direction of the arrow. The deflected laser light 11 is scanned by an endless belt 9a. The sheet 1 that has been conveyed is converged and scanned at a constant speed, and the sheet 1 is subjected to main scanning in the arrow X direction.
[0079]
From the portion of the sheet 1 scanned with the laser light 11, the stimulated emission light 13 a having a light amount corresponding to the image information stored and recorded therein is emitted, and the stimulated emission light 13 a is the main scan of the laser light 11. Light enters the light guide 14a from the incident end face 18a of the light guide 14a arranged along the line (parallel to the X direction), and is guided to the PMT 15a while repeating total reflection inside the light guide 14a. It should be noted that, at the connection portion between the light guide 14a and the PMT 15a, the laser light 11 incident on the light guide 14a together with the stimulated light emission 13a is prevented from entering the PMT 15a, and the incidence of the stimulated light emission 13a is allowed. A laser light cut filter 17a having a band set as described above is provided, and the laser light 11 scattered on the surface of the sheet 1 and the like and incident on the light guide 14a is cut by the laser light cut filter 17a and incident on the PMT 15a. Never do.
[0080]
The PMT 15a is applied with a high voltage corresponding to the sensitivity for high density by the voltage applying means 39a, detects the incident stimulated emission light 13a with the sensitivity for high density, and photoelectrically converts it to an analog image signal QA. Output. The analog image signal QA is input to the logarithmic amplifier 16a, converted into the logarithmic image signal QA 'by the logarithmic amplifier 16a set to the high frequency characteristic, and input to the adder 43a.
[0081]
On the other hand, the high-density shading correction data D1 stored in the memory 41a is converted by the D / A converter 42a into an analog signal D1 'at a sampling rate at a reference clock which is a high-density clock. .
[0082]
Here, the clock input to the D / A converter 42a is a reference clock that is switched and output by a selector 62 provided in the characteristic changing means 60, as shown in FIG.
[0083]
The shading correction analog signal D1 'is input to the adder 43a and added to the logarithmic image signal QA' input from the logarithmic amplifier 16a, whereby the logarithmic image signal QA 'is subjected to shading correction. And is input to the anti-aliasing filter 35a.
[0084]
The anti-aliasing filter 35a is switched to a high-density filter by the characteristic changing means 60, and the input image signal Q1 is appropriately freed of aliasing noise by the high-density filter, and the A / D converter 36a. Is input. The A / D converter 36a converts the input image signal Q1 'into the digital image signal S1 at the sampling rate based on the reference clock switched by the selector 62 of the characteristic changing means 60, and outputs it to the pixel density converting means 37a. .
[0085]
The pixel density conversion unit 37a performs pixel density conversion by multiplying the digital image signal S1 by 1 / m times in the main scanning direction and 1 / n times in the sub-scanning direction. Here, m = n = 1. Therefore, the image signal S1 ′ is obtained without performing any pixel density conversion processing and is output to the image processing apparatus or the like.
[0086]
Next, an operation when “low density” is selected by the operator will be described.
[0087]
When a signal representing “low density” is input to the input means 70 by the operator, the input means 70 sets a parameter (m, n) = (2, 2) corresponding to “low density” as shown in FIG. Output to the characteristic changing means 60. The characteristic changing means 60, according to the input parameter (m, n) = (2, 2), the rotational speed of the motor that drives the endless belt 9a, the position of the scanning lens 21, the control signal to the voltage applying means 39a, D The sampling clock of the / A converter 42a, the sampling clock of the A / D converter 36a, the frequency characteristic of the logarithmic amplifier 16a, the anti-aliasing filter 35a and the pixel density conversion means 37a are set so as to be for low density. To do. Specifically, the rotational speed of the motor that drives the endless belt 9a is changed to a double speed, and the position of the scanning lens 21 is moved to a position where the beam diameter of the laser beam 11 is substantially doubled on the sheet 1. Then, the control signal to the voltage application means 39a is a signal that lowers the sensitivity of the photomultiplier 15a, and the selector 62 (FIG. 2) is a clock output from the frequency divider circuit 61 (obtained by dividing the reference clock). The sampling clock input to the D / A converter 42a and the A / D converter 36a is changed, and the frequency characteristic of the logarithmic amplifier 16a is changed. Is changed, the anti-aliasing filter 35a is switched to a low density filter, and the parameters of the pixel density conversion means 37a are changed.
[0088]
In this way, the characteristics of each part are changed, and image information is read in the same manner as in the case of the high-density reading described above. That is, the stimulable phosphor sheet 1 set at a predetermined position on the endless belt 9a is conveyed (sub-scanned) by the endless belt 9a in the arrow Y direction at a speed twice the high-density speed. On the other hand, the laser light 11 emitted from the laser light source 10 is reflected and deflected by a rotating polygon mirror 12 that rotates at a high speed at the same rotational speed as in high-density reading, and this deflected laser light 11 is scanned by a scanning lens 21. The sheet 1 conveyed on the endless belt 9a is converged and scanned at a constant speed, and the sheet 1 is main-scanned in the arrow X direction. At this time, the beam diameter on the sheet 1 is converged to be twice as large as that in high-density reading.
[0089]
The stimulated emission light 13a emitted from the portion of the sheet 1 scanned with the laser light 11 is guided to the PMT 15a through the light guide 14a.
[0090]
The voltage is applied to the PMT 15a by the voltage applying means 39a so that the sensitivity is lower than that for high-density reading. The incident stimulated emission light 13a is detected with this low-density sensitivity, and the analog image signal QA is detected. Photoelectrically converted to output. The analog image signal QA is input to the logarithmic amplifier 16a, converted into the logarithmic image signal QA 'by the logarithmic amplifier 16a set to the frequency characteristic for low density, and input to the adder 43a.
[0091]
On the other hand, the high-density shading correction data D1 stored in the memory 41a is converted into an analog signal D1 'by the D / A converter 42a at a divide-by-two clock (sampling rate) which is a low-density clock. Converted. That is, the frequency dividing circuit 61 provided in the characteristic changing unit 60 divides the reference clock by two to generate a clock having a cycle twice that of the reference clock, and the selector 62 outputs the clock divided by two. It has been switched to. As a result, the number of pixels of the shading correction analog signal D1 ′ is halved in the main scanning direction with respect to the high-density shading correction data D1 ′.
[0092]
The shading correction analog signal D1 'is input to the adder 43a and added to the logarithmic image signal QA' input from the logarithmic amplifier 16a, whereby the logarithmic image signal QA 'is subjected to shading correction. ′ And input to the anti-aliasing filter 35a.
[0093]
The anti-aliasing filter 35a is switched to a low-density filter by the characteristic changing means 60, and the input image signal Q1 'is appropriately freed of aliasing noise by the low-density filter so that an A / D converter is used. It is input to 36a. The A / D converter 36a converts the input image signal Q1 'into a digital image signal S1 at a sampling rate based on the divide-by-2 clock switched by the selector 62 of the characteristic changing means 60.
[0094]
The pixel density conversion unit 37a performs pixel density conversion of 1 / m times in the main scanning direction and 1 / n times in the sub scanning direction of the digital image signal S1. Here, since m = n = 2, pixel density conversion processing is performed in which the number of pixels is halved in the main scanning direction and the sub-scanning direction of the digital image signal S1. As this pixel density conversion process, a one-dimensional mask calculation will be described here. An example of a one-dimensional filter used for this one-dimensional mask operation is shown below.
[0095]
a (x, 1) = (-8 / 105, -5 / 105,34 / 105,63 / 105,34 / 105, -5 / 105, -8 / 105)
The filter a (x, 1) is used to perform filtering processing at intervals of 1 pixel in the main scanning direction of the digital image signal S1, and then perform filtering processing at intervals of 1 pixel in the sub-scanning direction to perform pixel density conversion. Done. Specifically, assuming that the pixel value of the digital image signal S1 is S1 (x, y) and the pixel value after pixel density conversion in the main scanning direction is S1A (x / 2, y), the pixel value S1A (x / 2 , Y) is calculated by the following equation (1).
[0096]

However, k = 1 to N (N is the number of pixels in the main scanning direction (pixel position or pixel number))
l = 1 to M (M is the number of pixels in the sub-scanning direction (pixel position or pixel number))
Similarly, the image signal S1 ′ having undergone pixel density conversion is obtained by performing the calculation of (1) also in the sub-scanning direction.
[0097]
On the other hand, in such a mask calculation using a one-dimensional filter, data for performing the mask calculation is insufficient at the edge portion of the digital image signal S1. Therefore, when performing filtering processing on pixels at such edge portions, a virtual pixel position is determined outside the pixel, and an appropriate pixel value is assigned to each pixel at the virtual pixel position. The filtering process may be performed with
[0098]
The pixel density conversion in the pixel density conversion unit 37a is not limited to the mask calculation using the one-dimensional filter, and the pixel density conversion may be performed by a process of thinning out pixels or an interpolation calculation. Here, as the interpolation calculation, a high-order interpolation calculation such as a B-spline interpolation calculation focusing on smoothness and a Cubic spline interpolation calculation focusing on sharpness can be applied in addition to linear interpolation.
[0099]
The image signal S1 ′ thus obtained in the pixel density conversion means 37a has a pixel density of 1/16 when “low density” is selected, compared to when “high density” is selected. And output to an image processing apparatus or the like.
[0100]
As described above, according to the image information reading apparatus of the present embodiment, the sub-scanning is 1/2 in the main scanning direction of the laser beam L as compared with the case of high-density reading without changing the main scanning speed of the laser beam. A low-density image signal having a pixel density of ¼, which is ½ the number of pixels in the direction, is obtained. By performing the pixel density conversion process as described above, a low-density image signal having a pixel density of 1/16 as a whole can be obtained. In addition, the characteristic changing unit 60 determines the position of the scanning lens 21, the control signal to the voltage applying unit 39a, the sampling clock of the D / A converter 42a, the frequency characteristic of the logarithmic amplifier 16a, according to the parameter that defines the pixel density. In order to change the parameters of the anti-aliasing filter 35a and the pixel density conversion means 37a, energy per pixel, photoelectric detection sensitivity setting, shading correction, suppression of aliasing noise, etc. suitable for the read pixel density are performed. Image signals can be obtained.
[0101]
In the image information reading apparatus according to the present embodiment, high-density reading is set as an initial setting. However, the image information reading method and apparatus according to the present invention are not limited to this mode. “Standard density reading” is set as the setting, and it may be selectively switched between “high density reading” and “low density reading”.
[0102]
For example, when the main scanning frequency (main scanning speed) is 160 Hz and the pixel density is 10 pix / mm, the main scanning sampling interval, sub-scanning pixel pitch, sub-scanning speed, and anti-aliasing filter cutoff frequency are as follows: Shown in
[0103]
Main scanning sampling interval: 100 μm Sub-scanning pixel pitch: 100 μm
Main scanning sampling period: 1.0 μsec Sub scanning speed: 16 mm / sec
Anti-aliasing filter cutoff frequency: 500 kHz
(Because it is an analog filter, it is desirable to apply 500 kHz or less, for example, 400 kHz.)
On the other hand, at the time of high density reading with a pixel density of 20 pix / mm, the main scanning frequency is assumed to be 160 Hz invariant.
Main scanning sampling interval: 50 μm Sub-scanning pixel pitch: 50 μm
Main scanning sampling period: 0.5 μsec Sub scanning speed: 8 mm / sec
Anti-aliasing filter cutoff frequency: 1000 kHz
On the other hand, at the time of low density reading with a pixel density of 5 pix / mm, the main scanning frequency is set to 160 Hz invariant,
Main scanning sampling interval: 200 μm Sub-scanning pixel pitch: 200 μm
Main scanning sampling period: 2.0 μsec Sub scanning speed: 32 mm / sec
Anti-aliasing filter cutoff frequency: 250 kHz
It becomes.
[0104]
Note that the reading density such as “high density reading” and “low density reading” as described above is not limited to those set in advance, and parameters (m, n) that define the reading density are arbitrarily selected. It may be possible.
[0105]
Details of a method for changing the shading correction data stored in the memory 41a by the characteristic changing means 60 will be described with reference to FIG.
[0106]
As shown in FIG. 4, the memory 41a has a large-capacity hard disk 41c in which shading correction data D1 corresponding to m and n that can be selected is stored in association with these m and n, and the hard disk 41c. A shading memory (SHD memory) 41d, which is a temporary memory for passing the read shading correction data to a shading circuit (SHD circuit) that performs shading correction, is configured. Memory control may be performed for two memories (the hard disk 41c and the SHD memory 41d). Here, as the memory control, for example, shading correction data set in advance for each value of m and n is stored in the hard disk 41c in advance, and shading correction data corresponding to the selected value of m and n is selected. Each time the data is transferred from the hard disk 41c to the SHD memory 41d, the transferred shading correction data is read from the SHD memory 41d and sent to the SHD circuit, or shading correction data set in advance for each of the values of m and n. Are stored in advance in the hard disk 41c, and when desired, such as at startup, all of these shading correction data are stored in the SHD having storage areas corresponding to different addresses for the values of m and n from the hard disk 41c. Transfer to the memory 41d according to the values of m and n, and select Been m, shading correction data corresponding to the value of n, can be applied a method of reading the address of the SHD memory to send the SHD circuit corresponding to the value of the selected m, n.
[0107]
Here, according to the method of transferring only specific shading correction data to the SHD memory 41d for each shading correction, the capacity of the SHD memory 41d can be reduced, and the hardware configuration can be simplified. On the other hand, according to the method of reading all the shading correction data from the hard disk 41c to the SHD memory 41d, the software configuration can be simplified and the reading speed of the correction data from the SHD memory 41d can be increased.
[0108]
FIG. 5 is a diagram showing an embodiment of the second image information reading apparatus of the present invention. As shown in FIG. 5, the image information reading apparatus according to the present embodiment obtains image signals representing a radiation image from both sides of a stimulable phosphor sheet on which a radiation image of a subject is accumulated and recorded. The stimulable phosphor sheet 1 is disposed on endless belts 9 a and 9 b that are rotated by a motor 8. Above the sheet 1, a laser light source 10 that emits laser light 11 as excitation light, a rotary polygon mirror 12 that is rotated by a motor 20 that reflects and deflects the laser light 11 and performs main scanning on the sheet 1, and a laser A scanning lens 21 for forming an image of the light 11 on the sheet 1 is disposed. Further, above the position where the laser beam 11 is scanned, a condensing guide 14a that condenses the stimulated emission light emitted by the scanning of the laser beam 11 from above is arranged close to the sheet 1, and the position A condensing guide 14b that condenses the stimulated emission light from below is disposed substantially perpendicular to the sheet 1. The light collecting guides 14a and 14b are connected to PMTs 15a and 15b for photoelectrically detecting the stimulated emission light, respectively. The PMTs 15a and 15b are connected to logarithmic amplifiers 16a and 16b, and the analog image signals QA and QB detected by the PMTs 15a and 15b are logarithmically amplified according to a preset frequency characteristic to obtain the logarithmic image signal QA. 'And QB' are output.
[0109]
On the other hand, shading correction data D1 and D2 corresponding to a preset sampling interval are stored in the memories 41a and 41b, and the correction data D1 and D2 are preset in the memories 41a and 41b. D / A converters 42a and 42b that convert analog signals D1 'and D2' with a reference clock that is connected to the D / A converters 42a and 42b are connected to the logarithmic amplifiers 16a and 16b. Adders 43a and 43b for adding the correction analog signals D1 'and D2' to the image signals QA 'and QB' and outputting the image signals Q1 and Q2 subjected to shading correction are connected.
[0110]
Furthermore, anti-aliasing filters 35a and 35b for removing aliasing noise (folding noise) due to A / D conversion described later are connected to the adders 43a and 43b. A / D converters 36a and 36b are provided for converting the image signals Q1 'and Q2' into digital image signals S1 and S2 with a preset reference clock. The anti-aliasing filters 35a and 35b are composed of a high-density filter and a low-density filter. The high-density filter is initially selected. However, the anti-aliasing filters 35a and 35b are selected according to the input signal from the characteristic changing means 60 described later. Therefore, it can be switched to a low density filter.
[0111]
Furthermore, the A / D converters 36a and 36b are connected to pixel density conversion means 37a and 37b for converting the pixel density of the digital image signals S1 and S2 to obtain the image signals S1 'and S2'. The image signals S1 ′ and S2 ′ having undergone pixel density conversion are added by the adding means 38 to obtain an added image signal S3.
[0112]
Further, as shown in FIG. 6, the image information reading apparatus according to the present embodiment has a “high density” (10 pix / mm) that is initially set as a read pixel density of image information, In response to the input of the density selected by the operator among “low density” (5 pix / mm), the parameters (m, n) are set to m = n = 1, In the case of “low density”, the input means 70 that outputs the parameter (m, n) with m = n = 2, and the parameter (m, n) output from the input means 70 are input, and these parameters (m , N), the rotational speed of the motor 61 that drives the endless belts 9a, 9b is changed, the output of the laser light source 10 is changed to change the power of the laser light 11, and the scanning lens 21 is moved in the optical axis direction. Laser beam 1 that moves and scans sheet 1 Are changed, the voltage application means 39a and 39b are controlled to change the sensitivity of the PMTs 15a and 15b, and the sampling clocks of the D / A converters 42a and 42b are changed and stored in the memories 41a and 41b. The shading correction data D1 and D2 are changed and output, the timing at which the D / A converters 42a and 42b read the shading correction data from the memories 41a and 41b is changed, and the sampling clocks of the A / D converters 36a and 36b , The frequency characteristics of the logarithmic amplifiers 16a and 16b are changed, the anti-aliasing filters 35a and 35b are switched between high density and low density, and pixel density conversion means 37a and 37b perform pixel density conversion. Characteristic changing means 60 for changing parameters.
[0113]
Here, in the pixel density conversion means 37a and 37b, the pixels which are 1 / m times in the main scanning direction and 1 / n times in the sub scanning direction of the digital image signals S1 and S2 according to the parameters (m, n). 1 / (m × n) than when m = n = 1 after density conversion processing ² Image signals S1 'and S2' having double pixel density are obtained. Specifically, a method by performing a one-dimensional mask operation in both the main and sub scanning directions of the digital image signals S1 and S2, a method of thinning out pixels according to the pixel density, a B-spline interpolation operation, a Cubic spline interpolation operation, etc. Pixel density conversion is performed by a high-order interpolation calculation method, a linear interpolation calculation method, or the like. At this time, the pixel density conversion parameter is changed according to the parameter (m, n). For example, the mask coefficient is changed when a one-dimensional mask calculation is performed, the interval between thinnings is performed when a thinning process is performed, and the type of interpolation calculation applied to the digital image signals S1 and S2 is changed when an interpolation calculation is performed.
[0114]
In addition, in the adding means 38, as described in the above-mentioned JP-A-7-287330, filtering processing by a filter having a frequency response characteristic that increases the S / N of the added image signal S3 is performed on the image signal S1 ′, Although it is preferable to adopt a method of obtaining the added image signal S3 after applying to S2 ', the image signals S1' and S2 'may be simply added. In addition, when performing a filtering process, you may make it perform in the pixel density conversion means 37a and 37b.
[0115]
Next, the operation of the radiation image information reading apparatus of this embodiment will be described.
[0116]
First, a signal representing “high density” selected by the operator is input to the input means 70. “High density” is an initial setting of the image information reading apparatus, and a parameter (m, n) = (1, 1) corresponding to “high density” is output from the input means 70 and input to the characteristic changing means 60. Is done.
[0117]
The characteristic changing means 60 determines the rotational speed of the motor 8 that drives the endless belts 9a and 9b, the output of the laser light source 10, the position of the scanning lens 21, and the voltage according to the input parameters (m, n) = (1, 1). Control signals to the application means 39a, 39b, sampling clocks of the D / A converters 42a, 42b, timings at which the D / A converters 42a, 42b read the shading correction data D1, D2 from the memories 41a, 41b, A / D The sampling clocks of the converters 36a and 36b, the frequency characteristics of the logarithmic amplifiers 16a and 16b, the anti-aliasing filters 35a and 35b, and the pixel density conversion means 37a and 37b are set to initial settings (for high density), respectively. set.
[0118]
When the stimulable phosphor sheet 1 on which the radiographic image of the subject is accumulated and recorded is placed on the endless belts 9a and 9b, it is conveyed (sub-scanned) in the arrow Y direction by the endless belts 9a and 9b. On the other hand, the laser light 11 emitted from the laser light source 10 is reflected and deflected by a rotating polygon mirror 12 driven by a motor 20 and rotated at a high speed in the direction of an arrow, enters a sheet 1 through a scanning lens 21, and enters a sub-scanning direction (arrow). Main scanning is performed in the direction of the arrow X substantially perpendicular to the Y direction. From the location of the sheet 1 irradiated with the laser beam 11, the stimulated emission lights 13a and 13b having a light quantity corresponding to the stored and recorded radiographic image information (here, the stimulated emission lights 13a and 13b are respectively the sheet 1). (Showing a divergence from the upper side (front surface) and the lower side (back surface)). The stimulated emission light 13a is guided by the light collecting guide 14a and is detected photoelectrically by the PMT 15a. The stimulated emission light 13a that has entered the condensing guide 14a from the incident end face 18a travels through the inside of the condensing guide 14a repeatedly, undergoes total reflection, exits from the exit end face, is received by the PMT 15a, and is displayed as a radiation image. The amount of the emitted light 13a is converted into an analog image signal QA by the PMT 15a. Similarly, the stimulated emission light 13b is guided by the light collecting guide 14b, is detected photoelectrically by the PMT 15b, and is converted into an analog image signal QB.
[0119]
These analog image signals QA and QB are input to logarithmic amplifiers 16a and 16b, converted into logarithmic image signals QA 'and QB' by a logarithmic amplifier 34 set to a frequency characteristic for high density, and adders 43a and 43b. Is input.
[0120]
On the other hand, the high-density shading correction data D1 and D2 stored in the memories 41a and 41b are read by the D / A converters 42a and 42b at a high-density timing, and at a high-density clock. It is converted into analog signals D1 'and D2' at a sampling rate with a certain reference clock.
[0121]
Here, the clocks input to the D / A converters 42a and 42b are reference clocks that are switched and output by a selector 62 provided in the characteristic changing means 60, as shown in FIG.
[0122]
The shading correction analog signals D1 'and D2' are input to the adders 43a and 43b and added to the logarithmic image signals QA 'and QB' input from the logarithmic amplifiers 16a and 16b. 'And QB' are converted into image signals Q1 and Q2 subjected to shading correction and input to the anti-aliasing filters 35a and 35b.
[0123]
The anti-aliasing filters 35a and 35b are switched to high-density filters by the characteristic changing means 60, and the input image signals Q1 and Q2 are appropriately freed of aliasing noise by the high-density filters, and A / The signals are input to the D converters 36a and 36b.
[0124]
The A / D converters 36a and 36b convert the input image signals Q1 'and Q2' into digital image signals S1 and S2, respectively, at the sampling rate based on the reference clock switched by the selector 62 of the characteristic changing means 60.
[0125]
The pixel density conversion units 37a and 37b perform pixel density conversion by multiplying the digital image signals S1 and S2 by 1 / m times in the main scanning direction and 1 / n times in the sub-scanning direction. Here, m = n = 1, the image signals S1 ′ and S2 ′ are obtained without performing any pixel density conversion processing.
[0126]
The adding means 38 is a filter having a frequency response characteristic for increasing the S / N of the added image signal S3 as described in Japanese Patent Laid-Open No. 7-287330 with respect to the image signals S1 'and S2'. A filtering process is performed, and the image signals S1 ′ and S2 ′ subjected to the filtering process are added together with corresponding pixels to obtain an added image signal S3, which is output to an image processing apparatus or the like.
[0127]
Next, an operation when “low density” is selected by the operator will be described.
[0128]
When a signal representing “low density” is input to the input unit 70 by the operator, the input unit 70 outputs a parameter (m, n) = (2, 2) corresponding to “low density” to the characteristic changing unit 60. .
[0129]
The characteristic changing means 60 determines the rotational speed of the motor 8 that drives the endless belts 9a and 9b, the output of the laser light source 10, the position of the scanning lens 21, and the voltage according to the input parameters (m, n) = (2, 2). Control signals to the application means 39a, 39b, sampling clocks of the D / A converters 42a, 42b, timings at which the D / A converters 42a, 42b read the shading correction data D1, D2 from the memories 41a, 41b, A / D The sampling clocks of the converters 36a and 36b, the frequency characteristics of the logarithmic amplifiers 16a and 16b, the anti-aliasing filters 35a and 35b, and the pixel density conversion means 37a and 37b are set so as to be for low density.
[0130]
Specifically, the rotational speed of the motor 8 that drives the endless belts 9a and 9b is changed to a double speed, the output of the laser light source 10 is approximately doubled, and the position of the scanning lens 21 is set to the beam diameter of the laser light 11. Is moved to a position approximately doubled on the sheet 1, and the control signal to the voltage applying means 39a and 39b is made a signal that lowers the sensitivity of the photomultipliers 15a and 15b, and the D / A converters 42a and 42b The timing at which the shading correction data D1 and D2 are read from the memories 41a and 41b is changed, and the selector 62 (see FIG. 7) is output from the frequency divider circuit 61 (the clock obtained by dividing the reference clock). Switching to a clock having a cycle twice that of the reference clock), and input to the D / A converters 42a and 42b and the A / D converters 36a and 36b. Change the ring clock, the logarithmic amplifier 16a, to change the frequency characteristic of 16b, switching the anti-aliasing filter 35a, and 35b to the low density filter, change the parameters of the pixel density converting means 37a, 37b.
[0131]
In this way, the characteristics of each part are changed, and image information is read in the same manner as in the case of the high-density reading described above.
[0132]
That is, the stimulable phosphor sheet 1 set at a predetermined position on the endless belts 9a and 9b is conveyed by the endless belts 9a and 9b in the direction of the arrow Y at a speed twice as high as the above-mentioned high-density speed. On the other hand, the laser light 11 having twice the power for high density emitted from the laser light source 10 is reflected and deflected by the rotating polygon mirror 12 that rotates at the same rotational speed as that during high-density reading, The deflected laser light 11 is converged by the scanning lens 21 on the sheet 1 conveyed on the endless belts 9a and 9b and scanned at a constant speed, and the sheet 1 is main-scanned in the arrow X direction. At this time, the beam diameter on the sheet 1 is converged to be twice as large as that in high-density reading.
[0133]
The photostimulated light 13a and 13b emitted from the portion of the sheet 1 scanned with the laser light 11 is guided to the PMTs 15a and 15b through the light collecting guides 14a and 14b. The PMTs 15a and 15b are applied with a voltage that has a lower sensitivity than that for high-density reading by the voltage applying means 39a and 39b, and the incident stimulated emission lights 13a and 13b are detected with this low-density sensitivity. The analog image signals QA and QB are photoelectrically converted and output. The analog image signals QA and QB are input to logarithmic amplifiers 16a and 16b, converted into logarithmic image signals QA 'and QB' by logarithmic amplifiers 16a and 16b set to low frequency characteristics, and adders 43a and 16B. 43b.
[0134]
On the other hand, the high-density shading correction data D1 and D2 stored in the memories 41a and 41b are read out by the D / A converters 42a and 42b at a low-density timing, and at a low-density clock. It is converted into analog signals D1 'and D2' at a sampling rate with a certain frequency divided by two. That is, the frequency dividing circuit 61 provided in the characteristic changing unit 60 divides the reference clock by two to generate a clock having a cycle twice that of the reference clock, and the selector 62 outputs the clock divided by two. It has been switched to. As a result, the number of pixels of the shading correction analog signals D1 'and D2' is halved in the main scanning direction with respect to the high density shading correction data D1 and D2.
[0135]
The shading correction analog signals D1 'and D2' are input to the adders 43a and 43b and added to the logarithmic image signals QA 'and QB' input from the logarithmic amplifiers 16a and 16b. 'And QB' are converted into image signals Q1 and Q2 subjected to shading correction and input to the anti-aliasing filters 35a and 35b.
[0136]
The anti-aliasing filters 35a and 35b are switched to low-density filters by the characteristic changing means 60, and the input image signals Q1 and Q2 are appropriately freed of aliasing noise by the low-density filters, and the A / A The signals are input to the D converters 36a and 36b.
[0137]
The A / D converters 36a and 36b convert the input image signals QA 'and QB' into digital image signals S1 and S2 at a sampling rate based on the divide-by-two clock switched by the selector 62 of the characteristic changing means 60. To do.
[0138]
The pixel density conversion units 37a and 37b perform pixel density conversion of 1 / m times in the main scanning direction and 1 / n times in the sub scanning direction of the digital image signals S1 and S2. Here, since m = n = 2, pixel density conversion processing is performed in which the number of pixels is halved in the main scanning direction and the sub-scanning direction of the digital image signals S1 and S2. As this pixel density conversion process, a one-dimensional mask calculation will be described here. An example of a one-dimensional filter used for this one-dimensional mask operation is shown below.
[0139]
a (x, 1) = (-8 / 105, -5 / 105,34 / 105,63 / 105,34 / 105, -5 / 105, -8 / 105)
Then, after filtering the digital image signals S1 and S2 in the main scanning direction using the filter a (x, 1) at intervals of 1 pixel, the filtering processing is performed at intervals of 1 pixel in the sub-scanning direction. Conversion is performed. More specifically, the pixel value of the digital image signal S1 (S2 is the same, so only S1 will be described here) is set to S1 (x, y), and the pixel value after pixel density conversion in the main scanning direction is set to S1A. If (x / 2, y), the pixel value S1A (x / 2, y) is calculated by the following equation (1).
[0140]

However, k = 1 to N (N is the number of pixels in the main scanning direction (pixel position or pixel number))
l = 1 to M (M is the number of pixels in the sub-scanning direction (pixel position or pixel number))
Similarly, the image signal S1 ′, S2 ′ having undergone pixel density conversion is obtained by performing the calculation of Expression (1) also in the sub-scanning direction.
[0141]
On the other hand, in the mask calculation using such a one-dimensional filter, data for performing the mask calculation is insufficient at the edge portions of the digital image signals S1 and S2. For example, in the image signal shown in FIG. 8, when the filtering process is performed on the pixels of S1 (1, 1) and S1 (N, 1) (shaded area), data for three pixels is insufficient. In this case, the virtual pixel positions S1 (-1,1), S1 (-2,1), S1 (-3,1) and S1 (N + 1,1), S1 (N + 2,1), S1 (N + 3, 1), the data value of the pixel positions S1 (1,1) and S1 (N, 1) is copied to this virtual pixel position, and the filtering process is performed assuming that the data value exists at the virtual pixel position. Can be done.
[0142]
The pixel density conversion in the pixel density conversion units 37a and 37b is not limited to the mask calculation using the one-dimensional filter, and the pixel density conversion may be performed by a process of thinning out pixels or an interpolation calculation.
[0143]
Here, as the interpolation calculation, a high-order interpolation calculation such as a B-spline interpolation calculation focusing on smoothness and a Cubic spline interpolation calculation focusing on sharpness can be applied in addition to linear interpolation.
[0144]
Here, the Cubic spline interpolation calculation and the B spline interpolation calculation will be described. The image signals S1 and S2 used in this embodiment are sampling points (pixels) X arranged in one direction sampled at equal intervals. _k-2 , X _k-1 , X _k , X _{k + 1} , X _{k + 2} ,... Corresponding signal values (S _k-2 , S _k-1 , S _k , S _{k + 1} , S _{k + 2} , ...). Cubic spline interpolation operation is the original sampling point (pixel) X _k ~ X _{k + 1} Interpolation point X provided between _p Interpolation data Y in the cubic Cubic spline interpolation equation (2) representing the interpolation data Y ′ _k-1 , Y _k , Y _{k + 1} , Y _{k + 2} Interpolation coefficient c corresponding to each _k-1 , C _k , C _{k + 1} , C _{k + 2} Are obtained by the operations shown below.
[0145]
Y '= c _k-1 Y _k-1 + C _k Y _k + C _{k + 1} Y _{k + 1} + C _{k + 2} Y _{k + 2} (2)
c _k-1 = (-T ^Three + 2t ² -T) / 2
c _k = (3t ^Three -5t ² +2) / 2
c _{k + 1} = (-3t ^Three + 4t ² + T) / 2
c _{k + 2} = (T ^Three -T ² ) / 2
(However, t (0 ≦ t ≦ 1) is set to 1 for the lattice interval and the pixel X _k Interpolation point X with reference to _p Pixel X _{k + 1} Indicates the position in the direction. )
The B-spline interpolation operation uses the original sampling point X _k ~ X _{k + 1} Interpolation point X provided between _p Interpolation data Y in the cubic B-spline interpolation equation (3) representing the interpolation data Y ′ _k-1 , Y _k , Y _{k + 1} , Y _{k + 2} Interpolation coefficient b respectively corresponding to _k-1 , B _k , B _{k + 1} , B _{k + 2} Are obtained by the operations shown below.
[0146]
Y '= b _k-1 Y _k-1 + B _k Y _k + B _{k + 1} Y _{k + 1} + B _{k + 2} Y _{k + 2} (3)
b _k-1 = (-T ^Three + 3t ² -3t + 1) / 6
b _k = (3t ^Three -6t ² +4) / 6
b _{k + 1} = (-3t ^Three + 3t ² + 3t + 1) / 6
b _{k + 2} = T ^Three / 6
(However, t (0 ≦ t ≦ 1) is set to 1 for the lattice interval and the pixel X _k Interpolation point X with reference to _p Pixel X _{k + 1} Indicates the position in the direction. )
In the present embodiment, the type of interpolation calculation including linear interpolation calculation may be selected according to the values of m and n.
[0147]
The image signals S1 ′ and S2 ′ thus obtained in the pixel density conversion means 37a and 37b are input to the addition means 38. Here, when “low density” is selected, the pixel density is 1/16 compared to when “high density” is selected.
[0148]
The adding means 38 is a filter having a frequency response characteristic for increasing the S / N of the added image signal S3 as described in Japanese Patent Laid-Open No. 7-287330 with respect to the image signals S1 'and S2'. A filtering process is performed, and the image signals S1 ′ and S2 ′ subjected to the filtering process are added together with corresponding pixels to obtain an added image signal S3, which is output to an image processing apparatus or the like.
[0149]
As described above, according to the image information reading apparatus of this embodiment, the main scanning speed of the laser beam 11 is not changed, and the sub scanning direction of the laser beam 11 is ½, compared to the case of high density reading. An image signal having a pixel density of 1/4, which is 1/2 the number of pixels in the scanning direction, is obtained, and further, the number of pixels is 1/2 in the main scanning direction and 1/2 in the sub-scanning direction. A low density image signal having a pixel density of 1/16 can be obtained by performing the pixel density conversion process. In addition, the characteristic changing means 60 determines the position of the scanning lens 21, the control signal to the voltage applying means 39a and 39b, the sampling clock of the D / A converters 42a and 42b, and the logarithmic amplifier 16a according to the parameters that define the pixel density. , 16b frequency characteristics, anti-aliasing filters 35a, 35b, and pixel density conversion means 37a, 37b are each changed, so that energy per pixel suitable for read pixel density, photoelectric detection sensitivity setting, shading An image signal subjected to correction, suppression of aliasing noise, and the like can be obtained.
[0150]
In particular, when performing double-sided reading as in this embodiment, in order to sufficiently apply energy from the laser beam 11 to the back side of the sheet 1, the scanning speed is reduced as compared with a method of reading from only one side. In this case, the sub-scanning speed can be increased if the pixel density is allowed to be rough, and the scanning time per sheet can be shortened.
[0151]
In addition, by performing pixel density conversion processing on the two digital image signals S1 and S2, compared to the case where pixel density conversion is performed on the addition image signal, addition mask processing when obtaining the addition image signal is performed. The amount of calculation to be performed can be reduced, thereby shortening the calculation time of the addition calculation and performing processing at high speed.
[0152]
In the image information reading apparatus according to the present embodiment, high-density reading is set as an initial setting. However, the image information reading method and apparatus according to the present invention are not limited to this mode. “Standard density reading” is set as the setting, and it may be switched to “high density reading” or “low density reading”.
[0153]
For example, when the main scanning frequency (main scanning speed) is 160 Hz and the pixel density of 10 pix / mm is standard density reading, the main scanning sampling interval, sub scanning pixel pitch, sub scanning speed, and anti-aliasing filter cutoff frequency are as follows: Shown in
[0154]
Main scanning sampling interval: 100 μm Sub-scanning pixel pitch: 100 μm
Main scanning sampling period: 1.0 μsec Sub scanning speed: 16 mm / sec
Anti-aliasing filter cutoff frequency: 500 kHz
(Because it is an analog filter, the cut-off frequency is preferably 500 kHz or less, and preferably 400 kHz, for example).
On the other hand, at the time of high-density reading with a pixel density of 20 pix / mm, the main scanning frequency is assumed to be 160 Hz unchanged,
Main scanning sampling interval: 50 μm Sub-scanning pixel pitch: 50 μm
Main scanning sampling period: 0.5 μsec Sub scanning speed: 8 mm / sec
Anti-aliasing filter cutoff frequency: 1000 kHz
On the other hand, in the case of low density reading with a pixel density of 5 pix / mm, the main scanning frequency is assumed to be 160 Hz unchanged,
Main scanning sampling interval: 200 μm Sub-scanning pixel pitch: 200 μm
Main scanning sampling period: 2.0 μsec Sub scanning speed: 32 mm / sec
Anti-aliasing filter cutoff frequency: 250 kHz
It becomes.
[0155]
Note that the reading density such as “high density reading” and “low density reading” as described above is not limited to those set in advance, and parameters (m, n) that define the reading density are arbitrarily selected. It may be possible.
[0156]
In the above embodiment, pixel density conversion processing is performed on the digital image signals S1 and S2. However, the digital image signals S1 and S2 are added first to obtain an added image signal S3, and this added image signal S3. Pixel density conversion processing may be performed on the.
[0157]
Further, in the above embodiment, the pixel density conversion means 37a, 37b performs pixel density conversion so that the digital image signals S1, S2 are 1 / m times in the main scanning direction and 1 / n times in the sub scanning direction. However, the pixel density conversion may be performed so that a / m (a> 0) times in the main scanning direction and a / n times in the sub-scanning direction. In this case, the pixel density of the added image signal S3 is (a / (m × n)) ² Doubled.
[0158]
FIG. 9 is a diagram showing an embodiment of the third image information reading apparatus of the present invention. In the illustrated image information reading apparatus, a stimulable phosphor sheet 1 on which radiation image information is accumulated and recorded is disposed on an endless belt 9 a that is rotated by a motor 8, and a laser that excites the sheet 1 above the sheet 1. A laser light source 10 that emits light 11, a rotary polygon mirror 20 (corresponding to a main scanning frequency of 160 Hz) that is rotated by a motor 12 to reflect and deflect the laser light 11, and a laser beam 11 that is reflected and deflected by the rotary polygon mirror 20 is a sheet. A scanning lens 21 that converges on 1 and performs main scanning at a constant speed is disposed.
[0159]
Further, immediately above the sheet 1 to which the laser beam 11 is scanned, the stimulated emission light 13a emitted from the upper surface of the sheet 1 is excited by the laser beam 11 and corresponding to the stored and recorded image information. A light guide 14a that collects light more closely is disposed. Connected to the light guide 14a is a photomultiplier (photomultiplier tube) 15a that photoelectrically detects the condensed stimulated emission light 13a and converts it into an analog image signal QA. The photomultiplier 15a detects the stimulated emission light 13a with a sensitivity corresponding to the voltage applied by the voltage applying means 39a.
[0160]
Further, a logarithmic amplifier 16a is connected to the photomultiplier 15a, and the analog image signal QA detected by the photomultiplier 15a is logarithmically amplified according to a preset frequency characteristic to obtain a logarithmic image signal QA. ′ Is output.
[0161]
On the other hand, shading correction data D1 corresponding to a preset sampling interval is stored in the memory 41a, and the correction data D1 is stored in the memory 41a with an analog signal D1 ′ using a preset reference clock. Is connected to the D / A converter 41a. The D / A converter 42a adds the correction analog signal D1 'to the logarithmic image signal QA' output from the logarithmic amplifier 16a. An adder 43a for outputting the image signal Q1 subjected to the shading correction is connected.
[0162]
Further, an anti-aliasing filter 35a that removes aliasing noise (folding noise) caused by A / D conversion, which will be described later, is connected to the adder 43a, and the filtered image signal Q1 'is connected to the subsequent stage. Is converted to a digital image signal S1 with a preset reference clock. The anti-aliasing filter 35a includes a high-density filter and a low-density filter, and the high-density filter is initially selected. However, the anti-aliasing filter 35a is low depending on the input signal from the characteristic changing means 60 described later. It can also be switched to a density filter.
[0163]
Furthermore, the image information reading apparatus of the present embodiment has a “high density” (10 pix / mm) that is initially set as a pixel density for reading image information, and a lower density than this high density. It receives the density selected by the operator from “Low Density” (5 pix / mm). When “High Density”, the parameter (m, n) is set to m = n = 1, and “Low Density” In some cases, the input means 70 outputs the parameter (m, n) as m = n = 2, and the parameter (m, n) output from the input means 70 is input to these parameters (m, n). Accordingly, the rotational speed of the motor 8 that drives the endless belt 9a is changed, the scanning lens 21 is moved in the optical axis direction, the beam diameter of the laser light 11 that scans the sheet 1 is changed, and the voltage applying means 39a is controlled. Photo multiplier 15 , Change the sampling clock of the D / A converter 42a to change and output the shading correction data stored in the memory 41a, change the sampling clock of the A / D converter 36a, There is provided characteristic changing means 60 for changing the frequency characteristic of the logarithmic amplifier 16a and switching the anti-aliasing filter 35a between high density and low density.
[0164]
Next, the operation of the radiation image information reading apparatus of this embodiment will be described.
[0165]
First, a signal representing “high density” selected by the operator is input to the input means 70. “High density” is an initial setting of the image information reading apparatus, and a parameter (m, n) = (1, 1) corresponding to “high density” is output from the input means 70 and input to the characteristic changing means 60. Is done.
[0166]
The characteristic changing means 70, according to the input parameter (m, n) = (1, 1), the rotational speed of the motor 8 that drives the endless belt 9a, the position of the scanning lens 21, the control signal to the voltage applying means 39a, The sampling clock of the D / A converter 42a, the sampling clock of the A / D converter 36, the frequency characteristic of the logarithmic amplifier 16a, and the anti-aliasing filter 35a are set so as to have initial settings (for high density), respectively. To do.
[0167]
Next, the stimulable phosphor sheet 1 set at a predetermined position on the endless belt 9a is conveyed (sub-scanned) by the endless belt 9a in the arrow Y direction at the high density speed.
[0168]
On the other hand, the laser beam 11 emitted from the laser light source 10 is reflected and deflected by a rotating polygon mirror 20 driven by a motor 12 and rotated at a high speed in the direction of the arrow. The deflected laser beam 11 is scanned by an endless belt 9a. The sheet 1 that has been conveyed is converged and scanned at a constant speed, and the sheet 1 is subjected to main scanning in the arrow X direction.
[0169]
From the portion of the sheet 1 scanned with the laser light 11, the stimulated emission light 13 a having a light amount corresponding to the image information stored and recorded therein is emitted, and the stimulated emission light 13 a is the main scan of the laser light 11. Light enters the light guide 14a from the incident end face 18a of the light guide 14a disposed along the line, and is guided to the photomultiplier 15a through the laser light cut filter 17a while repeating total reflection inside the light guide 14a. Lighted.
[0170]
The photomultiplier 15a is applied with a high voltage corresponding to the sensitivity for high density by the voltage applying means 39a, detects the incident stimulated emission light 13a with the sensitivity for high density, and converts the analog image signal QA to the analog image signal QA. Convert and output.
[0171]
The analog image signal QA is input to the logarithmic amplifier 16a, converted into the logarithmic image signal QA 'by the logarithmic amplifier 16a set to the high frequency characteristic, and input to the adder 43a.
[0172]
On the other hand, the high-density shading correction data D1 stored in the memory 41a is converted by the D / A converter 42a into an analog signal D1 'at a sampling rate at a reference clock which is a high-density clock. .
[0173]
Here, the clock input to the D / A converter 42a is a reference clock that is switched and output by a selector 62 provided in the characteristic changing means 60, as shown in FIG.
[0174]
The shading correction analog signal D1 'is input to the adder 43a and added to the logarithmic image signal QA' input from the logarithmic amplifier 16a, whereby the logarithmic image signal QA 'is subjected to shading correction. And is input to the anti-aliasing filter 35a.
[0175]
The anti-aliasing filter 35a is switched to a high-density filter by the characteristic changing means 60, and the input image signal Q1 is converted into a signal Q1 'from which aliasing noise has been appropriately removed by this high-density filter. To the A / D converter 36a.
[0176]
The A / D converter 36a converts the input image signal Q1 'into the digital image signal S1 at the sampling rate based on the reference clock switched by the selector 62 of the characteristic changing means 60, and outputs the digital image signal S1 to an image processing apparatus or the like. .
[0177]
Next, an operation when “low density” is selected by the operator will be described.
[0178]
When a signal representing “low density” is input to the input unit 70 by the operator, the input unit 70 outputs a parameter (m, n) = (2, 2) corresponding to “low density” to the characteristic changing unit 60. .
[0179]
The characteristic changing means 70, based on the input parameters (m, n) = (2, 2), the rotational speed of the motor that drives the endless belt 9a, the position of the scanning lens 21, the control signal to the voltage applying means 39a, D The sampling clock of the / A converter 42a, the sampling clock of the A / D converter 36a, the frequency characteristic of the logarithmic amplifier 16a, and the anti-aliasing filter 35a are set so as to be for low density. Specifically, the rotational speed of the motor that drives the endless belt 9a is changed to a double speed, and the position of the scanning lens 21 is moved to a position where the beam diameter of the laser beam 11 is substantially doubled on the sheet 1. Then, the control signal to the voltage application means 39a is a signal that lowers the sensitivity of the photomultiplier 15a, and the selector 62 (see FIG. 2) outputs the clock output from the frequency divider circuit 61 (the reference clock is divided). The sampling clock input to the D / A converter 42a and the A / D converter 36a is changed, and the frequency of the logarithmic amplifier 16a is changed. The characteristic is changed, and the anti-aliasing filter 35a is switched to a low density filter.
[0180]
In this way, the characteristics of each part are changed, and image information is read in the same manner as in the case of the high-density reading described above.
[0181]
That is, the stimulable phosphor sheet 1 set at a predetermined position on the endless belt 9a is conveyed (sub-scanned) by the endless belt 9a in the arrow Y direction at a speed twice the high-density speed. On the other hand, the laser light 11 emitted from the laser light source 10 is reflected and deflected by a rotating polygon mirror 20 that rotates at a high speed at the same rotational speed as in high-density reading, and the deflected laser light 11 is reflected by a scanning lens 21. The sheet 1 conveyed on the endless belt 9a is converged and scanned at a constant speed, and the sheet 1 is main-scanned in the arrow X direction. At this time, the beam diameter on the sheet 1 is converged to be twice as large as that in high-density reading.
[0182]
The stimulated emission light 13a emitted from the portion of the sheet 1 scanned with the laser light 11 is guided to the photomultiplier 15a through the light guide 14a and the laser light cut filter 17a.
[0183]
The photomultiplier 15a is applied with a voltage that has a lower sensitivity than that for high-density reading by the voltage applying means 39a, detects the incident stimulated emission light 13a with this low-density sensitivity, The image signal QA is photoelectrically converted and output.
[0184]
The analog image signal QA is input to the logarithmic amplifier 16a, converted into the logarithmic image signal QA 'by the logarithmic amplifier 16a set to the frequency characteristic for low density, and input to the adder 43a.
[0185]
On the other hand, the high-density shading correction data D1 stored in the memory 41a is converted into an analog signal D1 ′ by the D / A converter 42a at a sampling rate at a divide-by-two clock that is a low-density clock. Converted. That is, the frequency dividing circuit 61 provided in the characteristic changing unit 60 divides the reference clock by two to generate a clock having a cycle twice that of the reference clock, and the selector 62 outputs the clock divided by two. It has been switched to. As a result, the number of pixels of the shading correction analog signal D1 ′ is halved in the main scanning direction with respect to the high density shading correction data QA ′.
[0186]
The shading correction analog signal D1 'is input to the adder 43a and added to the logarithmic image signal QA' input from the logarithmic amplifier 16a, whereby the logarithmic image signal QA 'is subjected to shading correction. And is input to the anti-aliasing filter 35a.
[0187]
The anti-aliasing filter 35a is switched to a low density filter by the characteristic changing means 60, and the input image signal Q1 is converted into a signal Q1 'from which aliasing noise has been appropriately removed by the low density filter. To the A / D converter 36a.
[0188]
The A / D converter 36a converts the input image signal Q1 'into a digital image signal S1 at a sampling rate based on the divide-by-2 clock switched by the selector 62 of the characteristic changing means 60.
[0189]
As described above, according to the image information reading apparatus of the present embodiment, the sub-scanning is 1/2 in the main scanning direction of the laser beam L as compared with the case of high-density reading without changing the main scanning speed of the laser beam. A low-density image signal having a pixel density of 1/4 as a whole, which is 1/2 the number of pixels in the direction, can be obtained. In addition, the characteristic changing unit 60 determines the position of the scanning lens 21, the control signal to the voltage applying unit 39a, the sampling clock of the D / A converter 42a, the frequency characteristic of the logarithmic amplifier 16a, according to the parameter that defines the pixel density. Since the anti-aliasing filter 35a is changed, it is possible to obtain an image signal subjected to energy application per pixel, photoelectric detection sensitivity setting, shading correction, aliasing noise suppression, and the like suitable for the read pixel density. it can.
[0190]
In the image information reading apparatus according to the present embodiment, high-density reading is set as an initial setting. However, the image information reading method and apparatus according to the present invention are not limited to this mode. “Standard density reading” is set as the setting, and it may be switched to “high density reading” or “low density reading”.
[0191]
For example, when the main scanning frequency (main scanning speed) is 160 Hz and the pixel density is 10 pix / mm, the main scanning sampling interval, the sub scanning pixel pitch, the sub scanning speed, and the anti-aliasing filter cutoff frequency are as follows: Shown in
[0192]
Main scanning sampling interval: 100 μm Sub-scanning pixel pitch: 100 μm
Main scanning sampling period: 1.0 μsec Sub scanning speed: 16 mm / sec
Anti-aliasing filter cutoff frequency: 500 kHz
(Because it is an analog filter, it is preferably 500 kHz or less, and preferably 400 kHz or the like is applied.)
On the other hand, at the time of high-density reading with a pixel density of 20 pix / mm, the main scanning frequency is assumed to be 160 Hz unchanged,
Main scanning sampling interval: 50 μm Sub-scanning pixel pitch: 50 μm
Main scanning sampling period: 0.5 μsec Sub scanning speed: 8 mm / sec
Anti-aliasing filter cutoff frequency: 1000 kHz
On the other hand, in the case of low density reading with a pixel density of 5 pix / mm, the main scanning frequency is assumed to be 160 Hz unchanged,
Main scanning sampling interval: 200 μm Sub-scanning pixel pitch: 200 μm
Main scanning sampling period: 2.0 μsec Sub scanning speed: 32 mm / sec
Anti-aliasing filter cutoff frequency: 250 kHz
It becomes.
[0193]
Note that the reading density such as “high density reading” and “low density reading” as described above is not limited to those set in advance, and parameters (m, n) that define the reading density are arbitrarily selected. It may be possible.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of an embodiment of a first image information reading apparatus of the present invention.
FIG. 2 is a diagram showing an embodiment of a configuration for changing a clock;
3 is a diagram showing a configuration of characteristic changing means in the embodiment shown in FIG. 1;
FIG. 4 is a diagram for explaining details of memory management in the embodiment shown in FIG. 1;
FIG. 5 is a diagram showing an embodiment of a second image information reading apparatus of the present invention.
6 is a diagram showing a configuration of characteristic changing means in the embodiment shown in FIG. 5;
FIG. 7 is a diagram showing an embodiment of a configuration for changing a clock;
FIG. 8 is a diagram for explaining filtering processing;
FIG. 9 is a diagram showing an embodiment of a third image information reading apparatus of the present invention.
[Explanation of symbols]
1 Storage phosphor sheet
8 Motor
9a, 9b Endless belt
10 Laser light source
11 Laser light
12 rotating polygon mirror
14a, 14b Light guide
15a, 15b Photo multiplayer
16a, 16b logarithmic amplifier
17a, 17b Laser light cut filter
20 Motor
21 Scanning lens
35a, 35b Anti-aliasing filter
36a, 36b A / D converter
37a, 37b Pixel density conversion means
38 Adding means
39a, 39b Voltage applying means
41a, 41b memory
42a, 42b A / D converter
43a, 43b Adder
60 Characteristic changing means
70 Input means

Claims (14)

The light beam is sub-scanned in a direction substantially perpendicular to the main scanning direction while repeatedly scanning the light beam at a constant speed in a constant direction on the scanning sheet on which the image information is recorded. A digital image having a predetermined pixel density is obtained by scanning almost the entire surface of the scanning sheet, photoelectrically detecting signal light emitted from the scanned sheet by scanning the light beam, and sampling and quantizing the obtained analog image signal. In an image information reading method for obtaining a signal,
The sub-scan speed is multiplied by m (m> 0), the sampling interval is multiplied by n (n> 0),
An image information reading method, wherein at least one of the following characteristics (1) to ( 4 ) is changed in accordance with m and n.
( 1 ) Preset shading correction data when performing shading correction on the analog image signal ( 2 ) Timing for outputting the shading correction data from the memory storing the shading correction data ( 3 ( 4 ) Frequency transfer characteristics when the analog image signal is logarithmically amplified ( 4 ) Cut-off frequency when filtering to remove aliasing noise is performed prior to sampling the analog image signal   After the sub-scan speed is multiplied by m and the sampling interval is multiplied by n, the number of pixels in the main scanning direction is further increased by a / m (a> 0), and the number of pixels in the sub-scanning direction is determined by a / n. 2. The image information reading method according to claim 1, wherein a pixel density conversion process for doubling is performed. The light beam is sub-scanned in a direction substantially perpendicular to the main scanning direction while repeatedly scanning the light beam at a constant speed in a constant direction on the scanning sheet on which the image information is recorded. A digital image having a predetermined pixel density is obtained by scanning almost the entire surface of the scanning sheet, photoelectrically detecting signal light emitted from the scanned sheet by scanning the light beam, and sampling and quantizing the obtained analog image signal. In an image information reading method for obtaining a signal,
The sub-scanning speed is multiplied by m (m> 0), the sampling interval is multiplied by n (n> 0), and the number of pixels in the main scanning direction is a / m (a> 0) times. While performing pixel density conversion processing to increase the number of pixels in the scanning direction by a / n times,
An image information reading method, wherein a parameter of a filtering process in the pixel density conversion process is changed according to m and n. The light beam is sub-scanned in a direction substantially perpendicular to the main scanning direction while repeatedly scanning the light beam at a constant speed in a constant direction on the scanning sheet on which the image information is recorded. The scanning sheet is scanned over substantially the entire surface, the signal light emitted from both sides of the scanned sheet is photoelectrically detected by scanning the light beam, and the two analog image signals obtained are sampled and quantized to obtain two digital signals. In an image information reading method for obtaining an image signal and adding the two digital image signals to obtain an added image signal having a predetermined pixel density,
Multiplying the sub-scan speed by m (m> 0) and multiplying the sampling interval by n (n>0);
An image information reading method, wherein at least one of the following characteristics (1) to ( 4 ) is changed in accordance with m and n.
( 1 ) Preset shading correction data when performing shading correction on the analog image signal ( 2 ) Timing for outputting the shading correction data from the memory storing the shading correction data ( 3 ( 4 ) Frequency transfer characteristics when the analog image signal is logarithmically amplified ( 4 ) Cut-off frequency when filtering to remove aliasing noise is performed prior to sampling the analog image signal   A pixel density conversion process is performed on the two digital image signals so that the number of pixels in the main scanning direction is a / m (a> 0) times and the number of pixels in the sub-scanning direction is a / n times. The image information reading method according to claim 4, wherein: The light beam is sub-scanned in a direction substantially perpendicular to the main scanning direction while repeatedly scanning the light beam at a constant speed in a constant direction on the scanning sheet on which the image information is recorded. The scanning sheet is scanned over substantially the entire surface, the signal light emitted from both sides of the scanned sheet is photoelectrically detected by scanning the light beam, and the two analog image signals obtained are sampled and quantized to obtain two digital signals. In an image information reading method for obtaining an image signal and adding the two digital image signals to obtain an added image signal having a predetermined pixel density,
The sub-scanning speed is multiplied by m (m> 0), the sampling interval is multiplied by n (n> 0), and the number of pixels in the main scanning direction is a / m (a> 0) times. While performing pixel density conversion processing to increase the number of pixels in the scanning direction by a / n times,
An image information reading method, wherein a parameter of a filtering process in the pixel density conversion process is changed according to m and n. A main scanning means for repeatedly scanning a light beam emitted from a light source on a scanned sheet on which image information is recorded at a constant speed in a constant direction, and substantially orthogonal to the main scanning direction of the light beam. Sub-scanning means for sub-scanning the sheet or the light beam so that the sheet is relatively sub-scanned in the direction, and signal light emitted from the scanned sheet is detected photoelectrically by scanning the light beam. In an image information reading apparatus comprising photoelectric detection means and A / D conversion means for sampling and quantizing a detected analog image signal to obtain a digital image signal having a predetermined pixel density,
Sub-scanning speed changing means for changing the sub-scanning speed by the sub-scanning means to m times according to the input m (m>0);
Sampling interval changing means for changing the sampling interval by the A / D conversion means to n times according to the input n (n> 0) ;
An image information reading apparatus comprising: a characteristic changing unit that changes at least one of the following characteristics (1) to ( 4 ) according to m and n.
( 1 ) Preset shading correction data when performing shading correction on the analog image signal ( 2 ) Timing for outputting the shading correction data from the memory storing the shading correction data ( 3 ( 4 ) Frequency transfer characteristics when the analog image signal is logarithmically amplified ( 4 ) Cut-off frequency when filtering to remove aliasing noise is performed prior to sampling the analog image signal   The image processing apparatus further comprises pixel density conversion processing means for performing pixel density conversion processing for increasing the number of pixels in the main scanning direction by a / m (a> 0) times and setting the number of pixels in the sub-scanning direction by a / n times. The image information reading apparatus according to claim 7. A main scanning means for repeatedly scanning a light beam emitted from a light source on a scanned sheet on which image information is recorded at a constant speed in a constant direction, and substantially orthogonal to the main scanning direction of the light beam. Sub-scanning means for sub-scanning the sheet or the light beam so that the sheet is relatively sub-scanned in the direction, and signal light emitted from the scanned sheet is detected photoelectrically by scanning the light beam. In an image information reading apparatus comprising photoelectric detection means and A / D conversion means for sampling and quantizing a detected analog image signal to obtain a digital image signal having a predetermined pixel density,
Sub-scanning speed changing means for changing the sub-scanning speed by the sub-scanning means to m times according to the input m (m>0);
Sampling interval changing means for changing the sampling interval by the A / D conversion means to n times according to the input n (n>0);
Pixel density conversion processing means for performing a pixel density conversion process in which the number of pixels in the main scanning direction is a / m (a> 0) times and the number of pixels in the sub-scanning direction is a / n (a> 0) times;
An image information reading apparatus comprising: characteristic changing means for changing a parameter of filtering processing in the pixel density conversion processing according to m and n. A main scanning means for repeatedly scanning a light beam emitted from a light source on a scanned sheet on which image information is recorded at a constant speed in a constant direction, and substantially orthogonal to the main scanning direction of the light beam. Sub-scanning means for sub-scanning the sheet or the light beam so that the sheet is relatively sub-scanned in a direction, and signal light emitted from both sides of the scanned sheet by the scanning of the light beam photoelectrically. Photoelectric detection means for detecting; A / D conversion means for obtaining two digital image signals by sampling and quantizing two detected analog image signals; and adding the two digital image signals to obtain a predetermined pixel density In an image information reading apparatus provided with an adding means for obtaining an added image signal,
Sub-scanning speed changing means for changing the sub-scanning speed by the sub-scanning means to m (m> 0) times according to the input m;
Sampling interval changing means for changing the sampling interval by the A / D conversion means to n (n> 0) times according to the input n;
An image information reading apparatus comprising: a characteristic changing unit that changes at least one of the following characteristics (1) to ( 4 ) according to m and n.
( 1 ) Preset shading correction data when performing shading correction on the analog image signal ( 2 ) Timing for outputting the shading correction data from the memory storing the shading correction data ( 3 ( 4 ) Frequency transfer characteristics when the analog image signal is logarithmically amplified ( 4 ) Cut-off frequency when filtering to remove aliasing noise is performed prior to sampling the analog image signal   Pixel density for performing pixel density conversion processing on the two digital image signals so that the number of pixels in the main scanning direction is a / m (a> 0) times and the number of pixels in the sub-scanning direction is a / n times 11. The image information reading apparatus according to claim 10, further comprising a conversion processing unit. A main scanning means for repeatedly scanning a light beam emitted from a light source on a scanned sheet on which image information is recorded at a constant speed in a constant direction, and substantially orthogonal to the main scanning direction of the light beam. Sub-scanning means for sub-scanning the sheet or the light beam so that the sheet is relatively sub-scanned in a direction, and signal light emitted from both sides of the scanned sheet by the scanning of the light beam photoelectrically. Photoelectric detection means for detecting; A / D conversion means for obtaining two digital image signals by sampling and quantizing two detected analog image signals; and adding the two digital image signals to obtain a predetermined pixel density In an image information reading apparatus provided with an adding means for obtaining an added image signal,
Sub-scanning speed changing means for changing the sub-scanning speed by the sub-scanning means to m (m> 0) times according to the input m;
Sampling interval changing means for changing the sampling interval by the A / D conversion means to n (n> 0) times according to the input n;
Pixel density conversion processing means for performing a pixel density conversion process in which the number of pixels in the main scanning direction is a / m (a> 0) times and the number of pixels in the sub-scanning direction is a / n (a> 0) times;
An image information reading apparatus comprising: characteristic changing means for changing a parameter of filtering processing in the pixel density conversion processing according to m and n. A main scanning means for repeatedly scanning a light beam emitted from a light source on a scanned sheet on which image information is recorded at a constant speed in a constant direction, and substantially orthogonal to the main scanning direction of the light beam. Sub-scanning means for sub-scanning the sheet or the light beam so that the sheet is relatively sub-scanned in the direction, and signal light emitted from the scanned sheet is detected photoelectrically by scanning the light beam. In an image information reading apparatus comprising photoelectric detection means and A / D conversion means for sampling and quantizing a detected analog image signal to obtain a digital image signal having a predetermined pixel density,
Pixel density input means for receiving inputs of values m and n corresponding to a pixel density of 1 / m times in the main scanning direction and 1 / n times in the sub scanning direction with respect to the predetermined pixel density;
Sub-scanning speed changing means for changing the sub-scanning speed by the sub-scanning means to m (m> 0) times;
Sampling interval changing means for changing the sampling interval by the A / D converter to n (n> 0) times;
An image information reading apparatus comprising: a characteristic changing unit that changes at least one of the following characteristics (1) to ( 4 ) according to m and n.
( 1 ) Preset shading correction data when performing shading correction on the analog image signal ( 2 ) Timing for outputting the shading correction data from the memory storing the shading correction data ( 3 ( 4 ) Frequency transfer characteristics when the analog image signal is logarithmically amplified ( 4 ) Cut-off frequency when filtering to remove aliasing noise is performed prior to sampling the analog image signal A main scanning means for repeatedly scanning a light beam emitted from a light source on a scanned sheet on which image information is recorded at a constant speed in a constant direction, and substantially orthogonal to the main scanning direction of the light beam. Sub-scanning means for sub-scanning the sheet or the light beam so that the sheet is relatively sub-scanned in the direction, and signal light emitted from the scanned sheet is detected photoelectrically by scanning the light beam. In an image information reading apparatus comprising photoelectric detection means and A / D conversion means for sampling and quantizing a detected analog image signal to obtain a digital image signal having a predetermined pixel density,
Pixel density input means for receiving inputs of values m and n corresponding to a pixel density of 1 / m times in the main scanning direction and 1 / n times in the sub scanning direction with respect to the predetermined pixel density;
Sub-scanning speed changing means for changing the sub-scanning speed by the sub-scanning means to m (m> 0) times;
Sampling interval changing means for changing the sampling interval by the A / D converter to n (n> 0) times;
Pixel density conversion processing means for performing a pixel density conversion process in which the number of pixels in the main scanning direction is a / m (a> 0) times and the number of pixels in the sub-scanning direction is a / n (a> 0) times;
An image information reading apparatus comprising: characteristic changing means for changing a parameter of filtering processing in the pixel density conversion processing according to m and n.

Images