JP2004013361A - Image processor, image processing method and program for executing this method by computer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processor, an image processing method and a program for executing this method by a computer superior in color reproducibility, and efficiently correcting a color when a color reproducing area of an image input system and a color reproducing area of an image output system are different. <P>SOLUTION: The image processor 1 corrects the color expressed by a color image signal to a color suitable for an output device for outputting the color image signal, and has a hue area determining means for determining a hue area including a signal color expressed by the color image signal among a plurality of hue areas formed in a color space with a surface arranged in parallel to a lightness shaft as a boundary and a correcting means for correcting the signal color according to the hue areas. <P>COPYRIGHT: (C)2004,JPO

Description

・・・（１８）
【０１００】
他の色相領域に対する補正量演算係数Ｒｘ，Ｇｘ，Ｂｘ，Ｃｘについても同様に算出することができる。
【０１０１】
図４に示した補正量演算係数テーブル１２３において、色相領域コードに対応付けられている補正量演算係数は、（１８）式と同様にして、算出された値である。したがって、補正量演算係数メモリ１２２は、補正量演算係数テーブル１２３において、各色相領域コードに対応付けられている補正量演算係数を選択すればよい。
【０１０２】
Ｓ２０６において、補正量演算回路１２４が補正量Ｘを算出すると、次に、第１コンパレータ１２６は、補正量演算回路１２４から入力された補正量Ｘと「０」とを比較する。補正量Ｘが「０」以上の場合（Ｓ２１０、Ｙｅｓ）、補正量Ｘを第１セレクタ１２８に出力する（Ｓ２１２）。また、補正量Ｘが「０」よりも小さい場合（Ｓ２１０、Ｎｏ）、補正量として「０」を第１セレクタ１２８に出力する（Ｓ２１４）。
【０１０３】
式（１８）は、点Ｋにおける補正量Ｘが「−（Ｄｋ−Ｄｗ）」、点Ａおよび点Ｗにおける補正量Ｘが「０」となるように設定されている。すなわち、補正量Ｘが「０」以上になるのは、プリンタ色再現領域６７０の外側の領域の場合である。また、補正量Ｘが「０」よりも小さくなるのは、プリンタ色再現領域６７０の内側の場合である。したがって、補正量Ｘと「０」との比較結果からカラー画像信号がプリンタ色再現領域６７０の内側の点に対応するか否かを判定することができる。
【０１０４】
また、カラー画像信号がプリンタ色再現領域６７０の内側の点の場合には、補正の必要がないので、この場合には、補正量Ｘとして「０」を設定する。これにより、カラー画像信号がプリンタ色再現領域６７０の外側の点の場合にのみ、有効な補正量Ｘを設定することができる。
【０１０５】
このように、Ｓ２０８からＳ２１２の処理によって、画像処理装置１は、プリンタ色再現領域６７０の外側の領域の点に対応するカラー画像信号のみ補正することができる。
【０１０６】
次に、彩度評価値演算係数メモリ１３２は、色相領域コード生成回路１１４から入力された色相領域コードに基づいて、彩度評価値演算係数を決定する（Ｓ２２０）。次に、彩度評価値演算回路１３４は、彩度評価値演算係数メモリ１３２から入力された彩度評価値演算係数および外部から入力されたカラー画像信号（Ｄｒ，Ｄｇ，Ｄｂ）に基づいて、彩度評価値Ｓを算出する（Ｓ２２２）。
【０１０７】
ここで、彩度評価値Ｓの理論的な導出方法について説明する。例えば、図９に示した点Ｐが示す色は、点Ｐが示す色の色相におけるプリンタ色再現領域６７０での最大彩度よりも大きい彩度を示す。処理対象となるカラー画像信号の信号色が点Ｐに対応する場合、点Ｑと点Ｐとの距離に相当する量が、補正量として算出される。ここで、点Ｑは、点Ｐを通りＮ軸に平行な直線と、直線Ｄ−Ｗとの交点である。しかし、点Ｑは、プリンタ色再現領域６７０の外側に配置されている。すなわち、点Ｐを補正量Ｘだけ移動しても、プリンタ色再現領域６７０の内側に含ませることができない。
【０１０８】
このように、信号色が最大彩度以上の彩度を示す場合には、信号色の明度のみを補正しても、信号色をプリンタ色再現領域６７０の内側の点に対応する色に変換することができない。そこで、信号色が示す彩度が、最大彩度よりも大きいか否かを判断し、これに応じて、補正量Ｘを修正する。彩度評価値Ｓは、カラー画像信号が示す彩度を評価するための指標である。
【０１０９】
彩度評価値Ｓは、次式によって求めることができる。
Ｓ　＝　Ｒｓ・Ｄｒ　＋　Ｇｓ・Ｄｇ　＋　Ｂｓ・Ｄｂ　＋　Ｃｓ　　　　　　・・・（１９）
ここで、Ｄｓ（Ｒｓ，Ｇｓ，Ｂｓ，Ｃｓ）は色相領域毎に定まる彩度評価値演算係数である。
【０１１０】
例えばＣＢ色相領域の場合、（１９）式に対して、点Ｋ，Ｗにおいて「０」、点Ｃ，Ｂにおいて「１」となるように係数を定める。この条件を（１９）式に代入すると、次式が得られる。
０　＝　Ｒｓ・Ｄｋｒ　＋　Ｇｓ・Ｄｋｇ　＋　Ｂｓ・Ｄｋｂ　＋　Ｃｓ
０　＝　Ｒｓ・Ｄｗｒ　＋　Ｇｓ・Ｄｗｇ　＋　Ｂｓ・Ｄｗｂ　＋　Ｃｓ
１　＝　Ｒｓ・Ｄｃｒ　＋　Ｇｓ・Ｄｃｇ　＋　Ｂｓ・Ｄｃｂ　＋　Ｃｓ　　　・・・（２０）
１　＝　Ｒｓ・Ｄｂｒ　＋　Ｇｓ・Ｄｂｇ　＋　Ｂｓ・Ｄｂｂ　＋　Ｃｓ
（２０）式の連立方程式を解くことにより、次式で示される彩度評価値演算係数Ｒｓ，Ｇｓ，Ｂｓ，Ｃｓを得ることができる。
【数式２】

・・・（２１）
【０１１１】
他の色相領域に対する彩度評価値演算係数Ｒｓ，Ｇｓ，Ｂｓ，Ｃｓについても同様に算出することができる。彩度評価値演算係数メモリ１３２において、色相領域コードに対応付けられている彩度評価値演算係数は、（２１）式と同様に算出された値である。したがって、彩度評価値演算係数メモリ１３２は、彩度評価値演算係数テーブル１３３において、色相領域コード生成回路１１４から入力された色相領域コードに対応付けられている彩度評価値演算係数を選択すればよい。
【０１１２】
Ｓ２２２において、Ｓ１３４が彩度評価値演算係数を算出すると、次に、第２コンパレータ１３６は、彩度評価値演算回路１３４から入力された彩度評価値Ｓと「１」とを比較する。彩度評価値Ｓが「１」以下の場合（Ｓ２２４、Ｙｅｓ）、補正量Ｘを第２セレクタ１３８に出力する（Ｓ２２６）。また、彩度評価値Ｓが「１」よりも大きい場合（Ｓ２２４、Ｎｏ）、補正量Ｘとして「０」を第２セレクタ１３８に出力する（Ｓ２２８）。
【０１１３】
（２０）式および（２１）式は、点Ｋおよび点Ｗにおいて彩度評価値Ｓが「０」、各色相における最大彩度において「１」となるように設定されている。すなわち、信号色から算出された彩度評価値Ｓが「１」以上になるのは、信号色の彩度が高く、明度を補正してもプリンタ色再現領域６７０内の色座標に変換されない場合である。また、彩度評価値Ｓが「１」よりも小さくなるのは、明度を補正することによってプリンタ色再現領域６７０内の色座標に変換される場合である。このように、カラー画像信号から算出された彩度評価値Ｓと「１」とを比較することによって、信号色に対応する点が、プリンタ色再現領域６７０における最高彩度よりも大きい彩度に対応するか否かを判定することができる。
【０１１４】
また、信号色の彩度が高く、明度を補正してもプリンタ色再現領域６７０内の色座標に変換されない場合には、補正量として「０」を設定する。このように、本実施の形態における補正量算出回路１０によれば、明度を補正することによってプリンタ色再現領域６７０の内側の点に対応する色に補正できる場合にのみ、有効な補正量Ｘを設定することができるので、無駄に信号色を補正するのを避けることができる。
【０１１５】
また、実施の形態１における画像処理装置１は、ＬＵＴを必要としないので、メモリ容量が少なくてよく、効率的に色補正処理を行うことができる。
【０１１６】
なお、本実施の形態においては最高彩度において彩度評価値Ｓが「１」と設定されているため、彩度評価値Ｓと「１」とを比較した。しかし、被比較値である「１」は、これに限定されるものではない。例えば、最高彩度において彩度評価値Ｓが「０」、点Ｋおよび点Ｗにおいて彩度評価値Ｓが「１」となるように、彩度評価値演算係数が設定されている場合には、Ｓ２１６において、彩度評価値Ｓが「０」以上の場合にＳ２１８へ進み、彩度評価値Ｓが「０」よりも小さい場合にＳ２２０に進んでもよい。このように、比較対照となる被比較値は、彩度評価値演算係数の設定に応じて変化させてもよい。
【０１１７】
また、同様に、Ｓ２１０において被比較値となる値は、補正量演算係数Ｒｘ，Ｇｘ，Ｂｘ，Ｃｘの設定に応じて変化させてもよい。
【０１１８】
なお、実施の形態１における補正量算出回路１０は、色相領域判定部１１０、補正量演算部１２０、および高彩度修正部１３０を有したが、他の例としては、補正量算出回路１０は、色相領域判定部１１０および補正量演算部１２０のみで構成してもよい。色相領域判定部１１０および補正量演算部１２０において生成された補正量Ｘにおいても、画像データの色を、プリンタの特性に適した色に補正することができる。
【０１１９】
（実施の形態２）
図１０〜図１３を参照しつつ実施の形態２における画像処理装置について説明する。実施の形態２における画像処理装置１は、実施の形態１において説明した色相領域判定部１１０にかえて色相領域判定部３１０を備えている。実施の形態１の色相領域判定部１１０は、カラー画像信号を３次元の色空間における色座標を利用して処理したが、実施の形態２の色相領域判定部３１０は、色空間を、２次元平面に写像し、２次元平面における、カラー画像信号の色座標を利用して、カラー画像信号が含まれる色相領域を判定する。
【０１２０】
図１０は、カラー画像信号を写像すべき２次元平面を示している。この２次元平面において、「Ｄｇ−Ｄｒ」に相当する直線をＧＲ軸とし、「Ｄｂ−Ｄｇ」に相当する直線をＢＧ軸とする。ＧＲ軸とＢＲ軸とは互いに直交している。
【０１２１】
色空間上の点（Ｄｒ，Ｄｇ，Ｄｂ）は、次式により、本図に示す色平面に写像される。
ＧＲ　＝　Ｄｇ　−　Ｄｒ　　　・・・（２２）
ＢＧ　＝　Ｄｂ　−　Ｄｇ　　　・・・（２３）
【０１２２】
また、色空間におけるＮ軸上の点（Ｄｎｒ，Ｄｎｇ，Ｄｎｂ）は、図１０に示す色平面における点（Ｄｎｇ−Ｄｎｒ，　Ｄｎｂ−Ｄｎｇ）に写像される。Ｄｎｒ＝Ｄｎｇ＝Ｄｎｂであるから、
（Ｄｎｇ−Ｄｎｒ，　Ｄｎｂ・Ｄｎｇ　）　＝　（０，　０）　　　・・・（２４）
となる。すなわち、Ｎ軸上のすべての点は、図１０に示す平面における原点ｎに写像される。また、色空間における点Ｃ，Ｍ，Ｙ，Ｒ，Ｇ，Ｂは、原点ｎの周囲に図１０に示すように配置されている。したがって、図７に示した６つの色相領域６４０〜６４５は、色平面においてＮ軸と点Ｃ，Ｍ，Ｙ，Ｒ，Ｇ，Ｂとをそれぞれ結んだ直線で分割された領域７４０〜７４５に写像される。
【０１２３】
図１１は、実施の形態２における色相領域判定部３１０の構成を示すブロック図である。色相領域判定部３１０は、差分ＢＧ算出回路３１２、差分ＧＲ算出回路３１４、色相評価値演算回路３１６、および色相領域コード生成回路３１８および色相領域コードテーブル３２０を有している。
【０１２４】
カラー画像信号は、差分ＢＧ算出回路３１２および差分ＧＲ算出回路３１４に入力される。差分ＧＲ算出回路３１４は、入力されたカラー画像信号の各色の値から差分ＧＲを算出し、色相評価値演算回路３１６へ出力する。色相評価値演算回路３１６は、入力されたカラー画像信号の各色の値から差分ＢＧを算出し、色相領域コード生成回路３１８へ出力する。
【０１２５】
色相評価値演算回路３１６は、入力されたカラー画像信号から、各色相表価値Ｆｘ’（ｘ＝ｃ，ｍ，ｙ，ｒ，ｇ，ｂ）を算出し、色相領域コード生成回路３１８へ出力する。
【０１２６】
色相領域コード生成回路３１８は、色相領域コードテーブル３２０を有している。色相領域コードテーブル３２０は、図１２に示すように、色相評価値Ｆｘ’の条件と色相領域コードｃｏｄｅとを対応付けている。なお、色相評価値Ｆｘ’の条件については後述する。色相領域コード生成回路３１８は、色相領域コードテーブル３２０を利用して、色相評価値Ｆｘ’から定まる色相領域コードを示す領域コードｃｏｄｅを、補正量演算係数メモリ１２２および彩度評価値演算係数メモリ１３２へ出力する。また、システム制御部３４０は、色相評価値Ｆｘ’を設定する。
【０１２７】
次に、図１３示すフローチャートを参照しつつ、色相領域判定部３１０の動作について説明する。まず、色相領域判定部３１０にカラー画像信号が入力されると、カラー画像信号の値を２次元化する（Ｓ２５０）。具体的には、差分ＢＧ算出回路３１２は、カラー画像信号の値を（２２）式に代入して、差分ＧＲを得る。また、差分ＧＲ算出回路３１４は、カラー画像信号の値を（２３）式に代入して、差分ＢＧを得る。すなわち、カラー画像信号の色空間における値（Ｄｒ，Ｄｇ，Ｄｂ）を色平面における値（ＧＲ，ＢＧ）に変換する。
【０１２８】
次に、色相評価値演算回路３１６は、差分ＢＧ算出回路３１２から入力されたＧＲに基づいて、各色相評価値Ｆｘ’を算出する（Ｓ２５２）。つぎに、色相領域コード生成回路３１８は、色相評価値演算回路３１６から入力された各色相評価値Ｆｘ’、および差分ＧＲ算出回路３１４から入力された差分ＢＧに基づいて、色相領域コードテーブル３２０を利用して、信号色を含む色相領域の色相領域コードを決定する（Ｓ２５４）。
【０１２９】
ここで、色相評価値Ｆｘ’の理論的な導出方法について説明する。図１０に示した色平面において、点Ｎと、点Ｃ，Ｍ，Ｙ，Ｒ，Ｇ，Ｂとをそれぞれ結んだ直線、すなわち、直線ＮＣ、直線ＮＭ、直線ＮＹ、直線ＮＲ、直線ＮＧ、および直線ＮＢはそれぞれ以下のように表される。
ＢＧ　＝　（Ｄｃｂ−Ｄｃｇ）／（Ｄｃｇ−Ｄｃｒ）・ＧＲ　（但し、Ｄｃｇ−Ｄｃｒ≠０）　　　・・・（２５）
ＢＧ　＝　（Ｄｍｂ−Ｄｍｇ）／（Ｄｍｇ−Ｄｍｒ）・ＧＲ　（但し、Ｄｍｇ−Ｄｍｒ≠０）　　　・・・（２６）
ＢＧ　＝　（Ｄｙｂ−Ｄｙｇ）／（Ｄｙｇ−Ｄｙｒ）・ＧＲ　（但し、Ｄｙｇ−Ｄｙｒ≠０）　　　・・・（２７）
ＢＧ　＝　（Ｄｒｂ−Ｄｒｇ）／（Ｄｒｇ−Ｄｒｒ）・ＧＲ　（但し、Ｄｒｇ−Ｄｒｒ≠０）　　　・・・（２８）
ＢＧ　＝　（Ｄｇｂ−Ｄｇｇ）／（Ｄｇｇ−Ｄｇｒ）・ＧＲ　（但し、Ｄｇｇ−Ｄｇｒ≠０）　　　・・・（２９）
ＢＧ　＝　（Ｄｂｂ−Ｄｂｇ）／（Ｄｂｇ−Ｄｂｒ）・ＧＲ　（但し、Ｄｂｇ−Ｄｂｒ≠０）　　　・・・（３０）
【０１３０】
（２５）式〜（３０）式のそれぞれに、カラー画像信号のＧＲ値を代入して得られるＢＧ値と、実際のカラー画像信号のＢＧ値との大小関係から、各式によって定まる直線と、カラー画像信号に対応する点との位置関係がわかる。したがって、カラー画像信号が、いずれの色相領域に含まれるかは、（２５）式〜（３０）式にカラー画像信号のＧＲ値を代入して得られるＢＧ値と、カラー画像信号のＢＧ値との大小関係に基づいて、判定することができる。そこで、（２５）式〜（３０）式に基づいて色相評価値Ｆｘ’を定める。すなわち、（２５）式〜（３０）式の左辺をそれぞれＦｃ’，Ｆｍ’，Ｆｙ’，Ｆｒ’，Ｆｇ’，Ｆｂ’とする。
Ｆｃ’　＝　（Ｄｃｂ−Ｄｃｇ）／（Ｄｃｇ−Ｄｃｒ）・ＧＲ　　　・・・（３１）
Ｆｍ’　＝　（Ｄｍｂ−Ｄｍｇ）／（Ｄｍｇ−Ｄｍｒ）・ＧＲ　　　・・・（３２）
Ｆｙ’　＝　（Ｄｙｂ−Ｄｙｇ）／（Ｄｙｇ−Ｄｙｒ）・ＧＲ　　　・・・（３３）
Ｆｒ’　＝　（Ｄｒｂ−Ｄｒｇ）／（Ｄｒｇ−Ｄｒｒ）・ＧＲ　　　・・・（３４）
Ｆｇ’　＝　（Ｄｇｂ−Ｄｇｇ）／（Ｄｇｇ−Ｄｇｒ）・ＧＲ　　　・・・（３５）
Ｆｂ’　＝　（Ｄｂｂ−Ｄｂｇ）／（Ｄｂｇ−Ｄｂｒ）・ＧＲ　　　・・・（３６）
【０１３１】
すなわち、Ｓ２５２において色相評価値演算回路３１６は、（３１）式〜（３６）式において定められた色相評価値Ｆｘ’を算出する。
【０１３２】
例えば、色平面における任意の点（ＧＲ，ＢＧ）から算出されたＦｃ’およびＦｂ’が、「ＢＧ≦Ｆｃ’　ａｎｄ　ＢＧ＞Ｆｂ’」を満たす場合、この点は、ＣＢ色相領域に含まれることがわかる。すなわち、図１２に示した色相領域コードテーブル３２０において色相領域コードに対応付けられている色相評価値Ｆｘ’の条件は、以上の式から定められた条件である。このように、色相領域コードテーブル３２０において、色相評価値Ｆｘ’の条件が予め設定されている。したがって、色相領域コード生成回路３１８は、色相領域コードテーブル３２０において各色相領域コードに対応付けられている色相評価値Ｆｘ’の条件の中から、差分ＧＲ算出回路３１４から入力されたＢＧ、および色相評価値演算回路３１６から入力された色相評価値Ｆｘ’が満たす条件を特定し、色相領域コードテーブル３２０において、この条件に対応付けられている色相領域コードを選択すればよい。
【０１３３】
なお、図１２に示した色相領域コードテーブル３２０においては、Ｎ軸上の色座標をＧＣ色相領域に含めているが、他の色相領域に含めてもよい。
【０１３４】
また色相評価値Ｆｘ’は、（Ｄｉｒ，Ｄｉｇ，Ｄｉｂ）（ｉ＝ｃ，ｍ，ｙ，ｒ，ｇ，ｂ，ｗ，ｋ）の実際の値によって変化する。したがって、色相領域コードテーブル３２０において各色相領域コードに対応付けるべき色相評価値の条件は色相評価値Ｆｘ’の値に応じて変更してもよい。
【０１３５】
以上により、色相領域判定部３１０の動作が終了する。なお、Ｓ２５０〜Ｓ２５４における色相領域判定部３１０の動作は、実施の形態１において図８を参照しつつ説明したＳ２０２からＳ２０４における色相領域判定部１１０の動作にかえて行われる。
【０１３６】
なお、これ以外の画像処理装置１の構成および動作は、図１から図８を参照しつつ説明した実施の形態１における画像処理装置１の構成および動作と同様である。
【０１３７】
このように、実施の形態２によれば、カラー画像信号が表す色を２次元の色平面における２つの値で表現するので、カラー画像信号を３次元色空間において表現する場合に比べて、補正量算出回路１０における処理を簡素化することができる。
【０１３８】
なお、実施の形態２においては、（２２）式および（２３）式に示した変換式により、カラー画像信号（Ｄｒ，Ｄｇ，Ｄｂ）を色平面における値（ＧＲ，ＢＧ）に変換したが、これにかえて、以下に示す変換式により、変換してもよい。すなわち、
ＧＲ　＝　Ｒｉ・Ｄｒ　＋　Ｇｉ・Ｄｇ　＋　Ｂｉ・Ｄｂ　　　・・・（３７）
ＢＧ　＝　Ｒｊ・Ｄｒ　＋　Ｇｊ・Ｄｇ　＋　Ｂｊ・Ｄｂ　　　・・・（３８）
ここで、Ｒｉ　＝　Ｇｉ　＝　Ｂｉ　＝　０，　Ｒｊ　＝　Ｇｊ　＝　Ｂｊ　＝　０である。
【０１３９】
（実施の形態３）
図１４〜図１９を参照しつつ実施の形態３における画像処理装置について説明する。実施の形態３における画像処理装置は、実施の形態１において説明した色相領域判定部１１０にかえて色相領域判定部５１０を備えている。
【０１４０】
実施の形態３における色相領域判定部５１０は、実施の形態２において説明した色相領域判定部３１０と同様、カラー画像信号に対応する点を色空間から色平面に写像する。さらに実施の形態３における色相領域判定部５１０は、２次元平面での信号色に対する色座標　（ＧＲ，ＢＧ）を、原点ｎを中心とした回転角度に応じた値に変換し、変換後の値に基づいて、カラー画像信号が含まれる色相領域を判定する。
【０１４１】
図１４は、図１０で示した色平面と同一の色平面を示している。色相角ＨＵＥは、ＧＲ軸を０°として、点ｎを中心とする回転角である。また、８つの等分領域７００〜７１２は、色相角ＨＵＥが４５°の倍数の角度となる直線を境界とした領域である。各等分領域に対して色相角ＨＵＥに応じて単調増加する値、すなわち上位擬似色相角Ｈａを定める。具体的には、等分領域７００内では、上位擬似色相角Ｈａ＝０、等分領域７０２では、Ｈａ＝１、等分領域７０４ではＨａ＝２、等分領域７０６ではＨａ＝３、等分領域７０８ではＨａ＝４、等分領域７１０ではＨａ＝５、等分領域７１２ではＨａ＝６、等分領域７１４ではＨａ＝７である。
【０１４２】
さらに各等分領域内において、色相角ＨＵＥに応じて単調増加し、かつ上位擬似色相角Ｈａよりも小さい値である、下位擬似色相角Ｈｄを定める。
【０１４３】
カラー画像信号の色座標（ＧＲ，ＢＧ）に対して定められた上位擬似色相角Ｈａおよび下位擬似色相角Ｈｄに応じて定まる値は、色相角ＨＵＥ方向に対応して一意に定まる値である。したがって、この値に基づいて、カラー画像信号が含まれる色相領域を判定することができる。
【０１４４】
図１５は、実施の形態３における色相領域判定部５１０の構成を示すブロック図である。色相領域判定部５１０は、差分ＧＲ算出回路５１１、差分ＢＧ算出回路５１２、上位擬似色相角決定回路５１４、色座標変換回路５１７、下位擬似色相角決定回路５２０、および色相領域コード生成回路５２２を有している。また、図１６は、上位擬似色相角テーブル５１６におけるデータ構成を模式的に示している。また、図１７は、色座標変換テーブル５１８におけるデータ構成を模式的に示している。また、図１８は、色相領域コードテーブル５２４におけるデータ構成を模式的に示している。
【０１４５】
差分ＧＲ算出回路５１１および差分ＢＧ算出回路５１２は、実施の形態２において図１１を参照しつつ説明した差分ＢＧ算出回路３１２および差分ＧＲ算出回路３１４と同様の動作を行う。
【０１４６】
上位擬似色相角決定回路５１４は、上位擬似色相角テーブル５１６を有している。上位擬似色相角テーブル５１６は、図１６に示すように、色座標の条件と上位擬似色相角Ｈａとを対応付けている。なお、色座標の条件については、後述する。上位擬似色相角決定回路５１４は、上位擬似色相角テーブル５１６を利用して、差分ＧＲ算出回路５１１および差分ＢＧ算出回路５１２から入力されたカラー画像信号（ＧＲ，ＢＧ）に基づいて、上位擬似色相角Ｈａを決定する。
【０１４７】
色座標変換回路５１７は、色座標変換テーブル５１８を有している。色座標変換テーブル５１８は、図１７に示すように、上位擬似色相角Ｈａと色座標変換式とを対応付けている。ここで、色座標変換式とは、カラー画像信号の色平面における色座標を座標変換する場合に利用される式である。色座標変換回路５１７は、色座標変換テーブル５１８を利用して、上位擬似色相角決定回路５１４から入力された上位擬似色相角Ｈａに基づいて、差分ＧＲ算出回路５１１および差分ＢＧ算出回路５１２から入力されたカラー画像信号の色座標（ＧＲ，ＢＧ）を（ＧＲ’，ＢＧ’）に変換する。下位擬似色相角決定回路５２０は、色座標変換回路５１７から入力された、移動後の色座標（ＧＲ’，　ＢＧ’）に基づいて、下位擬似色相角Ｈｄを算出する。
【０１４８】
色相領域コード生成回路５２２は、色相領域コードテーブル５２４を有している。色相領域コードテーブル５２４は、図１８に示すように、擬似色相角Ｈの条件と色相領域コードｃｏｄｅとを対応付けている。色相領域コード生成回路５２２は、上位擬似色相角決定回路５１４から入力された上位擬似色相角Ｈａおよび下位擬似色相角決定回路５２０から入力された下位擬似色相角Ｈｄに基づいて、擬似色相角Ｈを算出する。さらに、色相領域コード生成回路５２２は、色相領域コードテーブル５２４を利用して、算出した擬似色相角Ｈから定まる色相領域コードｃｏｄｅを選択し、選択した色相領域コードｃｏｄｅを補正量演算係数メモリ１２２および彩度評価値演算係数メモリ１３２へ出力する。
【０１４９】
次に、図１９に示したフローチャートを参照しつつ、色相領域判定部５１０の動作について説明する。まず、色相領域判定部５１０に入力されたカラー画像信号を２次元化する（Ｓ２７０）。ここでの処理は、図１３において説明したＳ２５０における処理と同様である。
【０１５０】
次に、上位擬似色相角決定回路５１４は、上位擬似色相角テーブル５１６を利用して、差分ＧＲ算出回路５１１および差分ＢＧ算出回路５１２から入力されたカラー画像信号（ＧＲ，ＢＧ）に基づいて、カラー画像信号に対する上位擬似色相角Ｈａを決定する（Ｓ２７２）。具体的には、例えば、カラー画像信号の色座標（ＧＲ，ＢＧ）が、「ＧＲ＞０ａｎｄ　ＢＧ＞０　ａｎｄ　Ｂ　Ｇ＞ＧＲ」の条件を満たしている場合、カラー画像信号は等分領域７０２に含まれていることがわかる。したがって、この場合、等分領域７０２の上位擬似色相角Ｈａ、すなわち「１」を、カラー画像信号の上位擬似色相角Ｈａとして決定する。
【０１５１】
次に、色座標変換回路５１７は、色座標変換テーブル５１８において、５１２から入力された上位擬似色相角Ｈａに対応付けられている色座標変換式を選択する。色座標変換回路５１７は、さらに差分ＧＲ算出回路５１１および差分ＢＧ算出回路５１２から入力されたカラー画像信号（ＧＲ，ＢＧ）を、選択した色座標変換式に代入することにより、変換後の色座標（ＧＲ’，ＢＧ’）を算出する（Ｓ２７４）。すなわち、カラー画像信号の点を等分領域７００に回転移動する。
【０１５２】
なお、図１７に示した色座標変換式は、各等分領域における色座標を変換する式である。しかし、カラー画像信号が含まれる色相領域を判定する場合に、原点ｎからカラー画像信号までの距離の情報は利用されない。そこで、Ｈａ＝１，３，５，７の場合における色座標変換式において、１／√２倍しなくてもよい。
【０１５３】
次に、下位擬似色相角決定回路５２０は、色座標変換回路５１７から入力された変換後の色座標（ＧＲ’，ＢＧ’）を次式に代入することにより、下位擬似色相角Ｈｄを算出する（Ｓ２７６）。
Ｈｄ　＝　ＢＧ’／ＧＲ’　（但し、ＧＲ’＝０ならばＨｂ＝０）　　　　　　・・・（３９）
【０１５４】
すなわち、下位擬似色相角Ｈｄは、等分領域７００に移動後の色座標に対する色相角ＨＵＥに応じて定まる値である。次に、色相領域コード生成回路５２２は、上位擬似色相角決定回路５１４から入力された上位擬似色相角Ｈａおよび下位擬似色相角決定回路５２０から入力された下位擬似色相角Ｈｄから、次式により擬似色相角を決定する（Ｓ２７８）。
Ｈ　＝　Ｈａ＋　Ｈｄ　　　　　　　　　（４０）
（４０）式中のＨａは、色相角ＨＵＥに応じて単調増加する。また、Ｈｄは、等分領域７００における値なので、色相角ＨＵＥに応じて単調増加する。また、Ｈａの増加分は「１」であるのに対して、Ｈｄの増加分は「１」よりも小さい。したがって、擬似色相角Ｈは、色相角ＨＵＥに応じて単調増加する。
【０１５５】
このように、Ｓ２７０からＳ２７８の処理によって、カラー画像信号の色座標を色相角ＨＵＥに応じて単調増加する値、すなわち擬似色相角Ｈに変換することができる。したがって、この値から、カラー画像信号の点の位置を認識することができる。
【０１５６】
次に、色相領域コード生成回路５２２は、色相領域コードテーブル５２４を利用して、上位擬似色相角決定回路５１４から入力された上位擬似色相角Ｈａおよび下位擬似色相角決定回路５２０から入力された下位擬似色相角Ｈｄに基づいて、カラー画像信号が含まれる色相領域コードを決定する（Ｓ２８０）。
【０１５７】
点Ｃ，Ｍ，Ｙ，Ｒ，Ｇ，Ｂに対する擬似色相角Ｈｃ，Ｈｍ，Ｈｙ，Ｈｒ，Ｈｇ，Ｈｂを予め定めておけば、カラー画像信号に対する擬似色相角Ｈと、Ｈｃ，Ｈｍ，Ｈｙ，Ｈｒ，Ｈｇ，Ｈｂとを比較することによって、カラー画像信号が含まれる色相領域を判定することができる。例えば、点Ｙが、等分領域７０２に含まれ、かつ点Ｇが等分領域７０６に含まれている場合には、ＹＧ色相領域に含まれる点であるためには、「Ｈ≧Ｈｙ　ａｎｄ　Ｈ＜Ｈｇ」を満たすことが条件となる。色相領域コードテーブル５２４は、各色相領域に含まれるための条件として、擬似色相角ＨとＨｃ，Ｈｍ，Ｈｙ，Ｈｒ，Ｈｇ，Ｈｂとの関係を、各色相領域コードに対応付けている。
【０１５８】
また、図１８に示した色相領域コードテーブル５２４においては、便宜的にＮ軸上の座標をＧＣ色相領域に含めているが、他の色相領域に含めてもよい。
【０１５９】
以上により、色相領域判定部５１０の動作が終了する。Ｓ２７０〜Ｓ２８０における色相領域判定部３１０の動作は、実施の形態１において図８を参照しつつ説明したＳ２０２からＳ２０４における色相領域判定部１１０の動作にかえて行われる。
【０１６０】
なお、これ以外の画像処理装置１における構成および動作は、実施の形態１における画像処理装置１の構成および動作、および実施の形態２における画像処理装置１の構成および動作と同様である。
【０１６１】
このように、本実施の形態においては、色座標を１つの値に変換することができるので、補正量算出回路１０における処理をより簡素化することができる。
【０１６２】
なお、他の例としては、カラー画像信号の色平面における座標（ＧＲ，ＢＧ）を、三角関数などにより回転座標系における座標に変換してもよい。すなわち、変換式は次式で示される。
ＧＲ　＝　ｒｃｏｓθ　　　・・・（４１）
ＢＧ　＝　ｒｓｉｎθ　　　・・・（４２）
（４１）式および（４２）式に、座標（ＧＲ，ＢＧ）を代入することにより、回転角度θを算出することができる。回転角度θは、ＧＲ軸を０°として、単調増加する。したがって、Ｈにかえて、回転角度θを利用することによっても、同様に、カラー画像信号が含まれる色相領域を判定することができる。なお、この場合、擬似色相角Ｈｃ，Ｈｍ，Ｈｙ，Ｈｒ，Ｈｇ，Ｈｂにかえて、各点Ｃ，Ｍ，Ｙ，Ｒ，Ｇ，Ｂに対応する回転角度θ（θｃ，θｍ，θｙ，θｒ，θｇ，θｂ）を予め算出して、格納しておく。
【０１６３】
（実施の形態４）
次に、図２０を参照しつつ実施の形態４における画像処理装置について説明する。実施の形態４における画像処理装置は、実施の形態１において説明した処理に対応する色座標変換を実現するＬＵＴを備えている。
【０１６４】
図２０は、実施の形態４における画像処理装置の構成を示すブロック図である。画像処理装置２は、３次元ＬＵＴ１３を有する補正量メモリ１２と、画像処理部１４を利用して、カラー画像信号（Ｄｒ，Ｄｇ，Ｄｂ）を色座標（Ｄｒ’，Ｄｇ’，Ｄｂ’）に変換し、色座標（Ｄｒ’，Ｄｇ’，Ｄｂ’）を出力する補正部１１とを備えている。
【０１６５】
このように、ＬＵＴを有する画像処理装置においても、実施の形態１から３において説明したのと同様に、補正量Ｘを考慮した色補正を行うことができる。
【０１６６】
ＬＵＴデータは、ＣＭＳ等で用いられる手法により作成してもよい。以下、これを簡単に説明する。Ｃ，Ｍ，Ｙや、あるいはＫを加えた４色の、様々な組合せの記録信号を発生して、これをプリンタに供給する。そして記録信号に基づいて生成された多数色を有するカラーパッチ画像をプリンタに印刷させる。次に、このカラーパッチ画像を画像入力装置であるスキャナ等で読取らせ、対応するカラー画像信号を得る。
【０１６７】
以上により、プリンタの記録信号からカラー画像信号への関係が得られる。すなわち、この関係の逆の対応関係、すなわちカラー画像信号からプリンタの記録信号への関係を得る。この際、カラー画像信号がプリンタの色再現領域外の色に対応する場合、明度を補正することで、プリンタの色再現領域内に含まれる場合には、そのときの補正量Ｘを考慮した色座標（Ｄｒ’，Ｄｇ’，Ｄｂ’）を変換後のデータとして採用する。また、それ以外の場合には、補正のないデータを変換後のデータとして採用する。入力されうるすべてのカラー画像信号に対して、以上の処理を行うことによって、３次元ＬＵＴを作成することができる。
【０１６８】
また、他の例としては、間引かれた３次元ＬＵＴデータと補間処理を組み合わせて、補正部１１を実現してもよい。
【０１６９】
以上、実施の形態１において説明した画像処理装置は、図１および図２に示した回路と同様のモジュールを有する画像処理プログラムによって実現されてもよい。実施の形態２および実施の形態３において説明した画像処理装置も、それぞれが有する回路と同様のモジュールを有する画像処理プログラムによって実現されてもよい。また、実施の形態４において説明した画像処理装置も、当該画像処理装置における処理を実現する画像処理プログラムによって実現されてもよい。
【０１７０】
画像処理プログラムは、インストール可能な形式又は実行可能な形式のファイルでＣＤ−ＲＯＭ、フレキシブルディスク（ＦＤ）、ＤＶＤ等のコンピュータで読み取り可能な記録媒体に記録されて提供されてもよい。また、画像処理プログラムを、インターネット等のネットワークに接続されたコンピュータ上に格納し、ネットワーク経由でのダウンロードにより提供されてもよい。
【０１７１】
【発明の効果】
以上説明したように、請求項１にかかる発明によれば、色相領域判定手段は、色空間内に明度軸に平行に設けられた面を境界として形成された複数の色相領域のうち、カラー画像信号が表す信号色を含む色相領域を判定し、補正手段は、色相領域に応じて信号色を補正することができる。このように、色空間を色相に応じた複数の色相領域に分割し、色相領域に応じて定められた比較的簡単な演算により、信号色を出力装置に適した色に補正することができるという効果を奏する。
【０１７２】
請求項２にかかる発明によれば、補正手段は、彩度を補正せず、信号色の明度のみを補正することができる。色補正において色相および彩度を変化させると、人の視覚にとって色再現性が悪いと認識される場合がある。このような場合に、色相および彩度を保持することにより、色再現性を低下させることなく、色補正をすることができるという効果を奏する。
【０１７３】
また、請求項３にかかる発明によれば、信号色が出力装置において表現可能な色再現領域内に含まれない場合に、補正手段は、信号色を色再現領域内の色に補正するための最小の補正量だけ信号色を補正することができるので、不必要に色を変化させるのを避けることができる。したがって、画像データの色再現性を良好に保つことができるという効果を奏する。
【０１７４】
また、請求項４にかかる発明によれば、補正量格納手段は、補正手段が補正すべき補正量を、各色相領域に対応付けて格納しているので、色相領域判定手段によって色相領域が判定されると、補正手段は、補正量格納手段において色相領域に対応付けられている補正量を選択すればよいので、容易に補正量を決定することができるという効果を奏する。
【０１７５】
また、請求項５にかかる発明によれば、補正量調整手段は、補正手段が補正すべき補正量を調整することができるので、操作者は、補正量を任意に調整することができるという効果を奏する。
【０１７６】
また、請求項６にかかる発明によれば、信号色の彩度が、当該信号色の色相を示す色であってかつ色再現領域内に含まれる色の彩度のうち、最も高い彩度よりも低い場合に、補正手段は、信号色を補正することができる。このように、補正対象となる色の彩度に応じた補正を行うことができるので、画像データの色再現性をさらに良好な状態に保つことができるという効果を奏する。
【０１７７】
また、請求項７にかかる発明によれば、２次元化手段は、信号色の色空間における空間座標を、明度軸に垂直な平面上の平面座標に写像し、色相領域判定手段は、信号色の平面座標に基づいて、当該信号色を含む色相領域を判定することができる。このように、３色に対応する３つのデータを有する画像データを、２つのデータで表現される平面座標として扱うので、色補正におけるデータ処理の効率を向上させることができるという効果を奏する。
【０１７８】
また、請求項８にかかる発明によれば、擬似色相値算出手段は、信号色の色空間における空間座標を、明度軸を中心とする円周方向に沿って単調増加する擬似色相値に変換し、色相領域判定手段は、擬似色相値に基づいて、信号色を含む色相領域を判定することができる。このように、３色に対応する３つのデータを有する画像データを、１つのデータで表現される擬似色相値として扱うので、色補正におけるデータ処理の効率を向上させることができるという効果を奏する。
【０１７９】
また、請求項９にかかる発明によれば、擬似色相値は、明度軸を中心とする回転角度である。したがって、３つのデータを有する画像データを、１つのデータで表現することができるという効果を奏する。
【０１８０】
また、請求項１０の発明によれば、色相領域判定ステップは、色空間内に明度軸に平行に設けられた面を境界として形成された複数の色相領域のうち、カラー画像信号が表す信号色を含む色相領域を判定し、補正ステップは、色相領域に応じて信号色を補正することができる。このように、色空間を色相に応じた複数の色相領域に分割し、色相領域に応じて定められた比較的簡単な演算により、信号色を出力装置に適した色に補正することができるという効果を奏する。
【０１８１】
また、請求項１１の発明によれば、補正ステップは、彩度を補正せず、信号色の明度のみを補正する。色補正において色相および彩度を変化させると、人の視覚にとって色再現性が悪いと認識される場合がある。このような場合に、色相および彩度を保持することにより、色再現性を低下させることなく、色補正をすることができるという効果を奏する。
【０１８２】
また、請求項１２の発明によれば、信号色が出力装置において表現可能な色再現領域内に含まれない場合に、補正ステップは、信号色を色再現領域内の色に補正するための最小の補正量だけ信号色を補正するので、不必要に色を変化させるのを避けることができる。したがって、画像データの色再現性を良好に保つことができるという効果を奏する。
【０１８３】
また、請求項１３の発明によれば、補正量テーブルは、補正ステップが補正すべき補正量に関する情報を各色相領域に対応付けて格納しているので、色相領域判定ステップによって色相領域が判定されると、補正ステップは、補正量テーブルにおいて色相領域に対応付けられている、補正量に関する情報に基づいて、前記信号色を補正することができるという効果を奏する。
【０１８４】
また、請求項１４の発明によれば、補正量調整ステップは、補正ステップが補正すべき補正量を調整することができるので、操作者は、補正量を任意に調整することができ、操作者の便宜が図られるという効果を奏する。
【０１８５】
また、請求項１５の発明によれば、信号色の彩度が、当該信号色の色相を示す色であってかつ色再現領域内に含まれる色の彩度のうち、最も高い彩度よりも低い場合に、補正ステップは、信号色を補正するので、補正対象となる色の彩度に応じた補正を行うことができ、画像データの色再現性をさらに良好な状態に保つことができるという効果を奏する。
【０１８６】
また、請求項１６の発明によれば、２次元化ステップは、信号色の色空間における空間座標を、明度軸に垂直な平面上の平面座標に写像し、色相領域判定ステップは、信号色の平面座標に基づいて、当該信号色を含む色相領域を判定する。このように、３色に対応する３つのデータを有する画像データを、２つのデータで表現される平面座標として扱うので、色補正におけるデータ処理の効率を向上させることができるという効果を奏する。
【０１８７】
また、請求項１７の発明によれば、擬似色相値算出ステップは、信号色の色空間における空間座標を、明度軸を中心とする円周方向に沿って単調増加する擬似色相値に変換し、色相領域判定ステップは、擬似色相値に基づいて、信号色を含む前記色相領域を判定する。このように、３色に対応する３つのデータを有する画像データを、１つのデータで表現される擬似色相値として扱うので、色補正におけるデータ処理の効率を向上させることができるという効果を奏する。
【０１８８】
また、請求項１８の発明によれば、擬似色相値は、明度軸を中心とする回転角度である。したがって、３つのデータを有する画像データを、１つのデータで表現することができるという効果を奏する。
【０１８９】
また、請求項１９にかかる発明によれば、請求項１０から１８のいずれか一つの動作をコンピュータによって実行することができるという効果を奏する。
【図面の簡単な説明】
【図１】実施の形態１における画像処理装置１の構成を示すブロック図である。
【図２】図１に示した補正量算出回路１０の構成を示すブロック図である。
【図３】色相領域コードテーブル１１６のデータ構成を模式的に示す図である。
【図４】補正量演算係数テーブル１２３のデータ構成を模式的に示す図である。
【図５】画像処理装置１の動作を示すフローチャートである。
【図６】カラー画像信号（Ｄｒ，Ｄｇ，Ｄｂ）の色空間とプリンタの色再現領域との関係を示す図である。
【図７】複数の色相領域に分割された色空間を示す図である。
【図８】図５に示す補正量算出処理（Ｓ４０）における補正量算出回路１０の動作を示すフローチャートである。
【図９】図６に示した色空間をＮ軸を通り、かつＮ軸に平行な平面６５０で切断した断面図である。
【図１０】カラー画像信号を写像すべき２次元の色平面を示す図である。
【図１１】実施の形態２における色相領域判定部３１０の構成を示すブロック図である。
【図１２】実施の形態２における色相領域コードテーブル３２０のデータ構成を模式的に示す図である。
【図１３】実施の形態２における色相領域判定部３１０の動作を示すフローチャートである。
【図１４】色平面に形成された等分領域７００〜７１２を示す図である。
【図１５】実施の形態３における色相領域判定部５１０の構成を示すブロック図である。
【図１６】実施の形態３における上位擬似色相角テーブル５１６におけるデータ構成を模式的に示す図である。
【図１７】実施の形態３における色座標変換テーブル５１８におけるデータ構成を模式的に示す図である。
【図１８】実施の形態３における色相領域コードテーブル５２４におけるデータ構成を模式的に示す図である。
【図１９】実施の形態３における色相領域判定部５１０の動作を示すに示したフローチャートである。
【図２０】実施の形態４における画像処理装置の構成を示すブロック図である。
【符号の説明】
１，２　画像処理装置
１０　補正量算出回路
１１　補正部
２０　補正量調整回路
２２　調整量設定回路
３０　補正回路
１１０，３１０，５１０　色相領域判定部
１１２，３１６　色相評価値演算回路
１１４，３１８，５２２　色相領域コード生成回路
１１５　色相領域コードメモリ
１１６，３２０，５２４　色相領域コードテーブル
１２０　補正量演算部
１２２　補正量演算係数メモリ
１２３　補正量演算係数テーブル
１２４　補正量演算回路
１２６　第１コンパレータ
１２８　第１セレクタ
１３０　高彩度修正部
１３２　彩度評価値演算係数メモリ
１３３　彩度評価値演算係数テーブル
１３４　彩度評価値演算回路
１３４　値演算回路
１３６　第２コンパレータ
１３８　第２セレクタ
３１２，５１２　差分ＢＧ算出回路
３１４，５１２　差分ＧＲ算出回路
５１４　上位擬似色相角決定回路
５１６　上位擬似色相角テーブル
５１７　色座標変換回路
５１８　色座標変換テーブル
５２０　下位擬似色相角決定回路[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image processing apparatus and an image processing method for correcting a color represented by a color image signal into a color suitable for an output device that outputs the color image signal, and a program for causing a computer to execute the method.
[0002]
[Prior art]
Cameras, scanners, and CRTs (cathode ray tubes) that express colors in an additive color mixture, ie, R (red), G (green), B (blue), and subtractive color mixtures, ie, C (cyan) M (magenta) Y The color reproduction area is different from that of a printer that expresses colors in a (yellow) system or a CMYK (black) system.
[0003]
A color management system (CMS) is known as a method for accurately reproducing an original image when converting a representation system of image data representing an image. In the CMS, a difference in a color reproduction area between a CRT or the like and a printer is corrected. In CMS, original image data is converted into appropriate color data by, for example, compressing or expanding the entire or a part of the color reproduction area.
[0004]
When an image read by a scanner is printed by a printer, a process that converges the difference between the color of the document to be read by the scanner and the color reproduced by the printer is performed so that the difference between the color reproduction areas of the two can be obtained. Is known.
[0005]
[Problems to be solved by the invention]
However, when reproducing colors outside the color reproduction region, such as colors printed with special color inks, for example, hue and saturation, that is, minimization of chromaticity may not be optimal. For example, there are cases where the lightness and chromaticity of a multicolored map document are corrected in a well-balanced manner to minimize the color difference before and after correction, and when the chromaticity is corrected to a more appropriate state instead of minimizing the color difference. As a result, the result that the latter was preferred in the subjective evaluation by human vision was obtained.
[0006]
In many cases, terrain is represented by chromaticity on a map. Therefore, when a person recognizes the content drawn on the map, it must recognize a difference in chromaticity. For this reason, it is presumed that an image in which chromaticity reproducibility has priority over lightness is more likely to be recognized as a good image for human vision.
[0007]
As described above, even if a color has a theoretically smallest color difference, it is not always recognized as an optimal color in human vision. Therefore, there is a demand for correcting colors to be recognized as having less color difference, that is, good color reproducibility, to human vision.
[0008]
Further, the image data includes data corresponding to a huge variety of colors. Since color correction is performed on many types of data as described above, processing is often complicated. Therefore, it is desired to provide an efficient color correction method with good color reproducibility.
[0009]
SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and when the color reproduction area of an image input system is different from the color reproduction area of an image output system, it is possible to perform color correction with good color reproducibility and efficiently. It is an object to obtain an image processing apparatus, an image processing method, and a program for causing a computer to execute the method.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, an invention according to claim 1 is an image processing apparatus that corrects a color represented by a color image signal to a color suitable for an output device that is to output the color image signal. Among a plurality of hue regions formed with a plane provided in parallel with the lightness axis as a boundary, a hue region determination unit that determines a hue region including a signal color represented by the color image signal, and according to the hue region. And a correcting means for correcting the signal color.
[0011]
According to the first aspect of the present invention, the hue region determination means determines a signal color represented by a color image signal among a plurality of hue regions formed with a surface provided in parallel in the color space in parallel with the lightness axis as a boundary. The hue region included is determined, and the correction unit can correct the signal color according to the hue region. As described above, the color space is divided into a plurality of hue regions corresponding to the hue, and the signal color can be corrected to a color suitable for the output device by a relatively simple operation determined according to the hue region.
[0012]
According to a second aspect of the present invention, in the image processing apparatus according to the first aspect, the correction unit corrects the brightness of the signal color.
[0013]
According to the second aspect of the invention, the correction means does not correct the saturation, but corrects only the lightness of the signal color. If hue and saturation are changed in color correction, it may be recognized that color reproducibility is poor for human vision. In such a case, by maintaining the hue and saturation, color correction can be performed without reducing color reproducibility.
[0014]
According to a third aspect of the present invention, in the image processing apparatus according to the first or second aspect, when the signal color is not included in a color reproduction area that can be expressed by the output device, the correction unit includes: The signal color is corrected by a minimum correction amount for correcting the signal color to a color within the color reproduction area.
[0015]
According to the third aspect of the present invention, when the signal color is not included in the color reproduction area that can be expressed in the output device, the correction unit sets the minimum value for correcting the signal color to a color within the color reproduction area. Since the signal color is corrected by the correction amount, unnecessary color change can be avoided. Therefore, good color reproducibility of the image data can be maintained.
[0016]
According to a fourth aspect of the present invention, in the image processing apparatus according to any one of the first to third aspects, the correction unit stores information on a correction amount to be corrected by the correction unit in association with each hue region. When the hue region is determined by the hue region determination unit, the correction unit determines the hue region based on the information on the correction amount associated with the hue region in the correction amount storage unit. The signal color is corrected.
[0017]
According to the fourth aspect of the present invention, since the correction amount storing means stores the information on the correction amount to be corrected by the correcting means in association with each hue area, the hue area determining means determines the hue area. Then, the correction unit can calculate the correction amount based on the information on the correction amount associated with the hue region in the correction amount storage unit. Therefore, the correction amount can be easily determined.
[0018]
According to a fifth aspect of the present invention, in the image processing apparatus according to any one of the first to fourth aspects, the image processing apparatus further includes a correction amount adjustment unit that adjusts the correction amount to be corrected by the correction unit. It is characterized by.
[0019]
According to the fifth aspect of the present invention, since the correction amount adjusting means can adjust the correction amount to be corrected by the correcting means, the operator can arbitrarily adjust the correction amount, and the operator can adjust the correction amount. For convenience.
[0020]
According to a sixth aspect of the present invention, in the image processing apparatus according to any one of the first to fifth aspects, the saturation of the signal color is a color indicating a hue of the signal color, and The correction unit corrects the signal color when the saturation is lower than the highest saturation among colors included in a color reproduction area that can be expressed by the device.
[0021]
According to the sixth aspect of the present invention, the saturation of the signal color is a color indicating the hue of the signal color and lower than the highest saturation of the colors included in the color reproduction area. In this case, since the correction means corrects the signal color, correction can be performed according to the saturation of the color to be corrected, and the color reproducibility of the image data can be maintained in a more favorable state.
[0022]
According to a seventh aspect of the present invention, in the image processing apparatus according to any one of the first to sixth aspects, a spatial coordinate of the signal color in the color space is expressed by a plane on a plane perpendicular to the lightness axis. The image processing apparatus further includes two-dimensional conversion means for mapping to coordinates, wherein the hue area determination means determines a hue area including the signal color based on the plane coordinates of the signal color.
[0023]
According to the seventh aspect of the present invention, the two-dimensional conversion means maps the spatial coordinates of the signal color in the color space to the plane coordinates on a plane perpendicular to the lightness axis, and the hue region determination means outputs the signal color plane. A hue area including the signal color is determined based on the coordinates. As described above, since image data having three data corresponding to three colors is treated as plane coordinates represented by two data, the efficiency of data processing in color correction can be improved.
[0024]
According to an eighth aspect of the present invention, in the image processing apparatus according to any one of the first to sixth aspects, the spatial coordinates of the signal color in the color space are set in a circumferential direction around the lightness axis. Further comprising a pseudo hue value calculating means for converting into a pseudo hue value that monotonically increases along, wherein the hue area determination means determines the hue area including the signal color based on the pseudo hue value. I do.
[0025]
According to the eighth aspect of the present invention, the pseudo hue value calculating means converts the spatial coordinates of the signal color in the color space into pseudo hue values that monotonically increase along a circumferential direction centered on the lightness axis. The area determining means determines a hue area including the signal color based on the pseudo hue value. As described above, since image data having three data corresponding to three colors is handled as a pseudo hue value represented by one data, the efficiency of data processing in color correction can be improved.
[0026]
According to a ninth aspect of the present invention, in the image processing apparatus according to the eighth aspect, the pseudo hue value is a rotation angle about the lightness axis.
[0027]
According to the ninth aspect, the pseudo hue value is a rotation angle about the brightness axis. Therefore, image data having three data can be represented by one data.
[0028]
Further, the invention according to claim 10 is an image processing method for correcting a color represented by a color image signal to a color suitable for an output device that is to output the color image signal, wherein the color processing method comprises: A hue region determining step of determining a hue region including a signal color represented by the color image signal among a plurality of hue regions formed with the surface provided as a boundary, and correcting the signal color according to the hue region And a correction step of performing the correction.
[0029]
According to the tenth aspect of the present invention, the hue region determination step includes, among a plurality of hue regions formed with a surface provided in parallel with the lightness axis in the color space as a boundary, a signal color represented by a color image signal. The hue region included is determined, and the correction step can correct the signal color according to the hue region. As described above, the color space is divided into a plurality of hue regions corresponding to the hue, and the signal color can be corrected to a color suitable for the output device by a relatively simple operation determined according to the hue region.
[0030]
According to an eleventh aspect of the present invention, in the image processing method of the tenth aspect, the correcting step corrects the lightness of the signal color.
[0031]
According to the eleventh aspect, the correction step corrects only the brightness of the signal color without correcting the saturation. If hue and saturation are changed in color correction, it may be recognized that color reproducibility is poor for human vision. In such a case, by maintaining the hue and saturation, color correction can be performed without reducing color reproducibility.
[0032]
According to a twelfth aspect of the present invention, in the image processing method according to the tenth or eleventh aspect, when the signal color is not included in a color reproduction area that can be expressed by the output device, the correction step includes: The signal color is corrected by a minimum correction amount for correcting the signal color to a color within the color reproduction area.
[0033]
According to the twelfth aspect of the present invention, when the signal color is not included in the color reproduction region that can be expressed in the output device, the correction step is the minimum for correcting the signal color to a color in the color reproduction region. Since the signal color is corrected by the correction amount, unnecessary color change can be avoided. Therefore, good color reproducibility of the image data can be maintained.
[0034]
According to a thirteenth aspect of the present invention, in the image processing method according to any one of the tenth to twelfth aspects, if the hue area is determined by the hue area determination step, the correction step includes the correction. In the correction amount table in which the information relating to the correction amount to be corrected is associated with each hue region, the signal color is corrected based on the information relating to the correction amount associated with the hue region. .
[0035]
According to the thirteenth aspect, the correction amount table stores information on the correction amount to be corrected in the correction step in association with each hue region, so that the hue region is determined by the hue region determination step. And the correction step can correct the signal color based on information about the correction amount associated with the hue region in the correction amount table.
[0036]
According to a fourteenth aspect of the present invention, in the image processing method according to any one of the tenth to thirteenth aspects, the image processing method further includes a correction amount adjustment step of adjusting the correction amount to be corrected by the correction step. It is characterized by.
[0037]
According to the fourteenth aspect of the invention, in the correction amount adjusting step, the correction amount to be corrected in the correction step can be adjusted, so that the operator can arbitrarily adjust the correction amount, and For convenience.
[0038]
According to a fifteenth aspect of the present invention, in the image processing method according to any one of the tenth to fourteenth aspects, the saturation of the signal color is a color indicating a hue of the signal color, and The correction step corrects the signal color when the saturation is lower than the highest saturation among colors included in a color reproduction area that can be expressed by the device.
[0039]
According to the fifteenth aspect, the saturation of the signal color is the color indicating the hue of the signal color, and among the saturations of the colors included in the color reproduction area that can be expressed by the output device, When the saturation is lower than the high saturation, the correction step corrects the signal color, so that the correction according to the saturation of the color to be corrected can be performed, and the color reproducibility of the image data is further improved. Can be kept.
[0040]
According to a sixteenth aspect of the present invention, in the image processing method according to any one of the tenth to fifteenth aspects, a spatial coordinate of the signal color in the color space is represented by a plane on a plane perpendicular to the lightness axis. The image processing apparatus further includes a two-dimensional conversion step of mapping to coordinates, wherein the hue area determination step determines a hue area including the signal color based on the plane coordinates of the signal color.
[0041]
According to the sixteenth aspect of the present invention, in the two-dimensionalizing step, the spatial coordinates of the signal color in the color space are mapped to plane coordinates on a plane perpendicular to the lightness axis, and the hue region determining step is performed in the plane of the signal color. A hue area including the signal color is determined based on the coordinates. As described above, since image data having three data corresponding to three colors is treated as plane coordinates represented by two data, the efficiency of data processing in color correction can be improved.
[0042]
According to a seventeenth aspect of the present invention, in the image processing method according to any one of the tenth to fifteenth aspects, the spatial coordinates of the signal color in the color space are set in a circumferential direction around the lightness axis. Further comprising a pseudo hue value calculating step of converting into a pseudo hue value that monotonically increases along, wherein the hue region determining step determines the hue region including the signal color based on the pseudo hue value. I do.
[0043]
According to the seventeenth aspect of the present invention, the pseudo hue value calculating step converts the spatial coordinate of the signal color in the color space into a pseudo hue value that monotonically increases along a circumferential direction centered on the lightness axis. The area determination step determines a hue area including the signal color based on the pseudo hue value. As described above, since image data having three data corresponding to three colors is handled as a pseudo hue value represented by one data, the efficiency of data processing in color correction can be improved.
[0044]
The invention according to claim 18 is the image processing method according to claim 17, wherein the pseudo hue value is a rotation angle about the lightness axis.
[0045]
According to the eighteenth aspect, the pseudo hue value is a rotation angle about the lightness axis. Therefore, image data having three data can be represented by one data.
[0046]
The invention according to claim 19 is a program for causing a computer to execute the method according to claims 10 to 18, so that any one of the operations according to claims 10 to 18 can be executed by a computer.
[0047]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of an image processing apparatus according to the present invention will be described in detail with reference to the accompanying drawings.
[0048]
(Embodiment 1)
The image processing device according to the first embodiment receives a color image signal and corrects a color represented by the color image signal, that is, a signal color, to a color suitable for an output device that should output the color image signal. The output device may be a printer. The printer can express, for example, CMY or CMYK colors.
[0049]
Here, the color image signal is obtained by converting an output signal from a scanner or the like that reads an image by separating a color image into three primary color RGB values by additive color mixing into a signal proportional to the color density. Signal. The color image signal is represented by three values of (Dr, Dg, Db).
[0050]
FIG. 1 is a block diagram illustrating a configuration of the image processing apparatus 1 according to the first embodiment. The image processing apparatus 1 includes a correction amount calculation circuit 10, a correction amount adjustment circuit 20, an adjustment amount setting circuit 22, and a correction circuit 30.
[0051]
The color image signals (Dr, Dg, Db) are input to the correction amount calculation circuit 10. The correction amount calculation circuit 10 calculates a correction amount X for the color image signal based on the color image signal. Here, the correction amount X is a calculation amount when the signal color represented by the color image signal is corrected to a color suitable for the output device. The image processing apparatus 1 according to the present embodiment corrects only the lightness of the signal color. That is, the correction amount X is a correction amount related to lightness.
[0052]
The adjustment amount setting circuit 22 receives an input of the adjustment amount α from the operator and outputs the input to the correction amount adjustment circuit 20. Here, the adjustment amount α is an amount representing the degree to which the correction amount X is reflected in the correction of the color image signal.
[0053]
The correction amount adjustment circuit 20 calculates an adjusted correction amount X from the correction amount X input from the correction amount calculation circuit 10 and the adjustment amount α input from the adjustment amount setting circuit 22, and outputs the corrected correction amount X to the correction circuit 30. . The correction circuit 30 converts the color image signal (Dr, Dg, Db) into (Dr ′, Dg ′, Db ′) based on the correction amount X input from the correction amount adjustment circuit 20. Thereby, the lightness of the signal color is corrected. The color image signals (Dr ', Dg', Db ') thus obtained are output to a printer (not shown).
[0054]
Note that the correction amount adjustment circuit 20 may include a multiplier or the like. Further, the correction circuit 30 may include an adder and the like.
[0055]
As described above, the image processing apparatus 1 can correct the color image signal according to the characteristics of the printer that outputs the color image signal. Therefore, the printer can print a color image signal in a favorable state.
[0056]
Next, the configuration of the correction amount calculation circuit 10 will be described with reference to FIGS. FIG. 2 is a block diagram showing a configuration of the correction amount calculation circuit 10 shown in FIG. FIG. 3 schematically shows a data configuration of a hue area code table described later. FIG. 4 schematically shows a data configuration of a correction amount calculation coefficient table described later.
[0057]
The correction amount calculation circuit 10 calculates a correction amount X corresponding to the hue region determined by the hue region determination unit 110, which determines the hue region including the signal color of the color image signal. The system 120 includes a unit 120, a high saturation correction unit 130 that corrects the correction amount X according to the saturation of the signal color, and a system control unit 140. Here, the hue area is each area formed by dividing the color space. The hue area will be described later.
[0058]
The hue region determination unit 110 includes a hue evaluation value calculation circuit 112 that performs a product-sum operation, a hue region code generation circuit 114 that performs a logical operation, and a hue region code memory 115 that stores a hue region code.
[0059]
The correction amount calculation unit 120 includes a correction amount calculation coefficient memory 122 that stores correction amount calculation coefficients, a correction amount calculation circuit 124 that performs a product-sum calculation, a first comparator 126, and a first selector 128.
[0060]
The high saturation correction unit 130 includes a saturation evaluation value operation coefficient memory 132 that stores a saturation evaluation value operation coefficient, a saturation evaluation value operation circuit 134 that performs a product-sum operation, a second comparator 136, and a second selector 138. Have.
[0061]
The color image signal input to the correction amount calculation circuit 10 is input to a hue evaluation value calculation circuit 112, a correction amount calculation circuit 124, and a saturation evaluation value calculation circuit 134.
[0062]
The hue evaluation value calculation circuit 112 calculates each hue evaluation value Fx (x = c, m, y, r, g, b) based on the input color image signal. Here, the hue evaluation value is a value used when determining which hue region in the color space contains the signal color represented by the color image signal. The hue evaluation value calculation circuit 112 outputs the calculated hue evaluation value Fx to the hue area code generation circuit 114.
[0063]
The hue area code memory 115 has a hue area code table 116. As shown in FIG. 3, the hue area code table 116 associates the condition of the hue evaluation value Fx with the hue area code code. The conditions of the hue evaluation value Fx included in the hue area code table 116 will be described later. The hue area code generation circuit 114 uses the hue area code table 116 to determine a hue area code corresponding to each hue evaluation value input from the hue evaluation value calculation circuit 112. Further, the hue area code generation circuit 114 outputs the area code value code indicating the determined hue area to the correction amount operation coefficient memory 122 and the saturation evaluation value operation coefficient memory 132.
[0064]
The correction amount calculation coefficient memory 122 has a correction amount calculation coefficient table 123. The correction amount calculation coefficient table 123 associates the hue area codes “code” with the correction amount calculation coefficients Rx, Gx, Bx, and Cx as shown in FIG. Here, the correction amount calculation coefficient is a coefficient used when calculating the correction amount, and is a value predetermined for each hue region. When the hue region code is input, the correction amount operation coefficient memory 122 selects a correction amount operation coefficient corresponding to the input hue region code in the correction amount operation coefficient table 123. The correction amount calculation coefficient memory 122 outputs the selected correction amount calculation coefficient to the correction amount calculation circuit 124.
[0065]
The correction amount calculation circuit 124 calculates the correction amount X based on the input correction amount calculation coefficient, and outputs the calculated correction amount X to the comparator 126 and the selector 128. The comparator 126 and the selector 128 correct the correction amount X in cooperation.
[0066]
On the other hand, the saturation evaluation value calculation coefficient memory 132 has a saturation evaluation value calculation coefficient table 133. The saturation evaluation value calculation coefficient table 133 associates the hue region code “code” with the saturation evaluation value calculation coefficients Rs, Gs, Bs, and Cs. Here, the saturation evaluation value calculation coefficient is a coefficient used when the high saturation correction unit 130 evaluates the saturation of the signal color. The data configuration of the saturation evaluation value calculation coefficient table 133 is almost the same as the data configuration of the correction amount calculation coefficient table 123 shown in FIG. In the saturation evaluation value calculation coefficient table 133, a saturation evaluation value calculation coefficient is associated with the correction amount calculation coefficient in the correction amount calculation coefficient table 123. When the hue region code is input, the saturation evaluation value operation coefficient memory 132 selects a saturation evaluation value operation coefficient associated with the input hue region code in the saturation evaluation value operation coefficient table 133. . The saturation evaluation value calculation coefficient memory 132 outputs the selected saturation evaluation value calculation coefficient to the saturation evaluation value calculation circuit 134.
[0067]
The S value calculation circuit 134 calculates a saturation evaluation value S from the input saturation evaluation value calculation coefficient, and outputs the saturation evaluation value S to the comparator 136. Here, the saturation table value S is a value for evaluating the saturation of the signal color. The comparator 136 and the selector 138 correct the correction amount X in accordance with the value of the saturation evaluation value S, and output the corrected correction amount X.
[0068]
The system control unit 140 controls the entire image processing apparatus 1 and sets a hue evaluation value Fx, a correction amount calculation coefficient, and a saturation evaluation value calculation coefficient. The hue evaluation value Fx, the correction amount calculation coefficient, and the saturation evaluation value calculation coefficient are rewritable.
[0069]
Next, the operation of the image processing apparatus 1 will be described with reference to the flowchart of FIG. First, a color image signal is input to the correction amount calculation circuit 10. The correction amount calculation circuit 10 calculates the correction amount X of the brightness of the signal color represented by the color image signal (S40). Next, the correction amount adjustment circuit 20 multiplies the correction amount X by the adjustment amount α, and sets the calculation result (αX) as the correction amount (S50). Here, the adjustment amount α is a value that satisfies “0 ≦ α ≦ 1”, for example.
[0070]
When the adjustment amount α is input from the adjustment amount setting circuit 22, the correction amount adjustment circuit 20 calculates the correction amount using the adjustment amount α received from the adjustment amount setting circuit 22. As described above, the adjustment amount desired by the operator can be set using the adjustment amount setting circuit 22. Therefore, a desired value can be set when the operator does not want the adjustment or wants to reduce the degree of correction.
[0071]
Also, the degree of this adjustment is often determined by the type of image to be handled. Therefore, the adjustment amount setting circuit 22 may output the adjustment amount α according to the type of the image selected by the operator, with the type of the image to be handled being input from the operator. As the type of the image, for example, a color pencil, a crayon, a photograph, or the like may be set.
[0072]
Next, the correction circuit 30 converts the color image signal (Dr, Dg, Db) into (Dr ′, Dg ′, Db ′) according to the following equation. That is, the brightness is corrected (S60). Note that the correction amount X input from the correction amount adjustment circuit 20 is substituted for X in the following equation.
Dr '= Dr + X
Dg ′ = Dg + X (1)
Db '= Db + X
[0073]
The correction circuit 30 outputs the color image signals (Dr ′, Dg ′, Db ′) whose brightness has been corrected to the outside, and the processing of the image processing apparatus 1 ends.
[0074]
Next, the operation of the correction amount calculation circuit 10 in the correction amount calculation processing (S40) shown in FIG. 5 will be described. The correction amount calculation circuit 10 divides a color space expressing a signal color of an input color image signal into a plurality of hue regions, and calculates a correction amount corresponding to the hue region including the signal color. Therefore, the color space and the hue region including the signal color will be described first with reference to FIGS.
[0075]
FIG. 6 shows the relationship between the color space of the color image signals (Dr, Dg, Db) and the color reproduction area of the printer. The Dr axis, Dg axis, and Db axis shown in FIG. 6 are orthogonal to each other. The N axis is a straight line that satisfies Dr = Dg = Db. That is, points on this straight line indicate an achromatic color. A point W corresponding to white and a point K corresponding to black are arranged on the N axis.
[0076]
In the color space shown in FIG. 6, the saturation changes along the T axis provided perpendicular to the N axis. The hue changes along a rotation direction U about the N axis on a plane parallel to the T axis. That is, all points on the surface formed parallel to the N axis in the predetermined rotation direction U are points of a color indicating a hue determined by the rotation direction U.
[0077]
Points C, M, and Y are the points where the saturation is maximum in CMY, which is the primary color of the printer. Points R, G, and B are points where the saturation is maximum in RGB, which is the secondary color of the printer. The printer color reproduction area 672 is a substantially spherical area formed by connecting these points C, M, Y, R, G, B, points W, and K with a curve. That is, the inside of the printer color reproduction area 672 is a color area that can be output by the printer. The signal color region 660 is a color region that can take a signal color for a color image signal.
[0078]
When correcting the signal color in this color space, the image processing apparatus 1 regards the printer color reproduction area 670 as a printer color reproduction area 672 in order to simplify the processing. Here, the printer color reproduction area 670 is a dodecahedral area formed by connecting points C, M, Y, R, G, B, points W and K corresponding to the maximum values of eight colors with straight lines. It is. In this way, by regarding the printer color reproduction area 670 as the printer color reproduction area 672, no substantial error occurs in the correction amount X.
[0079]
Next, the hue area considered in the processing of the image processing apparatus 1 will be described with reference to FIG. FIG. 7 shows a color space divided into a plurality of hue regions. The C boundary surface 633 is a plane defined by points C, W, and K. Similarly, i boundary surfaces 634 to 638 (i = M, Y, R, G, B) are planes determined by points i, W, K (i = M, Y, R, G, B), respectively. . The color space is divided by these boundaries 633-638. In the color space divided by these boundary surfaces 633 to 638, a CB hue region 640, a BM hue region 641, an MR hue region 642, an RY hue region 643, a YG hue region 644, and a GC hue region 645 are formed.
[0080]
Hereinafter, the operation of the correction amount calculation circuit 10 will be described with reference to FIG. FIG. 8 is a flowchart showing the operation of the correction amount calculation circuit 10 in the correction amount calculation processing (S40) shown in FIG.
[0081]
When the color image signal is input to the correction amount calculation circuit 10, the hue evaluation value calculation circuit 112 calculates each hue evaluation value Fx (S202). Next, using the hue area code memory 115, the hue area code generation circuit 114 generates a hue area code of the hue area including the signal color based on each hue evaluation value Fx input from the hue evaluation value calculation circuit 112. Is determined (S204).
[0082]
Here, a method of theoretically deriving the hue evaluation value Fx will be described. The color coordinates indicating the points C, M, Y, R, G, B, W, and K shown in FIG. 7 are respectively represented by (Dir, Dig, Dib) (i = c, m, y, r, g, b, w , K). For example, the color coordinates corresponding to the point C are (Dcr, Dcg, Dcb).
[0083]
In this case, for example, the C boundary surface 633 is represented by the following equation.
(Dcg−Dcb) · Dr + (Dcb−Dcr) · Dg + (Dcr−Dcg) · Db = 0 (2)
It becomes. Similarly, the boundary surfaces 634 to 638 are respectively represented by the following equations.
(Dmg−Dmb) · Dr + (Dmb−Dmr) · Dg + (Dmr−Dmg) · Db = 0 (3)
(Dyg−Dyb) · Dr + (Dyb−Dyr) · Dg + (Dyr−Dyg) · Db = 0 (4)
(Drg−Drb) · Dr + (Drb−Drr) · Dg + (Drr−Drg) · Db = 0 (5)
(Dgg−Dgb) · Dr + (Dgg−Dgr) · Dg + (Dgr−Dgg) · Db = 0 (6)
(Dbg−Dbb) · Dr + (Dbb−Dbr) · Dg + (Dbr−Dbg) · Db = 0 (7)
[0084]
The color space is divided into two regions by q633, for example, a region including the CB hue region 640 and a region including the GC hue region 645. Similarly, the color space is divided into two regions by each boundary surface 634-638. Therefore, which hue area the color image signal is included in can be determined based on which of the two areas formed by the boundary surfaces 633 to 638 the color image signal is included in. . That is, the hue area including the color image signal is determined based on the sign of the value obtained by substituting the color image signal (Dr, Dg, Db) into each of the equations (2) to (7). Can be. Therefore, the hue evaluation value Fx is determined based on the equations (2) to (7). That is, the left sides of the equations (2) to (7) are Fc, Fm, Fy, Fr, Fg, and Fb, respectively.
Fc = (Dcg−Dcb) · Dr + (Dcb−Dcr) · Dg + (Dcr−Dcg) · Db (8)
Fm = (Dmg−Dmb) · Dr + (Dmb−Dmr) · Dg + (Dmr−Dmg) · Db (9)
Fy = (Dyg−Dyb) · Dr + (Dyb−Dyr) · Dg + (Dyr−Dyg) · Db (10)
Fr = (Drg−Drb) · Dr + (Drb−Drr) · Dg + (Drr−Drg) · Db (11)
Fg = (Dgg−Dgb) · Dr + (Dgg−Dgr) · Dg + (Dgr−Dgg) · Db (12)
Fb = (Dbg−Dbb) · Dr + (Dbb−Dbr) · Dg + (Dbr−Dbg) · Db (13)
[0085]
That is, in S202, the hue evaluation value calculation circuit 112 calculates each hue evaluation value Fx determined in the equations (8) to (13). For example, when Fc, Fg calculated from an arbitrary point (Dr, Dg, Db) in the color space satisfies “Fc ≦ 0 and Fb> 0”, it is understood that this point is included in the CB hue area. As described above, each hue region is defined by the hue evaluation value Fx. That is, the condition of the hue evaluation value Fx associated with the hue region code in the hue region code table 116 shown in FIG. 3 is a condition determined from the above equation.
[0086]
As described above, the condition of the hue evaluation value Fx is predetermined in the hue area code table 116. Accordingly, the hue area code generation circuit 114 satisfies the hue evaluation value Fx input from the hue evaluation value calculation circuit 112 among the conditions of the hue evaluation value Fx associated with each hue area in the hue area code table 116. The condition may be specified, and the hue region code corresponding to the condition may be selected in the hue region code table 116.
[0087]
In the hue area code table 116 shown in FIG. 3, the color coordinates on the N axis are included in the GC hue area for convenience, but may be included in other hue areas.
[0088]
Further, the hue evaluation value Fx changes depending on the actual value of (Dir, Dig, Dib) (i = c, m, y, r, g, b, w, k). Therefore, the condition of the hue evaluation value to be associated with each hue area code in the hue area code table 116 may be changed according to the value of the hue evaluation value.
[0089]
Next, the correction amount calculation coefficient memory 122 determines a correction amount calculation coefficient using the correction amount calculation coefficient table 123 (S206). Next, the correction amount calculation circuit 124 calculates the correction amount X based on the correction amount calculation coefficient input from the correction amount calculation coefficient memory 122 and the color image signal (Dr, Dg, Db) input from outside. (S208). Note that the correction amount X can be obtained by the following equation.
X = Rx · Dr + Gx · Dg + Bx · Db + Cx (14)
Here, Rx, Gx, Bx, and Cx are correction amount calculation coefficients determined for each hue region. As described above, the correction amount X can be obtained by the product-sum operation of the correction amount operation coefficient and the color image signal (Dr, Dg, Db).
[0090]
Here, a theoretical derivation method of the correction amount calculation coefficient will be described with reference to FIG. FIG. 9 is a cross-sectional view of the color space shown in FIG. 6 cut along a plane 650 that passes through the N axis and is parallel to the N axis.
[0091]
Point E shown in FIG. 9 is a point outside the printer color reproduction area 670. In other words, it represents a color that cannot be reproduced by the printer. Therefore, the point E can be included inside the printer color reproduction area 670 by moving the point E in the direction of K in parallel with the N axis. The movement amount of the point E at this time corresponds to the correction amount X.
[0092]
Thus, by lowering the brightness, the color is converted to a color that can be reproduced in the printer. In this case, the saturation at point E is kept constant. As described above, by moving the point outside the printer color reproduction area 670 in parallel with the N axis, it is possible to correct the color included in the printer color reproduction area 670 while maintaining the saturation before correction.
[0093]
For example, in the case of an image showing information due to a difference in saturation or hue, it may be difficult to recognize the information if the saturation is corrected. In such a case, by correcting only the brightness as in the method described above, the viewer can easily recognize that the image is reproduced in a good state.
[0094]
As the correction amount for the color image signal input to the correction amount calculation circuit 10 is smaller, the reproducibility of the image is maintained. Therefore, it is desirable to set a value as small as possible as the correction amount X. When the point E is moved inside the printer color reproduction area 670 in a direction parallel to the N axis, the point E may be moved to the point G in order to minimize the movement amount of the point E. The point G is the intersection of the straight line parallel to the N axis and the boundary of the printer color reproduction area 670 as point E. The minimum correction amount X at the point E corresponds to the distance between the points E and G. Therefore, the hue evaluation value indicates the relationship between the color coordinates at the point E and the distance between EG.
[0095]
A triangle having vertices at points E, G, and M and a triangle having vertices at points M, W, and K have a similar relationship. Therefore, the correction amount X can be calculated from the similarity ratio. Note that the point M is a point on a straight line determined by the points E and K and a point on the boundary of the printer color reproduction area 670.
[0096]
The correction amount X at the point E is obtained by the following equation.
Correction amount X = E-G distance
= (E-M distance) / (M-K distance) × (W-K distance) (15) Here, the W-K distance can be expressed as (Dk-Dw). here,
Dw = Dwr = Dwg = Dwb (16)
Dk = Dkr = Dkg = Dkb
It is.
[0097]
It is to be noted that the similarity ratio can be obtained by defining the correction amount X at the point K as “−1” and the correction amount at the point K and the line W passing through the point W as “0” with respect to the equation (15). . Further, the correction amount X can be calculated based on the similarity ratio.
[0098]
The correction amount X on the first hue surface 651 has been described above. By applying this to each hue area, that is, three-dimensional, an equation for calculating the correction amount X for all points in the color space can be obtained.
[0099]
For example, in the case of the CB hue region 640, the coefficient is determined such that the correction amount X is “− (Dk−Dw)” at K and the correction amount X is “0” at points C, B, and W. This condition is substituted into equation (14) to obtain the following equation.
− (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 (17)
0 = Rx · Dbr + Gx · Dbg + Bx · Dbb + Cx
By solving the simultaneous equations of equation (17), correction amount calculation coefficients Rx, Gx, Bx, and Cx represented by the following equations are obtained.
[Formula 1]

... (18)
[0100]
The correction amount calculation coefficients Rx, Gx, Bx, and Cx for the other hue regions can be calculated in the same manner.
[0101]
In the correction amount calculation coefficient table 123 illustrated in FIG. 4, the correction amount calculation coefficient associated with the hue region code is a value calculated in the same manner as in Expression (18). Therefore, the correction amount operation coefficient memory 122 may select the correction amount operation coefficient associated with each hue region code in the correction amount operation coefficient table 123.
[0102]
In step S206, when the correction amount calculation circuit 124 calculates the correction amount X, the first comparator 126 compares the correction amount X input from the correction amount calculation circuit 124 with “0”. If the correction amount X is equal to or greater than "0" (S210, Yes), the correction amount X is output to the first selector 128 (S212). If the correction amount X is smaller than “0” (S210, No), “0” is output to the first selector 128 as the correction amount (S214).
[0103]
Equation (18) is set such that the correction amount X at the point K is “− (Dk−Dw)”, and the correction amount X at the points A and W is “0”. That is, the correction amount X is equal to or greater than “0” in a region outside the printer color reproduction region 670. The correction amount X is smaller than “0” when the correction amount X is inside the printer color reproduction area 670. Therefore, it can be determined from the comparison result between the correction amount X and “0” whether or not the color image signal corresponds to a point inside the printer color reproduction area 670.
[0104]
Further, when the color image signal is a point inside the printer color reproduction area 670, no correction is required. Therefore, “0” is set as the correction amount X in this case. Thereby, the effective correction amount X can be set only when the color image signal is a point outside the printer color reproduction area 670.
[0105]
As described above, the image processing apparatus 1 can correct only the color image signal corresponding to the point of the area outside the printer color reproduction area 670 by the processing from S208 to S212.
[0106]
Next, the saturation evaluation value calculation coefficient memory 132 determines a saturation evaluation value calculation coefficient based on the hue region code input from the hue region code generation circuit 114 (S220). Next, the saturation evaluation value calculation circuit 134 calculates a saturation evaluation value calculation coefficient input from the saturation evaluation value calculation coefficient memory 132 and a color image signal (Dr, Dg, Db) input from the outside. The saturation evaluation value S is calculated (S222).
[0107]
Here, a theoretical derivation method of the saturation evaluation value S will be described. For example, the color indicated by the point P illustrated in FIG. 9 indicates saturation higher than the maximum saturation in the printer color reproduction area 670 in the hue of the color indicated by the point P. When the signal color of the color image signal to be processed corresponds to the point P, an amount corresponding to the distance between the point Q and the point P is calculated as the correction amount. Here, the point Q is an intersection of a straight line passing through the point P and parallel to the N axis and a straight line DW. However, the point Q is located outside the printer color reproduction area 670. That is, even if the point P is moved by the correction amount X, it cannot be included inside the printer color reproduction area 670.
[0108]
As described above, in the case where the signal color indicates saturation equal to or higher than the maximum saturation, the signal color is converted into a color corresponding to a point inside the printer color reproduction area 670 even if only the brightness of the signal color is corrected. I can't. Therefore, it is determined whether or not the saturation indicated by the signal color is greater than the maximum saturation, and the correction amount X is corrected accordingly. The saturation evaluation value S is an index for evaluating the saturation indicated by the color image signal.
[0109]
The saturation evaluation value S can be obtained by the following equation.
S = Rs · Dr + Gs · Dg + Bs · Db + Cs (19)
Here, Ds (Rs, Gs, Bs, Cs) is a saturation evaluation value calculation coefficient determined for each hue region.
[0110]
For example, in the case of the CB hue region, the coefficients are determined so that the points K and W are “0” and the points C and B are “1” with respect to the equation (19). By substituting this condition into equation (19), the following equation is obtained.
0 = Rs · Dkr + Gs · Dkg + Bs · Dkb + Cs
0 = Rs · Dwr + Gs · Dwg + Bs · Dwb + Cs
1 = Rs · Dcr + Gs · Dcg + Bs · Dcb + Cs (20)
1 = Rs · Dbr + Gs · Dbg + Bs · Dbb + Cs
By solving the simultaneous equations of the equation (20), the saturation evaluation value calculation coefficients Rs, Gs, Bs, and Cs represented by the following equations can be obtained.
[Formula 2]

... (21)
[0111]
The saturation evaluation value calculation coefficients Rs, Gs, Bs, and Cs for other hue regions can be calculated in the same manner. In the saturation evaluation value calculation coefficient memory 132, the saturation evaluation value calculation coefficient associated with the hue region code is a value calculated in the same manner as in Expression (21). Therefore, the saturation evaluation value calculation coefficient memory 132 selects the saturation evaluation value calculation coefficient associated with the hue region code input from the hue region code generation circuit 114 in the saturation evaluation value calculation coefficient table 133. Just fine.
[0112]
In S222, after S134 calculates the saturation evaluation value calculation coefficient, the second comparator 136 compares the saturation evaluation value S input from the saturation evaluation value calculation circuit 134 with "1". If the saturation evaluation value S is equal to or smaller than “1” (S224, Yes), the correction amount X is output to the second selector 138 (S226). If the saturation evaluation value S is larger than “1” (S224, No), “0” is output to the second selector 138 as the correction amount X (S228).
[0113]
Equations (20) and (21) are set such that the saturation evaluation value S is “0” at the points K and W, and is “1” at the maximum saturation in each hue. That is, the reason why the saturation evaluation value S calculated from the signal color becomes “1” or more is that the saturation of the signal color is high and the brightness is not converted to the color coordinates in the printer color reproduction area 670 even if the brightness is corrected. It is. The saturation evaluation value S becomes smaller than “1” when the brightness is corrected to be converted to the color coordinates in the printer color reproduction area 670. As described above, by comparing the saturation evaluation value S calculated from the color image signal with “1”, the point corresponding to the signal color is set to a saturation larger than the highest saturation in the printer color reproduction area 670. It can be determined whether or not they correspond.
[0114]
If the saturation of the signal color is high and the lightness is not converted into the color coordinates in the printer color reproduction area 670 even if the lightness is corrected, “0” is set as the correction amount. As described above, according to the correction amount calculating circuit 10 in the present embodiment, the effective correction amount X is set only when the brightness can be corrected to a color corresponding to a point inside the printer color reproduction area 670. Since it can be set, it is possible to avoid unnecessary correction of the signal color.
[0115]
Further, since the image processing apparatus 1 according to the first embodiment does not require an LUT, the memory capacity may be small, and the color correction processing may be performed efficiently.
[0116]
In the present embodiment, since the saturation evaluation value S is set to “1” at the maximum saturation, the saturation evaluation value S is compared with “1”. However, the compared value “1” is not limited to this. For example, when the saturation evaluation value calculation coefficient is set such that the saturation evaluation value S is “0” at the maximum saturation and the saturation evaluation value S is “1” at the points K and W, , S216, the process may proceed to S218 if the saturation evaluation value S is equal to or greater than “0”, and may proceed to S220 if the saturation evaluation value S is smaller than “0”. As described above, the compared value to be compared may be changed according to the setting of the saturation evaluation value calculation coefficient.
[0117]
Similarly, the value to be compared in S210 may be changed according to the setting of the correction amount calculation coefficients Rx, Gx, Bx, and Cx.
[0118]
The correction amount calculation circuit 10 according to the first embodiment includes the hue region determination unit 110, the correction amount calculation unit 120, and the high saturation correction unit 130. However, as another example, the correction amount calculation circuit 10 It may be configured by only the area determination unit 110 and the correction amount calculation unit 120. With the correction amount X generated by the hue region determination unit 110 and the correction amount calculation unit 120, the color of the image data can be corrected to a color suitable for the characteristics of the printer.
[0119]
(Embodiment 2)
The image processing apparatus according to the second embodiment will be described with reference to FIGS. The image processing apparatus 1 according to the second embodiment includes a hue area determination unit 310 instead of the hue area determination unit 110 described in the first embodiment. The hue region determination unit 110 according to the first embodiment processes a color image signal using color coordinates in a three-dimensional color space, but the hue region determination unit 310 according to the second embodiment converts a color space into a two-dimensional color space. A hue area including the color image signal is determined by using the color coordinates of the color image signal on the two-dimensional plane.
[0120]
FIG. 10 shows a two-dimensional plane on which a color image signal is to be mapped. In this two-dimensional plane, a straight line corresponding to "Dg-Dr" is defined as a GR axis, and a straight line corresponding to "Db-Dg" is defined as a BG axis. The GR axis and the BR axis are orthogonal to each other.
[0121]
The points (Dr, Dg, Db) on the color space are mapped to the color plane shown in FIG.
GR = Dg-Dr (22)
BG = Db-Dg (23)
[0122]
Further, points (Dnr, Dng, Dnb) on the N axis in the color space are mapped to points (Dng-Dnr, Dnb-Dng) on the color plane shown in FIG. Since Dnr = Dng = Dnb,
(Dng−Dnr, Dnb · Dng) = (0, 0) (24)
It becomes. That is, all points on the N axis are mapped to the origin n on the plane shown in FIG. Points C, M, Y, R, G, and B in the color space are arranged around the origin n as shown in FIG. Therefore, the six hue regions 640 to 645 shown in FIG. 7 are mapped to regions 740 to 745 divided by straight lines connecting the N axis and points C, M, Y, R, G, and B on the color plane. Is done.
[0123]
FIG. 11 is a block diagram illustrating a configuration of the hue region determination unit 310 according to the second embodiment. The hue area determination unit 310 includes a difference BG calculation circuit 312, a difference GR calculation circuit 314, a hue evaluation value calculation circuit 316, a hue area code generation circuit 318, and a hue area code table 320.
[0124]
The color image signal is input to the difference BG calculation circuit 312 and the difference GR calculation circuit 314. The difference GR calculation circuit 314 calculates a difference GR from each color value of the input color image signal, and outputs the difference GR to the hue evaluation value calculation circuit 316. The hue evaluation value calculation circuit 316 calculates a difference BG from each color value of the input color image signal, and outputs the difference BG to the hue area code generation circuit 318.
[0125]
The hue evaluation value calculation circuit 316 calculates each hue table value Fx ′ (x = c, m, y, r, g, b) from the input color image signal and outputs it to the hue area code generation circuit 318. .
[0126]
The hue area code generation circuit 318 has a hue area code table 320. As shown in FIG. 12, the hue area code table 320 associates the condition of the hue evaluation value Fx ′ with the hue area code code. The condition of the hue evaluation value Fx ′ will be described later. The hue area code generation circuit 318 uses the hue area code table 320 to store the area code code indicating the hue area code determined from the hue evaluation value Fx ′ in the correction amount operation coefficient memory 122 and the saturation evaluation value operation coefficient memory 132 Output to Further, the system control unit 340 sets a hue evaluation value Fx ′.
[0127]
Next, the operation of the hue region determination unit 310 will be described with reference to the flowchart shown in FIG. First, when a color image signal is input to the hue region determination unit 310, the value of the color image signal is two-dimensionalized (S250). Specifically, the difference BG calculation circuit 312 obtains the difference GR by substituting the value of the color image signal into the expression (22). Further, the difference GR calculation circuit 314 obtains a difference BG by substituting the value of the color image signal into Expression (23). That is, the values (Dr, Dg, Db) in the color space of the color image signal are converted into the values (GR, BG) in the color plane.
[0128]
Next, the hue evaluation value calculation circuit 316 calculates each hue evaluation value Fx ′ based on the GR input from the difference BG calculation circuit 312 (S252). Next, the hue area code generation circuit 318 converts the hue area code table 320 based on each hue evaluation value Fx ′ input from the hue evaluation value calculation circuit 316 and the difference BG input from the difference GR calculation circuit 314. The hue area code of the hue area including the signal color is determined using the signal color (S254).
[0129]
Here, a method of theoretically deriving the hue evaluation value Fx ′ will be described. In the color plane shown in FIG. 10, straight lines connecting the point N and the points C, M, Y, R, G, and B, that is, the straight line NC, the straight line NM, the straight line NY, the straight line NR, the straight line NG, and The straight lines NB are respectively expressed as follows.
BG = (Dcb−Dcg) / (Dcg−Dcr) · GR (However, Dcg−Dcr） 0) (25)
BG = (Dmb−Dmg) / (Dmg−Dmr) · GR (However, Dmg−Dmr ≠ 0) (26)
BG = (Dyb−Dyg) / (Dyg−Dyr) · GR (However, Dyg−Dyr ≠ 0) (27)
BG = (Drb−Drg) / (Drg−Drr) · GR (However, Drg−Drr ≠ 0) (28)
BG = (Dgb−Dgg) / (Dgg−Dgr) · GR (however, Dgg−Dgr ≠ 0) (29)
BG = (Dbb−Dbg) / (Dbg−Dbr) · GR (However, Dbg−Dbr ≠ 0) (30)
[0130]
From the magnitude relation between the BG value obtained by substituting the GR value of the color image signal into each of the equations (25) to (30) and the BG value of the actual color image signal, a straight line determined by each equation: The positional relationship with the point corresponding to the color image signal can be understood. Therefore, which hue area a color image signal is included in is determined by substituting the GR value of the color image signal into the equations (25) to (30) and the BG value of the color image signal. Can be determined based on the magnitude relation of. Therefore, the hue evaluation value Fx ′ is determined based on the equations (25) to (30). That is, the left sides of Expressions (25) to (30) are Fc ', Fm', Fy ', Fr', Fg ', and Fb', respectively.
Fc ′ = (Dcb−Dcg) / (Dcg−Dcr) · GR (31)
Fm ′ = (Dmb−Dmg) / (Dmg−Dmr) · GR (32)
Fy ′ = (Dyb−Dyg) / (Dyg−Dyr) · GR (33)
Fr ′ = (Drb−Drg) / (Drg−Drr) · GR (34)
Fg ′ = (Dgb−Dgg) / (Dgg−Dgr) · GR (35)
Fb ′ = (Dbb−Dbg) / (Dbg−Dbr) · GR (36)
[0131]
That is, in S252, the hue evaluation value calculation circuit 316 calculates the hue evaluation value Fx ′ determined in the equations (31) to (36).
[0132]
For example, when Fc ′ and Fb ′ calculated from an arbitrary point (GR, BG) on the color plane satisfy “BG ≦ Fc ′ and BG> Fb ′”, this point must be included in the CB hue area. I understand. That is, the condition of the hue evaluation value Fx ′ associated with the hue region code in the hue region code table 320 shown in FIG. 12 is a condition determined from the above equation. As described above, in the hue area code table 320, the condition of the hue evaluation value Fx ′ is set in advance. Therefore, the hue region code generation circuit 318 determines the BG and hue input from the difference GR calculation circuit 314 from the conditions of the hue evaluation value Fx ′ associated with each hue region code in the hue region code table 320. What is necessary is just to specify the condition that the hue evaluation value Fx ′ input from the evaluation value calculation circuit 316 satisfies, and to select the hue region code corresponding to this condition in the hue region code table 320.
[0133]
In the hue area code table 320 shown in FIG. 12, the color coordinates on the N axis are included in the GC hue area, but may be included in other hue areas.
[0134]
The hue evaluation value Fx ′ changes depending on the actual value of (Dir, Dig, Dib) (i = c, m, y, r, g, b, w, k). Therefore, the condition of the hue evaluation value to be associated with each hue area code in the hue area code table 320 may be changed according to the value of the hue evaluation value Fx ′.
[0135]
Thus, the operation of the hue region determination unit 310 ends. The operation of the hue region determination unit 310 in S250 to S254 is performed in place of the operation of the hue region determination unit 110 in S202 to S204 described in the first embodiment with reference to FIG.
[0136]
The configuration and operation of the image processing apparatus 1 other than the above are the same as the configuration and operation of the image processing apparatus 1 according to the first embodiment described with reference to FIGS.
[0137]
As described above, according to the second embodiment, a color represented by a color image signal is represented by two values in a two-dimensional color plane. The processing in the quantity calculation circuit 10 can be simplified.
[0138]
In the second embodiment, the color image signals (Dr, Dg, Db) are converted into the values (GR, BG) on the color plane by the conversion expressions shown in Expressions (22) and (23). Instead, conversion may be performed by the following conversion formula. That is,
GR = Ri · Dr + Gi · Dg + Bi · Db (37)
BG = Rj · Dr + Gj · Dg + Bj · Db (38)
Here, Ri = Gi = Bi = 0 and Rj = Gj = Bj = 0.
[0139]
(Embodiment 3)
An image processing apparatus according to the third embodiment will be described with reference to FIGS. The image processing device according to the third embodiment includes a hue region determination unit 510 instead of the hue region determination unit 110 described in the first embodiment.
[0140]
The hue region determination unit 510 according to the third embodiment maps a point corresponding to a color image signal from a color space to a color plane, similarly to the hue region determination unit 310 described in the second embodiment. Further, the hue region determination unit 510 according to Embodiment 3 converts the color coordinates (GR, BG) for the signal color on the two-dimensional plane into a value corresponding to the rotation angle about the origin n, and the converted value , The hue area including the color image signal is determined.
[0141]
FIG. 14 shows the same color plane as the color plane shown in FIG. The hue angle HUE is a rotation angle about the point n with the GR axis set to 0 °. The eight equally divided regions 700 to 712 are regions bounded by a straight line having a hue angle HUE that is a multiple of 45 °. A value that monotonically increases in accordance with the hue angle HUE, that is, an upper pseudo hue angle Ha is determined for each equally divided region. Specifically, in the equal area 700, the upper pseudo hue angle Ha = 0, in the equal area 702, Ha = 1, in the equal area 704, Ha = 2, in the equal area 706, Ha = 3, equal area. Ha = 4 in the area 708, Ha = 5 in the equal area 710, Ha = 6 in the equal area 712, and Ha = 7 in the equal area 714.
[0142]
Further, a lower pseudo hue angle Hd which monotonically increases in accordance with the hue angle HUE and is smaller than the upper pseudo hue angle Ha in each of the equally divided regions.
[0143]
The value determined according to the upper pseudo hue angle Ha and the lower pseudo hue angle Hd defined for the color coordinates (GR, BG) of the color image signal is a value uniquely determined corresponding to the hue angle HUE direction. Therefore, the hue area including the color image signal can be determined based on this value.
[0144]
FIG. 15 is a block diagram illustrating a configuration of the hue region determination unit 510 according to the third embodiment. The hue area determination unit 510 includes a difference GR calculation circuit 511, a difference BG calculation circuit 512, an upper pseudo hue angle determination circuit 514, a color coordinate conversion circuit 517, a lower pseudo hue angle determination circuit 520, and a hue area code generation circuit 522. are doing. FIG. 16 schematically shows the data configuration of the upper pseudo hue angle table 516. FIG. 17 schematically shows a data configuration in the color coordinate conversion table 518. FIG. 18 schematically shows a data configuration in the hue area code table 524.
[0145]
The difference GR calculation circuit 511 and the difference BG calculation circuit 512 perform the same operation as the difference BG calculation circuit 312 and the difference GR calculation circuit 314 described in the second embodiment with reference to FIG.
[0146]
The upper pseudo hue angle determination circuit 514 has an upper pseudo hue angle table 516. As shown in FIG. 16, the upper pseudo hue angle table 516 associates the color coordinate condition with the upper pseudo hue angle Ha. The conditions of the color coordinates will be described later. The upper pseudo hue angle determination circuit 514 uses the upper pseudo hue angle table 516 and, based on the color image signals (GR, BG) input from the difference GR calculation circuit 511 and the difference BG calculation circuit 512, uses the upper pseudo hue angle table 516. The angle Ha is determined.
[0147]
The color coordinate conversion circuit 517 has a color coordinate conversion table 518. As shown in FIG. 17, the color coordinate conversion table 518 associates the upper pseudo hue angle Ha with the color coordinate conversion formula. Here, the color coordinate conversion equation is an equation used when coordinate conversion is performed on color coordinates on a color plane of a color image signal. The color coordinate conversion circuit 517 uses the color coordinate conversion table 518 to input from the difference GR calculation circuit 511 and the difference BG calculation circuit 512 based on the upper pseudo hue angle Ha input from the upper pseudo hue angle determination circuit 514. The color coordinates (GR, BG) of the obtained color image signal are converted into (GR ′, BG ′). The lower pseudo hue angle determination circuit 520 calculates the lower pseudo hue angle Hd based on the moved color coordinates (GR ′, BG ′) input from the color coordinate conversion circuit 517.
[0148]
The hue area code generation circuit 522 has a hue area code table 524. As shown in FIG. 18, the hue area code table 524 associates the condition of the pseudo hue angle H with the hue area code code. The hue area code generation circuit 522 calculates the pseudo hue angle H based on the upper pseudo hue angle Ha input from the upper pseudo hue angle determination circuit 514 and the lower pseudo hue angle Hd input from the lower pseudo hue angle determination circuit 520. calculate. Further, the hue area code generation circuit 522 uses the hue area code table 524 to select a hue area code code determined from the calculated pseudo hue angle H, and stores the selected hue area code code in the correction amount operation coefficient memory 122 and Output to the saturation evaluation value calculation coefficient memory 132.
[0149]
Next, the operation of the hue region determination unit 510 will be described with reference to the flowchart shown in FIG. First, the color image signal input to the hue area determination unit 510 is two-dimensionalized (S270). The processing here is the same as the processing in S250 described in FIG.
[0150]
Next, the higher-order pseudo hue angle determination circuit 514 uses the higher-order pseudo hue angle table 516 based on the color image signals (GR, BG) input from the difference GR calculation circuit 511 and the difference BG calculation circuit 512. The upper pseudo hue angle Ha for the color image signal is determined (S272). Specifically, for example, when the color coordinates (GR, BG) of the color image signal satisfy the condition of “GR> 0 and BG> 0 and BG> GR”, the color image signal is stored in the equally divided area 702. You can see that it is included. Therefore, in this case, the upper pseudo hue angle Ha of the equally divided area 702, that is, “1” is determined as the upper pseudo hue angle Ha of the color image signal.
[0151]
Next, the color coordinate conversion circuit 517 selects, in the color coordinate conversion table 518, the color coordinate conversion formula associated with the upper pseudo hue angle Ha input from 512. The color coordinate conversion circuit 517 further substitutes the color image signals (GR, BG) input from the difference GR calculation circuit 511 and the difference BG calculation circuit 512 into the selected color coordinate conversion formula, thereby obtaining the converted color coordinates. (GR ', BG') is calculated (S274). That is, the point of the color image signal is rotationally moved to the equally divided area 700.
[0152]
Note that the color coordinate conversion formula shown in FIG. 17 is a formula for converting color coordinates in each equally divided region. However, when determining the hue area including the color image signal, information on the distance from the origin n to the color image signal is not used. Therefore, in the color coordinate conversion formula in the case of Ha = 1, 3, 5, and 7, it is not necessary to multiply by 1 / √2.
[0153]
Next, the lower pseudo hue angle determination circuit 520 calculates the lower pseudo hue angle Hd by substituting the converted color coordinates (GR ′, BG ′) input from the color coordinate conversion circuit 517 into the following equation. (S276).
Hd = BG ′ / GR ′ (However, if GR ′ = 0, Hb = 0) (39)
[0154]
That is, the lower pseudo hue angle Hd is a value determined according to the hue angle HUE with respect to the color coordinates after moving to the equal area 700. Next, the hue region code generation circuit 522 calculates the pseudo pseudo hue angle Ha input from the upper pseudo hue angle determination circuit 514 and the lower pseudo hue angle Hd input from the lower pseudo hue angle determination circuit 520 according to the following equation. The hue angle is determined (S278).
H = Ha + Hd (40)
Ha in the equation (40) monotonically increases according to the hue angle HUE. Further, since Hd is a value in the equal area 700, it monotonically increases according to the hue angle HUE. Further, while the increase in Ha is “1”, the increase in Hd is smaller than “1”. Therefore, the pseudo hue angle H monotonically increases according to the hue angle HUE.
[0155]
As described above, the color coordinates of the color image signal can be converted into a value that monotonically increases in accordance with the hue angle HUE, that is, the pseudo hue angle H by the processes of S270 to S278. Therefore, the position of the point of the color image signal can be recognized from this value.
[0156]
Next, the hue area code generation circuit 522 uses the hue area code table 524 to output the upper pseudo hue angle Ha input from the upper pseudo hue angle determination circuit 514 and the lower pseudo hue angle input from the lower pseudo hue angle determination circuit 520. A hue area code including a color image signal is determined based on the pseudo hue angle Hd (S280).
[0157]
If the pseudo hue angles Hc, Hm, Hy, Hr, Hg, and Hb for the points C, M, Y, R, G, and B are determined in advance, the pseudo hue angles H for the color image signal and Hc, Hm, Hy, By comparing Hr, Hg, and Hb, the hue region including the color image signal can be determined. For example, when the point Y is included in the equally-divided area 702 and the point G is included in the equally-divided area 706, “H ≧ Hy and H” is required to be included in the YG hue area. <Hg ”is a condition. The hue area code table 524 associates the relationship between the pseudo hue angle H and Hc, Hm, Hy, Hr, Hg, Hb with each hue area code as a condition for being included in each hue area.
[0158]
In the hue area code table 524 shown in FIG. 18, the coordinates on the N axis are included in the GC hue area for convenience, but may be included in other hue areas.
[0159]
Thus, the operation of the hue region determination unit 510 ends. The operation of the hue region determination unit 310 in S270 to S280 is performed in place of the operation of the hue region determination unit 110 in S202 to S204 described in the first embodiment with reference to FIG.
[0160]
The configuration and operation of the image processing apparatus 1 other than the above are the same as the configuration and operation of the image processing apparatus 1 according to the first embodiment and the configuration and operation of the image processing apparatus 1 according to the second embodiment.
[0161]
As described above, in the present embodiment, since the color coordinates can be converted into one value, the processing in the correction amount calculation circuit 10 can be further simplified.
[0162]
As another example, the coordinates (GR, BG) on the color plane of the color image signal may be converted into coordinates on a rotating coordinate system by a trigonometric function or the like. That is, the conversion equation is represented by the following equation.
GR = rcosθ (41)
BG = rsinθ (42)
By substituting the coordinates (GR, BG) into the equations (41) and (42), the rotation angle θ can be calculated. The rotation angle θ monotonically increases with the GR axis set to 0 °. Therefore, the hue area including the color image signal can be similarly determined by using the rotation angle θ instead of H. In this case, instead of the pseudo hue angles Hc, Hm, Hy, Hr, Hg, Hb, the rotation angles θ (θc, θm, θy, θr) corresponding to the respective points C, M, Y, R, G, B. , Θg, θb) are calculated in advance and stored.
[0163]
(Embodiment 4)
Next, an image processing apparatus according to Embodiment 4 will be described with reference to FIG. The image processing apparatus according to the fourth embodiment includes an LUT that implements color coordinate conversion corresponding to the processing described in the first embodiment.
[0164]
FIG. 20 is a block diagram illustrating a configuration of an image processing apparatus according to Embodiment 4. The image processing device 2 converts the color image signals (Dr, Dg, Db) into color coordinates (Dr ′, Dg ′, Db ′) by using a correction amount memory 12 having a three-dimensional LUT 13 and an image processing unit 14. And a correction unit 11 for converting and outputting color coordinates (Dr ′, Dg ′, Db ′).
[0165]
As described above, even in the image processing apparatus having the LUT, the color correction in consideration of the correction amount X can be performed as described in the first to third embodiments.
[0166]
The LUT data may be created by a method used in a CMS or the like. Hereinafter, this will be briefly described. A recording signal of various combinations of four colors including C, M, Y, or K is generated and supplied to the printer. Then, the printer prints a color patch image having a large number of colors generated based on the recording signal. Next, the color patch image is read by a scanner or the like which is an image input device, and a corresponding color image signal is obtained.
[0167]
As described above, the relationship between the recording signal of the printer and the color image signal is obtained. In other words, a relationship opposite to this relationship, that is, a relationship from the color image signal to the recording signal of the printer is obtained. At this time, if the color image signal corresponds to a color outside the color reproduction area of the printer, the brightness is corrected, and if the color image signal is included in the color reproduction area of the printer, the color in consideration of the correction amount X at that time is considered. The coordinates (Dr ', Dg', Db ') are adopted as the converted data. In other cases, data without correction is adopted as converted data. A three-dimensional LUT can be created by performing the above processing on all the color image signals that can be input.
[0168]
As another example, the correction unit 11 may be realized by combining the thinned three-dimensional LUT data and the interpolation processing.
[0169]
As described above, the image processing apparatus described in the first embodiment may be realized by an image processing program having modules similar to the circuits illustrated in FIGS. 1 and 2. The image processing apparatuses described in the second and third embodiments may also be realized by an image processing program having a module similar to a circuit included in each. Further, the image processing device described in the fourth embodiment may also be realized by an image processing program that realizes processing in the image processing device.
[0170]
The image processing program may be provided by being recorded in a computer-readable recording medium such as a CD-ROM, a flexible disk (FD), or a DVD in a file in an installable format or an executable format. Further, the image processing program may be stored on a computer connected to a network such as the Internet, and provided by downloading via the network.
[0171]
【The invention's effect】
As described above, according to the first aspect of the present invention, the hue region determination unit is configured to output a color image from a plurality of hue regions formed by using a surface provided in parallel with the lightness axis in the color space as a boundary. The hue region including the signal color represented by the signal is determined, and the correction unit can correct the signal color according to the hue region. As described above, the color space can be divided into a plurality of hue regions corresponding to the hue, and the signal color can be corrected to a color suitable for the output device by a relatively simple operation determined according to the hue region. It works.
[0172]
According to the second aspect of the present invention, the correction unit can correct only the lightness of the signal color without correcting the saturation. If hue and saturation are changed in color correction, it may be recognized that color reproducibility is poor for human vision. In such a case, by retaining the hue and saturation, there is an effect that color correction can be performed without lowering color reproducibility.
[0173]
According to the third aspect of the present invention, when the signal color is not included in the color reproduction area that can be expressed by the output device, the correction unit corrects the signal color to a color within the color reproduction area. Since the signal color can be corrected by the minimum correction amount, unnecessary color change can be avoided. Therefore, there is an effect that the color reproducibility of the image data can be kept good.
[0174]
According to the fourth aspect of the present invention, the correction amount storing means stores the correction amount to be corrected by the correction means in association with each hue area, so that the hue area determination means determines the hue area. Then, since the correction means only has to select the correction amount associated with the hue area in the correction amount storage means, there is an effect that the correction amount can be easily determined.
[0175]
Further, according to the fifth aspect of the invention, the correction amount adjusting means can adjust the correction amount to be corrected by the correcting means, so that the operator can arbitrarily adjust the correction amount. To play.
[0176]
According to the invention of claim 6, the saturation of the signal color is a color indicating the hue of the signal color and is higher than the highest saturation of the colors included in the color reproduction area. If the signal color is also low, the correction means can correct the signal color. As described above, since the correction according to the saturation of the color to be corrected can be performed, there is an effect that the color reproducibility of the image data can be kept more favorable.
[0177]
According to the seventh aspect of the present invention, the two-dimensionalizing means maps the spatial coordinates of the signal color in the color space to plane coordinates on a plane perpendicular to the lightness axis, and The hue area including the signal color can be determined based on the plane coordinates of. As described above, since image data having three data corresponding to three colors is treated as plane coordinates represented by two data, it is possible to improve the efficiency of data processing in color correction.
[0178]
According to the eighth aspect of the present invention, the pseudo hue value calculating means converts the spatial coordinates of the signal color in the color space into pseudo hue values that monotonically increase in a circumferential direction around the lightness axis. The hue area determination means can determine the hue area including the signal color based on the pseudo hue value. As described above, since image data having three data corresponding to three colors is handled as a pseudo hue value represented by one data, it is possible to improve the efficiency of data processing in color correction.
[0179]
According to the ninth aspect, the pseudo hue value is a rotation angle about the lightness axis. Therefore, there is an effect that image data having three data can be expressed by one data.
[0180]
According to the tenth aspect of the present invention, the hue region determination step includes the step of determining a signal color represented by a color image signal among a plurality of hue regions formed in the color space with a surface provided in parallel with the lightness axis as a boundary. And the correction step can correct the signal color according to the hue region. As described above, the color space can be divided into a plurality of hue regions corresponding to the hue, and the signal color can be corrected to a color suitable for the output device by a relatively simple operation determined according to the hue region. It works.
[0181]
According to the eleventh aspect, the correction step corrects only the brightness of the signal color without correcting the saturation. If hue and saturation are changed in color correction, it may be recognized that color reproducibility is poor for human vision. In such a case, by retaining the hue and saturation, there is an effect that color correction can be performed without lowering color reproducibility.
[0182]
According to the twelfth aspect of the present invention, when the signal color is not included in the color reproduction area that can be expressed by the output device, the correction step includes a minimum step for correcting the signal color to a color within the color reproduction area. Since the signal color is corrected by the correction amount of, it is possible to avoid unnecessary color change. Therefore, there is an effect that the color reproducibility of the image data can be kept good.
[0183]
According to the thirteenth aspect, the correction amount table stores information on the correction amount to be corrected in the correction step in association with each hue region, so that the hue region is determined by the hue region determination step. Then, the correction step has an effect that the signal color can be corrected based on the information on the correction amount associated with the hue region in the correction amount table.
[0184]
According to the fourteenth aspect, the correction amount adjusting step can adjust the correction amount to be corrected by the correction step, so that the operator can arbitrarily adjust the correction amount. Is achieved.
[0185]
According to the invention of claim 15, the saturation of the signal color is a color indicating the hue of the signal color and is higher than the highest saturation of the colors included in the color reproduction area. If the color is low, the correction step corrects the signal color, so that correction according to the saturation of the color to be corrected can be performed, and the color reproducibility of the image data can be kept in a better state. It works.
[0186]
According to the sixteenth aspect, the two-dimensionalization step maps the spatial coordinates of the signal color in the color space to plane coordinates on a plane perpendicular to the lightness axis. A hue area including the signal color is determined based on the plane coordinates. As described above, since image data having three data corresponding to three colors is treated as plane coordinates represented by two data, it is possible to improve the efficiency of data processing in color correction.
[0187]
According to the seventeenth aspect, the pseudo hue value calculating step converts the spatial coordinates of the signal color in the color space into pseudo hue values that monotonically increase along a circumferential direction around the lightness axis, The hue region determination step determines the hue region including the signal color based on the pseudo hue value. As described above, since image data having three data corresponding to three colors is handled as a pseudo hue value represented by one data, it is possible to improve the efficiency of data processing in color correction.
[0188]
According to the eighteenth aspect, the pseudo hue value is a rotation angle about the brightness axis. Therefore, there is an effect that image data having three data can be expressed by one data.
[0189]
According to the invention of claim 19, there is an effect that any one of the operations of claims 10 to 18 can be executed by a computer.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of an image processing apparatus 1 according to a first embodiment.
FIG. 2 is a block diagram showing a configuration of a correction amount calculation circuit 10 shown in FIG.
FIG. 3 is a diagram schematically illustrating a data configuration of a hue area code table.
FIG. 4 is a diagram schematically illustrating a data configuration of a correction amount calculation coefficient table 123.
FIG. 5 is a flowchart illustrating an operation of the image processing apparatus 1.
FIG. 6 is a diagram illustrating a relationship between a color space of a color image signal (Dr, Dg, Db) and a color reproduction area of a printer.
FIG. 7 is a diagram showing a color space divided into a plurality of hue regions.
8 is a flowchart showing the operation of the correction amount calculation circuit 10 in the correction amount calculation processing (S40) shown in FIG.
9 is a cross-sectional view of the color space shown in FIG. 6 cut along a plane 650 that passes through the N axis and is parallel to the N axis.
FIG. 10 is a diagram showing a two-dimensional color plane on which a color image signal is to be mapped.
FIG. 11 is a block diagram illustrating a configuration of a hue region determination unit 310 according to the second embodiment.
FIG. 12 is a diagram schematically showing a data configuration of a hue area code table 320 according to the second embodiment.
FIG. 13 is a flowchart illustrating an operation of a hue region determination unit 310 according to the second embodiment.
FIG. 14 is a diagram showing equal regions 700 to 712 formed on a color plane.
FIG. 15 is a block diagram showing a configuration of a hue region determination unit 510 according to the third embodiment.
FIG. 16 is a diagram schematically showing a data configuration of an upper pseudo hue angle table 516 according to the third embodiment.
FIG. 17 is a diagram schematically showing a data configuration in a color coordinate conversion table 518 according to the third embodiment.
FIG. 18 is a diagram schematically showing a data configuration in a hue area code table 524 according to the third embodiment.
FIG. 19 is a flowchart showing the operation of the hue region determination unit 510 according to the third embodiment.
FIG. 20 is a block diagram illustrating a configuration of an image processing apparatus according to a fourth embodiment.
[Explanation of symbols]
1,2 Image processing device
10 Correction amount calculation circuit
11 Correction unit
20 Correction amount adjustment circuit
22 Adjustment amount setting circuit
30 Correction circuit
110, 310, 510 Hue area determination unit
112,316 Hue evaluation value calculation circuit
114, 318, 522 Hue area code generation circuit
115 Hue area code memory
116,320,524 Hue area code table
120 Correction amount calculator
122 Correction amount calculation coefficient memory
123 Correction amount calculation coefficient table
124 correction amount calculation circuit
126 first comparator
128 1st selector
130 High saturation correction unit
132 Saturation evaluation value calculation coefficient memory
133 Saturation evaluation value calculation coefficient table
134 Saturation evaluation value calculation circuit
134 value operation circuit
136 Second comparator
138 second selector
312,512 Difference BG calculation circuit
314,512 difference GR calculation circuit
514 Upper-level pseudo hue angle determination circuit
516 Upper pseudo hue angle table
517 Color coordinate conversion circuit
518 Color coordinate conversion table
520 Lower pseudo hue angle determination circuit

Claims (19)

An image processing device that corrects a color represented by a color image signal to a color suitable for an output device that is to output the color image signal,
Among a plurality of hue regions formed with a surface provided in parallel with the lightness axis in the color space as a boundary, a hue region determination unit that determines a hue region including a signal color represented by the color image signal,
An image processing apparatus comprising: a correction unit configured to correct the signal color according to the hue region. The image processing apparatus according to claim 1, wherein the correction unit corrects the lightness of the signal color. When the signal color is not included in the color reproduction area that can be expressed in the output device, the correction unit may correct the signal color to a color in the color reproduction area by a minimum correction amount. The image processing device according to claim 1, wherein the signal color is corrected. A correction amount storage unit configured to store information on a correction amount to be corrected by the correction unit in association with each hue region;
When the hue region is determined by the hue region determination unit, the correction unit corrects the signal color based on the information on the correction amount associated with the hue region in the correction amount storage unit. The image processing apparatus according to any one of claims 1 to 3, wherein: The image processing apparatus according to claim 1, further comprising a correction amount adjustment unit configured to adjust a correction amount to be corrected by the correction unit. When the saturation of the signal color is a color indicating the hue of the signal color and is lower than the highest saturation among the saturations of the colors included in the color reproduction area that can be expressed in the output device. 6. The image processing apparatus according to claim 1, wherein the correction unit corrects the signal color. The image processing apparatus further includes a two-dimensional conversion unit that maps spatial coordinates of the signal color in the color space to plane coordinates on a plane perpendicular to the lightness axis,
The image processing apparatus according to claim 1, wherein the hue area determination unit determines a hue area including the signal color based on the plane coordinates of the signal color. A pseudo hue value calculating unit that converts a spatial coordinate of the signal color in a color space into a pseudo hue value that monotonically increases along a circumferential direction around the lightness axis;
7. The image processing apparatus according to claim 1, wherein the hue area determination unit determines the hue area including the signal color based on the pseudo hue value. 8. The image processing apparatus according to claim 8, wherein the pseudo hue value is a rotation angle about the lightness axis. An image processing method for correcting a color represented by a color image signal to a color suitable for an output device to output the color image signal,
A hue region determination step of determining a hue region including a signal color represented by the color image signal, among a plurality of hue regions formed with a surface provided in parallel with a lightness axis in a color space,
A correcting step of correcting the signal color according to the hue region. 11. The image processing method according to claim 10, wherein the correcting step corrects the lightness of the signal color. When the signal color is not included in the color reproduction area that can be expressed in the output device, the correction step includes the minimum correction amount for correcting the signal color to a color in the color reproduction area. The image processing method according to claim 10, wherein the signal color is corrected. When the hue area is determined by the hue area determination step, the correction step associates the information on the correction amount to be corrected by the correction step with the hue area in a correction amount table that associates the information with each hue area. The image processing method according to any one of claims 10 to 12, wherein the signal color is corrected based on the information on the correction amount. 14. The image processing method according to claim 10, further comprising a correction amount adjusting step of adjusting the correction amount to be corrected in the correction step. When the saturation of the signal color is a color indicating the hue of the signal color and is lower than the highest saturation among the saturations of the colors included in the color reproduction area that can be expressed in the output device. 15. The image processing method according to claim 10, wherein the correcting step corrects the signal color. Further comprising a two-dimensional conversion step of mapping the spatial coordinates of the signal color in the color space to plane coordinates on a plane perpendicular to the lightness axis,
16. The image processing method according to claim 10, wherein the hue region determining step determines a hue region including the signal color based on the plane coordinates of the signal color. A pseudo hue value calculating step of converting a spatial coordinate in the color space of the signal color into a pseudo hue value that monotonically increases along a circumferential direction around the lightness axis,
16. The image processing method according to claim 10, wherein the hue region determination step determines the hue region including the signal color based on the pseudo hue value. 18. The image processing method according to claim 17, wherein the pseudo hue value is a rotation angle about the lightness axis. A program for causing a computer to execute the method according to claim 10.

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