JP4154051B2 - Color processing apparatus and method - Google Patents

Description

【００６５】
明度調整部308は、得られた明度情報Loutおよび入力されるLab信号のab情報とから合成したLab信号を出力する。
【００６６】
本実施形態によれば、第1実施形態よりもさらに高精度のガマット圧縮を行うことができる。つまり、実際のプリンタの色域は非常に複雑な形状をもつので、第1実施形態のCmax_printerに応じて設定される圧縮率に基づく変換では、入力画像データをプリンタの色域に完全に変換することはできない。これに対して、本実施形態によれば、入力画像に関する圧縮後のデータである色域圧縮情報に基づき、ガマット圧縮を行うので、より高精度のガマット圧縮が実現される。
【００６７】
【第４実施形態】
以下、本発明にかかる第4実施形態の信号処理装置を説明する。なお、本実施形態において、第1および第3実施形態と略同様の構成については、同一符号を付して、その詳細説明を省略する。
【００６８】
本実施形態は、第3実施形態における明度調整部308の動作を変更したものである。明度調整部308は、入力されるLab信号からab情報を抽出し、抽出されたab情報およびプリンタ色域情報から、プリンタ色域内において、抽出されたab情報と同じ値を有する明度最大値Lmax_printer_abおよび明度最小値Lmin_printer_abを抽出する。続いて、抽出されたab情報および色域圧縮情報から、圧縮色域内において、抽出されたab情報と同じ値を有する明度最大値Lmax_compressed_abおよび明度最小値Lmin_compressed_abを抽出する。これらの抽出された情報と、入力されたLab信号のL情報Linとから、次の手順により明度情報Loutが算出される。
【００６９】
Lmax_printer_ab、Lmin_printer_ab、Lmax_compressed_abおよびLmin_compressed_abの何れかが抽出されなかった場合は、Lout=Linとする。
【００７０】
上記に該当しない場合は入出力関係を定義する関数h(・)を用いてLoutを算出する。つまり、Lout=h(Lin)とする。h(・)はn-1セグメントからなる区分的関数を用いて定義され、下記の条件がなり立つよう制御される。因みに、nは区分的関数h(・)の節点数である。

【００７１】
ここで、αおよびβ:は、台の端点における圧縮率を与えるパラメータで、上記条件を満たすという制限の下で自動的に計算される。また、miおよびniも上記条件を満たすという制限の下で自動的に計算される。自動計算アルゴリズムにより、できるだけmi=niなる関係を保持するように努めるが、階調性および上記条件を保つことを優先するため、前記関係(mi=ni)は必ずしも保証されない。しかしながら、入力と出力との差分絶対値|h(Lin) - Lin|が各点において、できるだけ小さくなるように努める。
【００７２】
本実施形態では、h(・)を3セグメントのC1連続な三次スプライン関数として実現する。また、m1=1/3×Cmax_monitorおよびm2=2/3×Cmax_monitorとする。
【００７３】
図9および図10は本実施形態を用いたあるプリンタ出力における、ある色度abにおける明度の入出力関係を示す図である。なお、図9におけるLmin_compressed_ab=40、Lmax_compressed_ab=68、Lmin_printer_ab=45およびLmax_printer_ab=64である。また、図10におけるLmin_compressed_ab=60、Lmax_compressed_ab=84、Lmin_printer_ab=46およびLmax_printer_ab=75である。
【００７４】
本実施形態によれば、明度圧縮において非線形変換を用いるので、より中明度領域における再現性を向上することができる。とくに、シアンのようにモニタの色域とプリンタの色域とが相似関係をもたない領域における色再現性を向上させることができる。
【００７５】
【第５実施形態】
以下、本発明にかかる第4実施形態の信号処理装置を説明する。なお、本実施形態において、第1、第3および第4実施形態と略同様の構成については、同一符号を付して、その詳細説明を省略する。
【００７６】
本実施形態は、第4実施形態における彩度圧縮部104の構成を変更したものである。図11は本実施形態の色信号変換器208の構成例を示すブロック図で、図8に示す構成と異なるのは、彩度圧縮部104へab信号とともに、L信号が入力されることである。
【００７７】
図12は本実施形態の彩度圧縮部104の構成例を示すブロック図である。図4に示した彩度圧縮部104と異なるのは、L信号が端子426を介して彩度計算部123へ入力されることである。
【００７８】
彩度計算部123は、モニタ色域情報およびプリンタ色域情報から抽出された、h信号から定められる色相、並びに、入力されるL信号から定められる明度における彩度レンジ情報と、所定の圧縮関係とから定められる入出力関係に従い、入力されるc信号から出力すべき彩度を計算する。計算結果のc信号は座標信号変換部124へ出力される。座標信号変換部124はhc信号をab信号に変換し出力する。
【００７９】
上記構成の彩度計算部123の動作を、図13に示すフローチャートを参照して説明する。
【００８０】
ステップS1000で、彩度圧縮部104に入力される色相hおよびプリンタ色域情報から、色相hにおけるプリンタ色域の最大彩度Cmax_printerを求め、ステップS1001で、彩度圧縮部104に入力される色相hおよびモニタ色域情報から、色相hにおけるモニタ色域の最大彩度Cmax_monitorを求め、ステップS1002で、彩度Cmax_printerと彩度Cmax_monitorとの比Rmax=Cmax_printer/Cmax_monitorを求める。
【００８１】
次に、ステップS1003で、彩度圧縮部104に入力される色相h、明度Lおよびプリンタ色域情報から、色相hかつ明度Lにおけるモニタ色域の最大彩度CL_monitorを求め、ステップS1004で、彩度圧縮部104に入力される彩度cと最大彩度CL_monitorとの比R=c/CL_monitorを求める。
【００８２】
次に、ステップS1005で、彩度比の入出力関係を定義する関数g(・)を用いて彩度比Rnew=g(R/Rmax)を求め、ステップS1006で、彩度比Rnewと最大彩度CL_monitorとを乗じた結果を彩度計算部123の計算結果として出力する。ここで、彩度比の入出力関係を定義する関数g(・)は、本実施形態においては三次関数を用いて定義されるとともに、次のように制御される。
g(・)の台は[0, 1]
g(0) = 0
g(1) = Rmax
g'(0) = 1
g'(Rmax) = γ, γ: γ > 0
g'(x)≠0, x: 0≦x≦1
【００８３】
ここで、γは、ある色相および明度における最大彩度付近において彩度圧縮の圧縮率を制御する値で、上記の条件を満たすという制限の下、Cmax_monitorおよびCmax_printerの関係に基づき、彩度計算部123が色相および明度の組合せごとに自動的に定める。γパラメータ自動設定に当っては、Cmax_monitor/Cmax_printerが大きくなるにつれ、γの値を小さくする。すなわち、圧縮率を大きくする。
【００８４】
なお、本実施形態において、入出力関係を定義する関数g(・)は三次関数を用いて実現されるが、第2実施形態のように区分的関数を用いて実現しても、何ら本質を損なうことはない。
【００８５】
本実施形態によれば、プリンタ色域外に対しては線形圧縮し、プリンタ色域内については高彩度領域の圧縮率を高くするように非線形圧縮することができる。つまり、モニタ色域の境界部に対しては線形に彩度圧縮することで、高彩度域の階調性をよりよく表現することができる。従って、DTPなどで多用される色の鮮やかなグラデーションなどにおいて再現性を向上させることができるとともに、人間が敏感である中明度領域および低彩度領域も高精度に再現できるため、自然（写真）画像なども併せて良好に再現することができる。
【００８６】
【第６実施形態】
以下、本発明にかかる第6実施形態の信号処理装置を説明する。なお、本実施形態において、第1実施形態と略同様の構成については、同一符号を付して、その詳細説明を省略する。
【００８７】
図14は本実施形態としての色信号変換器208の構成例を示すブロック図である。
【００８８】
モニタの色再現域（モニタガマット）上のLab信号を、プリンタの色再現域（プリンタガマット）上のLab信号へ変換する色信号変換器208へは、端子109を介して、メインメモリ202に保持されていた画像データのLab信号、すなわち変換元であるモニタガマット上の色信号が入力される。そして、プリンタへの出力画像、すなわち所望されるプリンタガマット上の色信号は端子110から出力される。
【００８９】
また、端子111からはプリンタの色再現域情報（プリンタ色域情報）が、端子112からはモニタの色再現域情報（モニタ色域情報）がそれぞれ入力され、モニタ色域情報は記憶部107へ、プリンタ色域情報は記憶部108へそれぞれ記憶される。
【００９０】
色信号分離部102は、入力されるLab信号を明度成分および色度成分に分離し、明度成分であるL信号を明度圧縮部103および彩度圧縮部104へ出力し、色度成分であるab信号を彩度圧縮部104へ出力する。
【００９１】
彩度圧縮部104は、モニタ色域情報およびプリンタ色域情報から抽出される彩度レンジ情報と、所定の圧縮関係とから定められる入出力関係に従い彩度圧縮を行い、その圧縮結果のab信号513を明度圧縮部103に出力する。また、彩度圧縮部104は、明度圧縮に必要な明度情報を、モニタ色域情報より取得して情報処理を行う。そして、抽出された彩度レンジ情報およびモニタ明度情報を信号512として明度圧縮部103に出力する。
【００９２】
明度圧縮部103は、彩度圧縮部104により情報処理されたモニタ明度情報および抽出された彩度レンジ情報、並びに、所定の圧縮関係から定められる入出力関係に従い、L信号に対して明度圧縮を行い、その圧縮結果のL信号と、彩度圧縮部104から入力されるab信号513とを合成して、Lab信号として色域検査部106に出力する。
【００９３】
●彩度圧縮部
図15は本実施形態の彩度圧縮部104の構成例を示すブロック図である。図12に示した彩度圧縮部104と異なるのは、明度情報計算部525を備えることである。明度情報計算部525は、彩度圧縮部104に入力されるL信号、ab信号およびモニタ色域情報から、色度abにおけるモニタ色域の最大明度と最小明度とを算出し、端子529より信号512として出力する。
【００９４】
●明度圧縮部
上記構成における明度圧縮部103の動作について説明する。明度圧縮部103は、入力されるab信号およびプリンタ色域情報から、色度abにおけるプリンタ色域の最大明度情報Lmax_printer_abと最小明度情報Lmin_printer_abとを算出する。次に、明度圧縮部103に入力される最大明度情報をLmax_monitor_abとし、最小明度情報をLmin_monitor_abとして、これら四つの明度情報から明度圧縮計算に必要なパラメータを算出する。
【００９５】
算出されたパラメータと、明度圧縮部103に入力される明度圧縮対象であるL信号Linと出力されるL信号Loutとの入出力関係を定義する関数f(・)によって、信号Loutを計算する。ここでf(・)はn-1セグメントからなる区分的関数を用いて定義され、下記の条件がなり立つように制限されている。因みに、nは区分的関数の節点数である。

【００９６】
本実施形態では、f(・)を5セグメントのC2連続な三次スプライン関数として実現する。ここで、接点数n、接点における値miならびにni、台の端点における圧縮率αならびにβは、Lmin_monitor_ab、Lmax_monitor_ab、Lmin_printer_abおよびLLmax_printer_abの四つの明度情報から自動的に計算される。ここでパラメータ自動設定アルゴリズムにより、階調性と上記条件とを満たす範囲において、できるだけf(x)=xになるようなパラメータが設定される。αおよびβについての自動設定アルゴリズムは、概略、次のようなものである。
【００９７】
αについて、Lmin_monitor_ab≦Lmin_printer_abである場合、Lmin_monitor_abとLmin_printer_abの差が大きくなるに従い、0≦α≦1という拘束条件の下においてαを小さくする。すなわち、最暗点付近における圧縮率を大きくする。
【００９８】
一方、Lmin_monitor_ab＞Lmin_printer_abである場合、Lmin_monitor_abとLmin_printer_abの差が大きくなるに従い、α＞1という拘束条件の下においてαを大きくする。すなわち、最暗点付近における伸長率を大きくする。
【００９９】
同様にβについて、Lmax_monitor_ab≧Lmax_printer_abである場合、Lmax_monitor_abとLmax_printer_abの差が大きくなるに従い、0≦β≦1という拘束条件の下においてβを小さくする。すなわち、最明点付近における圧縮率を大きくする。
【０１００】
一方、Lmax_monitor_ab＜Lmax_printer_abである場合、Lmax_monitor_abとLmax_printer_abの差が大きくなるに従い、β＞1という拘束条件の下においてβを大きくする。すなわち、最明点付近における伸長率を大きくする。
【０１０１】
【第７実施形態】
以下、本発明にかかる第7実施形態の信号処理装置を説明する。なお、本実施形態において、第1、第3および第4実施形態と略同様の構成については、同一符号を付して、その詳細説明を省略する。
【０１０２】
本実施形態は、第4実施形態における彩度圧縮部104の構成を変更したものである。図16は本実施形態の色信号変換器208の構成例を示すブロック図である。
【０１０３】
彩度調整情報入力部618は、ユーザが彩度調整情報を入力するためのものであり、例えば、CPU201によりカラーモニタ207にユーザインタフェイス画像として形成されるコントロールパネル、並びに、キーボード211および/またはマウス212などから構成される。ユーザが各節点における入力値および出力値を与えることにより入力された彩度調整情報は、CPU201により、然るべきデータ構造に変換された後、一旦、メインメモリ202に保持された後、端子617を介して色信号変換器208の彩度圧縮部104へ入力される。なお、彩度調整情報の入力は必須の動作ではない。
【０１０４】
メインメモリ202に保持された画像をプリンタ209から出力する指令を受けたCPU201は、メインメモリ202の記憶内容を調べて彩度調整情報の入力の有無を判断し、その有無情報を色信号変換器208へ送る。彩度調整情報の入力があった場合、CPU201は、メインメモリ202に保持されている彩度調整情報を、PCIバス214および端子617を介して、色信号変換器208へ送る。
【０１０５】
彩度圧縮部104は、モニタ色域情報およびプリンタ色域情報から抽出される彩度レンジ情報、並びに、入力される彩度調整情報により制御される圧縮関係から定められる入出力関係に従い彩度圧縮を行い、その圧縮結果であるab信号を色信号合成部105に出力する。
【０１０６】
なお、上記構成における彩度調整情報入力部618は、前述したように図2の構成における各ブロックが所定順に動作することで実現される。
【０１０７】
●彩度圧縮部
図17は彩度圧縮部104の構成例を表すブロック図である。
【０１０８】
図17において、記憶部625は、端子630を介して入力される彩度調整情報を記憶し、色信号分離部122から入力される色相情報であるh信号に対応する彩度調整値を彩度計算部123へ出力する。彩度計算部123は、モニタ色域情報およびプリンタ色域情報から抽出された、h信号から定められる色相における彩度レンジ情報と、彩度調整情報に制御された圧縮関係とから定められる入出力関係に従い、入力されるc信号から出力すべき彩度を計算し、その計算結果のc信号を座標信号変換部124へ出力する。
【０１０９】
上記の構成における彩度計算部123の動作について説明する。彩度計算部123は、入出力関係を定義する関数g(・)により制御され、入力されるc信号cinと出力されるc信号coutとの間には、cout=g(cin)なる関係がなり立つ。g(・)は三次関数を用いて定義され、下記の条件がなり立つように制御される。
g(・)の台は[0, Cmax_monitor]
g(0) = 0
g(Cmax_monitor) = Cmax_printer
g'(0) = α
g'(Cmax_monitor) = γ, γ: γ > 0
g'(x)≠0, x: 0≦x≦Cmax_monitor
【０１１０】
ここで、αは、記憶部625の出力値により定められるもので、すなわちh信号から定められる色相における彩度調整値である。Cmax_monitorは色相成分であるh信号およびモニタ色域情報から計算され、h信号から定められる色相においてモニタ色域の最大彩度値と定義される。また、Cmax_printerは色相成分であるh信号およびプリンタ色域情報から計算され、h信号から定められる色相においてプリンタ色域の最大彩度値と定義される。
【０１１１】
γは、最大彩度付近における彩度圧縮の圧縮率を制御する値で、上記条件を満たすという制限の下、Cmax_monitorおよびCmax_monitorの関係より彩度計算部123が自動的に定める。γパラメータ自動設定において、Cmax_monitor/Cmax_printerが大きくなるにつれ、γの値を小さくする。すなわち、圧縮率を大きくする。
【０１１２】
●彩度調整情報
ユーザは、彩度調整情報として、一つまたは複数の任意の色相において、彩度制御関数のx=0における傾きyを入力する。記憶部625は角度に対して線形に補間を行い、すべての色相における彩度調整情報を作成する。この情報は、各色相と、各色相における彩度調整値αとの集合として形成される。この集合情報が彩度調整情報として記憶部625に保持される。
【０１１３】
任意の色相における彩度制御関数のx=0における傾きyを彩度調整情報として、ユーザが入力するということは、指定した彩度におけるガマット圧縮後の理想的な彩度を、元の彩度のy倍にすることに等しく、直感的な彩度調整を非常に容易にするものである。
【０１１４】
【第８実施形態】
以下、本発明にかかる第8実施形態の信号処理装置を説明する。なお、本実施形態において、第1、第3および第4実施形態と略同様の構成については、同一符号を付して、その詳細説明を省略する。
【０１１５】
本実施形態は、第4実施形態における彩度圧縮部104の構成を変更したものである。図18は本実施形態の色信号変換器208の構成例を示すブロック図である。
【０１１６】
明度調整情報入力部718は、ユーザが明度調整情報を入力するためのものであり、例えば、CPU201によりカラーモニタ207にユーザインタフェイス画像として形成されるコントロールパネル、並びに、キーボード211および/またはマウス212などから構成される。ユーザが各節点における入力値および出力値を与えることにより入力された明度調整情報は、CPU201により、然るべきデータ構造に変換された後、一旦、メインメモリ202に保持された後、端子717を介して色信号変換器208の明度圧縮部103へ入力される。なお、明度調整情報の入力は必須の動作ではない。
【０１１７】
メインメモリ202に保持された画像をプリンタ209から出力する指令を受けたCPU201は、メインメモリ202の記憶内容を調べて明度調整情報の入力の有無を判断し、その有無情報を色信号変換器208へ送る。明度調整情報の入力があった場合、CPU201は、メインメモリ202に保持されている明度調整情報を、PCIバス214および端子717を介して、色信号変換器208へ送る。
【０１１８】
明度圧縮部103は、モニタ色域情報およびプリンタ色域情報から抽出される明度レンジ情報、所定の圧縮関係、並びに、入力される明度調整情報から定められる入出力関係に従い、入力されるL信号を明度圧縮し、その圧縮結果であるL信号を色信号合成部105に出力する。
【０１１９】
●明度圧縮部
明度圧縮部103は、入出力関係を定義する関数f(・)によって制御される。すなわち、明度圧縮部103に入力されるL信号Linと出力されるL信号Loutとの間には、Lout=f(Lin)なる関係がなり立つ。f(・)はn-1セグメントからなる区分的関数を用いて定義され、下記の条件がなり立つよう制御される。因みに、nは区分的関数の節点数であり、本実施形態においては明度調整情報入力部718からの入力によって制御される。

【０１２０】
ここで、Lmin_monitorはモニタの黒色が保持するL値、Lmax_monitorはモニタの白色が保持するL値、Lmin_printerはプリンタの黒色が保持するL値、および、Lmax_printerはモニタの白色が保持するL値である。本実施形態では、f(・)を各接点において少なくともC1連続である三次スプライン関数により実現する。ここで、α、β、接点数n、mi、niおよびγiは、明度調整情報の入力においてユーザにより設定されるものである。なお、α、βもしくは両者の入力がない場合、アルゴリズムがα、βもしくは両者を自動的に設定する。また、γiの入力がない場合には、接点iにおけるC2連続性からγiはアルゴリズムにより自動的に求められる。
【０１２１】
なお、ユーザからの明度調整情報の入力が一切なかった場合はn=5、mi=niおよびγi=1に定め、さらに前記条件の下、αとβとを自動的に計算し、概パラメータを関数f(・)に設定する。
【０１２２】
また、αおよびβの自動計算アルゴリズムにおいて、Lmin_monitorとLmin_printerの差が大きくなるに従い、αの値を小さくする。すなわち、最暗点付近における圧縮率を大きくする。他方、Lmax_monitorとLmax_printerの差が大きくなるに従い、βの値を小さくする。すなわち、最明点付近における圧縮率を大きくする。
【０１２３】
以上説明した各実施形態によれば、ガマット圧縮において、中程度の明度は保存され、非常に明度の高い色もしくは非常に明度の低い色は大きく明度圧縮される。また、ガマット圧縮において、彩度の低い色ほど彩度が保存され、逆に彩度の高い色ほど大きく彩度圧縮される。これらにより、モニタやプリンタの機種の相違による色再現性の違い、あるいは、記録媒体の色再現特性の相違による色再現性の違いによらず、知覚的に非常に近似した出力画像を得ることができる。
【０１２４】
【他の実施形態】
なお、本発明は、複数の機器（例えばホストコンピュータ、インタフェイス機器、リーダ、プリンタなど）から構成されるシステムに適用しても、一つの機器からなる装置（例えば、複写機、ファクシミリ装置など）に適用してもよい。
【０１２５】
また、本発明の目的は、前述した実施形態の機能を実現するソフトウェアのプログラムコードを記録した記憶媒体を、システムあるいは装置に供給し、そのシステムあるいは装置のコンピュータ（またはCPUやMPU）が記憶媒体に格納されたプログラムコードを読出し実行することによっても、達成されることは言うまでもない。この場合、記憶媒体から読出されたプログラムコード自体が前述した実施形態の機能を実現することになり、そのプログラムコードを記憶した記憶媒体は本発明を構成することになる。また、コンピュータが読出したプログラムコードを実行することにより、前述した実施形態の機能が実現されるだけでなく、そのプログラムコードの指示に基づき、コンピュータ上で稼働しているOS（オペレーティングシステム）などが実際の処理の一部または全部を行い、その処理によって前述した実施形態の機能が実現される場合も含まれることは言うまでもない。
【０１２６】
さらに、記憶媒体から読出されたプログラムコードが、コンピュータに挿入された機能拡張カードやコンピュータに接続された機能拡張ユニットに備わるメモリに書込まれた後、そのプログラムコードの指示に基づき、その機能拡張カードや機能拡張ユニットに備わるCPUなどが実際の処理の一部または全部を行い、その処理によって前述した実施形態の機能が実現される場合も含まれることは言うまでもない。
【０１２７】
また、上記の各実施形態においては、代表的なLab色空間において説明したが、本発明は、これに限定されるものではなく、Luv色空間やマンセル色空間などの明度および色度を有する色空間であれば適用することができる。
【０１２８】
【発明の効果】
以上説明したように、本発明によれば、異なるデバイスおよび/または異なる記録媒体に形成および/または表示される色が近似した色として知覚されるように色信号を変換する、高精度な色再現を実現することができる。
【図面の簡単な説明】
【図１】本発明にかかる第1実施形態の色信号変換装置のシステム構成例を示すブロック図、
【図２】図1に示される色信号変換器の構成例を示すブロック図、
【図３】第1実施形態における明度の入出力関係例を示す図、
【図４】図2に示される彩度圧縮部の構成例を示すブロック図、
【図５】第1実施形態における彩度の入出力関係例を示す図、
【図６】複数種類の紙質についてガマット圧縮を行った場合のそれぞれの明度圧縮入出力特性を示す図、
【図７】第2実施形態における彩度の入出力関係例を示す図、
【図８】第3実施形態の色信号変換器の構成例を示すブロック図、
【図９】ある色度abにおける明度の入出力関係を示す図、
【図１０】ある色度abにおける明度の入出力関係を示す図、
【図１１】第5実施形態の色信号変換器の構成例を示すブロック図、
【図１２】図11に示す彩度圧縮部の構成例を示すブロック図、
【図１３】図11に示す彩度計算部の動作を示すフローチャート、
【図１４】第6実施形態の色信号変換器の構成例を示すブロック図、
【図１５】図14に示す彩度圧縮部の構成例を示すブロック図、
【図１６】第7実施形態の色信号変換器の構成例を示すブロック図、
【図１７】図16に示す彩度圧縮部の構成例を示すブロック図、
【図１８】第8実施形態の色信号変換器の構成例を示すブロック図である。[0001]
[Industrial application fields]
The present invention performs gamut compressioncolorRegarding processing.
[0002]
[Prior art]
In a computer system or video printer having a color monitor and a color printer, a color image created and / or processed on a monitor or a color image received by a receiver may be printed out.
[0003]
With a color monitor that expresses a color image by emitting light of a specific wavelength using a phosphor and a color printer that absorbs light of a specific wavelength using ink or the like and expresses a color image with the remaining reflected light, As is well known, the color gamut differs greatly. In addition, color monitors also have different color gamuts, such as those using liquid crystal, those using an electron gun type cathode ray tube, and those using a plasma type. Similarly, in a color printer, the color gamut varies depending on differences in paper quality and ink usage.
[0004]
For this reason, in the image displayed on the color monitor, the image output by the color printer, or the color image output using a plurality of types of printers and a plurality of types of recording paper, the colors are measured. It is impossible to make them completely coincidental. Therefore, when a human perceives a color image displayed (formed) on each output medium, a great difference in color between the images is felt.
[0005]
As an image processing technique for absorbing the perceptual color difference of displayed (formed) color images between output media having different color gamuts, and for perceptual matching of the color, gamut ( gamut) compression or color matching exists.
[0006]
[Problems to be solved by the invention]
According to a certain image processing technique, for all colors, the sum of squares of differences between the color signal used in the color monitor and the color signal used in the color printer, that is, the sum of squares of the differences, is taken, and this sum of squares of the differences is minimized. Gamut compression is performed. However, this technique obtains good results within the color gamut of both devices, but the image information is significantly impaired due to the loss of gradation for color signals outside the range. For this reason, in images having color signals outside the color gamut of both devices, the colors of images displayed or formed by these devices are observed to be significantly different.
[0007]
In consideration of the above-described problem of gradation, various gamut compression techniques have been developed under the condition that gradation is not lost as much as possible. However, in these technologies, since the amplitude of the difference signal between the color signal of the color monitor and the color signal of the color printer when expressing a certain color becomes large in all colors, the display or formation by these devices is also necessary. The color of the resulting image is observed to be significantly different.
[0008]
Thus, there is a need for a gamut compression technique that can solve the above two problems simultaneously.
[0009]
The present invention converts color signals so that colors formed and / or displayed on different devices and / or different recording media are perceived as approximate colorsRealize high-precision color reproductionFor the purpose.
[0010]
[Means for Solving the Problems]
The present invention has the following configuration as one means for achieving the above object.
[0011]
The color processing apparatus according to the present invention includes:Of the first deviceThe color signal in the first color gamut is different from the first color gamut.Of the second deviceA color processing device for converting to a color signal in a second color gamut, wherein the lightness component of the color signal is a piecewise function comprising n-1 (where n is the number of nodes of the piecewise function) segments.Spline function indicated byMeans for compressing the lightness within the lightness range of the second color gamut, means for compressing the chroma component of the color signal within the saturation range of the second color gamut, and Used for lightness compressionsplineLightness compression control means for controlling the compression function of the lightness component by controlling a function, the lightness compression control means,Outputs the white color of the second color gamut to the white color input of the first color gamut, and outputs the black color of the second color gamut to the black color input of the first color gamut. Set the spline function to outputAs the difference in maximum brightness between the first and second color gamuts increases, the maximum brightness of the first color gamut increases at the maximum brightness.splineAs the value β of the first derivative of the function is decreased and the difference between the minimum brightness values of the first and second color gamuts increases, the minimum brightness value of the first color gamut increases.splineIt is characterized by reducing the value α of the first derivative of the function.
[0017]
The color processing method according to the present invention includes:Of the first deviceThe color signal in the first color gamut is different from the first color gamut.Of the second deviceA color processing method for converting to a color signal in a second color gamut, wherein the lightness component of the color signal is a piecewise function comprising n-1 (where n is the number of nodes of the piecewise function) segments.Spline function indicated byUsing a color compression within the lightness range of the second color reproduction range, and a step of compressing the saturation component of the color signal within the saturation range of the second color reproduction range, Used for lightness compressionsplineA brightness compression control step for controlling a compression ratio of the brightness component by controlling a function, and the brightness compression control step includes:Outputs the white color of the second color gamut to the white color input of the first color gamut, and outputs the black color of the second color gamut to the black color input of the first color gamut. Set the spline function to outputAs the difference in maximum brightness between the first and second color gamuts increases, the maximum brightness of the first color gamut increases at the maximum brightness.splineAs the value β of the first derivative of the function is decreased and the difference between the minimum brightness values of the first and second color gamuts increases, the minimum brightness value of the first color gamut increases.splineIt is characterized by reducing the value α of the first derivative of the function.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a signal processing device according to an embodiment of the present invention will be described in detail with reference to the drawings.
[0024]
[First Embodiment]
[System configuration]
FIG. 1 is a block diagram showing a system configuration example of the color signal conversion apparatus according to the first embodiment of the present invention.
[0025]
In FIG. 1, 201 is a CPU, 202 is a main memory composed of RAM, 203 is a SCSI (Small Computer Standard Interface) interface (I / F), 204 is a network interface, 205 is a hard disk driver (HDD), 206 is Graphic accelerator, 207 color monitor, 208 color signal converter, 209 color printer, 210 keyboard / mouse controller, 211 keyboard, 212 pointing device such as mouse, 213 local area network (LAN), and 214 is, for example, a PCI (Peripheral Component Interconnect) bus. The CPU 201 executes various processes to be described later according to programs and data stored in advance in the ROM 215 and / or the HDD 205.
[0026]
In the above configuration, image data stored in the HDD 205 is transferred to the main memory 202 via the SCSI I / F 203 and the PCI bus 214 in accordance with a command from the CPU 201. In addition, image data stored in a server connected to the LAN 213 or image data on the Internet is also transferred to the main memory 202 via the network I / F 204 and the PCI bus 214 according to a command from the CPU 201. The image data held in the main memory 202 is transferred to the graphic accelerator 206 via the PCI bus 214 according to a command from the CPU 201. The graphic accelerator 206 converts the image data into digital-analog (D / A), if necessary, and transmits it to the color monitor 207 through a display cable. Therefore, an image corresponding to the image data is displayed on the color monitor 207.
[0027]
Here, when receiving an instruction (print command) to print an image held in the main memory 202 by the color printer 209 from the user by the keyboard 211 or the mouse 212, the CPU 201 displays the color gamut information of the appropriate color monitor, and The appropriate color printer color gamut information is transferred from the HDD 205 to the main memory 202, and then the two color gamut information is transferred to the color signal converter 208. Next, the image data held in the main memory 202 is transferred to the color signal converter 208 via the PCI bus 214 in accordance with a command from the CPU 201. The color signal converter 208 performs color signal conversion on the input image data, and then transmits the converted image data to the color printer 209. The image corresponding to the image data is printed on the recording paper by the color printer 209. Printed.
[0028]
The user selects a printer model and recording paper type used for printing, and a monitor model in advance when issuing a print command. Based on this selection information, the CPU 201 determines which of the plurality of color gamut information held in the HDD 205 should be selected.
[0029]
[Color signal converter]
FIG. 2 is a block diagram illustrating a configuration example of the color signal converter 208. In this embodiment, an example in which gamut compression is performed in the Lab color space will be described.
[0030]
The color signal converter 208 converts the Lab signal on the monitor color reproduction range (monitor gamut) into the Lab signal on the printer color reproduction range (printer gamut). The color signal converter 208 receives the Lab signal of the image data held in the main memory 202, that is, the color signal on the monitor gamut that is the conversion source, via the terminal 109. An output image to the printer, that is, a desired color signal on the printer gamut is output from the terminal 110.
[0031]
In addition, printer color gamut information (printer gamut information) is input from terminal 111, and monitor color gamut information (monitor gamut information) is input from terminal 112. Monitor color gamut information is input to storage unit 107. The printer color gamut information is stored in the storage unit 108, respectively.
[0032]
102 is a color signal separation unit, which separates the input Lab signal into lightness component L and chromaticity component ab, and transmits L signal as lightness component to lightness compression unit 103, and ab signal as chromaticity component to chroma Each is output to the compression unit 104. The lightness compression unit 103 performs lightness compression on the input L signal according to an input / output relationship determined from lightness range information extracted from the monitor color gamut information and printer color gamut information and a predetermined compression relationship. The compression result L signal is output to the color signal synthesis unit 105. The saturation compression unit 104 performs saturation on the input ab signal according to the input / output relationship determined from the saturation range information extracted from the monitor color gamut information and the printer color gamut information and a predetermined compression relationship. Compression is performed, and an ab signal as a compression result is output to the color signal synthesis unit 105.
[0033]
The color signal synthesis unit 105 synthesizes the input L signal and ab signal, and outputs the result to the color gamut inspection unit 106 as an Lab signal. The color gamut inspection unit 106 determines whether the input Lab signal is within the printer color gamut or out of the printer color gamut, and if it is within the printer color gamut, outputs the input Lab signal and outputs the input Lab signal outside the printer color gamut. In some cases, the Lab signal in the printer color gamut that minimizes the color difference is output.
[0034]
In the above configuration, the color signal converter 208 operates as follows. Prior to the operation, the color gamut information of the color monitor and the color gamut information of the printer are transmitted in response to a command from the CPU 201, and are stored in the storage units 107 and 108 as monitor gamut information and printer gamut information, respectively. Thereafter, image data in which color information is described by Lab signals is transmitted to the color signal converter 208 via the PCI bus 214 in the order of raster scan. Here, the color signal converter 208 performs color signal conversion by gamut compression on the Lab signal of each pixel in the image data, and sequentially transmits it to the color printer 209.
[0035]
That is, in this color signal conversion operation, the input Lab signal is first separated into an L signal and an ab signal by the color signal separation unit 102, and then subjected to gamut compression processing in each circuit constituting the color signal converter 101. Applied.
[0036]
● Lightness compression section
The lightness compression unit 103 is controlled by a function f (•) that defines an input / output relationship. That is, the relationship Lout = f (Lin) is established between Lin, which is an L signal input to the lightness compression unit 103, and Lout, which is an L signal that is output. f (·) is defined using a piecewise function consisting of n-1 segments, and is controlled so that the following conditions hold. Incidentally, n is the number of nodes of the piecewise function.
The base of f (・) is [Lmin_monitor, Lmax_monitor]
F (・) is continuous at all points
f (Lmin_monitor) = Lmin_printer
f (Lmax_monitor) = Lmax_printer
f '(Lmin_monitor) = α, α: 0 ≦ α
f '(Lmax_monitor) = β, β: 0 ≦ β
f (mi) = mi, i: 0 ≦ i ≦ n-2, mi: Lmin_printer <mi <Lmax_printer
f '(mi) = 1, i: 0 ≦ i ≦ n-2, mi: Lmin_printer <mi <Lmax_printer
f '(x) ≠ 0, x: Lmin_monitor <x <Lmax_monitor
Where Lmin_monitor: Monitor black L value
        Lmax_monitor: White L value of the monitor
        Lmin_printer: Black L value of the printer
        Lmax_printer:PrinterL value of white
        α: Best value compressionDarkControl the compression ratio near the pointvalue
        β: The best value compressionLightNear the pointKickControl compression ratiovalue
        mi: Any value
[0037]
Control compression ratiovalueα decreases as the difference between Lmin_monitor and Lmin_printer increases.YouThe That is, the compression rate near the darkest point, which is the darkest pointThebigYouThe On the other hand, control the compression ratevalueβ decreases as the difference between Lmax_monitor and Lmax_printer increasesYouThe That is, the compression rate near the brightest point, which is the brightest pointThebigYouThe In the present embodiment, f (•) is realized as a C2 continuous cubic spline function of 5 knots, 4 segments, for example. For example, m1 = 40, m2 = 50, and m3 = 70.
[0038]
Here, FIG. 3 shows the input / output relationship of lightness when Lmin_monitor = 0, Lmax_monitor = 100, Lmin_printer = 20, and Lmax_printer = 90 in a certain printer output using this embodiment.
[0039]
● Saturation compression section
FIG. 4 is a block diagram illustrating a configuration example of the saturation compression unit 104. The ab signal is input from the terminal 125, and the ab signal with the saturation compressed is output from the terminal 126. Also, monitor color gamut information is input from the terminal 127 and printer color gamut information is input from the terminal 128.
[0040]
The coordinate signal conversion unit 121 converts an ab signal in which chromaticity is expressed by an orthogonal coordinate system into an hc signal that expresses chromaticity by a polar coordinate system. Here, h signal represents an angle in the polar coordinate system, that is, hue, and c signal represents a distance from the origin in the polar coordinate system, that is, saturation. The color signal separation unit 122 separates the input hc signal into a hue component h and a saturation component c, and the h signal, which is a hue component, is sent to the coordinate signal conversion unit 124 and the saturation calculation unit 123 as a saturation component. A certain c signal is output to the saturation calculation unit 123.
[0041]
The saturation calculation unit 123 is input in accordance with the input / output relationship determined from the saturation range information in the hue determined from the h signal extracted from the monitor color gamut information and the printer color gamut information and the predetermined compression relationship. c Calculate the saturation to be output from the signal. The calculated c signal is output to the coordinate signal converter 124. The coordinate signal converter 124 converts the hc signal into an ab signal and outputs it.
[0042]
The saturation calculation unit 123 is controlled by a function g (•) that defines an input / output relationship. That is, the relationship cout = g (cin) is established between the c signal cin input to the saturation calculation unit 123 and the output c signal cout. g (·) is defined using a cubic function and is controlled so that the following conditions are satisfied.
The stand for g (・) is [0, Cmax_monitor]
g (0) = 0
g (Cmax_monitor) = Cmax_printer
g '(0) = 1
g '(Cmax_monitor) = γ, γ: γ> 0
g '(x) ≠ 0, x: 0 ≦ x ≦ Cmax_monitor
[0043]
In the above equation, Cmax_monitor is calculated from the h signal and monitor color gamut information, and is defined as the maximum saturation value of the monitor color gamut in the hue determined from the h signal. Cmax_printer is calculated from the h signal and the moprinter gamut information, and is defined as the maximum saturation value of the printer gamut in the hue determined from the h signal. Also, γ is a value that controls the compression rate of saturation compression near the maximum saturation, and is automatically determined by the saturation calculation unit 123 based on the relationship between Cmax_monitor and Cmax_monitor under the restriction that the above condition is satisfied. For automatic γ parameter settingThisWhatIsAs the ratio Cmax_monitor / Cmax_printer between Cmax_monitor and Cmax_printer increases, the value of γThesmallYouThe That is, compression rateThebigYouThe
[0044]
FIG. 5 is a diagram showing the input / output relationship of saturation in a certain printer output using this embodiment. Note that Cmax_monitor = 60.51 and Cmax_printer = 40.17.
[0045]
According to the present embodiment, the lightness compression input / output characteristics obtained when gamut compression is performed on a plurality of types of paper quality such as plain paper or dedicated recording paper in a certain type of color monitor and a certain type of color printer. When superimposed, the result is as shown in FIG. That is, medium brightness is preserved regardless of the paper quality. On the other hand, in the vicinity of the brightest point or the darkest point, the compression ratio changes greatly according to the lightness range in which color reproduction is possible.
[0046]
According to the present embodiment, it is possible to maintain color continuity and reproduce gradation outside the color gamut of the printer. Furthermore, it is possible to reproduce the medium lightness area (see Fig. 3) and low saturation area (see Fig. 5), which are sensitive to humans and are frequently included in natural images (photographic images), with high accuracy. it can. Therefore, it is possible to satisfactorily reproduce an input image including colors outside the printer color gamut with the printer.
[0047]
In addition, since the medium lightness area and the low saturation area can be reproduced with high accuracy, as shown in FIG. 6, the medium lightness and low saturation can be obtained on various recording papers (recording media) having different color reproduction characteristics (color gamut). The color reproducibility with respect to the degree region can be matched, and the color of each recording sheet can be matched.
[0048]
Second Embodiment
The signal processing apparatus according to the second embodiment of the present invention will be described below. Note that in the present embodiment, the same reference numerals are given to substantially the same configurations as those in the first embodiment, and detailed description thereof will be omitted.
[0049]
In the present embodiment, the operation of the saturation compression unit 104 in the first embodiment is changed. The saturation calculation unit 123 of the saturation compression unit 104 is controlled by a function g (•) that defines an input / output relationship. That is, the relationship cout = g (cin) is established between the c signal cin input to the saturation calculation unit 123 and the output c signal cout. g (•) is defined using a piecewise function consisting of n-1 segments, and is controlled so that the following conditions are satisfied. Incidentally, n is the number of nodes of the piecewise function.
The stand for g (・) is [0, Cmax_monitor]
g (0) = 0
g (Cmax_monitor) = Cmax_printer
g '(0) = 1
g '(Cmax_monitor) = γ, γ: γ> 0
g (mi) = mi, i: 0 ≦ i ≦ n-2, mi: 0 <mi <Cmax_monitor
g '(mi) = 1, i: 0 ≦ i ≦ n-2, mi: 0 <mi <Cmax_monitor
g '(x) ≠ 0, x: 0 ≦ x ≦ Cmax_monitor
[0050]
Here, Cmax_monitor is calculated from the h signal and monitor color gamut information, and is defined as the maximum saturation value of the monitor color gamut in the hue determined from the h signal. Cmax_printer is calculated from the h signal and printer gamut information, and is defined as the maximum saturation value of the printer gamut in the hue determined from the h signal. Also, γ is a value that controls the compression ratio of saturation compression in the vicinity of the maximum saturation, and is automatically determined by the saturation calculation unit 123 based on the relationship between Cmax_printer and Cmax_monitor under the restriction that the above condition is satisfied. For automatic γ parameter settingThisAs the ratio Cmax_monitor / Cmax_printer between Cmax_monitor and Cmax_printer increases, the value of γThesmallYouThe That is, compression rateThebigYouThe
[0051]
In the present embodiment, g (•) is realized as, for example, a 2-segment C2 continuous cubic spline function. Further, for example, m1 = 1/2 × Cmax_monitor.
[0052]
FIG. 7 is a diagram showing the input / output relationship of saturation in a certain printer output using this embodiment. Note that Cmax_monitor = 60.51 and Cmax_printer = 40.17.
[0053]
[Third Embodiment]
The signal processing apparatus according to the third embodiment of the present invention will be described below. Note that in the present embodiment, the same reference numerals are given to substantially the same configurations as those in the first embodiment, and detailed description thereof will be omitted.
[0054]
FIG. 8 is a block diagram showing a configuration example of the color signal converter 208 according to the third embodiment of the present invention.
[0055]
The color signal converter 208 that converts the Lab signal in the monitor color reproduction area (monitor gamut) to the Lab signal in the printer color reproduction area (printer gamut) is held in the main memory 202 via the terminal 109. The input Lab signal of the image data, that is, the color signal on the monitor gamut that is the conversion source is input. An output image to the printer, that is, a desired color signal on the printer gamut is output from the terminal 110.
[0056]
In addition, printer color gamut information (printer gamut information) is input from terminal 111, and monitor color gamut information (monitor gamut information) is input from terminal 112. Monitor color gamut information is input to storage unit 107. The printer color gamut information is stored in the storage unit 108, respectively. In addition, the storage unit 312 stores information on the result of the lightness and saturation compression performed on the monitor color gamut.
[0057]
The multiplexer (MUX) 302 selects a signal input from the storage unit 107 or the terminal 109 based on a selection signal from the CPU 201 input via the terminal 313 and outputs the selected signal to the color signal separation unit 102. The processing performed by the color signal separation unit 102, the lightness compression unit 103, the saturation compression unit 104, and the color signal synthesis unit 105 is the same as the processing described with reference to FIG. 2 in the first embodiment, and thus description thereof is omitted. .
[0058]
The Lab signal output from the color signal synthesis unit 105 is input to the demultiplexer (DMUX) 307 and is output to the storage unit 312 or the brightness adjustment unit 308 according to the selection signal from the CPU 201. The brightness adjustment unit 308 converts the L signal according to the input / output relationship determined from the input Lab signal, the printer color gamut information, and the color gamut compression information stored in the storage unit 312, and converts the Lab signal that is the conversion result The data is output to the color gamut inspection unit 106 described above.
[0059]
In the above configuration, the color signal converter 208 operates as follows. Prior to the operation, the color gamut information of the color monitor and the color gamut information of the printer are transmitted in response to a command from the CPU 201, and are stored in the storage units 107 and 108 as monitor gamut information and printer gamut information, respectively. Next, the color signal converter 208 creates color gamut compression information that is monitor color gamut information subjected to lightness and saturation compression, and stores them in the storage unit 312. In this process, the MUX 302 selects a signal input from the storage unit 107, and the DMUX 307 selects an output to the storage unit 312.
[0060]
When the above processing is completed, the color signal converter 208 performs color signal conversion processing that applies gamut compression to the Lab signal on the input monitor gamut. In this process, the MUX 302 selects a signal input from the terminal 109, and the DMUX 307 selects an output to the brightness adjustment unit 308.
[0061]
When the above operation is completed, image data in which color information is described using Lab signals is transmitted to the color signal conversion device 301 via the PCI bus by the raster scan method. Here, the color signal conversion device 301 performs color signal conversion by gamut compression on the Lab signal of each pixel in the image data, and sequentially transmits it to the printer. Therefore, image data in which color information is described using Lab signals is transmitted to the color signal converter 208 via the PCI bus 214 in the order of raster scan, and the color signal converter 208 outputs the Lab signal for each pixel in the image data. Color signal conversion is performed by gamut compression and sequentially transmitted to the color printer 209.
[0062]
● Brightness adjuster
The brightness adjustment unit 308 extracts ab information from the input Lab signal, and from the extracted ab information and printer gamut information, the brightness maximum value Lmax_printer_ab having the same value as the extracted ab information in the printer gamut The brightness minimum value Lmin_printer_ab is extracted. Subsequently, the same as the extracted ab information in the monitor color gamut (hereinafter sometimes referred to as “compressed color gamut”) subjected to lightness and saturation compression from the extracted ab information and color gamut compression information. The brightness maximum value Lmax_compressed_ab and the brightness minimum value Lmin_compressed_ab having values are extracted. The brightness information Lout is calculated from the extracted information and the L information Lin of the input Lab signal by the following procedure.
[0063]
If any of Lmax_printer_ab, Lmin_printer_ab, Lmax_compressed_ab, and Lmin_compressed_ab is not extracted, Lout = Lin.
[0064]
If the above does not apply, Lout is calculated using the following formula.

[0065]
The brightness adjustment unit 308 outputs a Lab signal synthesized from the obtained brightness information Lout and the ab information of the input Lab signal.
[0066]
According to this embodiment, it is possible to perform gamut compression with higher accuracy than in the first embodiment. In other words, since the actual printer color gamut has a very complicated shape, the conversion based on the compression rate set according to the Cmax_printer of the first embodiment completely converts the input image data into the printer color gamut. It is not possible. On the other hand, according to the present embodiment, since gamut compression is performed based on color gamut compression information that is compressed data related to an input image, more accurate gamut compression is realized.
[0067]
[Fourth Embodiment]
The signal processing apparatus according to the fourth embodiment of the present invention will be described below. Note that in this embodiment, the same reference numerals as those in the first and third embodiments denote the same components, and a detailed description thereof will be omitted.
[0068]
In the present embodiment, the operation of the brightness adjustment unit 308 in the third embodiment is changed. The brightness adjustment unit 308 extracts ab information from the input Lab signal, and from the extracted ab information and printer gamut information, the brightness maximum value Lmax_printer_ab having the same value as the extracted ab information in the printer gamut The brightness minimum value Lmin_printer_ab is extracted. Subsequently, a maximum brightness value Lmax_compressed_ab and a minimum brightness value Lmin_compressed_ab having the same value as the extracted ab information are extracted from the extracted ab information and gamut compression information. The brightness information Lout is calculated from the extracted information and the L information Lin of the input Lab signal by the following procedure.
[0069]
If any of Lmax_printer_ab, Lmin_printer_ab, Lmax_compressed_ab, and Lmin_compressed_ab is not extracted, Lout = Lin.
[0070]
If the above does not apply, Lout is calculated using the function h (•) that defines the input / output relationship. That is, Lout = h (Lin). h (·) is defined using a piecewise function consisting of n-1 segments, and is controlled so that the following conditions hold. Incidentally, n is the number of nodes of the piecewise function h (•).

[0071]
Here, α and β: are parameters that give the compression rate at the end points of the table, and are automatically calculated under the restriction that the above conditions are satisfied. Mi and ni are also automatically calculated under the restriction that the above conditions are satisfied. The automatic calculation algorithm tries to keep the relationship mi = ni as much as possible, but the relationship (mi = ni) is not necessarily guaranteed because priority is given to the gradation and the above condition. However, the absolute value of the difference between input and output | h (Lin) − Lin | is tried to be as small as possible at each point.
[0072]
In the present embodiment, h (•) is realized as a three-segment C1 continuous cubic spline function. In addition, m1 = 1/3 × Cmax_monitor and m2 = 2/3 × Cmax_monitor.
[0073]
9 and 10 are diagrams showing the input / output relationship of lightness at a certain chromaticity ab in a certain printer output using this embodiment. Note that Lmin_compressed_ab = 40, Lmax_compressed_ab = 68, Lmin_printer_ab = 45, and Lmax_printer_ab = 64 in FIG. Further, Lmin_compressed_ab = 60, Lmax_compressed_ab = 84, Lmin_printer_ab = 46, and Lmax_printer_ab = 75 in FIG.
[0074]
According to the present embodiment, since non-linear transformation is used in lightness compression, reproducibility in the medium lightness region can be further improved. In particular, color reproducibility can be improved in an area where the color gamut of the monitor and the color gamut of the printer do not have a similar relationship, such as cyan.
[0075]
[Fifth Embodiment]
The signal processing apparatus according to the fourth embodiment of the present invention will be described below. Note that in this embodiment, the same reference numerals are given to substantially the same configurations as those in the first, third, and fourth embodiments, and detailed descriptions thereof are omitted.
[0076]
In the present embodiment, the configuration of the saturation compression unit 104 in the fourth embodiment is changed. FIG. 11 is a block diagram illustrating a configuration example of the color signal converter 208 of the present embodiment. The difference from the configuration illustrated in FIG. 8 is that the L signal is input to the saturation compression unit 104 together with the ab signal. .
[0077]
FIG. 12 is a block diagram illustrating a configuration example of the saturation compression unit 104 of the present embodiment. The difference from the saturation compression unit 104 shown in FIG. 4 is that the L signal is input to the saturation calculation unit 123 via the terminal 426.
[0078]
The saturation calculation unit 123 extracts the hue range determined from the h signal extracted from the monitor color gamut information and the printer color gamut information, and the saturation range information at the brightness determined from the input L signal, and a predetermined compression relationship. The saturation to be output is calculated from the input c signal according to the input / output relationship determined from The calculated c signal is output to the coordinate signal converter 124. The coordinate signal converter 124 converts the hc signal into an ab signal and outputs it.
[0079]
The operation of the saturation calculation unit 123 configured as described above will be described with reference to the flowchart shown in FIG.
[0080]
In step S1000, the maximum saturation Cmax_printer of the printer gamut in hue h is obtained from the hue h and printer gamut information input to the saturation compression unit 104. In step S1001, the hue input to the saturation compression unit 104 The maximum saturation Cmax_monitor of the monitor gamut in the hue h is obtained from h and the monitor gamut information, and the ratio Rmax = Cmax_printer / Cmax_monitor between the saturation Cmax_printer and the saturation Cmax_monitor is obtained in step S1002.
[0081]
Next, in step S1003, the maximum saturation CL_monitor of the monitor gamut at hue h and lightness L is obtained from the hue h, lightness L, and printer gamut information input to the saturation compression unit 104. A ratio R = c / CL_monitor between the saturation c and the maximum saturation CL_monitor input to the degree compression unit 104 is obtained.
[0082]
Next, in step S1005, a saturation ratio Rnew = g (R / Rmax) is obtained using a function g (•) that defines the input / output relationship of the saturation ratio, and in step S1006, the saturation ratio Rnew and the maximum saturation are calculated. The result obtained by multiplying the degree CL_monitor is output as the calculation result of the saturation calculation unit 123. Here, the function g (•) that defines the input / output relationship of the saturation ratio is defined using a cubic function in the present embodiment, and is controlled as follows.
The g (•) base is [0, 1]
g (0) = 0
g (1) = Rmax
g '(0) = 1
g '(Rmax) = γ, γ: γ> 0
g '(x) ≠ 0, x: 0 ≦ x ≦ 1
[0083]
Here, γ is a value that controls the compression ratio of saturation compression in the vicinity of the maximum saturation at a certain hue and brightness, and is based on the relationship between Cmax_monitor and Cmax_printer under the restriction that the above condition is satisfied. 123 is determined automatically for each combination of hue and lightness. For automatic γ parameter settingThisAs Cmax_monitor / Cmax_printer increases,γvalueThesmallYouThe That is, compression rateThebigYouThe
[0084]
In this embodiment, the function g (•) that defines the input / output relationship is realized using a cubic function, but even if it is realized using a piecewise function as in the second embodiment, the essence is There is no loss.
[0085]
According to the present embodiment, linear compression can be performed outside the printer color gamut, and nonlinear compression can be performed within the printer color gamut so as to increase the compression ratio in the high saturation region. In other words, the gradation of the high saturation region can be expressed better by linearly compressing the boundary portion of the monitor color gamut. Therefore, it is possible to improve reproducibility in vivid gradations of colors often used in DTP, etc., and to reproduce medium lightness and low saturation areas that are sensitive to humans with high accuracy, so natural (photos) Images and the like can also be reproduced well.
[0086]
[Sixth Embodiment]
The signal processing apparatus according to the sixth embodiment of the present invention will be described below. Note that in the present embodiment, the same reference numerals are given to substantially the same configurations as those in the first embodiment, and detailed description thereof will be omitted.
[0087]
FIG. 14 is a block diagram showing a configuration example of the color signal converter 208 as the present embodiment.
[0088]
The color signal converter 208 that converts the Lab signal in the monitor color reproduction area (monitor gamut) to the Lab signal in the printer color reproduction area (printer gamut) is held in the main memory 202 via the terminal 109. The input Lab signal of the image data, that is, the color signal on the monitor gamut that is the conversion source is input. An output image to the printer, that is, a desired color signal on the printer gamut is output from the terminal 110.
[0089]
In addition, printer color gamut information (printer gamut information) is input from terminal 111, and monitor color gamut information (monitor gamut information) is input from terminal 112. Monitor color gamut information is input to storage unit 107. The printer color gamut information is stored in the storage unit 108, respectively.
[0090]
The color signal separation unit 102 separates the input Lab signal into lightness components and chromaticity components, and outputs the L signal that is the lightness component to the lightness compression unit 103 and the saturation compression unit 104, and the ab that is the chromaticity component The signal is output to the saturation compression unit 104.
[0091]
The saturation compression unit 104 performs saturation compression according to an input / output relationship determined from saturation range information extracted from monitor color gamut information and printer color gamut information and a predetermined compression relationship, and an ab signal of the compression result 513 is output to the lightness compression unit 103. In addition, the saturation compression unit 104 performs information processing by acquiring lightness information necessary for lightness compression from the monitor color gamut information. Then, the extracted saturation range information and monitor lightness information are output as a signal 512 to the lightness compression unit 103.
[0092]
The lightness compression unit 103 performs lightness compression on the L signal in accordance with the monitor lightness information processed by the saturation compression unit 104, the extracted saturation range information, and the input / output relationship determined from the predetermined compression relationship. Then, the compression result L signal and the ab signal 513 input from the saturation compression unit 104 are combined and output to the color gamut inspection unit 106 as an Lab signal.
[0093]
● Saturation compression section
FIG. 15 is a block diagram illustrating a configuration example of the saturation compression unit 104 of the present embodiment. A difference from the saturation compression unit 104 shown in FIG. 12 is that a lightness information calculation unit 525 is provided. The lightness information calculation unit 525 calculates the maximum lightness and the minimum lightness of the monitor color gamut at the chromaticity ab from the L signal, ab signal, and monitor color gamut information input to the saturation compression unit 104, and the signal from the terminal 529 Output as 512.
[0094]
● Lightness compression section
The operation of the lightness compression unit 103 in the above configuration will be described. The lightness compression unit 103 calculates the maximum lightness information Lmax_printer_ab and the minimum lightness information Lmin_printer_ab of the printer color gamut at the chromaticity ab from the input ab signal and printer color gamut information. Next, the maximum lightness information input to the lightness compression unit 103 is Lmax_monitor_ab, and the minimum lightness information is Lmin_monitor_ab, and parameters necessary for lightness compression calculation are calculated from these four lightness information.
[0095]
The signal Lout is calculated by the calculated parameter and a function f (•) that defines the input / output relationship between the L signal Lin that is the lightness compression target input to the lightness compression unit 103 and the output L signal Lout. Here, f (•) is defined using a piecewise function consisting of n−1 segments, and is restricted so that the following conditions hold. Incidentally, n is the number of nodes of the piecewise function.

[0096]
In the present embodiment, f (•) is realized as a 5-segment C2 continuous cubic spline function. Here, the number n of contacts, the values mi and ni at the contacts, and the compression ratios α and β at the base end points are automatically calculated from the four brightness information of Lmin_monitor_ab, Lmax_monitor_ab, Lmin_printer_ab and LLmax_printer_ab. Here, the parameter is set so that f (x) = x as much as possible within the range satisfying the gradation and the above condition by the parameter automatic setting algorithm. The automatic setting algorithm for α and β is roughly as follows.
[0097]
For α, if Lmin_monitor_ab ≦ Lmin_printer_ab, then as the difference between Lmin_monitor_ab and Lmin_printer_ab increases, α satisfies the constraint of 0 ≦ α ≦ 1ThesmallYouThe That is, the compression ratio near the darkest pointThebigYouThe
[0098]
On the other hand, when Lmin_monitor_ab> Lmin_printer_ab, as the difference between Lmin_monitor_ab and Lmin_printer_ab increases, αThebigYouThe That is, near the darkest pointKickElongationThebigYouThe
[0099]
Similarly, when β is Lmax_monitor_ab ≧ Lmax_printer_ab, β increases under the constraint that 0 ≦ β ≦ 1 as the difference between Lmax_monitor_ab and Lmax_printer_ab increases.ThesmallYouThe That is, the compression rate near the brightest pointThebigYouThe
[0100]
On the other hand, when Lmax_monitor_ab <Lmax_printer_ab, as the difference between Lmax_monitor_ab and Lmax_printer_ab increases, βThebigYouThe That is, near the brightest pointKickElongationThebigYouThe
[0101]
[Seventh embodiment]
The signal processing apparatus according to the seventh embodiment of the present invention will be described below. Note that in this embodiment, the same reference numerals are given to substantially the same configurations as those in the first, third, and fourth embodiments, and detailed descriptions thereof are omitted.
[0102]
In the present embodiment, the configuration of the saturation compression unit 104 in the fourth embodiment is changed. FIG. 16 is a block diagram illustrating a configuration example of the color signal converter 208 of the present embodiment.
[0103]
The saturation adjustment information input unit 618 is for the user to input saturation adjustment information.For example, a control panel formed as a user interface image on the color monitor 207 by the CPU 201, and a keyboard 211 and / or It consists of a mouse 212 and the like. The saturation adjustment information input by the user giving the input value and output value at each node is converted into an appropriate data structure by the CPU 201, and then once stored in the main memory 202, then via the terminal 617. Are input to the saturation compression unit 104 of the color signal converter 208. Note that the input of saturation adjustment information is not an essential operation.
[0104]
Upon receiving a command to output the image held in the main memory 202 from the printer 209, the CPU 201 examines the content stored in the main memory 202 to determine whether or not the saturation adjustment information is input, and uses the presence / absence information as a color signal converter. Send to 208. When the saturation adjustment information is input, the CPU 201 sends the saturation adjustment information stored in the main memory 202 to the color signal converter 208 via the PCI bus 214 and the terminal 617.
[0105]
The saturation compression unit 104 performs saturation compression according to the input / output relationship determined from the saturation range information extracted from the monitor color gamut information and the printer color gamut information, and the compression relationship controlled by the input saturation adjustment information. Then, the ab signal as the compression result is output to the color signal synthesis unit 105.
[0106]
Note that the saturation adjustment information input unit 618 in the above configuration is realized by the blocks in the configuration in FIG. 2 operating in a predetermined order as described above.
[0107]
● Saturation compression section
FIG. 17 is a block diagram illustrating a configuration example of the saturation compression unit 104.
[0108]
In FIG. 17, the storage unit 625 stores the saturation adjustment information input via the terminal 630, and displays the saturation adjustment value corresponding to the h signal that is the hue information input from the color signal separation unit 122. Output to the calculation unit 123. The saturation calculation unit 123 is an input / output determined from saturation range information in a hue determined from the h signal extracted from the monitor color gamut information and printer color gamut information, and a compression relationship controlled by the saturation adjustment information. In accordance with the relationship, the saturation to be output is calculated from the input c signal, and the calculated c signal is output to the coordinate signal converter 124.
[0109]
The operation of the saturation calculation unit 123 in the above configuration will be described. The saturation calculation unit 123 is controlled by a function g (·) that defines the input / output relationship, and there is a relationship cout = g (cin) between the input c signal cin and the output c signal cout. Stand up. g (·) is defined using a cubic function, and is controlled so that the following conditions hold.
The stand for g (・) is [0, Cmax_monitor]
g (0) = 0
g (Cmax_monitor) = Cmax_printer
g '(0) = α
g '(Cmax_monitor) = γ, γ: γ> 0
g '(x) ≠ 0, x: 0 ≦ x ≦ Cmax_monitor
[0110]
Here, α is determined by the output value of the storage unit 625, that is, the saturation adjustment value in the hue determined from the h signal. Cmax_monitor is calculated from the h signal, which is a hue component, and monitor color gamut information, and is defined as the maximum saturation value of the monitor color gamut in the hue determined from the h signal. Cmax_printer is calculated from the h signal that is the hue component and the printer gamut information, and is defined as the maximum saturation value of the printer gamut in the hue determined from the h signal.
[0111]
γ is a value that controls the compression ratio of saturation compression in the vicinity of the maximum saturation, and is automatically determined by the saturation calculation unit 123 based on the relationship between Cmax_monitor and Cmax_monitor under the restriction that the above condition is satisfied. In γ parameter automatic setting, the value of γ increases as Cmax_monitor / Cmax_printer increases.ThesmallYouThe That is, compression rateThebigYouThe
[0112]
● Saturation adjustment information
The user inputs the gradient y at x = 0 of the saturation control function in one or more arbitrary hues as the saturation adjustment information. The storage unit 625 interpolates linearly with respect to the angle, and creates saturation adjustment information for all hues. This information is formed as a set of each hue and the saturation adjustment value α in each hue. This set information is held in the storage unit 625 as saturation adjustment information.
[0113]
Inputting the slope y of the saturation control function at x = 0 of the saturation control function in an arbitrary hue as saturation adjustment information means that the ideal saturation after gamut compression at the specified saturation is the original saturation. It is equivalent to y times that of, making intuitive saturation adjustment very easy.
[0114]
[Eighth Embodiment]
The signal processing apparatus according to the eighth embodiment of the present invention will be described below. Note that in this embodiment, the same reference numerals are given to substantially the same configurations as those in the first, third, and fourth embodiments, and detailed descriptions thereof are omitted.
[0115]
In the present embodiment, the configuration of the saturation compression unit 104 in the fourth embodiment is changed. FIG. 18 is a block diagram illustrating a configuration example of the color signal converter 208 of the present embodiment.
[0116]
The brightness adjustment information input unit 718 is used by the user to input brightness adjustment information. For example, a control panel formed as a user interface image on the color monitor 207 by the CPU 201, and a keyboard 211 and / or a mouse 212. Etc. The brightness adjustment information input by the user giving the input value and output value at each node is converted into an appropriate data structure by the CPU 201, and then once held in the main memory 202, via the terminal 717 This is input to the lightness compression unit 103 of the color signal converter 208. Note that the input of brightness adjustment information is not an essential operation.
[0117]
The CPU 201 that has received a command to output the image held in the main memory 202 from the printer 209 checks the stored contents of the main memory 202 to determine whether or not the brightness adjustment information is input, and the presence / absence information is converted to the color signal converter 208. Send to. When the brightness adjustment information is input, the CPU 201 sends the brightness adjustment information stored in the main memory 202 to the color signal converter 208 via the PCI bus 214 and the terminal 717.
[0118]
The lightness compression unit 103 converts the input L signal according to lightness range information extracted from the monitor color gamut information and printer color gamut information, a predetermined compression relationship, and an input / output relationship determined from the input lightness adjustment information. Lightness compression is performed, and the L signal that is the compression result is output to the color signal synthesis unit 105.
[0119]
● Lightness compression section
The lightness compression unit 103 is controlled by a function f (•) that defines an input / output relationship. That is, the relationship Lout = f (Lin) is established between the L signal Lin input to the lightness compression unit 103 and the output L signal Lout. f (·) is defined using a piecewise function consisting of n-1 segments, and is controlled so that the following conditions hold. Incidentally, n is the number of nodes of the piecewise function, and is controlled by an input from the brightness adjustment information input unit 718 in the present embodiment.

[0120]
Where Lmin_monitor is the L value held by the monitor black, Lmax_monitor is the L value held by the monitor white, Lmin_printer is the L value held by the printer black, and Lmax_printer is the L value held by the monitor white . In the present embodiment, f (•) is realized by a cubic spline function that is at least C1 continuous at each contact. Here, α, β, the number of contacts n, mi, ni, and γi are set by the user in the input of the brightness adjustment information. If there is no input of α, β or both, the algorithm automatically sets α, β or both. When there is no input of γi, γi is automatically obtained by an algorithm from the C2 continuity at the contact i.
[0121]
When no brightness adjustment information is input from the user, n = 5, mi = ni and γi = 1 are set, and α and β are automatically calculated under the above conditions. Set to function f (•).
[0122]
In the automatic calculation algorithm of α and β, the value of α increases as the difference between Lmin_monitor and Lmin_printer increases.ThesmallYouThe That is, the compression ratio near the darkest pointThebigYouThe On the other hand, as the difference between Lmax_monitor and Lmax_printer increases, the value of βThesmallYouThe That is, the compression rate near the brightest pointThebigYouThe
[0123]
According to each embodiment described above, in the gamut compression, the medium brightness is preserved, and the color with very high brightness or the color with very low brightness is greatly compressed. In the gamut compression, the saturation is preserved as the color is low in saturation, and conversely, the saturation is compressed as the color is high in saturation. As a result, it is possible to obtain an output image that is very perceptually approximate, regardless of differences in color reproducibility due to differences in monitor and printer models, or differences in color reproducibility due to differences in color reproduction characteristics of recording media. it can.
[0124]
[Other Embodiments]
Note that the present invention can be applied to a system including a plurality of devices (for example, a host computer, an interface device, a reader, and a printer), and a device (for example, a copying machine and a facsimile device) including a single device. You may apply to.
[0125]
Another object of the present invention is to supply a storage medium storing software program codes for realizing the functions of the above-described embodiments to a system or apparatus, and the computer (or CPU or MPU) of the system or apparatus stores the storage medium. Needless to say, this can also be achieved by reading and executing the program code stored in. In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the storage medium storing the program code constitutes the present invention. Further, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also an OS (operating system) operating on the computer based on the instruction of the program code. It goes without saying that a case where the function of the above-described embodiment is realized by performing part or all of the actual processing and the processing is included.
[0126]
Further, after the program code read from the storage medium is written to a memory provided in a function expansion card inserted into the computer or a function expansion unit connected to the computer, the function expansion is performed based on the instruction of the program code. It goes without saying that the CPU or the like provided in the card or the function expansion unit performs part or all of the actual processing, and the functions of the above-described embodiments are realized by the processing.
[0127]
In each of the above-described embodiments, the description has been given in the representative Lab color space. However, the present invention is not limited to this, and a color having lightness and chromaticity such as a Luv color space or a Munsell color space. Any space can be applied.
[0128]
【The invention's effect】
As described above, according to the present invention, color signals are converted so that colors formed and / or displayed on different devices and / or different recording media are perceived as approximate colors.Realize high-precision color reproductionbe able to.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a system configuration example of a color signal conversion apparatus according to a first embodiment of the present invention;
FIG. 2 is a block diagram showing a configuration example of the color signal converter shown in FIG.
FIG. 3 is a diagram showing an example of a lightness input / output relationship in the first embodiment;
4 is a block diagram showing a configuration example of a saturation compression unit shown in FIG.
FIG. 5 is a diagram illustrating an input / output relationship example of saturation in the first embodiment;
FIG. 6 is a diagram illustrating lightness compression input / output characteristics when gamut compression is performed for a plurality of types of paper quality;
FIG. 7 is a diagram illustrating an input / output relationship example of saturation in the second embodiment;
FIG. 8 is a block diagram illustrating a configuration example of a color signal converter according to a third embodiment;
FIG. 9 is a diagram showing a lightness input / output relationship at a certain chromaticity ab;
FIG. 10 is a diagram showing a lightness input / output relationship at a certain chromaticity ab;
FIG. 11 is a block diagram illustrating a configuration example of a color signal converter according to a fifth embodiment;
12 is a block diagram showing a configuration example of a saturation compression unit shown in FIG.
FIG. 13 is a flowchart showing the operation of the saturation calculation unit shown in FIG.
FIG. 14 is a block diagram illustrating a configuration example of a color signal converter according to a sixth embodiment;
15 is a block diagram showing a configuration example of a saturation compression unit shown in FIG.
FIG. 16 is a block diagram illustrating a configuration example of a color signal converter according to a seventh embodiment;
17 is a block diagram showing a configuration example of a saturation compression unit shown in FIG.
FIG. 18 is a block diagram illustrating a configuration example of a color signal converter according to an eighth embodiment.

Claims (6)

A first color gamut of the color signal of the first device, the first is different from the color gamut, a color processing apparatus for converting into the second second-color gamut of the color signals of the device ,
The brightness component of the color signal is compressed within the brightness range of the second color gamut using a spline function represented by a piecewise function consisting of n-1 (where n is the number of nodes of the piecewise function) segment. Means to
Means for compressing the saturation component of the color signal within the saturation range of the second color gamut;
A lightness compression control means for controlling a spline function used for the lightness compression and controlling a compression rate of the lightness component;
The lightness compression control means outputs the white color in the second color gamut to the white color input in the first color gamut and the first color reproduction color in the black color in the first color gamut. Set the spline function to output black in the second color gamut,
As the difference in maximum brightness between the first and second color gamuts increases, the value β of the first derivative of the spline function at the maximum brightness of the first color gamut is reduced,
A color process characterized by reducing the value α of the first derivative of the spline function at the minimum brightness of the first color gamut as the difference between the minimum brightness of the first and second color gamuts increases. apparatus. Furthermore, it has a saturation compression control means for controlling a compression rate of the saturation component by controlling a spline function used for the saturation compression,
The saturation compression control means outputs a 0 on input values 0, said second color gamut in the hue on the input of the maximum saturation of the first color gamut in the hue of the input color Set the saturation compression spline function to output the maximum saturation of
As the ratio C1max / C2max between the maximum saturation C1max of the first color gamut and the maximum saturation C2max of the second color gamut increases, the value γ of the first derivative of the spline function for saturation compression is increased. 2. The color processing apparatus according to claim 1, wherein the color processing apparatus is made small. Further, a combining means for combining the lightness-compressed lightness component and the saturation-compressed saturation component into a color signal,
When a color signal is input from the synthesizing unit and the input color signal is in the second color reproduction range, the input color signal is output, and the input color signal is out of the second color reproduction range. And a means for outputting a color signal in the second color gamut having a minimum color difference with respect to the input color signal. Color processing device. Furthermore, it has an input means for inputting a user instruction regarding the lightness compression,
The lightness compression control means controls the first derivative values α and β according to the user instruction when the user instruction is input, and the first derivative value α according to the difference when the user instruction is not input. 4. The color processing apparatus according to claim 1, wherein β is controlled. A first color gamut of the color signal of the first device, the first is different from the color gamut, a color processing method for converting into a second second color gamut of the color signals of the device ,
The brightness component of the color signal is compressed within the brightness range of the second color gamut using a spline function represented by a piecewise function consisting of n-1 (where n is the number of nodes of the piecewise function) segment. And steps to
Compressing the saturation component of the color signal within the saturation range of the second color reproduction range; and
A lightness compression control step of controlling a compression rate of the lightness component by controlling a spline function used for the lightness compression,
The lightness compression control step outputs the white color in the second color gamut to the white color input in the first color gamut and the first color reproduction color in the black color input in the first color gamut. Set the spline function to output black in the second color gamut,
As the difference in maximum brightness between the first and second color gamuts increases, the value β of the first derivative of the spline function at the maximum brightness of the first color gamut is reduced,
A color process characterized by reducing the value α of the first derivative of the spline function at the minimum brightness of the first color gamut as the difference between the minimum brightness of the first and second color gamuts increases. Method.   5. A computer-readable recording medium having recorded thereon a computer program for controlling the computer device to function as each unit of the color processing device according to any one of claims 1 to 4. .

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