JP2004242040A - Color image processing method and color image processing apparatus - Google Patents

Abstract

A color reproduction range of an image input system and an output image system are determined by determining a hue area to which a color represented by an input color image signal belongs and converting the color image signal into a color recording signal corresponding to a color material of a printer. Even if the color reproduction range is different, an image comparable to the original image can be obtained, and color reproduction is good and efficient even for image data in which color difference minimization is not optimal. To obtain an image processing method and an image processing apparatus capable of color correction.
A color space of a color image signal is divided by a plane passing through an achromatic axis N and primary colors C, M, Y and secondary colors R, G, B, and divided into six partial color spaces. A hue area is determined as to which partial color space the color image signal belongs to, a correction amount for making the input color image signal fall within the color reproduction range of the printer is calculated, and the input color image is calculated based on the calculated correction amount. The signal was corrected in the achromatic color axis direction, and the corrected color image signal was converted into a color recording signal corresponding to the color material of the printer according to the determined hue region.
[Selection diagram] FIG.

Description

他の色空間に関しても同様であり、例えば、Ｂ−Ｍの部分色空間では、
【数２】

となる。
実際の処理では、上述のような部分色空間毎の係数Ｒｘ、Ｇｘ、Ｂｘ、Ｃｘを予め求めておき、部分色空間の判定結果に応じて係数を切り換えて（１４）式に示した演算を実施し、補正量Ｘを求める。尚、得られた補正量Ｘは正の場合のみ有効で、負の場合はプリンタの色再現範囲内の色に相当するので、補正なしを示す補正量（＝０）に修正する。
以上のようにして求めた補正量Ｘは、そのままでも多くのプリンタの色再現範囲外の色に対して効果がある。
但し、この場合、彩度が高くて（無彩色軸から離れていて）、無彩色軸ＮのＫ方向（明度の低い方向）に移動させてもプリンタの色再現範囲内に入らない色が、補正なしを示す補正量にならないことがある。例えば、図７に示した色８０８に対しては、色８０４−Ｗ延長線上の色８０９に移動させる補正量が得られる。従ってこのような色を検出して、補正なしを示す補正量（＝０）に修正するとより良い。
【００１２】
図３の高彩度修正処理３０３は、このような色に対する処理を行なう。高彩度修正処理３０３では、始めに上述した部分色空間の判定結果に応じて、次式に示すような演算を行なって、彩度評価値Ｓを算出する。
Ｓ＝Ｒｓ・Ｄｒ＋Ｇｓ・Ｄｇ＋Ｂｓ・Ｄｂ＋Ｃｓ …（１９）
（ここで、Ｒｓ、Ｇｓ、Ｂｓ、Ｃｓは部分色空間毎に定まる係数）
（１９）式の係数は、例えばＣ−Ｂの部分色空間を例にすると、ＫおよびＷにおいて“０”、ＣおよびＢにおいて“１”となる係数で良く、この条件を（１９）式に代入し連立方程式を解けばその係数が求まる。
０＝Ｒｓ・Ｄｋｒ＋Ｇｓ・Ｄｋｇ＋Ｂｓ・Ｄｋｂ＋Ｃｓ
０＝Ｒｓ・Ｄｗｒ＋Ｇｓ・Ｄｗｇ＋Ｂｓ・Ｄｗｂ＋Ｃｓ
１＝Ｒｓ・Ｄｃｒ＋Ｇｓ・Ｄｃｇ＋Ｂｓ・Ｄｃｂ＋Ｃｓ
１＝Ｒｓ・Ｄｂｒ＋Ｇｓ・Ｄｂｇ＋Ｂｓ・Ｄｂｂ＋Ｃｓ
…（２０）
【数３】

他の色空間に関しても同様であり、例えば、Ｂ−Ｍの部分色空間では、
【数４】

となる。
実際の処理では、上述のような部分色空間毎の係数Ｒｓ、Ｇｓ、Ｂｓ、Ｃｓを予め求めておき、部分色空間の判定結果に応じて係数を切り換えて（１９）式に示した演算を実施し、彩度評価値Ｓを求める。（１９）式の演算の結果、彩度評価値Ｓが“１”を超えた場合が、彩度が高くて（無彩色軸から離れていて）、無彩色軸ＮのＫ方向（明度の低い方向）に移動させてもプリンタの色再現範囲内に入らない色である。従って、彩度評価値Ｓが“１”を超えた場合は、補正なしを示す補正量（＝０）に修正する。
以上のような処理を行なうことで高彩度修正処理３０３は実現され、これにより彩度が高くて（無彩色軸から離れていて）、無彩色軸ＮのＫ方向（明度の低い方向）に移動させてもプリンタの色再現範囲内に入らない色に対する補正量を、補正なし（＝０）にすることができる。
尚、以上では、彩度評価値Ｓが“１”を超えた場合に補正なしとしたが、この値（“１”）は、前記例のＣおよびＢにおける値（“１”）に対応する。即ち、両者が同値であれば、任意に値で良い。また、“超える”、“超えない”も、前記例のＫおよびＷにおける値（“０”）とＣおよびＢにおける値（“１”）の大小関係で、変わるものである。
【００１３】
次に、前記算出した補正量Ｘをどの程度入力されたカラー画像信号に反映するかを調整する補正量調整処理３０４を行なう。この補正量調整処理３０４は、例えば調整量をα（＝０〜１）とした時に、
Ｘ’＝α・Ｘ …（２３）
なる処理を行なって、得られたＸ’を実際の補正量とすることで実現する。尚、この補正量調整処理３０４は、本発明に必須のものではないが、画像処理を行なわせる操作者が、本発明による補正を望まない場合（α＝０）や補正が強すぎると判断した場合に調整可能なように（０＜α＜１）設けてある。また、この調整の要否の程度は取り扱う画像種類によることが多いので、色鉛筆・クレヨン等の画像種類の選択を可能にして、これに連動させて調整量を自動的に設定しても良い。
次に、得られた補正量Ｘ’を基にカラー画像信号（Ｄｒ，Ｄｇ，Ｄｂ）を無彩色軸ＮのＫ方向に補正する明度補正処理３０５を行なう。この明度補正処理３０５は、例えば次式のようなカラー画像信号（Ｄｒ，Ｄｇ，Ｄｂ）と補正量Ｘ’の加算処理で実現する。
Ｄｒ’＝Ｄｒ＋Ｘ’
Ｄｇ’＝Ｄｇ＋Ｘ’
Ｄｂ’＝Ｄｂ＋Ｘ’
…（２４）
以上のように本発明係るの画像処理方法では、明度が高くプリンタの色再現範囲外となっている色を、無彩色軸ＮのＫ方向に移動して、プリンタの色再現範囲内の色に変換する（α＝１の場合）。また、無彩色軸方向に移動するので、色度を保った補正が可能となり、元画像と遜色のない画像を得ることができる。
次に、得られたカラー画像信号（Ｄｒ’、Ｄｇ’、Ｄｂ’）を元に、プリンタで使用する色材Ｃ（シアン）、Ｍ（マゼンタ）、Ｙ（イエロー）およびＫ（ブラック）に応じたカラー記録信号（Ｄｃ、Ｄｍ、Ｄｙ、Ｄｋ）に変換する色変換処理３０６を行なう。
【００１４】
本発明の色変換処理３０６は、カラー画像信号（Ｄｒ’、Ｄｇ’、Ｄｂ’）の色空間を図６と同様に、無彩色軸Ｎ（Ｄｒ’＝Ｄｇ’＝Ｄｂ’）と１次色Ｃ、Ｍ、Ｙおよび２次色Ｒ、Ｇ、Ｂをそれぞれ通る平面で区切って６つの部分色空間に分割して、入力されたカラー画像信号（Ｄｒ’、Ｄｇ’、Ｄｂ’）がどの部分色空間に属するかを判定し、その部分色空間の判定結果に応じて行なう。
尚、ここで行なう色変換処理３０６は次式のように表すことできる。
【数５】

また、図１９に示したプリンタのＷとＫ、１次色Ｃ、Ｍ、Ｙおよび２次色Ｒ、Ｇ、Ｂに対応するプリンタ各色材の最適な記録信号を、図２０の値とする。
Ｃ−Ｂの部分色空間を例にすると、Ｗ、Ｋ、Ｃ、Ｂにおけるカラー画像信号（Ｄｒ’、Ｄｇ’、Ｄｂ’）とカラー記録信号（Ｄｃ、Ｄｍ、Ｄｙ、Ｄｋ）の対応関係は図２１のようになり、（２５）式の係数は、図２１の対応関係を元に、Ｗ、Ｋ、Ｃ、Ｂに関する連立方程式を解くことで求めることができる。
【数６】

【数７】

他の色空間に関しても同様であり、例えば、Ｂ−Ｍの部分色空間では、
【数８】

となる。
実際の処理では、上述のような部分色空間毎の係数Ｍｃｒ、Ｍｃｇ、…、Ｍｋｃを予め求めておき、部分色空間の判定結果に応じて係数を切り換えて（２５）式に示した演算を実施し、カラー記録信号（Ｄｃ、Ｄｍ、Ｄｙ、Ｄｋ）を得る。
【００１５】
ところで、本発明の補正量算出処理３０２、高彩度修正処理３０３および色変換処理３０６は、カラー画像信号の色空間を、無彩色軸Ｎと、１次色Ｃ、Ｍ、Ｙおよび２次色Ｒ、Ｇ、Ｂをそれぞれ通る平面で区切って６つの部分色空間に分割して行なっている。また、明度補正処理３０５では無彩色軸方向にカラー画像信号の移動するので、色度は保たれている。従って、移動前のカラー画像信号（Ｄｒ，Ｄｇ，Ｄｂ）に基づく色相領域判定結果と、移動後のカラー画像信号（Ｄｒ’、Ｄｇ’、Ｄｂ’）に基づく色相領域判定結果は、同じになる。よって本発明の色変換処理３０６では、移動前のカラー画像信号（Ｄｒ，Ｄｇ，Ｄｂ）に基づく色相領域判定処理３０１の結果をそのまま使用して、係数の切り換えを行なう。これにより、色変換処理３０６専用の色相領域判定処理が不要となり、処理の高速化が可能となる。
尚、本発明の色変換処理３０６が出力するカラー記録信号（Ｄｃ、Ｄｍ、Ｄｙ）は、Ｋの色材を使わない（Ｄｋ＝０）事を前提とした値になっている。よって、次にカラー記録信号Ｄｋに応じてカラー記録信号Ｄｃ、Ｄｍ、Ｄｙを補正するＵＣＲ（ＵｎｄｅｒＣｏｌｏｒＲｅｍｏｖａｌ：下色除去）処理３０７を行なう。ＵＣＲ処理３０７は、一般に（２９）式に示すように、カラー記録信号Ｄｃ、Ｄｍ、Ｄｙからカラー記録信号Ｄｋを減算することで実現する。
Ｄｃ’＝Ｄｃ−Ｄｋ
Ｄｍ’＝Ｄｍ−Ｄｋ
Ｄｙ’＝Ｄｙ−Ｄｋ
…（２９）
【００１６】
次に、図４に本発明に係る画像処理装置のブロック図の一例を示し、以下では図４を参照して本発明の説明を行なう。
図示しない画像信号入力装置が出力するカラー画像信号（Ｄｒ，Ｄｇ，Ｄｂ）は、色相領域判定回路４０１（色相領域判定手段）、補正量算出回路４０２（補正量算出手段）、高彩度修正回路４０３（高彩度修正手段）および明度補正回路４０４（明度補正手段）に入力される。
色相領域判定回路４０１は、カラー画像信号（Ｄｒ，Ｄｇ，Ｄｂ）がどの部分色空間に属するかを判定する回路で、図８にその詳細を示す。
図８を参照すると、カラー画像信号（Ｄｒ，Ｄｇ，Ｄｂ）はｆｘ値演算回路９０１に入力される。
ｆｘ値演算回路９０１は、前記（７）〜（１２）式に例示した積和演算をそれぞれ行なって結果を出力する回路で、演算結果ｆｃ、ｆｍ、ｆｙ、ｆｒ、ｆｇ、ｆｂは、領域コード生成回路９０２へ出力される。
領域コード生成回路９０２は、前記（１３）式に例示した比較および論理演算を行なって、どの部分色空間に属するかを判定し、その結果に応じて例えば以下に示すような領域コード信号ｃｏｄｅを出力する。
Ｃ−Ｂの部分色空間なら、領域コード：０
Ｂ−Ｍの部分色空間なら、領域コード：１
Ｍ−Ｒの部分色空間なら、領域コード：２
Ｒ−Ｙの部分色空間なら、領域コード：３
Ｙ−Ｇの部分色空間なら、領域コード：４
Ｇ−Ｃの部分色空間なら、領域コード：５
…（３０）
以上のように、ｆｘ値演算回路９０１および領域コード生成回路９０２によれば、カラー画像信号（Ｄｒ，Ｄｇ，Ｄｂ）の色空間を、図６に示すように無彩色軸Ｎ（Ｄｒ＝Ｄｇ＝Ｄｂ）と１次色Ｃ、Ｍ、Ｙおよび２次色Ｒ、Ｇ、Ｂをそれぞれ通る平面で区切って６つの部分色空間に分割し、入力されたカラー画像信号（Ｄｒ，Ｄｇ，Ｄｂ）がどの部分色空間に属するかを判定する色相領域判定回路４０１を実現できる。
【００１７】
一方、補正量算出回路４０２は、入力されたカラー画像信号（Ｄｒ，Ｄｇ，Ｄｂ）をプリンタの色再現範囲内とするために最低限必要な無彩色軸ＮのＫ方向の補正量Ｘ２を算出する回路で、色相領域判定回路４０１により得られた領域コード信号ｃｏｄｅも入力されている。図１５にその詳細を示す。
図１５を参照すると、領域コード信号ｃｏｄｅが入力されるＸ係数メモリ１６０１は、前記（１７）、（１８）式等で算出された部分色空間毎の係数Ｒｘ、Ｇｘ、Ｂｘ、Ｃｘを記憶するメモリ等で構成された回路で、入力された領域コード信号ｃｏｄｅに応じて対応する部分色空間の係数Ｒｘ、Ｇｘ、Ｂｘ、ＣｘをＸ値演算回路１６０２へ出力する。
カラー画像信号（Ｄｒ，Ｄｇ，Ｄｂ）が入力されるＸ値演算回路１６０２は、前記（１４）式に示した積和演算を行なって結果を出力する回路で、演算結果Ｘ１はコンパレータ１６０３およびセレクタ１６０４へ出力される。
コンパレータ１６０３は入力された演算結果Ｘ１を“値０”と比較する回路で、比較結果はセレクタ１６０４へ出力される。
セレクタ１６０４は入力された演算結果Ｘ１あるいは“値０”を選択出力する回路で、補正量Ｘ２として出力する。ここで、セレクタ１６０４の動作はコンパレータ１６０３の比較結果で制御されており、演算結果Ｘ１が０より小さい場合は、“値０”を選択出力する。
【００１８】
一方、高彩度修正回路４０３は、彩度が高くて（無彩色軸から離れていて）、無彩色軸ＮのＫ方向（明度の低い方向）に移動させてもプリンタの色再現範囲内に入らない色が、補正なしを示す補正量にならない場合の補正をする回路で、色相領域判定回路４０１により得られた領域コード信号ｃｏｄｅおよび補正量算出回路４０２により得られた補正量Ｘ２も入力されている。図１６にその詳細を示す。
図１６を参照すると、領域コード信号ｃｏｄｅが入力されるＳ係数メモリ１７０１は、前記（２１）、（２２）式等で算出された部分色空間毎の係数Ｒｓ、Ｇｓ、Ｂｓ、Ｃｓを記憶するメモリ等で構成された回路で、入力された領域コード値ｃｏｄｅに応じて対応する部分色空間の係数Ｒｓ、Ｇｓ、Ｂｓ、ＣｓをＳ値演算回路１７０２へ出力する。
カラー画像信号（Ｄｒ，Ｄｇ，Ｄｂ）が入力されるＳ値演算回路１７０２は、前記（１９）式に示した積和演算を行なって結果を出力する回路で、演算結果Ｓはコンパレータ１７０３に出力される。
コンパレータ１７０３は入力された演算結果Ｓを“値１”と比較する回路で、比較結果はセレクタ１７０４へ出力される。
セレクタ１７０４は入力された補正量Ｘ２あるいは“値０”を選択出力する回路で、補正量Ｘ３として出力する。ここで、セレクタ１７０４の動作はコンパレータ１７０３の比較結果で制御されており、演算結果Ｓが１を超えた場合は、“値０”を選択出力する。
以上のように、Ｘ係数メモリ１６０１、Ｘ値演算回路１６０２、コンパレータ１６０３およびセレクタ１６０４によれば、入力された色をプリンタの色再現範囲内とするために最低限必要な無彩色軸ＮのＫ方向の補正量を算出する補正量算出回路４０２を実現できる。尚、この補正量算出回路４０２の出力する補正量Ｘ２を、高彩度修正回路４０３を通さずそのまま出力しても、多くのプリンタの色再現範囲外の色に対して効果がある。
しかし、Ｓ係数メモリ１７０１、Ｓ値演算回路１７０２、コンパレータ１７０３およびセレクタ１７０４によれば、彩度が高くて（無彩色軸から離れていて）、無彩色軸ＮのＫ方向（明度の低い方向）に移動させてもプリンタの色再現範囲内に入らない色を補正なしにする高彩度修正回路４０３を実現できるので、入力された色をプリンタの色再現範囲内とするために最低限必要な無彩色軸ＮのＫ方向の補正量をより正確に算出することができる。
尚、上述したｆｘ値演算回路９０１における（７）〜（１２）式の係数と、Ｘ係数メモリ１６０１およびＳ係数メモリ１７０１の係数は書換え可能になっており、これらは画像処理装置全体を制御するシステム制御回路４１１によって予め設定されている。
【００１９】
次に、高彩度修正回路４０３により得られた補正量Ｘ３は、補正量調整回路４０５（補正量調整手段）に入力される。
補正量調整回路４０５は、入力された補正量Ｘ３をどの程度カラー画像信号（Ｄｒ，Ｄｇ，Ｄｂ）に反映するかを調整する回路で、例えば調整量をα（＝０〜１）とした時に、（２３）式に示したような演算を乗算器等で行なって、算出したＸ４を実際の補正量として出力する。尚、この補正量調整回路４０５は、本発明に必須のものではないが、画像処理を行なわせる操作者が、本発明による補正を望まない場合（α＝０）や補正が強すぎると判断した場合に調整可能なように（０＜α＜１）設けてある。尚、調整量αは、操作者による設定が可能な調整量設定回路４０６から入力される。また、この調整の要否の程度は取り扱う画像種類によることが多いので、色鉛筆・クレヨン等の画像種類の選択を可能にし、これに連動してシステム制御回路４１１が調整量αを設定しても良い。
次に、補正量調整回路４０５により得られた補正量補正量Ｘ４は、明度補正回路４０７（明度補正手段）に入力される。
明度補正回路４０７は、入力された補正量Ｘ４を基にカラー画像信号（Ｄｒ，Ｄｇ，Ｄｂ）を明度方向に補正する回路で、例えば（２４）式に示したような演算を加算器等で行なって、算出したＤｒ’、Ｄｇ’、Ｄｂ’をカラー画像信号として出力する。
以上のように本発明係るの画像処理装置では、明度が高くプリンタの色再現範囲外となっている色を、無彩色軸ＮのＫ方向に移動して、プリンタの色再現範囲内の色に変換する（α＝１の場合）。また、無彩色軸方向の移動するので、色度を保った補正が可能となり、元画像と遜色のない画像を得ることができる。
次に、明度補正回路４０７により得られたカラー画像信号（Ｄｒ’、Ｄｇ’、Ｄｂ’）は、色変換回路４０８（色変換手段）に入力される。
色変換回路４０８は、入力されたカラー画像信号（Ｄｒ’、Ｄｇ’、Ｄｂ’）を、プリンタで使用する色材Ｃ、Ｍ、ＹおよびＫに応じたカラー記録信号（Ｄｃ、Ｄｍ、Ｄｙ、Ｄｋ）に変換する回路である。
尚、本発明の色変換回路４０８では、カラー画像信号（Ｄｒ’、Ｄｇ’、Ｄｂ’）の色空間を図６と同様な、無彩色軸Ｎ（Ｄｒ’＝Ｄｇ’＝Ｄｂ’）と１次色Ｃ、Ｍ、Ｙおよび２次色Ｒ、Ｇ、Ｂをそれぞれ通る平面で区切って６つの部分色空間に分割して、入力されたカラー画像信号（Ｄｒ’、Ｄｇ’、Ｄｂ’）がどの部分色空間に属するかを判定し、その部分色空間の判定結果に応じた処理を行なう。このため、カラー画像信号（Ｄｒ’、Ｄｇ’、Ｄｂ’）に関しても、色相領域判定回路４０１と同等な回路が必要となる。
【００２０】
しかし、上述したように本発明の明度補正回路４０７は色度を保った補正を行なうので、カラー画像信号（Ｄｒ’、Ｄｇ’、Ｄｂ’）に基づく判定結果と、カラー画像信号（Ｄｒ，Ｄｇ，Ｄｂ）に基づく判定結果は同じになる。従って、本発明の色変換回路４０８は、色相領域判定回路４０１の領域コード信号ｃｏｄｅを参照して処理を行なう。図１７にその詳細を示す。
図１７を参照すると、領域コード信号ｃｏｄｅが入力されるＣ係数メモリ１８０１、Ｍ係数メモリ１８０２、Ｙ係数メモリ１８０３およびＫ係数メモリ１８０４は、前記（２７）、（２８）式等で算出された部分色空間毎の係数Ｍｃｒ、Ｍｃｇ、Ｍｃｂ、Ｍｃｃ、係数Ｍｍｒ、Ｍｍｇ、Ｍｍｂ、Ｍｍｃ、係数Ｍｙｒ、Ｍｙｇ、Ｍｙｂ、Ｍｙｃおよび係数Ｍｋｒ、Ｍｋｇ、Ｍｋｂ、Ｍｋｃをそれぞれ記憶するメモリ等で構成された回路で、入力された領域コード信号ｃｏｄｅに応じた部分色空間の係数を、対応するＣ演算回路１８０５、Ｍ演算回路１８０６、Ｙ演算回路１８０７およびＫ演算回路１８０８へそれぞれ出力する。
カラー画像信号（Ｄｒ’、Ｄｇ’、Ｄｂ’）が入力されるＣ演算回路１８０５、Ｍ演算回路１８０６、Ｙ演算回路１８０７およびＫ演算回路１８０８は、前記（２５）式に示した積和演算を分担して行なって、カラー記録信号（Ｄｃ、Ｄｍ、Ｄｙ、Ｄｋ）を結果として出力する。
以上のように色変換回路４０８は、色相領域判定回路４０１の領域コード信号ｃｏｄｅに応じて、入力されたカラー画像信号（Ｄｒ’、Ｄｇ’、Ｄｂ’）を、プリンタで使用する色材Ｃ、Ｍ、ＹおよびＫに応じたカラー記録信号（Ｄｃ、Ｄｍ、Ｄｙ、Ｄｋ）に変換するので、入力されたカラー画像信号（Ｄｒ’、Ｄｇ’、Ｄｂ’）がどの部分色空間に属するかを判定しなくても実現できる。
尚、上述したＣ係数メモリ１８０１、Ｍ係数メモリ１８０２、Ｙ係数メモリ１８０３およびＫ係数メモリ１８０４の係数は書換え可能になっており、これらは画像処理装置全体を制御するシステム制御回路４１１によって予め設定されている。
次に、色変換回路４０８により得られたカラー記録信号（Ｄｃ、Ｄｍ、Ｄｙ、Ｄｋ）は、ＵＣＲ回路４０９に入力される。
【００２１】
ここで、色変換回路４０８が出力するカラー記録信号（Ｄｃ、Ｄｍ、Ｄｙ）は、Ｋの色材を使わない（Ｄｋ＝０）事を前提としている。このためカラー記録信号Ｄｋに応じてカラー記録信号Ｄｃ、Ｄｍ、Ｄｙを補正する必要があり、ＵＣＲ回路４０９がこの役割を果たす。図１８にその詳細を示す。
図１８を参照すると、カラー記録信号Ｄｃ、Ｄｍ、ＤｙはそれぞれＣＵＣＲ回路１９０１、ＭＵＣＲ回路１９０２およびＹＵＣＲ回路１９０３に入力され、カラー記録信号Ｄｋは各ＵＣＲ回路１９０１〜１９０３に入力されている。
ＣＵＣＲ回路１９０１、ＭＵＣＲ回路１９０２およびＹＵＣＲ回路１９０３は、例えば前記（２９）式に示したような演算を加算器等で分担して行なって、算出したＤｃ’、Ｄｍ’、Ｄｙ’をカラー記録信号として出力する。
以上のようにＵＣＲ回路４０９は、カラー記録信号Ｄｋに応じてカラー記録信号Ｄｃ、Ｄｍ、Ｄｙを補正する。尚、ＵＣＲ回路４０９のカラー記録信号（Ｄｃ’、Ｄｍ’、Ｄｙ’、Ｄｋ）は、図示しない画像信号出力装置に出力され、画像の記録に使用される。
また以上で説明した色相領域判定処理３０１および色相領域判定回路４０１では、カラー画像信号（Ｄｒ，Ｄｇ，Ｄｂ）を３次元色空間のまま取り扱ったが、無彩色軸Ｎが１点に写像される２次元平面で取り扱うようにしても良い。
例えば、図６に示した部分色空間を、カラー画像信号の差分信号“Ｄｇ−Ｄｒ”および“Ｄｂ−Ｄｇ”を２軸とする平面に写像すると、図９のようになる。即ち、無彩色軸Ｎ上の色（Ｄｎｒ＝Ｄｎｇ＝Ｄｎｂ）は、
（Ｄｎｇ−Ｄｎｒ、Ｄｎｂ−Ｄｎｇ）＝（０、０） …（３１）
となって１点ｎに写像され、その周囲にはプリンタの１次色Ｃ、Ｍ、Ｙおよび２次色Ｒ、Ｇ、Ｂが配置される。そして６つの部分色空間は、無彩色ｎとＣ、Ｍ、Ｙ、Ｒ、Ｇ、Ｂをそれぞれ結んだ直線で区分された領域に写像される。
ここで、
ＧＲ＝Ｄｇ−Ｄｒ …（３２）
ＢＧ＝Ｄｂ−Ｄｇ …（３３）
とする。この場合、無彩色ｎとＣ、Ｍ、Ｙ、Ｒ、Ｇ、Ｂをそれぞれ結んだ直線は以下のようになる。
ＢＧ＝（Ｄｃｂ−Ｄｃｇ）／（Ｄｃｇ−Ｄｃｒ）・ＧＲ（但し、Ｄｃｇ−Ｄｃｒ≠０）…（３４）
ＢＧ＝（Ｄｍｂ−Ｄｍｇ）／（Ｄｍｇ−Ｄｍｒ）・ＧＲ（但し、Ｄｍｇ−Ｄｍｒ≠０）…（３５）
ＢＧ＝（Ｄｙｂ−Ｄｙｇ）／（Ｄｙｇ−Ｄｙｒ）・ＧＲ（但し、Ｄｙｇ−Ｄｙｒ≠０）…（３６）
ＢＧ＝（Ｄｒｂ−Ｄｒｇ）／（Ｄｒｇ−Ｄｒｒ）・ＧＲ（但し、Ｄｒｇ−Ｄｒｒ≠０）…（３７）
ＢＧ＝（Ｄｇｂ−Ｄｇｇ）／（Ｄｇｇ−ＤＧＲ）・ＧＲ（但し、Ｄｇｇ−ＤＧＲ≠０）…（３８）
ＢＧ＝（Ｄｂｂ−ＤＢＧ）／（ＤＢＧ−Ｄｂｒ）・ＧＲ（但し、ＤＢＧ−Ｄｂｒ≠０）…（３９）
【００２２】
また、（３４）〜（３９）式の右辺をそれぞれｆｃ’、ｆｍ’、ｆｙ’、ｆｒ’、ｆｇ’、ｆｂ’とすると、カラー画像信号の差分信号（Ｄｂ−Ｄｇ、Ｄｇ−Ｄｒ）が直線のどちら側にあるかは、それぞれｆｃ’、ｆｍ’、ｆｙ’、ｆｒ’、ｆｇ’、ｆｂ’の演算結果とＢＧ（＝Ｄｂ−Ｄｇ）との大小関係で判定できる。従って、カラー画像信号（Ｄｒ，Ｄｇ，Ｄｂ）が上述の部分色空間の何れに属するかも判定できる。
ｆｃ’＝（Ｄｃｂ−Ｄｃｇ）／（Ｄｃｇ−Ｄｃｒ）・ＧＲ …（４０）
ｆｍ’＝（Ｄｍｂ−Ｄｍｇ）／（Ｄｍｇ−Ｄｍｒ）・ＧＲ …（４１）
ｆｙ’＝（Ｄｙｂ−Ｄｙｇ）／（Ｄｙｇ−Ｄｙｒ）・ＧＲ …（４２）
ｆｒ’＝（Ｄｒｂ−Ｄｒｇ）／（Ｄｒｇ−Ｄｒｒ）・ＧＲ …（４３）
ｆｇ’＝（Ｄｇｂ−Ｄｇｇ）／（Ｄｇｇ−ＤＧＲ）・ＧＲ …（４４）
ｆｂ’＝（Ｄｂｂ−ＤＢＧ）／（ＤＢＧ−Ｄｂｒ）・ＧＲ …（４５）
より具体的には、一般に、
ＢＧ≦ｆｃ’且つＢＧ＞ｆｂ’なら、Ｃ−Ｂの部分色空間に属する
ＢＧ≦ｆｂ’且つＢＧ＜ｆｍ’なら、Ｂ−Ｍの部分色空間に属する
ＢＧ≧ｆｍ’且つＢＧ＜ｆｒ’なら、Ｍ−Ｒの部分色空間に属する
ＢＧ≧ｆｒ’且つＢＧ＜ｆｙ’なら、Ｒ−Ｙの部分色空間に属する
ＢＧ≧ｆｙ’且つＢＧ＞ｆｇ’なら、Ｙ−Ｇの部分色空間に属する
ＢＧ≦ｆｇ’且つＢＧ≧ｆｃ’なら、Ｇ−Ｃの部分色空間に属する
…（４６）
となる。尚、無彩色（Ｄｒ＝Ｄｇ＝Ｄｂ）も何れかの部分色空間に属させるため、前記ではＧ−Ｃの部分色空間のみ２つの不等式に等号記号を付けているが、無彩色（Ｄｒ＝Ｄｇ＝Ｄｂ）はどの部分色空間に属させても良い。
【００２３】
図１０に本発明に係る色相領域判定処理の流れ図の一例を示し、以下では図１０を参照して本発明の説明を行なう。
始めに、入力されたカラー画像信号（Ｄｒ，Ｄｇ，Ｄｂ）を無彩色軸Ｎが１点に写像される２次元平面写像して２次元座標値を得る２次元化処理１１０１を行なう。これは例えば上述の（３２）および（３３）式に対応する。
次に、得られた２次元座標値に基づいて評価値を算出する評価値算出処理１１０２を行なう。この評価値は例えば前記（４０）〜（４５）式のｆｃ’、ｆｍ’、ｆｙ’、ｆｒ’、ｆｇ’、ｆｂ’に対応する。尚、各式の傾き、例えば“（Ｄｃｂ−Ｄｃｇ）／（Ｄｃｇ−Ｄｃｒ）”等は、予め求めておくと良い。
次に、得られた２次元座標値および評価値に基づいて、どの部分色空間に属するかを決定する色相領域決定処理を行なう。これは例えば上述の（４６）式に対応する。
以上のように、図１０に示した色相領域判定処理によれば、入力されたカラー画像信号（Ｄｒ，Ｄｇ，Ｄｂ）がどの部分色空間に属するかを判定することができ、無彩色軸Ｎが１点に写像される２次元平面で扱うので、３次元色空間のまま取り扱う場合に比べて処理が容易になる。
【００２４】
また、図１１に本発明に係る色相領域判定回路のブロック図の一例を示し、以下では図１１を参照して本発明の説明を行なう。
図１１の色相領域判定回路は、上述した色相領域判定処理を実施する回路で、入力されたカラー画像信号（Ｄｒ，Ｄｇ，Ｄｂ）は差分回路１２０１、１２０２（第１二次元化手段）に入力される。
差分回路１２０１は、（３２）式に例示した差分を演算する回路で、演算結果ＧＲはｆｘ’値演算回路１２０３へ出力される。また差分回路１１０２は、（３３）式に例示した差分を演算する回路で、演算結果ＢＧは領域コード生成回路１２０４へ出力される。
ｆｘ’値演算回路１２０３は、（４０）〜（４５）式に例示した乗算をそれぞれ行なって結果を出力する回路で、演算結果ｆｃ’、ｆｍ’、ｆｙ’、ｆｒ’、ｆｇ’、ｆｂ’は、領域コード生成回路１２０４へ出力される。
領域コード生成回路１２０４は、前記（４６）式に例示した比較および論理演算を行なって、どの部分色空間に属するかを判定し、その結果に応じて前記例示した領域コード値ｃｏｄｅを出力する。
以上のように、図１１に示した色相領域判定回路によれば、入力されたカラー画像信号（Ｄｒ，Ｄｇ，Ｄｂ）がどの部分色空間に属するかを判定し、その結果に応じた領域コード値を出力するすることができ、無彩色軸Ｎが１点に写像される２次元平面で扱うので、３次元色空間のまま取り扱う場合に比べて回路規模を小さくなる。
尚、上述したｆｘ’値演算回路１２０３における（４０）〜（４５）式の係数は書換え可能になっており、これらは画像処理装置全体を制御するシステム制御回路１２０５によって予め設定されている。
また、以上で説明した図１０の色相領域判定処理および図１１の色相領域判定回路では、カラー画像信号（Ｄｒ，Ｄｇ，Ｄｂ）を無彩色軸Ｎが１点に写像される２次元平面に写像したまま取り扱ったが、例えば図９に示したように、特定方向を基準（＝０）とした色相角ＨＵＥを算出して取り扱っても、色相領域を判定できる。尚、この場合の色相角ＨＵＥは、差分信号の座標値（Ｄｇ−Ｄｒ、Ｄｂ−Ｄｇ）から三角関数等により算出する。
【００２５】
また、以下で説明するように色相角ＨＵＥに対して単調増加となる代替量（擬似色相角Ｈ）を算出して取り扱うようにしても良い。
この方法では、カラー画像信号の差分信号ＧＲ（＝Ｄｇ−Ｄｒ）およびＢＧ（＝Ｄｂ−Ｄｇ）を２軸とする平面を、例えば図１２に示すように８つ領域に均等に分割し、差分信号がどの領域に位置するかを始めに判定する。ここで、各領域には順番に“０〜７”の値Ｈａを割り当てる。この値Ｈａは上位の擬似色相角に相当し、具体的には以下のような処理を行なう。
ＧＲ＞０ 且つＢＧ＞０ 且つＢＧ≦ＧＲならば、Ｈａ＝０
ＧＲ＞０ 且つＢＧ＞０ 且つＢＧ＞ＧＲならば、Ｈａ＝１
ＧＲ≦０ 且つＢＧ＞０ 且つＢＧ＞−ＧＲならば、Ｈａ＝２
ＧＲ≦０ 且つＢＧ＞０ 且つＢＧ≦−ＧＲならば、Ｈａ＝３
ＧＲ≦０ 且つＢＧ≦０ 且つＢＧ＞ＧＲならば、Ｈａ＝４
ＧＲ≦０ 且つＢＧ≦０ 且つＢＧ≦ＧＲならば、Ｈａ＝５
ＧＲ＞０ 且つＢＧ≦０ 且つＢＧ≦−ＧＲならば、Ｈａ＝６
ＧＲ＞０ 且つＢＧ≦０ 且つＢＧ＞−ＧＲならば、Ｈａ＝７
…（４７）
次に、前記結果に応じて差分信号の座標値（ＧＲ、ＢＧ）を回転し、特定の領域、例えば第１３図の領域“Ｈａ＝０”に移動させた座標値（ｇｒ、ｂｇ）を得る。具体的には以下のような処理を行なう。
Ｈａ＝０ならば、ｇｒ＝ＧＲ、ｂｇ＝ＢＧ
Ｈａ＝１ならば、ｇｒ＝ＧＲ＋ＢＧ、ｂｇ＝−ＧＲ＋ＢＧ
Ｈａ＝２ならば、ｇｒ＝ＢＧ、ｂｇ＝−ＧＲ
Ｈａ＝３ならば、ｇｒ＝−ＧＲ＋ＢＧ、ｂｇ＝−ＧＲ−ＢＧ
Ｈａ＝４ならば、ｇｒ＝ＧＲ、ｂｇ＝ＢＧ
Ｈａ＝５ならば、ｇｒ＝−ＧＲ−ＢＧ、ｂｇ＝ＧＲ−ＢＧ
Ｈａ＝６ならば、ｇｒ＝ＧＲ、ｂｇ＝ＢＧ
Ｈａ＝７ならば、ｇｒ＝ＧＲ−ＢＧ、ｂｇ＝ＧＲ＋ＢＧ
…（４８）
尚、純粋に座標を回転する場合は、Ｈａ＝１、３、５、７の時にｇｒおよびｂｇをそれぞれ１／√２倍する必要がある。しかし、ここでは角度の検出だけを目的としているため、１／√２倍の処理を省略している。
【００２６】
次に、座標位置（ｇｒ、ｂｇ）における角度を表す量、例えばｇｒとｂｇの比Ｈｂを算出する。
Ｈｂ＝ｂｇ／ｇｒ （但し、ｇｒ＝０ならばＨｂ＝０） …（４９）
この値Ｈｂは、領域“Ｈａ＝０”に移動した時の角度を間接的に表しており、下位の擬似色相角に相当する。
次に、得られた上位の擬似色相角Ｈａおよび下位の擬似色相角Ｈｂから、最終的な擬似色相角Ｈを算出する。以上では、差分信号平面（ＧＲ、ＢＧ）を８領域に均等に分割し、これを領域“Ｈａ＝０”に回転しているので、“ｂｇ≦ｇｒ”となっている。従って“Ｈｂ≦１”となり、前記値Ｈａと加算しても単調増加が維持される。即ち、色相角ＨＵＥに対して単調増加となる代替量、擬似色相角Ｈを次式により得ることができる。
Ｈ＝Ｈａ＋Ｈｂ …（５０）
また、以上で説明した手順で求めた、プリンタの１次色Ｃ、Ｍ、Ｙおよび２次色Ｒ、Ｇ、Ｂの擬似色相角を、それぞれＨｃ、Ｈｍ、Ｈｙ、Ｈｒ、Ｈｇ、Ｈｂとすると、これらを得られた擬似色相角Ｈと比較することで、カラー画像信号（Ｄｒ，Ｄｇ，Ｄｂ）が上述した部分色空間の何れに属するかを決定できる。
より具体的には、図９の位置関係の場合、
Ｈ≧Ｈｃ且つＨ＜Ｈｂなら、Ｃ−Ｂの部分色空間に属する
Ｈ≧Ｈｂ且つＨ＜Ｈｍなら、Ｂ−Ｍの部分色空間に属する
Ｈ≧Ｈｍ且つＨ＜Ｈｒなら、Ｍ−Ｒの部分色空間に属する
Ｈ≧ＨｒまたはＨ＜Ｈｙなら、Ｒ−Ｙの部分色空間に属する
Ｈ≧Ｈｙ且つＨ＜Ｈｇなら、Ｙ−Ｇの部分色空間に属する
Ｈ≧Ｈｇ且つＨ＜Ｈｃなら、Ｇ−Ｃの部分色空間に属する
…（５１）
となる。尚、無彩色（Ｄｒ＝Ｄｇ＝Ｄｂ）も何れかの部分色空間に属させるため、前記では（４７）、（４９）式により“Ｈａ＝５、Ｈｂ＝０”、即ち、“Ｈ＝５．０”としたが、無彩色（Ｄｒ＝Ｄｇ＝Ｄｂ）はどの擬似色相角に変換しても良い。
【００２７】
図１３に本発明に係る色相領域判定処理の流れ図の一例を示し、以下では図１３を参照して本発明の説明を行なう。
始めに、入力されたカラー画像信号（Ｄｒ，Ｄｇ，Ｄｂ）を無彩色軸Ｎが１点に写像される２次元平面写像して２次元座標を得る２次元化処理１４０１を行なう。これは上述の２次元化処理１１０１と同じである。
次に、得られた２次元座標の上位の擬似色相角Ｈａを決定する上位色相決定処理１４０２を行なう。これは例えば上述の（４７）式に対応する。
次に、得られた上位の擬似色相角Ｈａに応じて２次元座標を回転し、特定の領域に移動する座標回転処理１４０３を行なう。これは例えば上述の（４８）式に対応する。
次に、移動した２次元座標に応じて下位の擬似色相角Ｈｂを決定する下位色相決定処理１４０４を行なう。これは例えば上述の（４９）式に対応する。
次に、得られた上位の擬似色相角Ｈａおよび下位の擬似色相角Ｈｂに基づいて擬似色相角Ｈを算出し、これを、予め同様な手順で求めておいたプリンタの１次色Ｃ、Ｍ、Ｙおよび２次色Ｒ、Ｇ、Ｂの擬似色相角をＨｃ、Ｈｍ、Ｈｙ、Ｈｒ、Ｈｇ、Ｈｂとの比較し、どの部分色空間に属するかを決定する色相領域決定処理１４０５を行なう。これは例えば上述の（５０）、（５１）式に対応する。
以上のように、図１３に示した色相領域判定処理によれば、入力されたカラー画像信号（Ｄｒ，Ｄｇ，Ｄｂ）がどの部分色空間に属するかを判定することができ、色相角ＨＵＥに対して単調増加となる代替量（擬似色相角Ｈ）を算出して取り扱うので、３次元色空間のまま取り扱う場合に比べて処理が容易になる。
【００２８】
また、図１４に本発明に係る色相領域判定回路のブロック図の一例を示し、以下では図１４を参照して本発明の説明を行なう。
図１４の色相領域判定回路は、上述した色相領域判定処理を実施する回路で、入力されたカラー画像信号（Ｄｒ，Ｄｇ，Ｄｂ）は差分回路１５０１、１５０２（第２二次元化手段）に入力される。
差分回路１５０１は上述の差分回路１２０１と同じ回路、差分回路１５０２は上述の差分回路１１０２はと同じ回路で、それぞれの演算結果ＧＲおよびＢＧは上位色相決定回路１５０３および座標回転回路１５０４へ出力される。
上位色相決定回路１５０３は、（４７）式に例示した比較および論理演算を行なって上位の擬似色相角Ｈａを決定する回路で、結果は座標回転回路１５０４および下位色相決定回路１５０５へ出力される。なお、請求項において、疑似色相角算出手段は上位色相決定回路１５０３、座標回転回路１５０４、下位色相決定回路１５０５を意味する。
座標回転回路１５０４は、（４８）式に例示したように上位の擬似色相角Ｈａに応じて、差分信号（ＧＲ、ＢＧ）を回転して特定の領域に移動する回路で、回転後の差分信号（ｇｒ、ｂｇ）は、下位色相決定回路１５０５へ出力される。
下位色相決定回路１５０５は、（４９）式に例示した座標位置における角度を表す量を算出する回路で、得られた下位の擬似色相角Ｈｂは領域コード生成回路１５０５へ出力される。
領域コード生成回路１５０５は、前記（５１）式に例示した比較および論理演算を行なって、どの部分色空間に属するかを決定し、その結果に応じて前記例示した領域コード値ｃｏｄｅを出力する。
以上のように、図１４に示した色相領域判定回路によれば、入力されたカラー画像信号（Ｄｒ，Ｄｇ，Ｄｂ）がどの部分色空間に属するかを判定し、その結果に応じた領域コード値を出力するすることができ、色相角ＨＵＥに対して単調増加となる代替量（擬似色相角Ｈ）を算出して取り扱うので、３次元色空間のまま取り扱う場合に比べて回路規模が小さくなる。
尚、上述した領域コード生成回路１５０５における（５１）式の擬似色相角Ｈｃ、Ｈｍ、Ｈｙ、Ｈｒ、Ｈｇ、Ｈｂは書換え可能になっており、これらは画像処理装置全体を制御するシステム制御回路１５０６によって予め設定されている。また以上では、カラー画像信号（Ｄｒ，Ｄｇ，Ｄｂ）を２次元平面に写像する際に、（２５）、（２６）式に例示し方法で説明したが、無彩色軸Ｎが１点に写像されれば良く他の方法で良く、一般的には以下のような式で表すことができる。
２次元座標（Ｉ、Ｊ）
Ｉ＝Ｒｉ・Ｄｒ＋Ｇｉ・Ｄｇ＋Ｂｉ・Ｄｂ
Ｊ＝Ｒｊ・Ｄｒ＋Ｇｊ・Ｄｇ＋Ｂｊ・Ｄｂ
但し、ｒｉ＋ｇｉ＋ｂｉ＝０ｒｊ＋ｇｊ＋ｂｊ＝０
…（５２）
したがって、（５２）式を用いてカラー画像信号を二次元平面に写像してもよい。
【００２９】
【発明の効果】
以上説明したように請求項１記載の発明によれば、カラー画像信号の色空間を無彩色軸Ｎと１次色Ｃ、Ｍ、Ｙおよび２次色Ｒ、Ｇ、Ｂをそれぞれ通る平面で区切り、６つの部分色空間に分割し、入力カラー画像信号がどの部分色空間に属するかを色相領域を判定し、前記入力カラー画像信号をプリンタの色再現範囲内とするための補正量を算出し、算出した補正量に基づいて入力カラー画像信号を無彩色軸方向に補正し、前記判定した色相領域に応じて前記補正したカラー画像信号をプリンタの色材に対応したカラー記録信号に変換したので、画像出力系の色再現範囲外の色の画像信号の入力に際し、その画像信号を明度方向に補正して元画像と遜色のないプリンタ用画像を得るための画像処理方法を容易に実現することができる。
請求項２記載の発明によれば、入力カラー画像信号の彩度が高く、無彩色軸方向に補正してもプリンタの色再現範囲内に入らない場合、前記補正量を抑制し、前記入力カラー画像信号を抑制した補正量に基づいて無彩色軸方向に補正したので、彩度が高くて無彩色軸方向に移動させてもプリンタの色再現範囲内に入らない色の補正量を抑制することができ、より精度の高い画像処理方法を実現することができる。
請求項３記載の発明によれば、前記算出された補正量を調整し、該調整した補正量に基づいて入力カラー画像信号を無彩色軸方向に補正したので無彩色軸方向の補正を望まない場合や補正が強すぎると判断した場合に調整可能でき、操作性に優れた画像処理方法を実現することができる。
【００３０】
請求項４記載の発明によれば、前記抑制された補正量を調整し、該調整した補正量に基づいて入力カラー画像信号を無彩色軸方向に補正したので、無彩色軸方向の補正を望まない場合や補正が強すぎると判断した場合に調整可能でき、操作性に優れた画像処理方法を実現することができる。
請求項５記載の発明によれば、入力したカラー画像信号を無彩色軸が１点に写像される２次元平面に写像して色相領域を判定したので、３次元色空間のまま取り扱う場合に比べて処理が容易になり、より容易な画像処理方法を実現することができる。
請求項６記載の発明によれば、入力したカラー画像信号を無彩色軸が１点に写像される２次元平面に写像し、写像されたカラー画像信号の色相角に対して単調増加となる代替量を算出し、色相領域を判定したので３次元色空間のまま取り扱う場合に比べて処理が容易になり、より容易な画像処理方法を実現することができる。
請求項７記載の発明によれば、入力されたカラー画像信号が表す色が属する色相領域を判定する色相領域判定手段と、前記判定した色相領域に応じて、前記入力カラー画像信号が表す色をプリンタの色再現範囲内とするために最低限必要な無彩色軸方向の補正量を算出する補正量算出手段と、前記補正量を基にカラー画像信号を無彩色軸方向に補正する明度補正手段と、前記判定した色相領域に応じて、前記補正されたカラー画像信号をプリンタの色材に対応したカラー記録信号に変換する色変換手段とを備えたので、明度補正手段がカラー画像信号を無彩色軸方向に補正するため、補正後カラー画像信号の色相領域判定は補正前カラー画像信号の色相領域判定と同じになり、更に色変換手段用の色相領域判定に色相領域判定手段の色相領域判定結果を使うことで、画像出力系の色再現範囲外の色の画像信号の入力に際し、その画像信号を明度方向に補正して元画像と遜色のないプリンタ用画像を得るための簡素な画像処理装置を実現することができる。
請求項８記載の発明によれば、前記入力カラー画像信号の表す色が、彩度が高くて無彩色軸方向に移動させてもプリンタの色再現範囲内に入らない時に、前記算出した補正量を抑制する高彩度修正手段を有し、前記明度補正手段は前記抑制された補正量を基にカラー画像信号を無彩色軸方向に補正したので、彩度が高くて無彩色軸方向に移動させてもプリンタの色再現範囲内に入らない色の補正量を抑制することができ、より精度の高い画像処理装置を実現することができる。
【００３１】
請求項９記載の発明によれば、前記算出した補正量の大きさを調整する補正量調整手段を有し、前記明度補正手段は前記調整された補正量を基にカラー画像信号を無彩色軸方向に補正したので、無彩色軸方向の補正を望まない場合や補正が強すぎると判断した場合に調整可能でき、操作性に優れた画像処理装置を実現することができる。
請求項１０記載の発明によれば、前記抑制された補正量の大きさを調整する補正量調整手段を有し、前記明度補正手段は前記調整された補正量を基にカラー画像信号を無彩色軸方向に補正したので、無彩色軸方向の補正を望まない場合や補正が強すぎると判断した場合に調整可能でき、操作性に優れた画像処理装置を実現することができる。
請求項１１記載の発明によれば、前記色相領域判定手段は、入力されたカラー画像信号を無彩色軸が１点に写像される２次元平面に写像する第１の２次元化手段を備えたので、３次元色空間のまま取り扱う場合に比べて回路規模が小さくなり、より簡素な画像処理装置を実現することができる。
請求項１２記載の発明によれば、前記色相領域判定手段は、入力されたカラー画像信号を無彩色軸が１点に写像される２次元平面に写像する第２の２次元化手段と、前記２次元平面に写像されたカラー画像信号の色相角に対して単調増加となる代替量を算出する擬似色相角算出手段とを備えたので、３次元色空間のまま取り扱う場合に比べて回路規模が小さくなり、より簡素な画像処理装置を実現することができる。
【図面の簡単な説明】
【図１】本発明のカラー画像信号（Ｄｒ，Ｄｇ，Ｄｂ）の色空間とプリンタの色再現範囲との関係の一例を示す図である。
【図２】本発明の図１のカラー画像信号（Ｄｒ，Ｄｇ，Ｄｂ）の色空間を無彩色軸Ｎが通る平面で切断した断面図である。
【図３】本発明の画像処理方法のフローを示す図である。
【図４】本発明の画像処理装置のブロック図である。
【図５】本発明のカラー画像信号の色空間の図である。
【図６】本発明のカラー画像信号（Ｄｒ，Ｄｇ，Ｄｂ）の色空間を、無彩色軸Ｎ（Ｄｒ＝Ｄｇ＝Ｄｂ）と１次色Ｃ、Ｍ、Ｙおよび２次色Ｒ、Ｇ、Ｂをそれぞれ通る平面で区切った図である。
【図７】本発明の図５のカラー画像信号の色空間を無彩色軸Ｎが通る平面で切断した断面図である。
【図８】本発明のカラー画像信号（Ｄｒ，Ｄｇ，Ｄｂ）がどの部分色空間に属するかを判定する回路図である。
【図９】本発明の図６に示した部分色空間を、カラー画像信号の差分信号“Ｄｇ−Ｄｒ”および“Ｄｂ−Ｄｇ”を２軸とする平面に写像した図である。
【図１０】本発明の色相領域判定処理のフロー図である。
【図１１】本発明の色相領域判定回路のブロック図である。
【図１２】本発明のカラー画像信号の差分信号ＧＲ（＝Ｄｇ−Ｄｒ）およびＢＧ（＝Ｄｂ−Ｄｇ）を２軸とする平面を、８つ領域に均等に分割した図である。
【図１３】本発明の色相領域判定処理のフロー図である。
【図１４】本発明の色相領域判定回路のブロック図である。
【図１５】本発明の補正量算出回路の詳細図である。
【図１６】本発明の高彩度修正回路４０３の詳細図である。
【図１７】本発明の色変換回路４０８の詳細図である。
【図１８】本発明のＵＣＲ回路４０９の詳細図である。
【図１９】本発明のプリンタのＷとＫ、１次色Ｃ、Ｍ、Ｙおよび２次色Ｒ、Ｇ、Ｂのカラー画像信号を表す図である。
【図２０】本発明の図１９に示したプリンタのＷとＫ、１次色Ｃ、Ｍ、Ｙおよび２次色Ｒ、Ｇ、Ｂに対応するプリンタ各色材の最適な記録信号を表す図である。
【図２１】本発明のＷ、Ｋ、Ｃ、Ｂにおけるカラー画像信号（Ｄｒ’、Ｄｇ’、Ｄｂ’）とカラー記録信号（Ｄｃ、Ｄｍ、Ｄｙ、Ｄｋ）の対応関係を表す図である。
【符号の説明】
４０１ 色相領域判定回路、４０２ 補正量算出回路、４０３ 高彩度修正回路、４０４ 明度補正回路、４０５ 補正量調整回路、４０６ 調整量設定回路、４０７ 明度補正回路、４０８ 色変換回路、４０９ ＵＣＲ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image processing method and an image processing apparatus when the color gamut of an image input system and the color gamut of an image output system are different, and particularly when an image signal of a color outside the color gamut of an image output system is input, The present invention relates to an image processing method and an image processing apparatus for correcting an image signal to obtain an image comparable to an original image.
[0002]
[Prior art]
Conventionally, the hue of color image data is detected based on R (red), G (green), and B (blue) signals, and the hue of C (cyan), M (magenta), Y (yellow), and K (black) is detected. Japanese Patent Application Laid-Open No. H10-257334 discloses a color correction processing device suitable for converting a color signal into a color signal. The color correction processing device determines a hue area to which a color represented by an input color image signal belongs and determines a color image. The signal is converted into a color recording signal corresponding to the color material of the printer.
On the other hand, as described above, a camera or a scanner that expresses colors in the RGB system, which is additive color mixture, and a printer that expresses colors in CMYK, which is subtractive color mixture, have different color reproduction areas. As a method for reproducing, there is known a method of correcting a difference between a color reproduction region by additive color mixture and a color reproduction region by subtractive color mixture, and converting original image data into appropriate color data.
[Patent Document 1] JP-A-10-257334
[0003]
[Problems to be solved by the invention]
However, when reproducing a color outside the color reproduction range, such as a special color ink, for example, minimizing the color difference may not be optimal. For example, in the case where the lightness and chromaticity of a multicolored map are corrected in a well-balanced manner and the chromaticity is corrected to a more appropriate state instead of minimizing the color difference before and after the correction, a subjective evaluation based on human visual perception In the results, the latter was preferred. This is because the color itself has a meaning in the map, and it is presumed that the change in chromaticity was not preferred because the meaning was ambiguous.
Therefore, the present invention determines a hue area to which a color represented by an input color image signal belongs, and converts the color image signal into a color recording signal corresponding to a color material of a printer, thereby obtaining a color reproduction range of an image input system. Even if the color reproduction range of the output image system is different, it is possible to obtain an image that is comparable to the original image, and it has good color reproducibility even with image data for which color difference minimization is not optimal. It is another object of the present invention to provide an image processing method and an image processing apparatus capable of performing color correction efficiently.
[0004]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, the color space of a color image signal passes through the achromatic axis N, the primary colors C, M, and Y, and the secondary colors R, G, and B, respectively. Separated by a plane, divided into six partial color spaces, a hue area is determined to which partial color space the input color image signal belongs, and a correction amount for keeping the input color image signal within the color reproduction range of the printer. Is calculated,
Correcting the input color image signal in the achromatic color axis direction based on the calculated correction amount, and converting the corrected color image signal into a color recording signal corresponding to a color material of a printer according to the determined hue region. Features.
According to the first aspect of the present invention, when an image signal of a color out of the color reproduction range of the image output system is input, the image signal is corrected in the brightness direction to obtain a printer image that is comparable to the original image. Can be realized.
According to a second aspect of the present invention, in addition to the first aspect, when the saturation of the input color image signal is high and the input color image signal does not fall within the color reproduction range of the printer even when corrected in the achromatic color axis direction, The correction amount is suppressed, and correction is performed in the achromatic color axis direction based on the correction amount in which the input color image signal is suppressed.
Thereby, a more accurate image processing method can be realized.
According to a third aspect of the present invention, in addition to the first aspect, the calculated correction amount is adjusted, and the input color image signal is corrected in the achromatic color axis direction based on the adjusted correction amount. It is characterized by the following.
Thereby, an image processing method excellent in operability can be realized.
According to a fourth aspect of the present invention, in addition to the second aspect, the suppressed correction amount is adjusted, and the input color image signal is corrected in the achromatic color axis direction based on the adjusted correction amount. It is characterized by the following.
Thereby, an image processing method excellent in operability can be realized.
According to a fifth aspect of the present invention, in addition to the first to fourth aspects, a hue region is determined by mapping an input color image signal on a two-dimensional plane where an achromatic axis is mapped to one point. It is characterized by the following.
This makes it possible to realize an even easier image processing method.
[0005]
According to a sixth aspect of the present invention, in addition to the first to fourth aspects, the input color image signal is mapped on a two-dimensional plane where the achromatic axis is mapped to one point, and the mapped color image is mapped. The method is characterized in that an alternative amount that increases monotonically with respect to the hue angle of the signal is calculated, and the hue area is determined.
This makes it possible to realize an even easier image processing method.
According to a seventh aspect of the present invention, there is provided a hue region determining means for determining a hue region to which a color represented by an input color image signal belongs, and a color represented by the input color image signal according to the determined hue region. Correction amount calculating means for calculating a minimum amount of correction in the achromatic color axis direction necessary to make the color change within the color reproduction range of the printer, and brightness correction for correcting the color image signal in the achromatic color axis direction based on the correction amount Means, and color conversion means for converting the corrected color image signal into a color recording signal corresponding to a color material of a printer in accordance with the determined hue region.
Thus, when an image signal of a color outside the color reproduction range of the image output system is input, a simple image processing apparatus for correcting the image signal in the brightness direction to obtain a printer image comparable to the original image. Can be realized.
According to an eighth aspect of the present invention, in addition to the seventh aspect, the color represented by the input color image signal has a high saturation and is within the color reproduction range of the printer even when moved in the achromatic color axis direction. A high-saturation correcting unit that suppresses the calculated correction amount when the calculated correction amount is not included, wherein the lightness correction unit corrects the color image signal in the achromatic color axis direction based on the suppressed correction amount. .
Thereby, a more accurate image processing device can be realized.
According to a ninth aspect of the present invention, in addition to the seventh aspect of the present invention, there is provided a correction amount adjusting means for adjusting the magnitude of the calculated correction amount, wherein the brightness correction means comprises the adjusted correction amount. The color image signal is corrected in the achromatic color axis direction based on
As a result, an image processing apparatus having excellent operability can be realized.
According to a tenth aspect of the present invention, in addition to the eighth aspect, there is provided a correction amount adjusting unit for adjusting the magnitude of the suppressed correction amount, and the brightness correction unit is configured to adjust the corrected correction amount. The color image signal is corrected in the achromatic color axis direction based on the amount.
As a result, an image processing apparatus having excellent operability can be realized.
According to an eleventh aspect of the present invention, in addition to the seventh to tenth aspects, the hue region determining means converts the input color image signal into a two-dimensional plane where an achromatic axis is mapped to one point. It is characterized by comprising first two-dimensional means for mapping.
Thereby, a simpler image processing apparatus can be realized.
According to a twelfth aspect of the present invention, in addition to the seventh to tenth aspects, the hue region determining means converts the input color image signal into a two-dimensional plane where an achromatic axis is mapped to one point. A second two-dimensional conversion means for mapping, and a pseudo hue angle calculation means for calculating a substitute amount that monotonically increases with respect to the hue angle of the color image signal mapped on the two-dimensional plane. I do.
Thereby, a simpler image processing apparatus can be realized.
[0006]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of an image processing method and an image processing apparatus according to the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 shows an example of the relationship between the color space of the color image signals (Dr, Dg, Db) and the color reproduction range of the printer. In this case, the color image signals (Dr, Dg, Db) are color-separated into, for example, R (red), G (green), and B (blue), which are three primary colors of additive color mixture, and output from a scanner or the like for reading the original document. The signal will be described as a color separation density signal that can be obtained by converting the signal into a signal proportional to the density. Therefore, in FIG. 1, the printer W (white) is located on the origin side and the printer K (black) is located at the diagonal apex, and a line connecting these two points is an achromatic axis N (Dr = Dg = Db ). The primary colors C (cyan), M (magenta), Y (yellow), and secondary colors R (red), G (green), and B (blue) of the printer are arranged around the achromatic axis N. The interior of the space having these eight colors as vertices is the color reproduction range of the printer.
[0007]
Next, FIG. 2 shows an example of a cross-sectional view of the color space of the color image signals (Dr, Dg, Db) of FIG. 1 cut along a plane through which the achromatic axis N passes. This cross-sectional view shows that the color reproduction range (shaded area) 202 of the printer is smaller than the range 201 in which the color image signal can be taken. The colors 203 and 204 correspond to colors having the highest saturation (distant from the achromatic axis) in this section (hues on both sides of the achromatic axis N) that can be reproduced by the printer. Further, the color 205 is a color having a high brightness and out of the color reproduction range of the printer. That is, the direction of the achromatic axis N coincides with the direction of lightness, and by moving the color 205 in the K direction of the achromatic axis N (lower direction of lightness), a color that falls within the color reproduction range of the printer is obtained. is there.
The present invention is characterized in that such a color having a high brightness and outside the color reproduction range of the printer is processed by moving the color in the K direction of the achromatic axis N. Further, according to this, it is possible to perform processing in which the saturation (here, the distance from the achromatic axis) and the hue (here, the plane passing through the achromatic axis), that is, the chromaticity, are stored.
FIG. 1 shows an example of the relationship between the color space of the color image signals (Dr, Dg, Db) and the color reproduction range of the printer. As shown in FIG. Even if the interior of the space connecting the eight colors of M, Y and the secondary colors R, G, B with a straight line is regarded as the color reproduction range of the printer, substantially no errors occur. Therefore, in the present invention, the processing is performed by regarding the color reproduction range of the printer as a dodecahedron as shown in FIG. This eliminates the need for processing the curved surface portion of the color reproduction range of the printer, and facilitates the processing.
[0008]
FIG. 3 is a diagram showing a flow of the image processing method according to the present invention, and the image processing method will be described below with reference to this flow.
First, the hue area determination processing 301 of the color image signal (Dr, Dg, Db) is performed. That is, the color space of the color image signal (Dr, Dg, Db) is defined by a plane passing through the achromatic axis N (Dr = Dg = Db), the primary colors C, M, Y, and the secondary colors R, G, B, respectively. 6, the image data is divided into six partial color spaces, and it is determined which partial color space the input color image signal (Dr, Dg, Db) belongs to.
[0009]
Here, the color image signals of the printers W and K, the primary colors C, M, and Y and the secondary colors R, G, and B are set to the values shown in FIG.
In this case, for example, the equation of the plane passing through the printer W and K and the primary color C is
(Dcg−Dcb) · Dr + (Dcb−Dcr) · Dg + (Dcr−Dcg) · Db = 0 (1)
It becomes. Similarly, the equations for the planes passing through the printer W and K and the primary colors M and Y and the secondary colors R, G and B are respectively
(Dmg−Dmb) · Dr + (Dmb−Dmr) · Dg + (Dmr−Dmg) · Db = 0 (2)
(Dyg−Dyb) · Dr + (Dyb−Dyr) · Dg + (Dyr−Dyg) · Db = 0 (3)
(Drg−Drb) · Dr + (Drb−Drr) · Dg + (Drr−Drg) · Db = 0 (4)
(Dgg−Dgb) · Dr + (Dgg−Dgr) · Dg + (DGR−Dgg) · Db = 0 (5)
(Dbg−Dbb) · Dr + (Dbb−Dbr) · Dg + (Dbr−Dgb) · Db = 0 (6)
It becomes.
If the left sides of the equations (1) to (6) are fc, fm, fy, fr, fg, and fb, respectively, it is determined which side of each plane the color image signal (Dr, Dg, Db) is on. It can be determined by the sign of the calculation result of fc, fm, fy, fr, fg, fb. Therefore, whether the color image signal (Dr, Dg, Db) belongs to the above-described partial color space can be determined by the sign of the calculation result of fc, fm, fy, fr, fg, fb.
fc = (Dcg−Dcb) · Dr + (Dcb−Dcr) · Dg + (Dcr−Dcg) · Db (7)
fm = (Dmg−Dmb) · Dr + (Dmb−Dmr) · Dg + (Dmr−Dmg) · Db (8)
fy = (Dyg−Dyb) · Dr + (Dyb−Dyr) · Dg + (Dyr−Dyg) · Db (9)
fr = (Drg−Drb) · Dr + (Drb−Drr) · Dg + (Drr−Drg) · Db (10)
fg = (Dgg−Dgb) · Dr + (Dgg−Dgr) · Dg + (Dgr−Dgg) · Db (11)
fb = (Dgb−Dbb) · Dr + (Dbb−Dbr) · Dg + (Dbr−Dbg) · Db (12)
More specifically, in general,
If fc ≦ 0 and fb> 0, it belongs to the CB partial color space
If fb ≦ 0 and fm> 0, it belongs to the BM partial color space
If fm ≦ 0 and fr> 0, it belongs to the MR partial color space
If fr ≦ 0 and fy> 0, it belongs to the RY partial color space
If fy ≦ 0 and fg> 0, it belongs to the YG partial color space
If fg ≦ 0 and fc ≧ 0, it belongs to the GC partial color space
… (13)
It becomes.
In addition, since the achromatic color (Dr = Dg = Db) also belongs to any of the partial color spaces, the equal sign is attached to the two inequalities only in the GC partial color space in the above, but the achromatic color (Dr = Dg = Db) may belong to any partial color space.
By performing the processing of the equations (7) to (13) as described above, it is determined which partial color space the input color image signal (Dr, Dg, Db) belongs to. Note that the direction of the inequality sign in the equation (13) may change with the specific values in FIG.
[0010]
Next, a correction amount calculation process 302 is performed according to the determination result of the partial color space. The correction amount calculation processing 302 performed here can be represented by the following equation.
X = Rx · Dr + Gx · Dg + Bx · Db + Cx (14)
(Where Rx, Gx, Bx, and Cx are coefficients determined for each partial color space)
Here, FIG. 7 shows an example of a cross-sectional view of the color space of the color image signal of FIG. 5 cut along a plane through which the achromatic axis N passes. In this cross-sectional view, the color reproduction range (shaded area) of the printer is a square like 802 with respect to the range 801 in which a color image signal can be taken, and colors 803 and 804 are the cross-sections ( It corresponds to the color with the highest saturation (distant from the achromatic axis) among the hues on both sides of the achromatic axis N.
A color 805 is an example of a color having a high brightness and out of the color reproduction range of the printer. That is, the color 805 is a color that falls within the color reproduction range of the printer by moving in the K direction (lower lightness) of the achromatic color axis N. A contact that falls within the color reproduction range of the printer when the color 805 is moved in the K direction of the printer is referred to as a color 807. What is desired here is the minimum amount of correction in the K direction of the achromatic axis N required to keep the input color within the color reproduction range of the printer. Become.
Incidentally, a triangle having colors 805, 806 and 807 as vertices and a triangle having colors 807, W and K as vertices are similar figures. The W-K distance is known as shown in FIG. 19 (= Dk-Dw). Therefore, if the ratio between the sizes of the two triangles is known, the correction amount (the distance between the colors 805 and 806) can be obtained.
Therefore, the ratio between the distance between the colors 805 and 807 and the distance between the colors 807 and K is calculated. This can be calculated by using a conversion formula that obtains “−1” for K and “0” for colors 803 and W, and uses this conversion formula.
The correction amount X is obtained by the following equation.
Correction amount X = distance between color 805 and color 806 = (distance between color 805 and color 807) / (distance between color 807 and K) × (distance between W and K) (15)
When the above conversion equation is obtained, an equation that becomes "-(WK distance)" instead of "-1" in K, that is, "-(Dk-Dw)", is obtained as follows. The multiplication in equation (15) can be omitted.
[0011]
The above is a description on a specific cross-sectional view, but if this is applied to the above-described partial color space, it can be used for actual processing.
In this case, taking the CB partial color space as an example, a conversion equation that becomes “− (Dk−Dw)” for K and “0” for C, B, and W may be obtained. That is, by substituting this condition into equation (16) and solving the simultaneous equations, a coefficient can be obtained.
− (Dk−Dw) = Rx · Dkr + Gx · Dkg + Bx · Dkb + Cx
0 = Rx · Dwr + Gx · Dwg + Bx · Dwb + Cx
0 = Rx · Dcr + Gx · Dcg + Bx · Dcb + Cx
0 = Rx · Dbr + Gx · Dbg + Bx · Dbb + Cx
… (16)
(Equation 1)

The same applies to other color spaces. For example, in the BM partial color space,
(Equation 2)

It becomes.
In the actual processing, the coefficients Rx, Gx, Bx, and Cx for each partial color space as described above are obtained in advance, and the coefficients are switched according to the determination result of the partial color space to perform the operation shown in Expression (14). Then, the correction amount X is obtained. Note that the obtained correction amount X is valid only when positive, and when negative, it corresponds to a color within the color reproduction range of the printer, and is corrected to a correction amount (= 0) indicating no correction.
The correction amount X obtained as described above is effective for colors outside the color reproduction range of many printers as it is.
However, in this case, a color that has high saturation (away from the achromatic axis) and does not fall within the color reproduction range of the printer even if it is moved in the K direction of the achromatic axis N (the direction of low lightness), The correction amount indicating no correction may not be obtained. For example, for the color 808 shown in FIG. 7, a correction amount for moving to the color 809 on the color 804-W extension line is obtained. Therefore, it is better to detect such a color and correct it to a correction amount (= 0) indicating no correction.
[0012]
The high saturation correction processing 303 in FIG. 3 performs processing on such a color. In the high-saturation correction process 303, the saturation evaluation value S is calculated by performing an operation represented by the following equation according to the determination result of the partial color space described above.
S = Rs · Dr + Gs · Dg + Bs · Db + Cs (19)
(Where Rs, Gs, Bs, and Cs are coefficients determined for each partial color space)
For example, in the case of a CB partial color space, for example, the coefficient of equation (19) may be a coefficient that is “0” for K and W and “1” for C and B. Substituting and solving the simultaneous equations gives the coefficients.
0 = Rs · Dkr + Gs · Dkg + Bs · Dkb + Cs
0 = Rs · Dwr + Gs · Dwg + Bs · Dwb + Cs
1 = Rs · Dcr + Gs · Dcg + Bs · Dcb + Cs
1 = Rs · Dbr + Gs · Dbg + Bs · Dbb + Cs
… (20)
[Equation 3]

The same applies to other color spaces. For example, in the BM partial color space,
(Equation 4)

It becomes.
In the actual processing, the coefficients Rs, Gs, Bs, and Cs for each partial color space as described above are obtained in advance, and the coefficients are switched according to the determination result of the partial color space to perform the operation shown in Expression (19). Then, a saturation evaluation value S is obtained. When the saturation evaluation value S exceeds “1” as a result of the calculation of the equation (19), the saturation is high (away from the achromatic axis) and the K direction of the achromatic axis N (low brightness). Direction), the color does not fall within the color reproduction range of the printer. Therefore, when the saturation evaluation value S exceeds “1”, the correction value is corrected to a correction amount (= 0) indicating no correction.
By performing the above-described processing, the high-saturation correction processing 303 is realized, whereby the saturation is high (away from the achromatic color axis), and the color is moved in the K direction (low brightness direction) of the achromatic axis N. However, the correction amount for colors that do not fall within the color reproduction range of the printer can be set to no correction (= 0).
In the above description, no correction is made when the saturation evaluation value S exceeds “1”. This value (“1”) corresponds to the value (“1”) in C and B in the above example. . That is, if both values are the same, any value may be used. Further, “exceed” and “not exceed” also vary depending on the magnitude relationship between the values (“0”) at K and W and the values (“1”) at C and B in the above example.
[0013]
Next, a correction amount adjustment process 304 is performed to adjust how much the calculated correction amount X is reflected in the input color image signal. This correction amount adjustment processing 304 is performed, for example, when the adjustment amount is α (= 0 to 1).
X ′ = α · X (23)
This processing is performed, and the obtained X ′ is used as the actual correction amount. Note that this correction amount adjustment processing 304 is not essential to the present invention, but the operator who performs image processing does not want the correction according to the present invention (α = 0) or judges that the correction is too strong. (0 <α <1) is provided so as to be adjustable in the case. The degree of necessity of the adjustment often depends on the type of image to be handled. Therefore, it is possible to select an image type such as a color pencil or a crayon, and automatically set the adjustment amount in conjunction with the selection.
Next, based on the obtained correction amount X ′, a brightness correction process 305 for correcting the color image signals (Dr, Dg, Db) in the K direction of the achromatic axis N is performed. The brightness correction processing 305 is realized by, for example, an addition processing of a color image signal (Dr, Dg, Db) and a correction amount X ′ as in the following equation.
Dr '= Dr + X'
Dg '= Dg + X'
Db '= Db + X'
… (24)
As described above, in the image processing method according to the present invention, a color having a high brightness and being out of the color reproduction range of the printer is moved in the K direction of the achromatic axis N to be changed to a color within the color reproduction range of the printer. Is converted (when α = 1). In addition, since the image moves in the achromatic color axis direction, it is possible to perform correction while maintaining the chromaticity, and it is possible to obtain an image comparable to the original image.
Next, based on the obtained color image signals (Dr ', Dg', Db '), according to the color materials C (cyan), M (magenta), Y (yellow) and K (black) used in the printer. A color conversion process 306 for converting the color recording signals (Dc, Dm, Dy, Dk) into the color recording signals is performed.
[0014]
In the color conversion processing 306 of the present invention, the color space of the color image signal (Dr ′, Dg ′, Db ′) is converted into the achromatic axis N (Dr ′ = Dg ′ = Db ′) and the primary color similarly to FIG. C, M, Y, and the secondary colors R, G, and B are divided into six partial color spaces by a plane passing through them, and the input color image signals (Dr ′, Dg ′, Db ′) It is determined whether the color space belongs to the color space, and the determination is made according to the determination result of the partial color space.
Note that the color conversion processing 306 performed here can be represented by the following equation.
(Equation 5)

Further, the optimum recording signals of the respective color materials of the printer corresponding to the W and K of the printer shown in FIG. 19, the primary colors C, M, and Y and the secondary colors R, G, and B are set to the values shown in FIG.
Taking the CB partial color space as an example, the correspondence between the color image signals (Dr ′, Dg ′, Db ′) and the color recording signals (Dc, Dm, Dy, Dk) in W, K, C, B is As shown in FIG. 21, the coefficient of the equation (25) can be obtained by solving a simultaneous equation relating to W, K, C, and B based on the correspondence shown in FIG.
(Equation 6)

(Equation 7)

The same applies to other color spaces. For example, in the BM partial color space,
(Equation 8)

It becomes.
In the actual processing, the coefficients Mcr, Mcg,..., Mkc for each partial color space as described above are obtained in advance, and the coefficients are switched according to the determination result of the partial color space, and the calculation shown in the equation (25) is performed. Then, color recording signals (Dc, Dm, Dy, Dk) are obtained.
[0015]
By the way, the correction amount calculation processing 302, the high saturation correction processing 303, and the color conversion processing 306 of the present invention convert the color space of the color image signal into the achromatic axis N, the primary colors C, M, Y, and the secondary colors R, It is divided into six partial color spaces separated by a plane passing through G and B respectively. In the brightness correction processing 305, the chromaticity is maintained because the color image signal moves in the achromatic color axis direction. Therefore, the hue region determination result based on the color image signal (Dr, Dg, Db) before the movement and the hue region determination result based on the color image signal (Dr ′, Dg ′, Db ′) after the movement are the same. . Therefore, in the color conversion processing 306 of the present invention, the coefficients are switched using the result of the hue area determination processing 301 based on the color image signals (Dr, Dg, Db) before movement as it is. This eliminates the need for the hue region determination process dedicated to the color conversion process 306, and allows the process to be speeded up.
Note that the color recording signals (Dc, Dm, Dy) output by the color conversion processing 306 of the present invention have values based on the premise that the K color material is not used (Dk = 0). Therefore, next, UCR (UnderColor Removal: under color removal) processing 307 for correcting the color recording signals Dc, Dm, and Dy according to the color recording signal Dk is performed. The UCR process 307 is generally realized by subtracting the color recording signal Dk from the color recording signals Dc, Dm, and Dy, as shown in Expression (29).
Dc ′ = Dc−Dk
Dm '= Dm-Dk
Dy '= Dy-Dk
… (29)
[0016]
Next, FIG. 4 shows an example of a block diagram of an image processing apparatus according to the present invention, and the present invention will be described below with reference to FIG.
A color image signal (Dr, Dg, Db) output from an image signal input device (not shown) is output to a hue area determination circuit 401 (hue area determination means), a correction amount calculation circuit 402 (correction amount calculation means), and a high saturation correction circuit 403 ( High brightness correction means) and the brightness correction circuit 404 (brightness correction means).
The hue area determination circuit 401 is a circuit that determines which partial color space the color image signal (Dr, Dg, Db) belongs to, and the details thereof are shown in FIG.
Referring to FIG. 8, the color image signals (Dr, Dg, Db) are input to the fx value calculation circuit 901.
The fx value operation circuit 901 is a circuit that performs each of the product-sum operations illustrated in the above equations (7) to (12) and outputs a result. The operation results fc, fm, fy, fr, fg, and fb are area codes. Output to the generation circuit 902.
The area code generation circuit 902 performs the comparison and the logical operation exemplified in the expression (13) to determine which partial color space belongs to, and, for example, generates an area code signal code as shown below according to the result. Output.
If the partial color space is CB, the area code is 0
In the case of the BM partial color space, the area code: 1
If the partial color space is MR, the area code is 2
For the RY partial color space, area code: 3
If the color space is YG, the area code is 4
If the partial color space is GC, the area code is 5
… (30)
As described above, according to the fx value calculation circuit 901 and the area code generation circuit 902, the color space of the color image signal (Dr, Dg, Db) is converted into the achromatic color axis N (Dr = Dg = Db) and the primary colors C, M, and Y and the secondary colors R, G, and B, and divides the plane into six partial color spaces. The input color image signals (Dr, Dg, and Db) are divided into six partial color spaces. The hue region determination circuit 401 that determines which partial color space belongs to can be realized.
[0017]
On the other hand, the correction amount calculation circuit 402 calculates a minimum correction amount X2 in the K direction of the achromatic axis N required to keep the input color image signals (Dr, Dg, Db) within the color reproduction range of the printer. In this circuit, the area code signal code obtained by the hue area determination circuit 401 is also input. FIG. 15 shows the details.
Referring to FIG. 15, an X coefficient memory 1601 to which the area code signal code is input stores coefficients Rx, Gx, Bx, and Cx for each partial color space calculated by the above-described equations (17) and (18). A circuit including a memory or the like outputs coefficients Rx, Gx, Bx, and Cx of the corresponding partial color space to the X-value calculation circuit 1602 according to the input area code signal code.
An X value operation circuit 1602 to which the color image signals (Dr, Dg, Db) are input is a circuit that performs the product-sum operation shown in the above equation (14) and outputs the result, and the operation result X1 is a comparator 1603 and a selector. Output to 1604.
The comparator 1603 is a circuit for comparing the input operation result X1 with “value 0”, and the comparison result is output to the selector 1604.
The selector 1604 is a circuit for selectively outputting the input operation result X1 or “value 0”, and outputs it as a correction amount X2. Here, the operation of the selector 1604 is controlled by the comparison result of the comparator 1603. When the operation result X1 is smaller than 0, “value 0” is selectively output.
[0018]
On the other hand, the high saturation correction circuit 403 has a high saturation (away from the achromatic axis) and does not fall within the color reproduction range of the printer even if it is moved in the K direction of the achromatic axis N (the direction of low lightness). This circuit performs correction when the color does not become the correction amount indicating no correction. The region code signal code obtained by the hue region determination circuit 401 and the correction amount X2 obtained by the correction amount calculation circuit 402 are also input. . FIG. 16 shows the details.
Referring to FIG. 16, an S coefficient memory 1701 to which the area code signal code is input stores coefficients Rs, Gs, Bs, and Cs for each partial color space calculated by the above equations (21) and (22). A circuit composed of a memory or the like outputs coefficients Rs, Gs, Bs, and Cs of the corresponding partial color space to the S value calculation circuit 1702 according to the input area code value code.
The S value calculation circuit 1702 to which the color image signals (Dr, Dg, Db) are input is a circuit that performs the product-sum operation shown in the above equation (19) and outputs the result. The calculation result S is output to the comparator 1703. Is done.
The comparator 1703 is a circuit for comparing the input operation result S with “value 1”, and the comparison result is output to the selector 1704.
The selector 1704 is a circuit for selectively outputting the input correction amount X2 or “value 0”, and outputs the correction amount X2 as the correction amount X3. Here, the operation of the selector 1704 is controlled by the comparison result of the comparator 1703, and when the operation result S exceeds 1, “value 0” is selectively output.
As described above, according to the X coefficient memory 1601, the X value calculation circuit 1602, the comparator 1603, and the selector 1604, the K of the achromatic color axis N which is the minimum necessary for keeping the input color within the color reproduction range of the printer. The correction amount calculation circuit 402 that calculates the correction amount in the direction can be realized. Even if the correction amount X2 output from the correction amount calculation circuit 402 is output as it is without passing through the high saturation correction circuit 403, it is effective for colors outside the color reproduction range of many printers.
However, according to the S coefficient memory 1701, the S value calculation circuit 1702, the comparator 1703, and the selector 1704, the saturation is high (away from the achromatic axis) and the K direction of the achromatic axis N (the direction of low brightness). , It is possible to realize a high-saturation correction circuit 403 that does not correct a color that does not fall within the color reproduction range of the printer even if the color is moved to the color reproduction range of the printer. The correction amount of the axis N in the K direction can be calculated more accurately.
Note that the coefficients of the equations (7) to (12) in the fx value calculation circuit 901 and the coefficients of the X coefficient memory 1601 and the S coefficient memory 1701 can be rewritten, and these control the entire image processing apparatus. It is set in advance by the system control circuit 411.
[0019]
Next, the correction amount X3 obtained by the high saturation correction circuit 403 is input to the correction amount adjustment circuit 405 (correction amount adjustment means).
The correction amount adjustment circuit 405 is a circuit for adjusting how much the input correction amount X3 is reflected on the color image signal (Dr, Dg, Db). For example, when the adjustment amount is α (= 0 to 1), , (23) is performed by a multiplier or the like, and the calculated X4 is output as an actual correction amount. Note that the correction amount adjustment circuit 405 is not essential to the present invention, but the operator who performs image processing does not want the correction according to the present invention (α = 0) or judges that the correction is too strong. (0 <α <1) is provided so as to be adjustable in the case. The adjustment amount α is input from an adjustment amount setting circuit 406 that can be set by the operator. In addition, since the degree of necessity of this adjustment often depends on the type of image to be handled, it is possible to select an image type such as a colored pencil or a crayon, and even if the system control circuit 411 sets the adjustment amount α in conjunction with this. good.
Next, the correction amount correction amount X4 obtained by the correction amount adjustment circuit 405 is input to the brightness correction circuit 407 (brightness correction unit).
The brightness correction circuit 407 is a circuit that corrects the color image signal (Dr, Dg, Db) in the brightness direction based on the input correction amount X4, and performs, for example, an operation shown in Expression (24) by an adder or the like. Then, the calculated Dr ', Dg', and Db 'are output as color image signals.
As described above, in the image processing apparatus according to the present invention, a color having a high brightness and being outside the color reproduction range of the printer is moved in the K direction of the achromatic color axis N to be changed to a color within the color reproduction range of the printer. Is converted (when α = 1). In addition, since the image moves in the achromatic color axis direction, it is possible to perform correction while maintaining the chromaticity, and an image comparable to the original image can be obtained.
Next, the color image signals (Dr ′, Dg ′, Db ′) obtained by the brightness correction circuit 407 are input to a color conversion circuit 408 (color conversion means).
The color conversion circuit 408 converts the input color image signals (Dr ', Dg', Db ') into color recording signals (Dc, Dm, Dy, Dy, K) corresponding to the color materials C, M, Y, and K used in the printer. Dk).
In the color conversion circuit 408 of the present invention, the color space of the color image signals (Dr ′, Dg ′, Db ′) is set to the achromatic axis N (Dr ′ = Dg ′ = Db ′), which is the same as FIG. Each of the color image signals (Dr ′, Dg ′, Db ′) is divided into six partial color spaces by dividing the plane into the planes passing the secondary colors C, M, Y and the secondary colors R, G, B. It is determined which partial color space it belongs to, and processing is performed according to the result of the determination of the partial color space. For this reason, a circuit equivalent to the hue area determination circuit 401 is required for the color image signals (Dr ′, Dg ′, Db ′).
[0020]
However, since the brightness correction circuit 407 of the present invention performs the correction while maintaining the chromaticity as described above, the determination result based on the color image signals (Dr ′, Dg ′, Db ′) and the color image signals (Dr, Dg) , Db) are the same. Therefore, the color conversion circuit 408 of the present invention performs processing with reference to the area code signal code of the hue area determination circuit 401. FIG. 17 shows the details.
Referring to FIG. 17, the C coefficient memory 1801, the M coefficient memory 1802, the Y coefficient memory 1803, and the K coefficient memory 1804, to which the area code signal code is input, include the parts calculated by the above equations (27) and (28). A circuit including a memory for storing coefficients Mcr, Mcg, Mcb, Mcc, coefficients Mmr, Mmg, Mmb, Mmc, coefficients Myr, Myg, Myb, Myc and coefficients Mkr, Mkg, Mkb, Mkc for each color space. Then, the coefficients of the partial color space corresponding to the input area code signal code are output to the corresponding C operation circuit 1805, M operation circuit 1806, Y operation circuit 1807, and K operation circuit 1808, respectively.
The C operation circuit 1805, the M operation circuit 1806, the Y operation circuit 1807, and the K operation circuit 1808, to which the color image signals (Dr ', Dg', Db ') are input, perform the product-sum operation shown in the above equation (25). The color recording signals (Dc, Dm, Dy, Dk) are output as a result.
As described above, the color conversion circuit 408 converts the input color image signals (Dr ′, Dg ′, Db ′) according to the area code signal code of the hue area determination circuit 401 into the color materials C, Since it is converted into color recording signals (Dc, Dm, Dy, Dk) corresponding to M, Y, and K, it is possible to determine which partial color space the input color image signal (Dr ′, Dg ′, Db ′) belongs to. It can be realized without making a judgment.
Note that the coefficients of the above-described C coefficient memory 1801, M coefficient memory 1802, Y coefficient memory 1803, and K coefficient memory 1804 are rewritable, and are set in advance by a system control circuit 411 that controls the entire image processing apparatus. ing.
Next, the color recording signals (Dc, Dm, Dy, Dk) obtained by the color conversion circuit 408 are input to the UCR circuit 409.
[0021]
Here, it is assumed that the color recording signals (Dc, Dm, Dy) output from the color conversion circuit 408 do not use the K color material (Dk = 0). Therefore, it is necessary to correct the color recording signals Dc, Dm, and Dy according to the color recording signal Dk, and the UCR circuit 409 plays this role. FIG. 18 shows the details.
Referring to FIG. 18, color recording signals Dc, Dm, and Dy are input to CUCR circuit 1901, MUCR circuit 1902, and YUCR circuit 1903, respectively, and color recording signal Dk is input to each of UCR circuits 1901-1903.
The CUCR circuit 1901, the MUCR circuit 1902, and the YUCR circuit 1903 perform, for example, an operation as shown in the above equation (29) by using an adder or the like, and calculate the calculated Dc ′, Dm ′, and Dy ′ in a color recording signal. Is output as
As described above, the UCR circuit 409 corrects the color recording signals Dc, Dm, and Dy according to the color recording signal Dk. The color recording signals (Dc ′, Dm ′, Dy ′, Dk) of the UCR circuit 409 are output to an image signal output device (not shown) and used for recording an image.
In the above-described hue area determination processing 301 and hue area determination circuit 401, the color image signals (Dr, Dg, Db) are handled in a three-dimensional color space, but the achromatic color axis N is mapped to one point. You may make it handle on a two-dimensional plane.
For example, when the partial color space shown in FIG. 6 is mapped onto a plane having two axes of difference signals “Dg-Dr” and “Db-Dg” of a color image signal, the result is as shown in FIG. That is, the color on the achromatic axis N (Dnr = Dng = Dnb) is
(Dng-Dnr, Dnb-Dng) = (0, 0) (31)
Are mapped to one point n, and the primary colors C, M, and Y and the secondary colors R, G, and B of the printer are arranged around the point n. Then, the six partial color spaces are mapped to regions divided by straight lines connecting the achromatic color n and C, M, Y, R, G, and B, respectively.
here,
GR = Dg−Dr (32)
BG = Db−Dg (33)
And In this case, straight lines connecting the achromatic color n and C, M, Y, R, G, and B are as follows.
BG = (Dcb−Dcg) / (Dcg−Dcr) · GR (however, Dcg−Dcr ≠ 0) (34)
BG = (Dmb−Dmg) / (Dmg−Dmr) · GR (However, Dmg−Dmr ≠ 0) (35)
BG = (Dyb−Dyg) / (Dyg−Dyr) · GR (however, Dyg−Dyr ≠ 0) (36)
BG = (Drb−Drg) / (Drg−Drr) · GR (However, Drg−Drr ≠ 0) (37)
BG = (Dgb−Dgg) / (Dgg−DGR) · GR (however, Dgg−DGR ≠ 0) (38)
BG = (Dbb−DBG) / (DBG−Dbr) · GR (DBG−Dbr ≠ 0) (39)
[0022]
When the right sides of the equations (34) to (39) are fc ′, fm ′, fy ′, fr ′, fg ′, and fb ′, respectively, the difference signals (Db−Dg, Dg−Dr) of the color image signals are obtained. Which side of the straight line is located can be determined by the magnitude relationship between the calculation results of fc ′, fm ′, fy ′, fr ′, fg ′, fb ′ and BG (= Db−Dg). Therefore, it can be determined which of the above-described partial color spaces the color image signal (Dr, Dg, Db) belongs to.
fc ′ = (Dcb−Dcg) / (Dcg−Dcr) · GR (40)
fm ′ = (Dmb−Dmg) / (Dmg−Dmr) · GR (41)
fy ′ = (Dyb−Dyg) / (Dyg−Dyr) · GR (42)
fr ′ = (Drb−Drg) / (Drg−Drr) · GR (43)
fg ′ = (Dgb−Dgg) / (Dgg−DGR) · GR (44)
fb ′ = (Dbb−DBG) / (DBG−Dbr) · GR (45)
More specifically, in general,
If BG ≦ fc ′ and BG> fb ′, it belongs to the CB partial color space
If BG ≦ fb ′ and BG <fm ′, it belongs to the BM partial color space
If BG ≧ fm ′ and BG <fr ′, it belongs to the MR partial color space
If BG ≧ fr ′ and BG <fy ′, it belongs to the RY partial color space
If BG ≧ fy ′ and BG> fg ′, it belongs to the YG partial color space
If BG ≦ fg ′ and BG ≧ fc ′, it belongs to the GC partial color space
… (46)
It becomes. In addition, since the achromatic color (Dr = Dg = Db) also belongs to any of the partial color spaces, the equal sign is attached to the two inequalities only in the GC partial color space in the above, but the achromatic color (Dr = Dg = Db) may belong to any partial color space.
[0023]
FIG. 10 shows an example of a flowchart of the hue region determination processing according to the present invention, and the present invention will be described below with reference to FIG.
First, the input color image signal (Dr, Dg, Db) is subjected to a two-dimensional plane mapping in which the achromatic axis N is mapped to one point, and a two-dimensional processing 1101 for obtaining two-dimensional coordinate values is performed. This corresponds to, for example, the equations (32) and (33) described above.
Next, an evaluation value calculation process 1102 for calculating an evaluation value based on the obtained two-dimensional coordinate values is performed. This evaluation value corresponds to, for example, fc ′, fm ′, fy ′, fr ′, fg ′, fb ′ in the above equations (40) to (45). Note that the slope of each equation, for example, "(Dcb-Dcg) / (Dcg-Dcr)" may be obtained in advance.
Next, based on the obtained two-dimensional coordinate values and evaluation values, a hue area determination process is performed to determine which partial color space belongs to. This corresponds to, for example, the above equation (46).
As described above, according to the hue region determination processing shown in FIG. 10, it is possible to determine which partial color space the input color image signal (Dr, Dg, Db) belongs to, and determine the achromatic color axis N Is handled in a two-dimensional plane mapped to one point, so that the processing is easier than in the case of handling in a three-dimensional color space.
[0024]
FIG. 11 shows an example of a block diagram of a hue region determination circuit according to the present invention. Hereinafter, the present invention will be described with reference to FIG.
The hue region determination circuit shown in FIG. 11 is a circuit for performing the above-described hue region determination processing. Is done.
The difference circuit 1201 is a circuit that calculates the difference exemplified in Expression (32), and the calculation result GR is output to the fx ′ value calculation circuit 1203. The difference circuit 1102 is a circuit that calculates the difference exemplified in the equation (33), and the calculation result BG is output to the area code generation circuit 1204.
The fx ′ value operation circuit 1203 is a circuit that performs the multiplications exemplified in the equations (40) to (45) and outputs the results, and the operation results fc ′, fm ′, fy ′, fr ′, fg ′, fb ′. Is output to the area code generation circuit 1204.
The region code generation circuit 1204 performs the comparison and the logical operation exemplified in the above equation (46) to determine which partial color space belongs to, and outputs the exemplified region code value code according to the result.
As described above, according to the hue region determination circuit shown in FIG. 11, it is determined which partial color space the input color image signal (Dr, Dg, Db) belongs to, and the region code corresponding to the result is determined. Since a value can be output and the achromatic color axis N is handled on a two-dimensional plane mapped to one point, the circuit scale is reduced as compared with a case where the achromatic color axis N is handled as it is in a three-dimensional color space.
Note that the coefficients of the equations (40) to (45) in the fx 'value calculation circuit 1203 described above are rewritable, and are set in advance by a system control circuit 1205 that controls the entire image processing apparatus.
In the above-described hue region determination processing in FIG. 10 and the hue region determination circuit in FIG. 11, the color image signal (Dr, Dg, Db) is mapped on a two-dimensional plane where the achromatic axis N is mapped to one point. However, as shown in FIG. 9, for example, the hue area can be determined by calculating and handling the hue angle HUE with the specific direction as a reference (= 0). The hue angle HUE in this case is calculated from the coordinate values (Dg-Dr, Db-Dg) of the difference signal by a trigonometric function or the like.
[0025]
Further, as described below, an alternative amount (pseudo hue angle H) that increases monotonously with respect to the hue angle HUE may be calculated and handled.
In this method, a plane having two axes of difference signals GR (= Dg-Dr) and BG (= Db-Dg) of a color image signal is equally divided into, for example, eight regions as shown in FIG. It is first determined in which area the signal is located. Here, the values Ha of “0 to 7” are sequentially assigned to the respective areas. This value Ha corresponds to a higher pseudo hue angle, and specifically, the following processing is performed.
If GR> 0 and BG> 0 and BG ≦ GR, Ha = 0
If GR> 0 and BG> 0 and BG> GR, Ha = 1
If GR ≦ 0 and BG> 0 and BG> −GR, Ha = 2
If GR ≦ 0 and BG> 0 and BG ≦ −GR, Ha = 3
Ha = 4 if GR ≦ 0 and BG ≦ 0 and BG> GR
Ha = 5 if GR ≦ 0 and BG ≦ 0 and BG ≦ GR
If GR> 0 and BG ≦ 0 and BG ≦ −GR, Ha = 6
If GR> 0 and BG ≦ 0 and BG> −GR, Ha = 7
… (47)
Next, the coordinate values (GR, BG) of the difference signal are rotated according to the result to obtain coordinate values (gr, bg) moved to a specific area, for example, the area “Ha = 0” in FIG. . Specifically, the following processing is performed.
If Ha = 0, gr = GR, bg = BG
If Ha = 1, gr = GR + BG, bg = −GR + BG
If Ha = 2, gr = BG, bg = −GR
If Ha = 3, gr = −GR + BG, bg = −GR−BG
If Ha = 4, gr = GR, bg = BG
If Ha = 5, gr = -GR-BG, bg = GR-BG
If Ha = 6, gr = GR, bg = BG
If Ha = 7, gr = GR−BG, bg = GR + BG
… (48)
When the coordinates are purely rotated, gr and bg must be multiplied by 1 / √2 when Ha = 1, 3, 5, and 7, respectively. However, since the purpose here is to detect only the angle, the processing of 1 / √2 times is omitted.
[0026]
Next, an amount representing an angle at the coordinate position (gr, bg), for example, a ratio Hb between gr and bg is calculated.
Hb = bg / gr (However, if gr = 0, Hb = 0) (49)
This value Hb indirectly represents the angle at the time of moving to the area “Ha = 0”, and corresponds to the lower pseudo hue angle.
Next, a final pseudo hue angle H is calculated from the obtained upper pseudo hue angle Ha and lower pseudo hue angle Hb. In the above, the difference signal plane (GR, BG) is equally divided into eight regions, and this is rotated to the region “Ha = 0”, so that “bg ≦ gr”. Accordingly, “Hb ≦ 1” holds, and the monotonic increase is maintained even when the value is added to the value Ha. That is, the pseudo-hue angle H, which is a substitute amount that increases monotonously with respect to the hue angle HUE, can be obtained by the following equation.
H = Ha + Hb (50)
Also, if the pseudo hue angles of the primary colors C, M, and Y and the secondary colors R, G, and B of the printer obtained by the above-described procedure are Hc, Hm, Hy, Hr, Hg, and Hb, respectively. By comparing these with the obtained pseudo hue angle H, it is possible to determine which of the above-described partial color spaces the color image signal (Dr, Dg, Db) belongs to.
More specifically, in the case of the positional relationship of FIG.
If H ≧ Hc and H <Hb, it belongs to the CB partial color space
If H ≧ Hb and H <Hm, it belongs to the BM partial color space
If H ≧ Hm and H <Hr, it belongs to the MR partial color space
If H ≧ Hr or H <Hy, it belongs to the RY partial color space
If H ≧ Hy and H <Hg, it belongs to the YG partial color space
If H ≧ Hg and H <Hc, it belongs to the GC partial color space
… (51)
It becomes. In addition, since the achromatic color (Dr = Dg = Db) also belongs to any of the partial color spaces, “Ha = 5, Hb = 0”, that is, “H = 5” according to the equations (47) and (49). However, the achromatic color (Dr = Dg = Db) may be converted to any pseudo hue angle.
[0027]
FIG. 13 shows an example of a flowchart of the hue region determination processing according to the present invention, and the present invention will be described below with reference to FIG.
First, a two-dimensional processing 1401 for obtaining a two-dimensional coordinate by performing a two-dimensional plane mapping on the input color image signal (Dr, Dg, Db) in which the achromatic axis N is mapped to one point is performed. This is the same as the two-dimensional processing 1101 described above.
Next, a high-order hue determination process 1402 for determining a high-order pseudo hue angle Ha of the obtained two-dimensional coordinates is performed. This corresponds to, for example, the above equation (47).
Next, coordinate rotation processing 1403 for rotating the two-dimensional coordinates according to the obtained upper pseudo hue angle Ha and moving to a specific area is performed. This corresponds to, for example, the above equation (48).
Next, lower hue determination processing 1404 for determining a lower pseudo hue angle Hb according to the moved two-dimensional coordinates is performed. This corresponds to, for example, equation (49) described above.
Next, a pseudo hue angle H is calculated based on the obtained upper pseudo hue angle Ha and lower pseudo hue angle Hb, and the calculated primary hue angle H is determined in advance by a similar procedure. , Y, and the secondary colors R, G, and B are compared with Hc, Hm, Hy, Hr, Hg, and Hb, and a hue region determination process 1405 is performed to determine which partial color space belongs. This corresponds to, for example, the above equations (50) and (51).
As described above, according to the hue region determination processing shown in FIG. 13, it is possible to determine which partial color space the input color image signal (Dr, Dg, Db) belongs to, and to determine the hue angle HUE On the other hand, since the substitute amount (pseudo hue angle H) that increases monotonically is calculated and handled, the processing becomes easier compared to the case where the three-dimensional color space is handled as it is.
[0028]
FIG. 14 shows an example of a block diagram of a hue region determination circuit according to the present invention. Hereinafter, the present invention will be described with reference to FIG.
The hue area determination circuit in FIG. 14 is a circuit that performs the above-described hue area determination processing, and the input color image signals (Dr, Dg, Db) are input to difference circuits 1501 and 1502 (second two-dimensional unit). Is done.
The difference circuit 1501 is the same circuit as the difference circuit 1201 described above, and the difference circuit 1502 is the same circuit as the difference circuit 1102 described above, and the respective calculation results GR and BG are output to the upper hue determination circuit 1503 and the coordinate rotation circuit 1504. .
The upper hue determination circuit 1503 performs the comparison and the logical operation exemplified in the equation (47) to determine the upper pseudo hue angle Ha. The result is output to the coordinate rotation circuit 1504 and the lower hue determination circuit 1505. In the claims, the pseudo hue angle calculation means means the upper hue determination circuit 1503, the coordinate rotation circuit 1504, and the lower hue determination circuit 1505.
The coordinate rotation circuit 1504 is a circuit for rotating the difference signal (GR, BG) and moving it to a specific area according to the higher pseudo hue angle Ha as exemplified in the equation (48). (Gr, bg) is output to the lower hue determination circuit 1505.
The lower hue determination circuit 1505 is a circuit that calculates an amount representing an angle at the coordinate position exemplified in Expression (49), and the obtained lower pseudo hue angle Hb is output to the area code generation circuit 1505.
The area code generation circuit 1505 performs the comparison and the logical operation exemplified in the equation (51) to determine which partial color space belongs to, and outputs the exemplified area code value code according to the result.
As described above, according to the hue region determination circuit shown in FIG. 14, it is determined which partial color space the input color image signal (Dr, Dg, Db) belongs to, and the region code corresponding to the result is determined. Since a value can be output and a substitute amount (pseudo hue angle H) that increases monotonously with respect to the hue angle HUE is calculated and handled, the circuit scale is reduced as compared with a case where the three-dimensional color space is used as it is. .
Note that the pseudo hue angles Hc, Hm, Hy, Hr, Hg, and Hb in the above-described region code generation circuit 1505 in equation (51) are rewritable, and these are system control circuits 1506 that control the entire image processing apparatus. Is set in advance. In the above description, when the color image signal (Dr, Dg, Db) is mapped on a two-dimensional plane, the method has been described by way of example in equations (25) and (26), but the achromatic axis N is mapped to one point. Any other method may be used, and can be generally expressed by the following equation.
Two-dimensional coordinates (I, J)
I = Ri · Dr + Gi · Dg + Bi · Db
J = Rj · Dr + Gj · Dg + Bj · Db
Where ri + gi + bi = 0 rj + gj + bj = 0
… (52)
Therefore, the color image signal may be mapped onto a two-dimensional plane using the equation (52).
[0029]
【The invention's effect】
As described above, according to the first aspect of the present invention, the color space of the color image signal is divided by a plane passing through the achromatic axis N and the primary colors C, M, Y and the secondary colors R, G, B. Is divided into six partial color spaces, a hue area is determined to which partial color space the input color image signal belongs, and a correction amount for keeping the input color image signal within the color reproduction range of the printer is calculated. Since the input color image signal was corrected in the achromatic color axis direction based on the calculated correction amount, and the corrected color image signal was converted into a color recording signal corresponding to the color material of the printer according to the determined hue region, When inputting an image signal of a color out of the color reproduction range of the image output system, an image processing method for correcting the image signal in the brightness direction to obtain a printer image comparable to the original image can be easily realized. Can be.
According to the second aspect of the present invention, when the saturation of the input color image signal is high and does not fall within the color reproduction range of the printer even when corrected in the achromatic color axis direction, the correction amount is suppressed, Since the correction was made in the achromatic color axis direction based on the correction amount that suppressed the image signal, it was possible to suppress the correction amount of colors that were high in saturation and did not fall within the color reproduction range of the printer even when moved in the achromatic color axis direction Thus, a more accurate image processing method can be realized.
According to the third aspect of the present invention, since the calculated correction amount is adjusted and the input color image signal is corrected in the achromatic color axis direction based on the adjusted correction amount, the correction in the achromatic color axis direction is not desired. In this case, the adjustment can be made when it is determined that the correction is too strong, and an image processing method with excellent operability can be realized.
[0030]
According to the fourth aspect of the present invention, the suppressed correction amount is adjusted, and the input color image signal is corrected in the achromatic color axis direction based on the adjusted correction amount. When there is no correction or when it is determined that the correction is too strong, the adjustment can be performed, and an image processing method excellent in operability can be realized.
According to the fifth aspect of the present invention, the input color image signal is mapped to a two-dimensional plane where the achromatic axis is mapped to one point, and the hue region is determined. Thus, the processing is facilitated, and an easier image processing method can be realized.
According to the sixth aspect of the present invention, the input color image signal is mapped onto a two-dimensional plane where the achromatic axis is mapped to one point, and the color image signal is monotonically increased with respect to the hue angle of the mapped color image signal. Since the amount is calculated and the hue area is determined, the processing becomes easier as compared with the case where the three-dimensional color space is handled as it is, and an easier image processing method can be realized.
According to the seventh aspect of the present invention, a hue region determination unit that determines a hue region to which a color represented by an input color image signal belongs, and a color represented by the input color image signal according to the determined hue region. Correction amount calculating means for calculating a minimum amount of correction in the achromatic color axis direction required to be within the color reproduction range of the printer, and brightness correction means for correcting a color image signal in the achromatic color axis direction based on the correction amount And color conversion means for converting the corrected color image signal into a color recording signal corresponding to a color material of a printer in accordance with the determined hue region. Since the correction is performed in the chromatic axis direction, the hue area determination of the color image signal after correction is the same as the hue area determination of the color image signal before correction. By using the fixed result, when inputting an image signal of a color outside the color reproduction range of the image output system, the image signal is corrected in the brightness direction to obtain a simple image for obtaining a printer image comparable to the original image A processing device can be realized.
According to the invention described in claim 8, when the color represented by the input color image signal has a high saturation and does not fall within the color reproduction range of the printer even when moved in the achromatic color axis direction, the calculated correction amount Has a high saturation correction means for suppressing, the lightness correction means corrected the color image signal in the achromatic color axis direction based on the suppressed correction amount, so that the saturation is high, it is moved in the achromatic color axis direction Also, the amount of correction of colors that do not fall within the color reproduction range of the printer can be suppressed, and a more accurate image processing apparatus can be realized.
[0031]
According to the ninth aspect of the present invention, there is provided a correction amount adjusting means for adjusting the magnitude of the calculated correction amount, wherein the brightness correction means converts a color image signal into an achromatic color axis based on the adjusted correction amount. Since the correction is made in the direction, the correction can be performed when the correction in the achromatic color axis direction is not desired or when it is determined that the correction is too strong, and an image processing apparatus excellent in operability can be realized.
According to the tenth aspect of the present invention, the image processing apparatus further includes a correction amount adjusting unit that adjusts the magnitude of the suppressed correction amount, wherein the brightness correction unit converts the color image signal to an achromatic color based on the adjusted correction amount. Since the correction is performed in the axial direction, the adjustment can be performed when correction in the achromatic color axis direction is not desired or when it is determined that the correction is too strong, and an image processing apparatus with excellent operability can be realized.
According to an eleventh aspect of the present invention, the hue region determination unit includes a first two-dimensional unit that maps the input color image signal onto a two-dimensional plane in which an achromatic axis is mapped to one point. Therefore, the circuit scale is reduced as compared with the case where the three-dimensional color space is handled as it is, and a simpler image processing apparatus can be realized.
According to the twelfth aspect of the present invention, the hue region determining means maps the input color image signal to a two-dimensional plane in which an achromatic axis is mapped to one point, A pseudo hue angle calculating means for calculating an alternative amount that monotonically increases with respect to the hue angle of a color image signal mapped on a two-dimensional plane is provided. A smaller image processing device can be realized.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an example of a relationship between a color space of a color image signal (Dr, Dg, Db) of the present invention and a color reproduction range of a printer.
FIG. 2 is a sectional view of the color space of the color image signals (Dr, Dg, Db) of FIG. 1 cut along a plane through which an achromatic axis N passes.
FIG. 3 is a diagram showing a flow of an image processing method of the present invention.
FIG. 4 is a block diagram of an image processing apparatus according to the present invention.
FIG. 5 is a diagram of a color space of a color image signal of the present invention.
FIG. 6 shows that the color space of the color image signal (Dr, Dg, Db) of the present invention is defined by an achromatic axis N (Dr = Dg = Db), primary colors C, M, Y and secondary colors R, G, It is the figure divided by the plane which respectively passes through B.
7 is a cross-sectional view of the color space of the color image signal of FIG. 5 of the present invention cut along a plane through which an achromatic axis N passes.
FIG. 8 is a circuit diagram for determining which partial color space the color image signal (Dr, Dg, Db) of the present invention belongs to.
9 is a diagram in which the partial color space shown in FIG. 6 of the present invention is mapped onto a plane having two axes of difference signals “Dg-Dr” and “Db-Dg” of a color image signal.
FIG. 10 is a flowchart of a hue region determination process according to the present invention.
FIG. 11 is a block diagram of a hue region determination circuit according to the present invention.
FIG. 12 is a diagram in which a plane having two axes of a difference signal GR (= Dg−Dr) and BG (= Db−Dg) of a color image signal of the present invention is equally divided into eight regions.
FIG. 13 is a flowchart of a hue region determination process according to the present invention.
FIG. 14 is a block diagram of a hue region determination circuit according to the present invention.
FIG. 15 is a detailed diagram of a correction amount calculation circuit according to the present invention.
FIG. 16 is a detailed diagram of a high saturation correction circuit 403 of the present invention.
FIG. 17 is a detailed diagram of a color conversion circuit 408 of the present invention.
FIG. 18 is a detailed diagram of a UCR circuit 409 of the present invention.
FIG. 19 is a diagram illustrating color image signals of W and K, primary colors C, M, and Y and secondary colors R, G, and B of the printer of the present invention.
20 is a diagram showing optimum print signals of respective color materials of the printer corresponding to W and K, primary colors C, M, Y and secondary colors R, G, B of the printer shown in FIG. 19 of the present invention. is there.
FIG. 21 is a diagram illustrating a correspondence relationship between color image signals (Dr ′, Dg ′, Db ′) and color recording signals (Dc, Dm, Dy, Dk) in W, K, C, B of the present invention.
[Explanation of symbols]
401 hue area determination circuit, 402 correction amount calculation circuit, 403 high saturation correction circuit, 404 lightness correction circuit, 405 correction amount adjustment circuit, 406 adjustment amount setting circuit, 407 lightness correction circuit, 408 color conversion circuit, 409 UCR

Claims (12)

The color space of the color image signal is divided by a plane passing through the achromatic color axis N and the primary colors C, M, Y and the secondary colors R, G, B, and divided into six partial color spaces. Determine the hue area that belongs to which partial color space,
Calculating a correction amount for setting the input color image signal within the color reproduction range of the printer,
The input color image signal is corrected in the achromatic color axis direction based on the calculated correction amount,
A color image processing method comprising: converting the corrected color image signal into a color recording signal corresponding to a color material of a printer according to the determined hue region. If the saturation of the input color image signal is high and does not fall within the color reproduction range of the printer even when corrected in the achromatic color axis direction, the correction amount is suppressed, and based on the correction amount that suppresses the input color image signal. 2. The color image processing method according to claim 1, wherein the correction is performed in an achromatic color axis direction. 2. The color image processing method according to claim 1, wherein the calculated correction amount is adjusted, and the input color image signal is corrected in the achromatic axis direction based on the adjusted correction amount. 3. The color image processing method according to claim 2, wherein the suppressed correction amount is adjusted, and the input color image signal is corrected in the achromatic color axis direction based on the adjusted correction amount. 5. The color image processing method according to claim 1, wherein the input color image signal is mapped to a two-dimensional plane where the achromatic axis is mapped to one point to determine a hue area. The input color image signal is mapped to a two-dimensional plane where the achromatic axis is mapped to one point, and a substitute amount that increases monotonically with respect to the hue angle of the mapped color image signal is calculated to determine a hue area. 5. The color image processing method according to claim 1, wherein: Hue region determining means for determining a hue region to which a color represented by the input color image signal belongs;
Correction amount calculation means for calculating a minimum amount of correction in the achromatic color axis direction necessary for setting the color represented by the input color image signal within the color reproduction range of the printer, according to the determined hue region,
A lightness correction unit that corrects a color image signal in the achromatic color axis direction based on the correction amount; and, in accordance with the determined hue region, converts the corrected color image signal into a color recording signal corresponding to a color material of a printer. Color conversion means for converting;
A color image processing apparatus comprising: When the color represented by the input color image signal has high saturation and does not fall within the color reproduction range of the printer even when moved in the achromatic color axis direction, the high color saturation correction means for suppressing the calculated correction amount,
8. The color image processing apparatus according to claim 7, wherein said brightness correction means corrects a color image signal in an achromatic color axis direction based on said suppressed correction amount. Having a correction amount adjusting means for adjusting the magnitude of the calculated correction amount,
8. The color image processing apparatus according to claim 7, wherein said brightness correction means corrects the color image signal in the achromatic color axis direction based on the adjusted correction amount. Having a correction amount adjusting means for adjusting the magnitude of the suppressed correction amount,
9. The color image processing apparatus according to claim 8, wherein said brightness correction means corrects the color image signal in the achromatic color axis direction based on the adjusted correction amount. 11. The device according to claim 7, wherein the hue region determination unit includes a first two-dimensional unit that maps the input color image signal onto a two-dimensional plane in which an achromatic axis is mapped to one point. Color image processing device. The hue region determination means includes: a second two-dimensional conversion means for mapping the input color image signal on a two-dimensional plane in which an achromatic axis is mapped to one point; and a color image signal mapped on the two-dimensional plane. 11. The color image processing apparatus according to claim 7, further comprising: a pseudo hue angle calculating unit configured to calculate a substitute amount that increases monotonously with respect to the hue angle.

Images