JP4205839B2 - Color conversion method and color conversion apparatus - Google Patents

Description

【００６４】
ここで、例えばＲ_SRGBを８ビットで表現したものをＲ_8bitで表記すると、
Ｒ_8bit＝２５５×１２．９２Ｒ_SRGB （０＜Ｒ_SRGB＜０．００３０４）
Ｒ_8bit＝２５５×１．０５５Ｒ_SRGB ^(1.0/2.4) −０．０５５
（０．００３０４≦Ｒ_SRGB≦１）
となる。Ｇ_SRGB，Ｂ_SRGBを８ビットで表現したＧ_8bit，Ｂ_8bitも同様に、それぞれＧ_SRGB，Ｂ_SRGBから変換することができる。
【００６５】
もしくは、リバーサルフィルムのｃｍｙ濃度で定義される色空間を共通色空間として採用してもよい。これにより共通色空間における色再現範囲が明確に定義される。
【００６６】
ここで共通色空間における色変換テーブルは、例えば３次元の参照テーブル（ＬＵＴ；Ｌｏｏｋ Ｕｐ Ｔａｂｌｅ）で記述されており，その色変換テーブルによる色変換特性は以下の様にして求められる。尚、以下では、共通色空間として、その共通色空間の一例であるＬ^*ａ^*ｂ^*色空間を取り上げて説明する。Ｌ^*ａ^*ｂ^*色空間以外の共通色空間を採用したときも、その採用した共通色空間をＬ^*ａ^*ｂ^*色空間に変換したときに以下の説明がそのまま成立する。
【００６７】
まず共通色空間のＣ，Ｍ，Ｙの領域内に各基本色（Ｌ_c，ａ_c，ｂ_c）、（Ｌ_m，ａ_m，ｂ_m）、（Ｌ_y，ａ_y，ｂ_y）を定める。
【００６８】
ここでは、これらの基本色はそれぞれ赤、緑、青領域に主たる吸収が存在する色材に相当する色が望ましく、基本色の座標を様々に変化させてテストした結果、以下の色範囲で顕著な効果が確認された。
【００６９】

すなわち、Ｃ，Ｍ，Ｙの各基本色は、これらの各色領域内の各一点として定義される。
【００７０】
ここで、入力の色（Ｌ_i，ａ_i，ｂ_i）に対し以下の様に修正を施す。
【００７１】
Ｌ’＝Ｌ_i＋ΔＬ
ａ’＝ａ_i＋Δａ
ｂ’＝ｂ_i＋Δｂ ……（２）
ここで、（ΔＬ，Δａ，Δｂ）は色補正ベクトルであり、更に以下の式で求められる。
【００７２】
ΔＬ＝ｇ_cｃ_cΔＬ_c＋ｇ_mｃ_mΔＬ_m＋ｇ_yｃ_yΔＬ_y
Δａ＝ｇ_cｃ_cΔａ_c＋ｇ_mｃ_mΔａ_m＋ｇ_yｃ_yΔａ_y
Δｂ＝ｇ_cｃ_cΔｂ_c＋ｇ_mｃ_mΔｂ_m＋ｇ_yｃ_yΔｂ_y ……（３）
上式で（ΔＬ_c，Δａ_c，Δｂ_c）、（ΔＬ_m，Δａ_m，Δｂ_m）、（ΔＬ_y，Δａ_y，Δｂ_y）は、以下で定義される基準白色を始点とし、それぞれ、Ｃ基本色、Ｍ基本色、Ｙ基本色の色座標点を終点とする色ベクトル（基本色ベクトルと称する）である。ここで基準白色（Ｌ_w，ａ_w，ｂ_w）は、
８０＜Ｌ_w≦１００，｜ａ_w｜＜１０，｜ｂ_w｜＜１０
で定義される。
【００７３】
図８は、Ｌ^*ａ^*ｂ^*色空間における、Ｌ^*ａ^*平面に投影した基本色ベクトルを示す図、図９は、Ｌ^*ａ^*ｂ^*色空間におけるａ^*ｂ^*平面に投影した基本色ベクトルを示す図である。
【００７４】
また、（３）式におけるｃ_c，ｃ_m，ｃ_yは、それぞれ、Ｃ基本色ベクトルの方向、Ｍ基本色ベクトルの方向、Ｙ基本色ベクトルの方向に対する各補正係数であり、入力色の色相に応じてそれぞれ次のように設定される。
【００７５】
Ｈ_i＝ｔａｎ^-1（ｂ_i／ａ_i）を入力色（Ｌ_i，ａ_i，ｂ_i）の色相角、Ｈ_c＝ｔａｎ^-1（ｂ_c／ａ_c）、Ｈ_m＝ｔａｎ（ｂ_m／ａ_m）、Ｈ_y＝ｔａｎ（ｂ_y／ａ_y）をそれぞれＣ基本色（Ｌ_c，ａ_c，ｂ_c）、Ｍ基本色（Ｌ_m，ａ_m，ｂ_m）、Ｙ基本色（Ｌ_y，ａ_y，ｂ_y）の各色相角としたとき、
ｃ_c＜０（但し、Ｈ＞Ｈ_c＋９０°、およびＨ＜Ｈ_c−９０°）
ｃ_c≧０（但し、Ｈ_c−９０°≦Ｈ_i≦Ｈ_c＋９０°）
ｃ_m＜０（但し、Ｈ＞Ｈ_m＋９０°、およびＨ＜Ｈ_m−９０°）
ｃ_m≧０（但し、Ｈ_m−９０°≦Ｈ_i≦Ｈ_m＋９０°）
ｃ_y＜０（但し、Ｈ＞Ｈ_y＋９０°、およびＨ＜Ｈ_y−９０°）
ｃ_y≧０（但し、Ｈ_y−９０°≦Ｈ_i≦Ｈ_y＋９０°）
図１０は、補正係数の概念図である。この図には、各補正係数ｃ_c，ｃ_m，ｃ_yを代表させて補正係数ｃ_cが示されている。
【００７６】
上記（６）式および図１０の実線に示すように、補正係数ｃ_cは、Ｈ＞Ｈ_c＋９０°の領域およびＨ＜Ｈ_c−９０°の領域ではｃ_c＜０、Ｈ_c−９０°≦Ｈ_i≦Ｈ_c＋９０°の領域ではｃ_c＞０の関数である。但し、図１０に破線で示すように、Ｈ_c−９０°≦Ｈ_i≦Ｈ_c＋９０°の領域では、ｃ_c＝０であってもよい。
【００７７】
図８，図９に座標を示す入力色の位相角Ｈ_iはＣ基本色ベクトルの位相角Ｈ_cとの関係では、
Ｈ_c−９０°≦Ｈ_i≦Ｈ_c＋９０°
を満足している。ここではこの領域ではｃ_c＝０が採用されており、したがってＣ基本色ベクトルの方向の色補正は行なわれない。図８，図９にはＣ基本色ベクトルの方向の色補正ベクトルは示されておらず、これはＣ基本色ベクトルの方向には入力色の色補正を行なわない（静止したままである）ことを意味している。
【００７８】
また、図８，図９に座標を示す入力色の位相角Ｈ_iは、Ｍ基本色ベクトルの位相角Ｈ_mおよびＹ基本色ベクトルの位相角Ｈ_yの関係では、いずれも、
Ｈ_m−９０°≦Ｈ_i≦Ｈ_m＋９０°
Ｈ_y−９０°≦Ｈ_i≦Ｈ_y＋９０°
の領域から外れており、したがってＭ基本色ベクトルの方向、およびＹ基本ベクトルの方向に関する各補正係数ｃ_m，ｃ_yは、いずれもｃ_m＜０，ｃ_y＜０であり、入力色の座標が、Ｍ基本色ベクトルの方向、Ｙ基本色ベクトルの方向とはそれぞれ反対側の方向に移動される。
【００７９】
尚、ここでは、Ｈ_c−９０°≦Ｈ_i≦Ｈ_c＋９０°のときはｃ_c＝０であってＣ基本色ベクトルの方向には入力座標の移動を行なわない（その方向には静止させたままとする）旨説明したが、Ｈ_c−９０°≦Ｈ_i≦Ｈ_c＋９０°の場合にｃ_c＞０とし、そのＣ基本色ベクトルの方向と同方向に積極的に移動（補正）してもよい。ｃ_m，ｃ_yについても同様である。本発明者による多くの実験結果によれば基本色に対し位相角で±９０°の内側にあるときはその基本色に関しては入力色の座標移動は必ずしも行なわなくても本発明で狙っている効果を得ることができるが、±９０°の内側にある場合であっても入力色の座標をその基本色ベクトルの方向と同じ方向に移動することにより、より強い効果を得ることができることが多くの例で確認されている。
【００８０】
ここでは、理解の容易のため、（３）式に含まれている各ゲイン係数ｇ_c，ｇ_m，ｇ_yは無視して説明したが、（３）式の各ゲイン係数ｇ_c，ｇ_m，ｇ_yは、各補正係数ｃ_c，ｃ_m，ｃ_yをどの程度強調するか、すなわち、Ｃ，Ｍ，Ｙの各基本色ベクトルの方向にどの程度強く補正するかを決める、０≦ｇ_c，ｇ_m，ｇ_y≦１であって、かつ入力色に依存して変化する係数である。各ゲイン係数ｇ_c，ｇ_m，ｇ_yは、例えば以下のように定義することが好ましい。
【００８１】
ｇ_c＝ｇ_coｒｃｏｓθ
ｇ_m＝ｇ_moｒｃｏｓθ
ｇ_y＝ｇ_yoｒｃｏｓθ ……（５）
ここで、ｒは、基準白点から入力色の座標点までを結んだ入力色ベクトルの絶対値であり、θは、その入力色ベクトルとＣＭＹ３つの基本色ベクトルそれぞれとの成す角度のうちの最小の角度である。またｇ_co，ｇ_mo，ｇ_yoは各基本色ごとの定数である。ここで、最小の角度θはＣ，Ｍ，Ｙの各基本色によらず各ゲイン係数ｇ_c，ｇ_m，ｇ_yについて共通であり、したがって、ｃｏｓθは、いずれかの基本色ベクトルに近いほど大きな値をとり（これはゲインを上げることを意味する）、いずれの基本色ベクトルからも離れている場合、例えばグレーに近い色の場合には小さな値となる（これはゲインを下げることを意味する）。また、ｒは、上述のように基本白色から入力色の座標点までを結ぶ入力色ベクトルの絶対値であり、その絶対値が小さいほど、すなわち白色に近い（色が薄い）いほどゲインを下げ、その入力色ベクトルの絶対値が大きいほど、すなわち色が濃いほどゲインを上げることを意味する。
【００８２】
ここでは、上述の入力色変換アルゴリズムに基づいて入力色の濃度と出力色の座標との対応関係があらかじめ定められて、色変換テーブルが作成され、実際の色変換にあたってはその色変換テーブルが参照されて、画像データを構成する各入力色データが各出力色データに変換される。
【００８３】
つぎにこの色変換テーブルを使って実際に色変換を行なった結果について説明する。
【００８４】
ここでは、ＣＭＹの各基本色をＣ（５４，−３７，−４９）、Ｍ（４４，７１，−８）、Ｙ（８５，−８，８８）にとり、基準白点を（９２，−１，−２）とした。また、入力色として、カラー画像の中から以下の赤色、黄色、紫、緑のサンプル点を抽出し、その色に対する色変換テーブルの応答を調べた。入力色のＬ^*ａ^*ｂ値を表１に示す。
【００８５】
【表１】

【００８６】
表１に示す入力色に対する色変換テーブルの応答、すなわち出力色は表２のようになっていた。
【００８７】
【表２】

【００８８】
表１，表２からわかるように、例えば赤色（表１，表２の最上段）に関しては、Ｃ基本色ベクトル（−３６，−３６，−４７）の方向とは逆の方向に移動し、かつＭ基本色ベクトル（−４８，７２，−６）の方向と同じ方向に移動している。また緑色（表１，表２の最下段）に関してはＭ基本色ベクトルの方向とは逆の方向に大きく移動している。
【００８９】
この色変換テーブルによる色変換処理を通した後の画像データと、この色変換テーブルによる色変換処理を通さない画像データとのそれぞれをＣＭＹＫの網点データへ変換し、実際にオフセットカラー印刷を行なった。上記の色変換テーブルによる色変換処理を行なった場合は表１と表２との比較から分かるように色相の忠実性は保たれていないが、非常に鮮やかで色濁りの少ないプリントとなっており、印刷物としてははるかに好ましい色再現が得られていた。
【００９０】
更に、色変換テーブルを通した画像データと色変換テーブルを通さなかった画像データとの両者について変換後の網点データを調べてみた。その結果は表３のようになっていた。
【００９１】
【表３】

【００９２】
この表３において、Ｃ，Ｍ，Ｙ，Ｋは色変換テーブルを通さなかったときの網点データ、Ｃ’，Ｍ’，Ｙ’，Ｋ’は色変換テーブルを通したときの網点データである。
【００９３】
この表３において、例えば赤に関しては、Ｃ＝４５に対し、Ｃ’＝３７となっており、緑に関してはＭ＝５６に対しＭ’＝３０となっている。このように、上述の色変換テーブルにより、インク網点量において反対色、つまり濁り色となる成分を減らす効果が得られており、その結果として、先に述べたような鮮やかなプリントが得られたものと考えられる。
【００９４】
また、上述の色変換テーブルを通した場合と通さなかった場合を、別の印刷プロセス（ケミカルプルーフや昇華型プリンタ、インクジェットプリンタ、電子写真方式のプリンタ）でも行なってみた結果、いずれの印刷プロセスの場合も、上述の色変換テーブルを通した場合の方が、濁りの少ない鮮やかなプリントが得られた。
【００９５】
ここで、上述のアルゴリズムにより作成された色変換テーブルを用いた色変換処理と、従来から知られている色変換処理との比較結果を説明する。
【００９６】
ここでは、上記の色変換テーブルを用いた色変換処理従来良く知られている共通色空間での処理である色相を保存して彩度を上げる彩度強調処理も行ない、そそれらの結果を比較した。彩度強調処理を行なった結果、赤色は（３５，５０，３７）へと変換された。この変換では色相は保存され彩度も増加した。しかしながら、上記と同じ印刷プロセスで印刷を行ないプリントを見たところ、期待された結果とは異なり、鮮やかな色は得られなかった。インク網点量を確認したところ（４、９６、９２、４０）となっておりＫが多く入れられている事がわかった。さらにこれを改善すべくＫインクを使う工程を省いた印刷を行なったが、その結果、赤色の彩度は向上したものの色相がずれ、全体の調子再現やカラーバランスが大きく崩れ、品質の悪いプリントとなった。
【００９７】
次に、図７に示す色変換テーブルの、もう１つの作成方法について説明する。
【００９８】
図１１は、その色変換テーブルのもう１つの作成方法の説明図である。
【００９９】
先ず、共通色空間、例えばＬ^*ａ^*ｂ^*色空間の色データを上記のＣＭＹ３色の基本色に対する割合で表現される色データＣＭＹに変換する。
【０１００】
そのＣＭＹから以下の式で定義される関係にある変換後の色データＣ’Ｍ’Ｙ’を得る。
【０１０１】
Ｃ＝ Ｃ’＋ｍ_r／ｍ_gＭ’＋ｙ_r／ｙ_bＹ’
Ｍ＝ｃ_g／ｃ_rＣ’＋ Ｍ’＋ｙ_g／ｙ_bＹ’
Ｙ＝ｃ_b／ｃ_rＣ’＋ｍ_b／ｍ_gＭ’＋ Ｙ’ ……（６）
ここで、ｃ_r，ｃ_g，ｃ_b，ｍ_r，ｍ_g，ｍ_b，ｙ_r，ｙ_g，ｙ_bは、それぞれ、シアン（Ｃ）色材の赤（Ｒ）領域の光吸収率、シアン（Ｃ）色材の緑（Ｇ）領域の光吸収率、シアン（Ｃ）色材の青（Ｂ）領域の光吸収率、マゼンタ（Ｍ）色材の赤（Ｒ）領域の光吸収率、マゼンタ（Ｍ）色材の緑（Ｇ）領域の光吸収率、マゼンタ（Ｍ）色材の青（Ｂ）領域の光吸収率、イエロー（Ｙ）色材の赤（Ｒ）領域の光吸収率、イエロー（Ｙ）色材の緑（Ｇ）領域の光吸収率、イエロー（Ｙ）色材の青（Ｂ）領域の光吸収率である。
【０１０２】
上記の（６）式により得られたＣ’Ｍ’Ｙ’を、再び共通色空間、例えばＬ^*ａ^*ｂ^*色空間の色データに変換する。
【０１０３】
以上の経路を経る前の共通色空間（Ｌ^*ａ^*ｂ^*色空間）の色データと、以上の経路を経た後の共通色空間（Ｌ^*ａ^*ｂ^*色空間）の色データを対応づけることにより色変換テーブルを作成する。
【０１０４】
以上のアルゴリズムにより作成された色変換テーブルは、作成された結果としての色変換テーブルどうしを比較したとき、図８〜図１０を参照して説明した方法により作成された色変換テーブルと同様な色変換テーブルとなる。
【０１０５】
図１２は、本発明の色変換装置の一実施形態の機能ブロック図である。
【０１０６】
この図１２に示す色変換装置は、図２，図３に示すパーソナルコンピュータ２０と、そのパーソナルコンピュータで実行されるプログラムとの結合により実現される。
【０１０７】
この図１２に示す色変換装置は、データ取得部３１０と、データ変換部３２０と、データ出力部３３０と、定義記憶部３４０と、指定部３５０とから構成されている。
【０１０８】
定義記憶部３４０には、複数種類の入力デバイスそれぞれに対応した複数種類の入力プロファイル３４１ａ，３４１ｂ，…，３４１ｎと、色変換テーブル３４２と、複数種類の出力デバイスそれぞれに対応した複数種類の出力プロファイル３４３ａ，３４３ｂ，…，３４３ｍが記憶されている。
【０１０９】
入力プロファイル３４１ａ，３４１ｂ，…，３４１ｎのそれぞれは、各種の入力デバイスについて、基本的には図４を参照した作成方法により作成されたものである。尚、図１には、入力デバイスはカラースキャナ１０の一種類のみ示されているが、図１２の色変換装置には、汎用性を持たせるため、複数種類の入力デバイスそれぞれに対応する複数種類の入力プロファイルが用意されている。
【０１１０】
図１２に示す色変換装置の定義記憶部３４０に記憶された色変換テーブル３４２は、図７を参照して説明した、共通色空間（本実施形態ではＬ^*ａ^*ｂ^*色空間）における、本発明に特有の色変換を行なうための色変換テーブルである。この色変換テーブルは、例えば図８〜図１０を参照しながら説明した作成方法により、あるいは、図１１を参照しながら説明した作成方法により作成されたものである。
【０１１１】
また、定義記憶部３４０に記憶された出力プロファイル３４３ａ，３４３ｂ，…，３４３ｍは、各種の出力デバイスについて、基本的には図５を参照して説明した作成方法により作成されるものである。
【０１１２】
尚、入力プロファイルの場合と同様、図１には、出力デバイスとして一種類の印刷系３０のみ示されているが、図１２の色変換装置は、出力デバイスに関しても汎用性を持たせるため、複数種類の出力デバイスそれぞれに対応する複数種類の出力プロファイルが用意されている。
【０１１３】
なお、この定義記憶部３４０は、ハードウェア上は、図３に示すハードディスク装置２１３の内部に設定されており、この定義記憶部３４０（図３に示すハードディスク装置）は、本発明の色変換定義記憶媒体の一実施形態にも相当する。
【０１１４】
指定部３５０では、入力デバイスの指定、および出力デバイスの指定が行なわれる。この指定部３５０は、ハードウェア上は、図２，図３に示すキーボード２３あるいはマウス２４がその役割りを担っている。
【０１１５】
指定部３５０で入力デバイス、出力デバイスが指定されると、定義記憶部３４０に記憶された複数の入力プロファイルのうちの指定された入力デバイスに対応する入力プロファイル（ここでは入力プロファイル３４１ａとする）が読み出されてデータ変換部３２０に入力されるとともに、定義記憶部３４０に記憶された複数の出力プロファイル３４３ａ，３４３ｂ，…，３４３ｍのうちの指定された出力デバイスに対応する出力プロファイル（ここでは出力プロファイル３４３ａとする）が読み出されてデータ変換部３２０に入力される。さらに、定義変換部３４０からは色変換テーブル３４２も読み出されてデータ変換部３２０に入力される。
【０１１６】
データ変換部３２０では、それら入力プロファイル３４１ａ，色変換テーブル３４２、出力プロファイル３４２ａが入力されると、それらを合体して１つの色変換用のＬＵＴ（ルックアップテーブル）が作成される。
【０１１７】
データ取得部３１０は、入力デバイスで得られた色データを受け取る役割りをなすものであり、ハードウェア上は、図３に示す入力インタフェース２１６がこれに相当する。
【０１１８】
また、データ出力部３３０は、データ変換部３２０で色変換された後の色データの出力を担うものであり、ハードウェア上は、図３に示す出力インタフェース２１７がこれに相当する。
【０１１９】
入力デバイス、例えば図１に示すカラースキャナ１０で得られた色データがデータ取得部３１０を経由してデータ変換部３２０に入力されると、データ変換部３２０では、入力プロファイル３４１ａ、色変換テーブル３４２、および出力プロファイル３４３ａの合体により作成された色変換用ＬＵＴによる色データの変換が行なわれる。この変換後の色データはデータ出力部３３０を経由して、出力デバイス、例えば図１に示す印刷系３０に向けて出力される。
【０１２０】
このデータ変換部３２０による色データの変換は、本発明に特有な色変換を行なう色変換テーブルが参照された変換であり、色相は必ずも保存されないものの、濁りの少ない鮮やかな、色品質の高い出力画像を得ることができる。
【０１２１】
ここで、図１２に示す色変換装置において、定義記憶部３４０に記憶された複数の出力プロファイル３４３ａ，３４３ｂ，…，３４３ｍのうちの１つとして、図２，図３に示す画像表示装置２２に対応する出力プロファイルを用意しておき、データ変換部３２０で変換された後の色データに基づく画像をその画像表示装置２２の表示画面２２ａ（図２参照）上に表示し、かつ、指定部３５０（キーボード２３やマウス２４）に色変換テーブル３４２を補正する機能を持たせ、表示画面上に表示された画像を見ながら、その画像がより好ましい色品質の画像となるように色変換テーブル３４２を補正できるように構成することが好ましい。
【０１２２】
図１３は、本発明の色変換装置のもう１つの実施形態の機能ブロック図である。この図１３に示す色変換装置において、図１２に示す色変換装置の各要素に対応する要素には、図１２に付した符号と同一の符号を付して示し、図１２に示す色変換装置との相違点についてのみ説明する。
【０１２３】
この図１３に示す色変換装置は、図１２に示す色変換装置の場合と同様、図２，図３に示すパーソナルコンピュータ２０と、そのパーソナルコンピュータで実行されるプログラムとの組合せにより実現される。
【０１２４】
この図１３に示す色変換装置の、図１２に示す色変換装置との主な相違点は、定義記憶部３４０の記憶内容にある。その定義記憶部３４０には、図１２に示す色変換装置の定義記憶部に記憶されたものと同様の複数種類の入力プロファイル３４１ａ，３４１ｂ，…，３４１ｎや複数種類の出力プロファイル３４３ａ，３４３ｂ，…，３４３ｍのほか、図１２に示す色変換装置の定義記憶部には色変換テーブルが一種類のみ記憶されていたことに代わり、複数種類の色変換テーブル３４２ａ，３４２ｂ，…，３４２ｐが記憶されている。これら複数種類の色変換テーブル３４２ａ，３４２ｂ，…，３４２ｐは、いずれも、図７を参照して説明した、共通色空間（本実施形態ではＬ^*ａ^*ｂ^*色空間）における、本発明に特有の色変換を行なうための色変換テーブルである。これらの色変換テーブル３４２ａ，３４２ｂ，…，３４２ｐは、いずれも、例えば図８〜図１０を参照しながら説明した作成方法により、あるいは図１１を参照しながら説明した作成方法により作成されたものであるが、例えば（３）式の各補正係数Ｃ_e，Ｃ_m，Ｃ_yや（５）式の各定数ｇ_co，ｇ_mo，ｇ_yoが異なるなど、相互に異なる色変換テーブルである。
【０１２５】
また、図１３に示す色変換装置の定義記憶部３４０に記憶された複数種類の入力プロファイル３４１ａ，３４１ｂ，…，３４１ｎのそれぞれ、および複数種類の出力プロファイル３４３ａ，３４３ｂ，…，３４３ｍのそれぞれには定義指定情報が添付されている。これらの定義指定情報は、定義記憶部３４０に記憶された複数種類の色変換テーブル３４３ａ，３４２ｂ，…，３４２ｐの中からその入力プロファイルあるいは出力プロファイルに最も適合した色変換テーブルを指定するための情報である。
【０１２６】
指定部３５０で入力デバイス、出力デバイスが指定されると、定義記憶部３４０に記憶された複数の入力プロファイルのうちの、指定された入力デバイスに対応する入力プロファイル（例えば入力プロファイル３４１ａ）が読み出されてデータ変換部３２０に入力されるとともに、定義記憶部３４０に記憶された複数の出力プロファイルのうちの、指定された出力デバイスに対応する出力プロファイル（例えば出力プロファイル３４３ａ）が読み出されてデータ変換部３２０に入力され、さらに指定された入力デバイスに対応する入力プロファイルに添付されてた定義指定情報と指定された出力デバイスに対応する出力プロファイルに添付された定義指定情報により指定された色変換テーブル（例えば色変換テーブル３４２ａ）が読み出されてデータ変換部３２０に入力される。
【０１２７】
ここで、指定部３５０により指定された入力デバイスに対応する入力プロファイルに添付されていた定義指定情報と指定部３５０により指定された出力デバイスに対応する出力プロファイルに添付されていた定義指定情報との双方は、いずれも同一の色変換テーブルを指定する定義指定情報であることが原則であるが、それら双方の定義指定情報により指定される色変換テーブルが相互に異なるときは、本実施形態では、入力プロファイルに添付されていた定義指定情報の方が優先されるとともに、オペレータに向けて、双方の定義指定情報により指定される色変換テーブルが相互に異なるものであった旨警告が出される。
【０１２８】
上記のようにして定義指定情報により指定された色変換テーブルは、デフォルトとして指定されたものであり、特に必要があるときは、オペレータによる指定部３５０からの操作により、別の色変換テーブルを指定し直すことができる。
【０１２９】
上記のようにして、入力デバイスや出力デバイスを指定したときにデフォルトとしての色変換テーブルを指定することにより、デバイスの指定の度に色変換テーブルを指定し直す必要から解放され、使い勝手の良い装置が構成される。
【０１３０】
尚、図１３に示すブロック図では、入力プロファイルと出力プロファイルとの全てに定義指定情報が添付されているが、入力プロファイルにのみ、あるいは出力プロファイルにのみ定義指定情報を添付してもよい。あるいは入力プロファイルや出力プロファイルの一部にのみ定義指定情報を添付し、定義指定情報が添付された入力プロファイルあるいは出力プロファイルが指定されたときにのみ、そこに添付された定義指定情報に基づいて色変換テーブルを自動指定するようにしてもよい。
【０１３１】
図１４は、本発明の色変換方法の一実施形態のフローチャートである。
【０１３２】
ここでは、先ず、ステップ（ａ）のデータ取得過程において、例えば図１のカラースキャナ１０を用いてそのカラースキャナ１０（入力デバイス）に依存した入力デバイス色空間内の座標値で定義される入力色データを取得する。
【０１３３】
次に、ステップ（ｂ）のデータ変換過程において、本発明に特有のデータ変換が行なわれる。
【０１３４】
ここでは、これまでにも説明してきた、入力プロファイルと、色変換テーブルと、出力プロファイルとを用いて、ステップ（ａ）のデータ取得過程で得られた入力色データが、画像を出力する出力デバイスに依存した出力デバイス色空間内の座標値で定義される出力色データに変換される。このデータ変換過程では、入力プロファイル、色変換テーブル、および出力プロファイルを順次作用させてデータ変換を行なってもよいが、好ましくは、それら入力プロファイル、色変換テーブル、出力プロファイルを合体させて１つの色変換定義を作成し、その合体させた１つの色変換定義を用いてデータ変換を行なうことが、データ変換処理の高速化のために好ましい。
【０１３５】
ここで、ステップ（ｂ）のデータ変換過程で採用される入力プロファイルは、本発明にいう第１の色変換定義の一例であって、ステップ（ａ）のデータ取得過程での画像データの取得に用いた入力デバイス（例えば図１のカラースキャナ１０）に依存した入力デバイス色空間内の座標値と、入力デバイスにも出力デバイスにも非依存の共通色空間（本実施形態ではＬ^*ａ^*ｂ^*色空間）の座標値との対応を定義したものである。また、色変換テーブルは、本発明にいう第２の色変換定義の一例であって、図７を参照して説明した、共通色空間（本実施形態ではＬ^*ａ^*ｂ^*色空間）における、本発明に特有の色変換を行なうためのものである。この色変換テーブルは、例えば図８〜図１０を参照しながら説明した作成方法により作成され、あるいは図１１を参照して説明した作成方法により作成されたものである。また、ステップ（ｂ）のデータ変換過程で採用される出力プロファイルは、本発明にいう第３の色変換定義の一例であって、共通色空間（本実施形態ではＬ^*ａ^*ｂ^*色空間）内の座標値と、画像を出力しようとしている出力デバイスに依存した、出力デバイス色空間内の座標値との対応を定義したものである。
【０１３６】
図１５は、本発明の色変換定義記憶媒体のもう１つの実施形態を示す図である。
【０１３７】
図１２を参照して、図１２の色変換装置の定義記憶部３４０が本発明の色変換定義記憶媒体の一実施形態に相当する旨説明したが、この図１５には、本発明の色変換定義記憶媒体のもう１つの例として、ＣＤ−ＲＯＭ１１０に色変換テーブル３４２が記憶された例が示されている。
【０１３８】
前述したように、この色変換テーブル３４２は共通色空間で色変換を行なうためのものであり、入力プロファイルや出力プロファイルとは独立に、好ましい色変換を行なう色変換テーブル３４２のみを、例えばＣＤ−ＲＯＭ１１０等の可搬型記憶媒体に記憶させて流通させることも可能である。
【０１３９】
このような色変換テーブルを入手したユーザは、例えば図１２に示すような機能を持つ自分の色変換装置にその入手した色変換テーブルをアップロードし、その色変換テーブルを使ってより鮮やかな色品質の高い色変換を行なうことができる。
【０１４０】
【発明の効果】
以上、説明したように、本発明によれば多様な入力・出力デバイスの組合せにおいても色品質の高いカラー画像を得るための色変換を行なうことができる。
【図面の簡単な説明】
【図１】本発明の一実施形態が適用された画像入力−色変換−画像出力システムの全体構成図である。
【図２】図１に１つのブロックで示すパーソナルコンピュータの外観斜視図である。
【図３】パーソナルコンピュータのハードウェア構成図である。
【図４】色変換定義の１つをなす入力プロファイルの概念図である。
【図５】もう１つの色変換定義である出力プロファイルの概念図である。
【図６】入力プロファイルと出力プロファイルとの双方からなる色変換定義を示す概念図である。
【図７】図１〜図３に示すパーソナルコンピュータの内部で実行される、本実施形態に特徴的な色変換処理を示す概念図である。
【図８】Ｌ^*ａ^*ｂ^*色空間における、Ｌ^*ａ^*平面に投影した基本色ベクトルを示す図である。
【図９】Ｌ^*ａ^*ｂ^*色空間におけるａ^*ｂ^*平面に投影した基本色ベクトルを示す図である。
【図１０】補正係数の概念図である。
【図１１】色変換テーブルのもう１つの作成方法の説明図である。
【図１２】本発明の色変換装置の一実施形態の機能ブロック図である。
【図１３】本発明の色変換装置のもう１つの実施形態の機能ブロック図である。
【図１４】本発明の色変換方法の一実施形態を示すフローチャートである。
【図１５】本発明の色変換定義記憶媒体の実施形態を示す図である。
【符号の説明】
１０ カラースキャナ
１１ 原稿画像
２０ パーソナルコンピュータ
２１ 本体装置
２２ 画像表示装置
２２ａ 表示画面
２３ キーボード
２４ マウス
２５ バス
３０ 印刷系
１００ フロッピィディスク
１１０ ＣＤ−ＲＯＭ
２１１ ＣＰＵ
２１２ 主メモリ
２１３ ハードディスク装置
２１４ ＦＤドライバ
２１５ ＣＤ−ＲＯＭドライバ
２１６ 入力インタフェース
２１７ 出力インタフェース
３１０ データ取得部
３２０ データ変換部
３３０ データ出力部
３４０ 定義記憶部
３４１ａ，３４１ｂ，…，３４１ｎ 入力プロファイル
３４２，３４２ａ，３４２ｂ，…，３４２ｐ 色変換テーブル
３４３ａ，３４３ｂ，…，３４３ｍ 出力プロファイル
３５０ 指定部[0001]
BACKGROUND OF THE INVENTION
The present invention outputs an image based on image data obtained by an input device that inputs an image and obtains image data (including not only print output but also output forms such as display and printing). The present invention relates to a color conversion method and a color conversion device that perform color conversion so that a suitable color tone can be obtained when an image is output, and a color conversion definition storage medium that stores a color conversion definition that provides a suitable color tone.
[0002]
[Prior art]
In order to obtain a favorable finish in a system that takes a manuscript with reversal film or DSC (digital still camera) and corrects the color tone and then creates reflection print output data such as printing or photography, the skill of an expert is required. is necessary. In addition to being familiar with the correspondence between digital data and the finish, this skill includes “what color tone should be finished” or “how can an image with the desired impression be obtained?” "Knowing" is included.
[0003]
Conventionally, in a plate-making color separation scanner, a skilled operator has the characteristics of a scanning scanner system and an output system (halftone recorder / press plate / printing), and an adjustment dial operation amount and data of a built-in color processing system. A desired finished color tone is obtained after fully knowing the correspondence with the movement of the image and the resulting change in the finished color. In the general usage of such plate making scanners, the color processing system adjustment parameter (this parameter is used so that the expert of the supplier or the expert of the purchase side can obtain the optimum color conversion for the application at the time of introduction. Preset values (basic conditions) of tens to hundreds are created. After several weeks of adjustment work, several sets of preset values are created that are divided by work content. In actual color separation work, fine adjustment for each original is performed based on the preset value, and print data for obtaining a desired finish is created.
[0004]
On the input side, data handled by the plate making scanner is handled as CMY density data obtained by converting the RGB values of the reading sensor into reading density, or equivalent neutral CMY density data in which gray balance is adjusted. This CMY density data is subjected to gray range setting (highlight, shadow balance), gray tone conversion, color correction (color correction), UCR and K plate generation, and then the density value is converted to halftone dot%. This is output data. All these set values are related to the reproduction color, and it is not possible to optimize a single parameter. Color correction has the most parameters. In a typical example, a function for extracting a pseudo lightness signal, a saturation signal, and a hue signal from a CMY signal and determining a correction coefficient corresponding to CMYK according to each signal intensity is defined. The color correction is further divided into a main color collection and a selective color correction according to the hue range to be influenced. The main color collection covers the hue range of 180 degrees as the necessary colors CMY from the meaning that each of the CMY three primary colors forming the color is necessary or unnecessary, that is, the vividness and turbidity of the colors are controlled independently. Covers a hue range of 180 degrees centering on each of RGB. In the selective color correction, functions for six hues are prepared so as to be effective in a hue range of about 120 degrees from the meaning of controlling the same system color. Since the brightness, hue, and saturation signals are formed from the CMY signals input to the color correction unit, the color correction characteristics change if the tone conversion at the previous stage of the color correction unit changes. In addition, the amount of correction affects each other between the two main and selective collections, and also between the hue channels in the main, so the work of creating this condition set requires skill. However, by optimally adjusting these, the color range that can be expressed by the print color material is effectively used to give a three-dimensional effect and depth, and to express vividness and clearness. This is the reason why such work is called “picture making”.
[0005]
On the other hand, in a system composed of a personal computer and an input / output terminal device, any combination of input / output devices is possible, but the color expressed by each control color signal (RGB, CMYK) depends on the device. To do. On the other hand, in US Pat. No. 4,500,909, a desired image expression is created while interactively correcting colors while displayed on a CRT monitor, and converted to an output signal so that the “look” is the same as that signal. A scheme was proposed. Furthermore, I / O display device signals are converted to human visual characteristics (CIEXYZ and CIE L^*a^*b^*A method for obtaining the same color reproduction in any input / output device by expressing it in a common color space (CCS) (device profile) associated with the same color space is proposed. This conversion is now supported at the OS level and has become established as a color management system. Here, the device data is converted into a color representation in the common color space (CCS) based on the reproduced color, and the color representation in the common color space (CCS) is converted into another device data. In both conversions, there are various mapping methods to the color range (Gamut) that the device can reproduce, such as mapping that accurately represents colors, mapping that emphasizes tone reproduction, and mapping that maintains saturation. A technique is possible. Since the common color space corresponds to the CIE color system, color matching between different devices is basically supported, and adjustments corresponding to human vision such as brightness enhancement and saturation enhancement are easy.
[0006]
Furthermore, a method for improving the consistency of appearance by absorbing the reproduction characteristic difference depending on the observation environment (US Pat. No. 5,754,184) and the result of aesthetic correction of the image in the common color space are stored as a three-dimensional table and applied to others. A method (US Pat. No. 5,583,665) has also been attempted. In such a method, the color is interactively controlled on the monitor, and if a desired image is obtained, a print color in an expected direction can be obtained. However, it effectively uses the color range that can be expressed by color materials such as those obtained by plate-making scanners, provides a sense of depth and depth, expresses vividness and clearness, and reproduces favorable colors with appropriate brightness and memory colors. It is very difficult to realize this method. The reason why it is difficult to implement this method is that it is difficult to achieve subtle control from the minimum to the maximum amount of color material necessary to obtain a preferable print finish with the LCH parameters. Further, the fact that the saturation range that can be reproduced by printing is not isotropic with respect to hue and lightness is also a factor that makes LCH and RGB processing unsuitable. For example, since both hue change and lightness change must be used together in a process for increasing saturation, the LCH process requires a three-dimensional simultaneous operation and is extremely difficult. Furthermore, in the processing system in the common color space, gamut conversion to actual device data is performed after processing, and at this time, compression processing is performed particularly in an area close to the color gamut boundary. Adjustment in this region is particularly effective for saturation and gradation reproduction. However, if color reproduction region compression processing is performed after color adjustment with LCH, the adjustment result is not accurately reflected in the print color.
[0007]
Thus, in the conventional color conversion system, it has been impossible to achieve both applicability (openness) and finished quality for various device combinations.
[0008]
[Problems to be solved by the invention]
In view of the above circumstances, the present invention provides a color conversion method and color conversion apparatus for performing color conversion capable of obtaining a color output image with good color quality even in various combinations of input and output devices, and various input and output An object of the present invention is to provide a color conversion definition storage medium that stores color conversion definitions that can be suitably used to obtain a color output image with good color quality even in a combination of devices.
[0009]
[Means for Solving the Problems]
The color conversion method of the present invention that achieves the above object provides:
A data acquisition process for acquiring input color data defined by coordinate values in an input device color space depending on an input device that inputs an image and obtains image data;
The input color data acquired by the data acquisition unit
A first color conversion definition defining a correspondence between coordinate values in the input device color space and coordinate values in a common color space independent of the input device and the output device;
An input coordinate value in at least a partial space of the common color space, and a reference white coordinate point defined in the white area of the common color space as a starting point, in the cyan color area of the common color space, Of the basic colors defined in the magenta color area and the yellow color area, the coordinate point of the basic color whose input coordinate value is outside the ± 90 ° hue angle with respect to the hue of the basic color is the end point. A second color conversion definition for converting to an output coordinate value moved in the direction opposite to the direction of the vector to be
Using the third color conversion definition that defines the correspondence between the coordinate values in the common color space and the coordinate values in the output device color space,
And a data conversion process for converting into output color data defined by coordinate values in an output device color space depending on an output device that outputs an image based on the image data.
[0010]
When the above second color conversion definition is adopted, the hue is not necessarily stored and may be converted into an output color having a hue different from the hue of the input color, but it is not always necessary to faithfully store the hue. According to the color conversion method of the present invention, it is possible to obtain output color data for generating a color output image with higher color quality than when the hue is faithfully stored.
[0011]
In addition, according to the present invention, the second color conversion definition described above performs color conversion in a common color space, and therefore can be commonly applied to various input / output devices.
[0012]
Here, in the color conversion method of the present invention, the common color space is L.^*a^*b^*If the color space, or L^*a^*b^*When converted to color space,
Of the above basic colors, the coordinate points (L) of the cyan basic color defined in the cyan area, the magenta basic color defined in the magenta area, and the yellow basic color defined in the yellow area, respectively._c, A_c, B_c), (L_m, A_m, B_m), (L_y, A_y, B_y)But,
40 <L_c<65, −25 <a_c<-55, -35 <b_c<-60
30 <L_m<60, 40 <a_m<90, −20 <b_m<20
70 <L_y<90, −20 <a_y<20, 50 <b_y<130
And the reference white coordinate point (L_w, A_w, B_w)But,
80 <L_w≦ 100, | a_w| <10, | b_w| <10
Is preferably satisfied.
[0013]
By defining the coordinate point of each basic color and the coordinate point of the basic white in each color region, the color quality can be sufficiently improved as compared with the case where the second color conversion definition is not adopted.
[0014]
In the color conversion method of the present invention, as the second color conversion definition, the input coordinate values in at least a partial space of the common color space are used, the reference white coordinate point is the starting point, and each basic color Of which the input coordinate value is converted to the output coordinate value that remains stationary in the direction of the vector whose end point is the coordinate point of the basic color existing within ± 90 ° in hue angle with respect to the hue of the basic color A conversion definition may be adopted, or, as the second color conversion definition, an input coordinate value in at least a partial space of the common color space, a reference white coordinate point as a starting point, and each basic color Of the colors, the input coordinate value is converted to the output coordinate value moved in the same direction as the direction of the vector with the coordinate point of the basic color existing within ± 90 ° in hue angle with respect to the hue of the basic color. A color conversion definition may be adopted.
[0015]
If the input coordinate value is within ± 90 ° in hue angle with respect to the hue of the basic color, it may not be corrected, or even in this case, it may be positively corrected. In this case, output color data that can generate a color output image with high color quality can be obtained.
[0016]
Furthermore, in the color conversion method of the present invention, the data conversion process includes one color obtained by combining the first color conversion definition, the second color conversion definition, and the third color conversion definition. It is preferable that the conversion definition is created and input color data is converted to output color data based on the one color conversion definition.
[0017]
Create a color conversion definition combined into one as described above, and convert the actual color data by converting the color data based on the color conversion definition combined into one Is possible.
[0018]
In the color conversion method of the present invention, the data conversion process includes a color conversion definition for adjusting the brightness range of the image in a common color space in addition to the first and second color conversion definitions. It is preferable that the color conversion is performed using them.
[0019]
In addition, the color conversion device of the present invention that achieves the above object provides:
A data acquisition unit that acquires input color data defined by coordinate values in an input device color space depending on an input device that inputs an image and obtains image data;
A data conversion unit that converts input color data acquired by the data acquisition unit into output color data defined by coordinate values in an output device color space depending on an output device that outputs an image based on the image data;
A data output unit for outputting the output color data after being converted by the data conversion unit,
The data converter is
A first color conversion definition defining a correspondence between coordinate values in the input device color space and coordinate values in a common color space independent of the input device and the output device;
An input coordinate value in at least a partial space of the common color space, and a reference white coordinate point defined in the white area of the common color space as a starting point, in the cyan color area of the common color space, Of the basic colors defined in the magenta color area and the yellow color area, the coordinate point of the basic color whose input coordinate value is outside the ± 90 ° hue angle with respect to the hue of the basic color is the end point. A second color conversion definition for converting to an output coordinate value moved in the direction opposite to the direction of the vector to be
Using the third color conversion definition that defines the correspondence between the coordinate values in the common color space and the coordinate values in the output device color space,
The input color data is converted into output color data.
[0020]
When the above second color conversion definition is adopted, the hue is not necessarily stored and may be converted into an output color having a hue different from the hue of the input color, but it is not always necessary to faithfully store the hue. However, according to the color conversion apparatus of the present invention, it is possible to obtain a color output image with higher color quality than when the hue is stored.
[0021]
In addition, according to the present invention, the second color conversion definition described above performs color conversion in a common color space, and therefore can be commonly applied to various input / output devices.
[0022]
Here, in the color conversion apparatus of the present invention, the common color space is L.^*a^*b^*If the color space, or L^*a^*b^*When converted to color space,
Of the above basic colors, the coordinate points (L) of the cyan basic color defined in the cyan area, the magenta basic color defined in the magenta area, and the yellow basic color defined in the yellow area, respectively._c, A_c, B_c), (L_m, A_m, B_m), (L_y, A_y, B_y)But,
40 <L_c<65, −25 <a_c<-55, -35 <b_c<-60
30 <L_m<60, 40 <a_m<90, −20 <b_m<20
70 <L_y<90, −20 <a_y<20, 50 <b_y<130
And the reference white coordinate point (L_w, A_w, B_w)But,
80 <L_w≦ 100, | a_w| <10, | b_w| <10
Is preferably satisfied.
[0023]
By defining the coordinate point of each basic color and the coordinate point of the basic white in each color area as described above, the color quality of the color output image can be sufficiently improved as compared with the case where the second color conversion definition is not adopted. It is done.
[0024]
Here, in the color conversion device of the present invention, the data conversion unit uses the input coordinate values in at least a partial space of the common color space as the second color conversion definition, as a reference white coordinate point. Of the basic color, and the input coordinate value remains stationary in the direction of the vector whose basic coordinate point is within ± 90 ° of the hue angle of the basic color. A color conversion definition for converting to an output coordinate value may be used. Alternatively, as the second color conversion definition, an input coordinate value in at least a partial space of the common color space may be used as a reference white coordinate point. The input coordinate value of each basic color is moved to the same direction as the direction of the vector with the coordinate point of the basic color existing within ± 90 ° in hue angle with respect to the hue of the basic color as the start point. You may use a color conversion definition that converts to output coordinate values
[0025]
If the input coordinate value is within ± 90 ° in hue angle with respect to the hue of the basic color, it may not be corrected, or even in this case, it may be positively corrected. In this case, a color output image with high color quality can be obtained.
[0026]
Furthermore, in the color conversion device according to the present invention, the data conversion unit combines one color of the first color conversion definition, the second color conversion definition, and the third color conversion definition. It is preferable to create a conversion definition and convert input color data to output color data based on the one color conversion definition.
[0027]
In actual data conversion, high-speed conversion is possible by converting color data based on the color conversion definition combined into one as described above.
[0028]
In the color conversion apparatus of the present invention, one or more types of first color conversion definitions corresponding to one or more types of input devices,
A plurality of types of second color conversion definitions;
Storing one or more types of second color conversion definitions corresponding to each of the one or more types of output devices;
It is preferable to provide a definition storage unit that stores definition designation information for designating one second color conversion definition from a plurality of types of second color conversion definitions corresponding to the input device and / or the output device.
[0029]
In this case, a designation unit for designating an input device and an output device is provided, and the data conversion unit selects the designation from the first, second, and third color conversion definitions stored in the definition storage unit. First, second and second selected one by one based on the input device and output device specified by the unit and the definition specifying information corresponding to the input device and / or output device specified by the specification unit Preferably, the input color data is converted to output color data using the color conversion definition of No. 3.
[0030]
A plurality of types are stored for the first, second, and third color conversion definitions, particularly the second color conversion definition, and further, definition designation information corresponding to the input device and / or the output device is stored. Thus, when an input device or an output device is specified, the second color conversion definition as a default is also specified. That is, by specifying the input device (first color conversion definition) and the output device (second color conversion definition), the second color conversion definition is also specified, and separately from the input device and output device specification, Furthermore, the troublesome and troublesome of specifying the second color conversion definition is saved.
[0031]
In the color conversion apparatus of the present invention, the data conversion unit further includes a color conversion definition for adjusting a brightness range in a common color space for each image in addition to the first to third color conversion definitions. It is preferable that color conversion is also performed using the above.
[0032]
The color conversion definition storage medium of the present invention also includes at least a part of a common color space independent of an input device that inputs an image and obtains image data and an output device that outputs an image based on the image data. The input coordinate value in the subspace is set to the reference white coordinate point defined in the white area of the common color space as the starting point, and in the cyan area, magenta area, and yellow area of the common color space. Out of the defined basic colors, the input coordinate value is moved in the direction opposite to the direction of the vector whose end point is the coordinate point of the basic color that exists outside the hue angle of ± 90 ° with respect to the hue of the basic color. A color conversion definition to be converted into coordinate values is stored.
[0033]
By converting color data using the color conversion definition (second color conversion definition referred to in the color conversion device of the present invention) stored in the color conversion definition storage medium of the present invention, a color output image with good color quality is obtained. Obtainable. In addition, since this conversion definition performs color conversion in a common color space, it is suitable for various input / output devices.
[0034]
Here, the color conversion definition storage medium of the present invention is an input device for obtaining image data by inputting an image in addition to the color conversion definition (second color conversion definition referred to in the color conversion apparatus of the present invention). Conversion definition (first color conversion definition referred to in the color conversion apparatus of the present invention) for converting coordinate values in the input device color space depending on the color to coordinate values in the common color space, and coordinate values in the common color space Is stored as a color conversion definition (third color conversion definition referred to in the color conversion apparatus of the present invention) for converting the image data into coordinate values in the output device color space depending on the output device that outputs the image based on the image data. It may be a thing.
[0035]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described.
[0036]
FIG. 1 is an overall configuration diagram of an image input-color conversion-image output system to which an embodiment of the present invention is applied.
[0037]
Here, a color scanner 10 is shown. The color scanner 10 reads an original image 11 and generates RGB three-color image data. The RGB image data is input to the personal computer 20. In this personal computer 20, the image data obtained by the color scanner 10 is converted into CMYK four-color image data for image output suitable for the printing system 30 described later. The image data for image output is further converted into halftone dot data representing the halftone dot area ratio of the image and input to the printing system 30. In the printing system 30, a printing film original corresponding to each plate of CMYK is created based on the input halftone data, a printing plate is created from the original, and the created printing plate is mounted on a printing machine. In the printing machine, printing with process inks of four colors of CMYK is performed, and a halftone image 31 is formed.
[0038]
In the system shown in FIG. 1, a color scanner that reads a document image and generates image data is shown as an example of an input device that inputs an image and obtains image data. In addition, for example, DSC (digital still camera), a system that records images on the reversal film by photography using a reversal film, reads the recorded image with a color scanner or the like, and obtains other image data. Any device may be used as long as it can input and obtain image data.
[0039]
In the system shown in FIG. 1, the printing system 30 including a printing machine or the like is shown as an example of an output device that outputs an image based on image data. However, a color printer that prints a color image or a color image is displayed. A color display device or the like may be used as long as it can output a color image (hard output or display).
[0040]
However, here, description will be made on the premise of a system including the color scanner 10 and the printing system 30 as an example of an input device and an output device.
[0041]
Here, the feature of the system shown in FIG. 1 as an embodiment of the present invention resides in the processing contents executed inside the personal computer 20, and the personal computer 20 will be described below.
[0042]
2 is an external perspective view of the personal computer 20 shown as one block in FIG. 1, and FIG. 3 is a hardware configuration diagram of the personal computer 20. As shown in FIG.
[0043]
The personal computer 20 has an appearance configuration, a main body device 21, an image display device 22 that displays an image on a display screen 22a in accordance with an instruction from the main body device 21, and a main body device 21 in accordance with various key operations. A keyboard 23 for inputting information and a mouse 24 for inputting an instruction corresponding to, for example, an icon or the like displayed at that position by designating an arbitrary position on the display screen 22a are provided. The main body device 21 has a floppy disk loading slot 21a for loading a floppy disk and a CD-ROM loading slot 21b for loading a CD-ROM.
[0044]
As shown in FIG. 3, the main body device 21 includes a CPU 211 that executes various programs, a main memory 212 that is read out by a program stored in the hard disk device 213 and developed for execution by the CPU 211, and various programs. And a hard disk device 213 storing data and data, a floppy disk 100 loaded with an FD drive 214 accessing the loaded floppy disk 100, a CD-ROM 110 loaded, and a CD-ROM accessing the loaded CD-ROM 110 The ROM drive 215 and the color scanner 10 (see FIG. 1) are connected, and an input interface 216 that receives image data from the color scanner 10 and an output interface 217 that sends image data to the printing system 30 are built in. The The image display device 22 shown in FIG. 2, a keyboard 23, a mouse 24 are connected to each other via a bus 25 to.
[0045]
Here, the CD-ROM 110 stores a color conversion program and a color conversion definition for operating the personal computer 20 as a color conversion device. The CD-ROM 110 is loaded in a CD-ROM drive 515, and The color conversion program and color conversion definition stored in the CD-ROM 110 are uploaded to the personal computer 20 and stored in the hard disk device 213.
[0046]
Next, a method for creating a color conversion definition stored in the personal computer 20 will be described.
[0047]
FIG. 4 is a conceptual diagram of an input profile forming one of the color conversion definitions.
[0048]
When the input profile can be obtained from the manufacturer of the color scanner 10 or the like, it is not necessary to create a new input profile. Here, a basic method for creating the input profile will be described.
[0049]
A color patch image made up of a large number of color patches is prepared as the original image shown in FIG. 1, and the color patch image is read by the color scanner 10 on the RGB space (an example of the input device color space referred to in the present invention) for each color patch. Color data is obtained, and the original image is measured with a colorimeter. For each color patch, for example, L which is an example of a common color space.^*a^*b^*Color data representing coordinate points on the color space is obtained. A detailed description of the common color space will be given later.
[0050]
In this way, the coordinate points on the RGB color space and L^*a^*b^*An input profile in which the correspondence with the coordinate points on the color space is defined is obtained. This input profile is a profile depending on the input device, which differs depending on the type of color scanner 10 and, more generally, the type of input device.
[0051]
FIG. 5 is a conceptual diagram of an output profile which is another color conversion definition.
[0052]
An output profile (printing profile) corresponding to typical printing conditions is often provided by a printer, and if an output profile corresponding to desired printing conditions can be obtained, it is not necessary to create an output profile. Here, a basic creation method when the output profile is newly created will be described.
[0053]
From the personal computer 20 shown in FIG. 1, halftone dot data in which halftone is sequentially changed to 0%, 10%,..., 100%, for example, as CMYK four-color halftone data is generated. A color patch image based on the halftone dot data generated in this way is created. Although the image 31 shown in FIG. 1 is not an image representing a color patch image, it is assumed that a color patch image is printed instead of the image 31, and each color patch constituting the color patch image is printed by a colorimeter. taking measurement. By doing so, the coordinate values on the color space of CMYK 4 colors (an example of the output device color space referred to in the present invention) and the common color space (here, L^*a^*b^*An output profile representing the correspondence with the coordinate values on the color space) is constructed.
[0054]
This output profile differs depending on the printing machine constituting the printing system 30, the type of ink, and the like, and further depends on the output device, which is different depending on the output device including not only printing but also other output devices. It is a profile.
[0055]
FIG. 6 is a conceptual diagram illustrating a color conversion process including both an input profile and an output profile.
[0056]
The input profile and output profile described with reference to FIGS. 4 and 5 are stored in the personal computer 20 shown in FIG. 1, and the RGB image data obtained by the color scanner 10 is as shown in FIG. L depending on the input profile^*a^*b^*Convert to image data in color space^*a^*b^*The image data in the color space is converted into CMYK image data according to the output profile, further converted into halftone dot data, and transmitted to the printing system 30 shown in FIG. By doing so, the printing system 30 can obtain a printed image 31 that faithfully reproduces the color expression of the original image 11 as much as possible. However, in this case, even if the color expression is performed as faithfully as possible, it does not mean that it is a print image with good color quality, and the image may not be attractive due to insufficient saturation. There is. Hereinafter, a color conversion method for improving this and further improving the color quality will be described.
[0057]
FIG. 7 is a conceptual diagram showing color conversion processing characteristic of the present embodiment, which is executed inside the personal computer 20 shown in FIGS.
[0058]
Here, the RGB image data obtained by the color scanner 10 (see FIG. 1) is converted into a common color space (here, L) by the input profile described with reference to FIG.^*a^*b^*The image data in the (color space)^*a^*b^*In the color space, first, “range adjustment” for adjusting the brightness range for each input image is performed. This range adjustment is performed when the image data is obtained with a DSC (digital still camera), for example, when the image becomes dark as a whole due to underexposure or when the image becomes too bright as a whole due to overexposure. In addition, it is a process of converting it into an image having a brightness equivalent to appropriate exposure.
[0059]
This common color space (L^*a^*b^*On the color space), the color conversion table is then referred to and color conversion is performed. This color conversion is performed using a common color space (L^*a^*b^*Color conversion performed on the color space), and thus color conversion that can be performed regardless of the type of input device or the type of output device. Here, although details will be described later, a common color space (L^*a^*b^*Color conversion is performed with emphasis on color vividness even with a change in hue in at least a part of the area on the color space. The image data generated by this color conversion is converted into CMYK image data by the output profile described with reference to FIG. The CMYK image data is further converted into halftone dot data and transmitted to the printing system 30 shown in FIG. By doing so, the printing system 30 is more vivid than the original document image 11 even when the color changes slightly, as compared with the case where color reproduction is performed as faithfully as possible described with reference to FIG. A printed image 31 with improved color quality is obtained.
[0060]
Here, in the input profile, the color space of the input device (RGB color space in the above example) to the common color space (L^*a^*b^*Color space) and a common color space (L^*a^*b^*Conversion from the color space) to the output device color space (CMYK color space in the above example). In these input profiles and output profiles, the color gamuts of the output device color space and the common color space, respectively. A process (gamut mapping) for correcting a difference and a color gamut difference between the common color space and the output device color space is included. In these input profiles and output profiles, it is preferable to perform color conversion that corrects the color gamut difference and preserves the color appearance in the necessary color gamut.
[0061]
Next, a method for creating a color conversion table in the common color space will be described.
[0062]
Here, the common color space will be described first. For this common color space, L^*a^*b^*We explained that color space is one example, but L^*a^*b^*The color space does not need to be a color space, and may be a color space defined so as not to depend on a specific input device or a specific output device. For example L^*a^*b^*In addition to the color space, it may be an XYZ color space, or a coordinate system clearly defined so that each coordinate point on the color space is associated with the color space on a one-to-one basis. Good. An example of such a coordinate system is a standard RGB signal defined as follows.
[0063]
[Expression 1]

[0064]
Here, for example, R_SRGBIs expressed in 8-bit as R_8bitIs written as
R_8bit= 255 x 12.92R_SRGB    (0 <R_SRGB<0.00304)
R_8bit= 255 x 1.055R_SRGB ^{(1.0 / 2.4)}  -0.055
(0.00304 ≦ R_SRGB≦ 1)
It becomes. G_SRGB, B_SRGBG expressed in 8 bits_8bit, B_8bitSimilarly, each G_SRGB, B_SRGBCan be converted from
[0065]
Alternatively, a color space defined by the cmy density of the reversal film may be adopted as the common color space. This clearly defines the color reproduction range in the common color space.
[0066]
Here, the color conversion table in the common color space is described by, for example, a three-dimensional reference table (LUT; Look Up Table), and the color conversion characteristics based on the color conversion table are obtained as follows. In the following, the common color space is an example of the common color space L^*a^*b^*The color space will be described. L^*a^*b^*Even when a common color space other than the color space is adopted, the adopted common color space is L^*a^*b^*The following description is valid as it is when converted to the color space.
[0067]
First, each basic color (L in the C, M, Y area of the common color space)_c, A_c, B_c), (L_m, A_m, B_m), (L_y, A_y, B_y).
[0068]
Here, these basic colors are desirably colors corresponding to color materials having main absorption in the red, green, and blue regions, respectively. As a result of testing by changing the coordinates of the basic colors, the following color ranges are prominent. The effect was confirmed.
[0069]

That is, each basic color of C, M, and Y is defined as one point in each of these color regions.
[0070]
Here, the input color (L_i, A_i, B_i) Is modified as follows.
[0071]
L ′ = L_i+ ΔL
a ’= a_i+ Δa
b '= b_i+ Δb (2)
Here, (ΔL, Δa, Δb) is a color correction vector and is further obtained by the following equation.
[0072]
ΔL = g_cc_cΔL_c+ G_mc_mΔL_m+ G_yc_yΔL_y
Δa = g_cc_cΔa_c+ G_mc_mΔa_m+ G_yc_yΔa_y
Δb = g_cc_cΔb_c+ G_mc_mΔb_m+ G_yc_yΔb_y                  ...... (3)
(ΔL_c, Δa_c, Δb_c), (ΔL_m, Δa_m, Δb_m), (ΔL_y, Δa_y, Δb_y) Is a color vector (referred to as a basic color vector) having a reference white color defined below as a start point and having color coordinate points of the C basic color, M basic color, and Y basic color as end points, respectively. Where reference white (L_w, A_w, B_w)
80 <L_w≦ 100, | a_w| <10, | b_w| <10
Defined by
[0073]
FIG.^*a^*b^*L in color space^*a^*FIG. 9 is a diagram showing basic color vectors projected onto a plane.^*a^*b^*A in color space^*b^*It is a figure which shows the basic color vector projected on the plane.
[0074]
In addition, c in equation (3)_c, C_m, C_yAre correction coefficients for the direction of the C basic color vector, the direction of the M basic color vector, and the direction of the Y basic color vector, respectively, and are set as follows according to the hue of the input color.
[0075]
H_i= Tan^-1(B_i/ A_i) For the input color (L_i, A_i, B_i) Hue angle, H_c= Tan^-1(B_c/ A_c), H_m= Tan (b_m/ A_m), H_y= Tan (b_y/ A_y) For each C basic color (L_c, A_c, B_c), M basic color (L_m, A_m, B_m), Y basic color (L_y, A_y, B_y) For each hue angle,
c_c<0 (however, H> H_c+ 90 ° and H <H_c-90 °)
c_c≧ 0 (however, H_c-90 ° ≦ H_i≦ H_c+ 90 °)
c_m<0 (however, H> H_m+ 90 ° and H <H_m-90 °)
c_m≧ 0 (however, H_m-90 ° ≦ H_i≦ H_m+ 90 °)
c_y<0 (however, H> H_y+ 90 ° and H <H_y-90 °)
c_y≧ 0 (however, H_y-90 ° ≦ H_i≦ H_y+ 90 °)
FIG. 10 is a conceptual diagram of the correction coefficient. This figure shows each correction coefficient c_c, C_m, C_yThe correction coefficient c_cIt is shown.
[0076]
As shown in the above equation (6) and the solid line in FIG._cH> H_c+ 90 ° region and H <H_cC in the -90 ° region_c<0, H_c-90 ° ≦ H_i≦ H_cC in the + 90 ° region_cA function of> 0. However, as shown by the broken line in FIG._c-90 ° ≦ H_i≦ H_cIn the + 90 ° region, c_c= 0.
[0077]
The phase angle H of the input color whose coordinates are shown in FIGS._iIs the phase angle H of the C basic color vector_cIn relation to
H_c-90 ° ≦ H_i≦ H_c+ 90 °
Is satisfied. Here in this region c_c= 0 is adopted, and therefore color correction in the direction of the C basic color vector is not performed. 8 and 9 do not show the color correction vector in the direction of the C basic color vector, and this does not perform color correction of the input color in the direction of the C basic color vector (still remains stationary). Means.
[0078]
Also, the phase angle H of the input color whose coordinates are shown in FIGS._iIs the phase angle H of the M basic color vector_mAnd phase angle H of Y basic color vector_yIn any relationship,
H_m-90 ° ≦ H_i≦ H_m+ 90 °
H_y-90 ° ≦ H_i≦ H_y+ 90 °
Therefore, each correction coefficient c relating to the direction of the M basic color vector and the direction of the Y basic vector is_m, C_yAre all c_m<0, c_y<0, and the coordinates of the input color are moved in directions opposite to the directions of the M basic color vector and the Y basic color vector, respectively.
[0079]
Here, H_c-90 ° ≦ H_i≦ H_cC for + 90 °_c= 0 and the input coordinate is not moved in the direction of the C basic color vector (it remains stationary in that direction)._c-90 ° ≦ H_i≦ H_cC for + 90 °_cIt may be set to> 0 and may be positively moved (corrected) in the same direction as the direction of the C basic color vector. c_m, C_yThe same applies to. According to many experimental results by the inventor, when the phase angle is within ± 90 ° with respect to the basic color, the effect of the present invention is aimed at even if the coordinate of the input color is not necessarily moved for the basic color. However, it is often possible to obtain a stronger effect by moving the coordinates of the input color in the same direction as the direction of the basic color vector even when it is within ± 90 °. Confirmed with examples.
[0080]
Here, for easy understanding, each gain coefficient g included in the equation (3)_c, G_m, G_yWas ignored, but each gain coefficient g in equation (3)_c, G_m, G_yIs the correction coefficient c_c, C_m, C_y, I.e., how strongly the correction is made in the direction of the basic color vectors of C, M, and Y, 0 ≦ g_c, G_m, G_y≦ 1 and a coefficient that varies depending on the input color. Each gain coefficient g_c, G_m, G_yIs preferably defined as follows, for example.
[0081]
g_c= G_cor cos θ
g_m= G_mor cos θ
g_y= G_yorcos θ (5)
Here, r is the absolute value of the input color vector connecting from the reference white point to the coordinate point of the input color, and θ is the smallest of the angles formed by the input color vector and each of the three CMY basic color vectors. Is the angle. G_co, G_mo, G_yoIs a constant for each basic color. Here, the minimum angle θ is independent of each basic color of C, M, and Y, and each gain coefficient g_c, G_m, G_yTherefore, cos θ takes a larger value as it is closer to one of the basic color vectors (this means increasing the gain), and if it is far from any of the basic color vectors, for example, gray For close colors, the value is small (this means lowering the gain). Also, r is the absolute value of the input color vector connecting from the basic white color to the coordinate point of the input color as described above, and the gain decreases as the absolute value is smaller, that is, closer to white (the color is lighter). The larger the absolute value of the input color vector, that is, the darker the color, the higher the gain.
[0082]
Here, the correspondence between the density of the input color and the coordinates of the output color is determined in advance based on the input color conversion algorithm described above, a color conversion table is created, and the color conversion table is referred to for actual color conversion. Thus, each input color data constituting the image data is converted into each output color data.
[0083]
Next, the result of actual color conversion using this color conversion table will be described.
[0084]
Here, the basic colors of CMY are C (54, -37, -49), M (44, 71, -8), Y (85, -8, 88), and the reference white point is (92, -1). , -2). Further, the following red, yellow, purple, and green sample points were extracted from the color image as input colors, and the response of the color conversion table for the colors was examined. Input color L^*a^*The b value is shown in Table 1.
[0085]
[Table 1]

[0086]
Table 2 shows the response of the color conversion table to the input colors shown in Table 1, that is, the output colors.
[0087]
[Table 2]

[0088]
As can be seen from Tables 1 and 2, for example, for red (the top row of Tables 1 and 2), the direction of the C basic color vector (−36, −36, −47) moves in the opposite direction, And it is moving in the same direction as the direction of the M basic color vector (−48, 72, −6). Further, with respect to the green color (the lowermost stage in Tables 1 and 2), it has moved greatly in the direction opposite to the direction of the M basic color vector.
[0089]
Each of the image data after passing through the color conversion process using this color conversion table and the image data not passing through the color conversion process using this color conversion table are converted into CMYK halftone dot data, and actual offset color printing is performed. It was. When color conversion processing using the above color conversion table is performed, as shown in the comparison between Table 1 and Table 2, hue fidelity is not maintained, but the prints are very vivid and have less color turbidity. As a printed matter, a color reproduction much more preferable was obtained.
[0090]
Further, the halftone data after conversion was examined for both the image data that passed the color conversion table and the image data that did not pass the color conversion table. The result was as shown in Table 3.
[0091]
[Table 3]

[0092]
In Table 3, C, M, Y, and K are halftone dot data when not passing through the color conversion table, and C ′, M ′, Y ′, and K ′ are halftone dot data when passing through the color conversion table. is there.
[0093]
In Table 3, for example, for red, C ′ = 37 for C = 45, and for green, M ′ = 30 for M = 56. As described above, the above-described color conversion table has an effect of reducing the opposite color in the ink halftone dot amount, that is, the component that becomes turbid color, and as a result, a vivid print as described above can be obtained. It is thought that.
[0094]
In addition, as a result of performing the case where the color conversion table is passed through and the case where it is not passed through another printing process (chemical proof, sublimation printer, ink jet printer, electrophotographic printer) Even in this case, a vivid print with less turbidity was obtained when the above color conversion table was passed.
[0095]
Here, a comparison result between a color conversion process using the color conversion table created by the above-described algorithm and a conventionally known color conversion process will be described.
[0096]
Here, color conversion processing using the above color conversion table The saturation enhancement processing that saves the hue and saves the hue, which is a well-known processing in a common color space, is also performed, and the results are compared. did. As a result of the saturation enhancement processing, red color was converted to (35, 50, 37). This conversion preserved the hue and increased saturation. However, when printing was performed using the same printing process as described above, a bright color could not be obtained unlike the expected result. When the amount of ink halftone dots was confirmed, it was (4, 96, 92, 40) and it was found that a large amount of K was added. In order to improve this, printing without the process of using K ink was performed. As a result, although the saturation of red was improved, the hue shifted, and the overall tone reproduction and color balance were greatly lost, resulting in poor quality printing. It became.
[0097]
Next, another method for creating the color conversion table shown in FIG. 7 will be described.
[0098]
FIG. 11 is an explanatory diagram of another method for creating the color conversion table.
[0099]
First, a common color space, for example L^*a^*b^*Color data in the color space is converted into color data CMY expressed as a ratio of the above three CMY basic colors.
[0100]
The converted color data C′M′Y ′ having the relationship defined by the following formula is obtained from the CMY.
[0101]
C = C '+ m_r/ M_gM ’+ y_r/ Y_bY ’
M = c_g/ C_rC '+ M' + y_g/ Y_bY ’
Y = c_b/ C_rC '+ m_b/ M_gM '+ Y' (6)
Where c_r, C_g, C_b, M_r, M_g, M_b, Y_r, Y_g, Y_bAre the light absorption rate of the red (R) region of the cyan (C) color material, the light absorption rate of the green (G) region of the cyan (C) color material, and the blue (B) region of the cyan (C) color material, respectively. Light absorption rate, light absorption rate of magenta (M) color material in red (R) region, light absorption rate of magenta (M) color material in green (G) region, magenta (M) color material in blue (B) The light absorption rate of the region, the light absorption rate of the red (R) region of the yellow (Y) color material, the light absorption rate of the green (G) region of the yellow (Y) color material, and the blue (B of the yellow (Y) color material ) The light absorption rate of the region.
[0102]
C′M′Y ′ obtained by the above equation (6) is again converted into a common color space, for example, L^*a^*b^*Convert to color space color data.
[0103]
Common color space (L^*a^*b^*Color data) and the common color space (L^*a^*b^*A color conversion table is created by associating color data in the color space.
[0104]
The color conversion table created by the above algorithm has the same color as the color conversion table created by the method described with reference to FIGS. 8 to 10 when the created color conversion tables are compared with each other. It becomes a conversion table.
[0105]
FIG. 12 is a functional block diagram of an embodiment of the color conversion apparatus of the present invention.
[0106]
The color conversion apparatus shown in FIG. 12 is realized by combining the personal computer 20 shown in FIGS. 2 and 3 and a program executed on the personal computer.
[0107]
The color conversion apparatus shown in FIG. 12 includes a data acquisition unit 310, a data conversion unit 320, a data output unit 330, a definition storage unit 340, and a designation unit 350.
[0108]
The definition storage unit 340 includes a plurality of types of input profiles 341a, 341b,..., 341n corresponding to a plurality of types of input devices, a color conversion table 342, and a plurality of types of output profiles corresponding to a plurality of types of output devices. 343a, 343b, ..., 343m are stored.
[0109]
Each of the input profiles 341a, 341b,..., 341n is basically created by a creation method with reference to FIG. Although only one type of input device is shown in FIG. 1 as the input device, the color conversion device shown in FIG. 12 has a plurality of types corresponding to a plurality of types of input devices in order to provide versatility. Input profiles are available.
[0110]
The color conversion table 342 stored in the definition storage unit 340 of the color conversion apparatus shown in FIG. 12 is the common color space (L in this embodiment) described with reference to FIG.^*a^*b^*2 is a color conversion table for performing color conversion unique to the present invention in a color space). This color conversion table is created, for example, by the creation method described with reference to FIGS. 8 to 10 or by the creation method described with reference to FIG.
[0111]
The output profiles 343a, 343b,..., 343m stored in the definition storage unit 340 are basically created by the creation method described with reference to FIG.
[0112]
As in the case of the input profile, FIG. 1 shows only one type of printing system 30 as an output device. However, the color conversion apparatus in FIG. Multiple types of output profiles corresponding to each type of output device are prepared.
[0113]
The definition storage unit 340 is set in the hardware of the hard disk device 213 shown in FIG. 3, and the definition storage unit 340 (hard disk device shown in FIG. 3) is the color conversion definition of the present invention. This also corresponds to an embodiment of the storage medium.
[0114]
The designation unit 350 designates an input device and an output device. In the specification unit 350, the keyboard 23 or the mouse 24 shown in FIGS. 2 and 3 plays a role in hardware.
[0115]
When an input device and an output device are specified by the specifying unit 350, an input profile (here, referred to as an input profile 341a) corresponding to the specified input device among a plurality of input profiles stored in the definition storage unit 340 is obtained. An output profile (here, output) corresponding to a specified output device among the plurality of output profiles 343a, 343b,..., 343m read out and input to the data conversion unit 320 and stored in the definition storage unit 340 Profile 343a) is read and input to the data converter 320. Further, the color conversion table 342 is also read from the definition conversion unit 340 and input to the data conversion unit 320.
[0116]
In the data conversion unit 320, when the input profile 341a, the color conversion table 342, and the output profile 342a are input, they are combined to create one color conversion LUT (lookup table).
[0117]
The data acquisition unit 310 serves to receive color data obtained by the input device, and the input interface 216 shown in FIG. 3 corresponds to this in hardware.
[0118]
The data output unit 330 is responsible for outputting color data after color conversion by the data conversion unit 320, and corresponds to the output interface 217 shown in FIG. 3 in hardware.
[0119]
When the color data obtained by the input device, for example, the color scanner 10 shown in FIG. The color data is converted by the color conversion LUT created by combining the output profile 343a. The converted color data is output to an output device, for example, the printing system 30 shown in FIG.
[0120]
The conversion of the color data by the data conversion unit 320 is a conversion with reference to a color conversion table for performing a color conversion unique to the present invention, and although the hue is not always preserved, it is vivid with low turbidity and high color quality. An output image can be obtained.
[0121]
Here, in the color conversion apparatus shown in FIG. 12, one of the plurality of output profiles 343a, 343b,..., 343m stored in the definition storage unit 340 is displayed in the image display apparatus 22 shown in FIGS. A corresponding output profile is prepared, an image based on the color data converted by the data conversion unit 320 is displayed on the display screen 22a (see FIG. 2) of the image display device 22, and the designation unit 350 is displayed. (Keyboard 23 and mouse 24) have a function of correcting the color conversion table 342, and the color conversion table 342 is set so that the image becomes a more preferable color quality image while viewing the image displayed on the display screen. It is preferable to configure so that correction is possible.
[0122]
FIG. 13 is a functional block diagram of another embodiment of the color conversion apparatus of the present invention. In the color conversion apparatus shown in FIG. 13, the elements corresponding to the elements of the color conversion apparatus shown in FIG. 12 are given the same reference numerals as those shown in FIG. 12, and the color conversion apparatus shown in FIG. Only the differences will be described.
[0123]
The color conversion apparatus shown in FIG. 13 is realized by a combination of the personal computer 20 shown in FIGS. 2 and 3 and a program executed by the personal computer, as in the case of the color conversion apparatus shown in FIG.
[0124]
The main difference between the color conversion apparatus shown in FIG. 13 and the color conversion apparatus shown in FIG. 12 is the content stored in the definition storage unit 340. The definition storage unit 340 includes a plurality of types of input profiles 341a, 341b,..., 341n, and a plurality of types of output profiles 343a, 343b,. , 343m, a plurality of types of color conversion tables 342a, 342b,..., 342p are stored instead of storing only one type of color conversion table in the definition storage unit of the color conversion apparatus shown in FIG. Yes. These plural types of color conversion tables 342a, 342b,..., 342p are all the common color space (L in this embodiment) described with reference to FIG.^*a^*b^*2 is a color conversion table for performing color conversion unique to the present invention in a color space). These color conversion tables 342a, 342b,..., 342p are all created by the creation method described with reference to FIGS. 8 to 10 or the creation method described with reference to FIG. For example, each correction coefficient C in equation (3)_e, C_m, C_yAnd each constant g in equation (5)_co, G_mo, G_yoThe color conversion tables are different from each other.
[0125]
Further, each of the plurality of types of input profiles 341a, 341b,..., 341n and the plurality of types of output profiles 343a, 343b,..., 343m stored in the definition storage unit 340 of the color conversion device shown in FIG. Definition specification information is attached. The definition designation information is information for designating a color conversion table most suitable for the input profile or output profile from among a plurality of types of color conversion tables 343a, 342b, ..., 342p stored in the definition storage unit 340. It is.
[0126]
When an input device and an output device are designated by the designation unit 350, an input profile (for example, the input profile 341a) corresponding to the designated input device is read from the plurality of input profiles stored in the definition storage unit 340. The output profile corresponding to the specified output device (for example, the output profile 343a) is read out from the plurality of output profiles stored in the definition storage unit 340 and input to the data conversion unit 320, and the data is read out. The color conversion specified by the definition specifying information attached to the input profile corresponding to the specified input device and the definition specifying information attached to the input profile corresponding to the specified output device. A table (for example, color conversion table 342a) is read Is input to the data conversion unit 320.
[0127]
Here, the definition designation information attached to the input profile corresponding to the input device designated by the designation unit 350 and the definition designation information attached to the output profile corresponding to the output device designated by the designation unit 350 In principle, both are definition designation information for designating the same color conversion table. However, when the color conversion tables designated by the definition designation information for both are different from each other, in this embodiment, The definition designation information attached to the input profile is given priority, and a warning is issued to the operator that the color conversion tables designated by both definition designation information are different from each other.
[0128]
The color conversion table specified by the definition specifying information as described above is specified as a default, and when necessary, a different color conversion table is specified by an operation from the specifying unit 350 by the operator. Can be redone.
[0129]
By specifying the default color conversion table when an input device or output device is specified as described above, it is freed from the need to respecify the color conversion table each time the device is specified, and is a user-friendly device Is configured.
[0130]
In the block diagram shown in FIG. 13, the definition designation information is attached to all of the input profile and the output profile. However, the definition designation information may be attached only to the input profile or only to the output profile. Alternatively, the definition specification information is attached only to a part of the input profile or output profile, and only when the input profile or output profile to which the definition specification information is attached is specified, the color is based on the definition specification information attached thereto. The conversion table may be automatically specified.
[0131]
FIG. 14 is a flowchart of one embodiment of the color conversion method of the present invention.
[0132]
Here, first, in the data acquisition process of step (a), for example, using the color scanner 10 of FIG. 1, the input color defined by the coordinate values in the input device color space depending on the color scanner 10 (input device). Get the data.
[0133]
Next, in the data conversion process of step (b), data conversion unique to the present invention is performed.
[0134]
Here, using the input profile, the color conversion table, and the output profile that have been described so far, the input color data obtained in the data acquisition process of step (a) outputs an image. Is converted into output color data defined by coordinate values in the output device color space depending on the. In this data conversion process, the input profile, the color conversion table, and the output profile may be sequentially operated to perform data conversion. However, preferably, the input profile, the color conversion table, and the output profile are combined into one color. Creating a conversion definition and performing data conversion using the combined color conversion definition is preferable for speeding up the data conversion process.
[0135]
Here, the input profile employed in the data conversion process of step (b) is an example of the first color conversion definition referred to in the present invention, and is used to acquire image data in the data acquisition process of step (a). Coordinate values in the input device color space depending on the input device used (for example, the color scanner 10 in FIG. 1), and a common color space independent of the input device and the output device (in this embodiment, L^*a^*b^*This defines the correspondence with coordinate values of (color space). The color conversion table is an example of the second color conversion definition referred to in the present invention, and is the common color space (L in this embodiment) described with reference to FIG.^*a^*b^*(Color space) for performing color conversion unique to the present invention. This color conversion table is created by the creation method described with reference to FIGS. 8 to 10, for example, or created by the creation method described with reference to FIG. The output profile employed in the data conversion process of step (b) is an example of the third color conversion definition referred to in the present invention, and is a common color space (L in this embodiment).^*a^*b^*The relationship between the coordinate values in the color space) and the coordinate values in the output device color space depending on the output device to which the image is to be output is defined.
[0136]
FIG. 15 is a diagram showing another embodiment of the color conversion definition storage medium of the present invention.
[0137]
With reference to FIG. 12, it has been explained that the definition storage unit 340 of the color conversion apparatus of FIG. 12 corresponds to an embodiment of the color conversion definition storage medium of the present invention. As another example of the definition storage medium, an example in which a color conversion table 342 is stored in the CD-ROM 110 is shown.
[0138]
As described above, this color conversion table 342 is for performing color conversion in a common color space, and only the color conversion table 342 for performing preferable color conversion, for example, CD-, is independent of the input profile and output profile. It can also be stored in a portable storage medium such as the ROM 110 for distribution.
[0139]
A user who obtains such a color conversion table uploads the obtained color conversion table to his / her own color conversion apparatus having the function shown in FIG. 12, for example, and uses the color conversion table to obtain more vivid color quality. High color conversion can be performed.
[0140]
【The invention's effect】
As described above, according to the present invention, color conversion for obtaining a color image with high color quality can be performed even in various combinations of input / output devices.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram of an image input-color conversion-image output system to which an embodiment of the present invention is applied.
FIG. 2 is an external perspective view of a personal computer shown by one block in FIG.
FIG. 3 is a hardware configuration diagram of a personal computer.
FIG. 4 is a conceptual diagram of an input profile forming one of color conversion definitions.
FIG. 5 is a conceptual diagram of an output profile which is another color conversion definition.
FIG. 6 is a conceptual diagram illustrating a color conversion definition including both an input profile and an output profile.
7 is a conceptual diagram showing color conversion processing characteristic of the present embodiment, which is executed in the personal computer shown in FIGS. 1 to 3; FIG.
FIG. 8 L^*a^*b^*L in color space^*a^*It is a figure which shows the basic color vector projected on the plane.
FIG. 9 L^*a^*b^*A in color space^*b^*It is a figure which shows the basic color vector projected on the plane.
FIG. 10 is a conceptual diagram of correction coefficients.
FIG. 11 is an explanatory diagram of another method of creating a color conversion table.
FIG. 12 is a functional block diagram of an embodiment of a color conversion apparatus of the present invention.
FIG. 13 is a functional block diagram of another embodiment of the color conversion apparatus of the present invention.
FIG. 14 is a flowchart illustrating an embodiment of a color conversion method according to the present invention.
FIG. 15 is a diagram showing an embodiment of a color conversion definition storage medium of the present invention.
[Explanation of symbols]
10 Color scanner
11 Document image
20 Personal computer
21 Main unit
22 Image display device
22a Display screen
23 keyboard
24 mice
25 bus
30 Printing system
100 floppy disks
110 CD-ROM
211 CPU
212 Main memory
213 Hard disk device
214 FD driver
215 CD-ROM driver
216 input interface
217 Output interface
310 Data acquisition unit
320 Data converter
330 Data output section
340 definition storage unit
341a, 341b, ..., 341n Input profile
342, 342a, 342b, ..., 342p color conversion table
343a, 343b, ..., 343m Output profile
350 Designated part

Claims (10)

Data acquisition step acquires the input color data to input image is defined by coordinate values in the input device color space dependent on an input device to obtain image data, and the input color data acquired by the data acquisition process,
Coordinate values in the input device color space;
Cyan basic color defined in the cyan area of the L ^* a ^* b ^* color space, magenta basic color defined in the magenta area, and yellow basic color defined in the yellow area, which are independent of the input device and the output device The respective coordinate points (L _c , a _c , b _c ), (L _m , a _m , b _m ), (L _y , a _y , b _y ) are
40 <L _c <65, −25 <a _c <−55, −35 <b _c <−60
30 <L _m <60, 40 <a _m <90, −20 <b _m <20
70 <L _y <90, −20 <a _y <20, 50 <b _y <130
And the reference white coordinate points (L _w , a _w , b _w ) defined in the white region of the L ^* a ^* b ^* color space are
A first color conversion definition defining a correspondence with coordinate values satisfying 80 <L _w ≦ 100, | a _w | <10, | b _w | <10 ;
At least a portion of said L ^* a ^* b ^* color space, the input coordinate values in the subspace that try the vividness of colors, defined white region of the L ^* a ^* b ^* color space The input coordinates of the basic colors determined in the cyan, magenta, and yellow areas of the L ^* a ^* b ^* color space , starting from the reference white coordinate point. A second color conversion definition that converts the value to an output coordinate value that is moved in the direction opposite to the direction of the vector whose end point is the coordinate point of the basic color existing outside the ± 90 ° hue angle with respect to the hue of the basic color When,
Using a third color conversion definition that defines the correspondence between the coordinate values in the L ^* a ^* b ^* color space and the coordinate values in the output device color space,
A color conversion method comprising a data conversion step of converting to output color data defined by coordinate values in an output device color space depending on an output device that outputs an image based on image data. In the second color conversion definition, the input coordinate value in the partial space of the common color space is set as the starting point of the reference white coordinate point, and the input coordinate value of the basic colors is the basic coordinate value. A color conversion definition for converting to an output coordinate value that remains stationary in the direction of a vector whose end point is a coordinate point of a basic color existing within ± 90 ° in hue angle with respect to the hue of the color The color conversion method according to claim 1. The second color conversion definition, the input coordinate values in the partial space, and starting from the coordinate point of the reference white, among the basic colors, the input coordinate values basic among the common color space It is a color conversion definition for converting into an output coordinate value moved in the same direction as the direction of a vector whose end point is a coordinate point of a basic color existing within ± 90 ° in hue angle with respect to the hue of the color. The color conversion method according to claim 1. The data conversion process creates one color conversion definition by combining the first color conversion definition, the second color conversion definition, and the third color conversion definition, and the one color conversion definition 2. The color conversion method according to claim 1 , wherein the input color data is converted into the output color data based on a definition . A data acquisition unit for acquiring input color data defined by coordinate values in an input device color space depending on an input device that inputs an image and obtains image data;
  A data conversion unit that converts the input color data acquired by the data acquisition unit into output color data defined by coordinate values in an output device color space depending on an output device that outputs an image based on the image data; and
  A data output unit that outputs the output color data after being converted by the data conversion unit;
  The data converter is
  Coordinate values in the input device color space;
  L independent of both input and output devices ^* a ^* b ^* Defined within the cyan area of the color space Coordinate points (L) for the cyan basic color, the magenta basic color defined in the magenta area, and the yellow basic color defined in the yellow area _c , A _c , B _c ), (L _m , A _m , B _m ), (L _y , A _y , B _y )But,
      40 <L _c <65, −25 <a _c <-55, -35 <b _c <-60
      30 <L _m <60, 40 <a _m <90, −20 <b _m <20
      70 <L _y <90, −20 <a _y <20, 50 <b _y <130
And satisfying the L ^* a ^* b ^* Reference white coordinate point (L _w , A _w , B _w )But,
      80 <L _w ≦ 100, | a _w | <10, | b _w A first color conversion definition defining a correspondence with coordinate values satisfying | <10;
  L ^* a ^* b ^* The input coordinate value in the partial space to increase the vividness of the color of at least a part of the color space is expressed as L ^* a ^* b ^* The reference white coordinate point defined in the white area of the color space is used as the starting point, and the L ^* a ^* b ^* Of the basic colors defined in the cyan color area, magenta color area, and yellow color area of the color space, the input coordinate value is outside the ± 90 ° hue angle with respect to the hue of the basic color. A second color conversion definition for converting to an output coordinate value moved in the direction opposite to the direction of the vector whose end point is a coordinate point of an existing basic color;
  L ^* a ^* b ^* The input color data is converted to the output color data using a third color conversion definition that defines the correspondence between the coordinate values in the color space and the coordinate values in the output device color space. Characteristic color conversion device. In the second color conversion definition, the input coordinate value in the partial space of the common color space is set as the starting point of the reference white coordinate point, and the input coordinate value of the basic colors is the basic coordinate value. A color conversion definition for converting to an output coordinate value that remains stationary in the direction of a vector whose end point is a coordinate point of a basic color existing within ± 90 ° in hue angle with respect to the hue of the color The color conversion apparatus according to claim 5 . In the second color conversion definition, the input coordinate value in the partial space of the common color space is set as the starting point of the reference white coordinate point, and the input coordinate value of the basic colors is the basic coordinate value. It is a color conversion definition for converting into an output coordinate value moved in the same direction as the direction of a vector whose end point is a coordinate point of a basic color existing within ± 90 ° in hue angle with respect to the hue of the color. The color conversion apparatus according to claim 5 . The data conversion unit creates one color conversion definition by combining the first color conversion definition, the second color conversion definition, and the third color conversion definition, and the one color conversion 6. The color conversion apparatus according to claim 5, wherein the input color data is converted to the output color data based on a definition . One or more first color conversion definitions corresponding to each of one or more input devices;
A plurality of types of the second color conversion definitions;
Storing one or more types of the second color conversion definitions corresponding to each of the one or more types of output devices;
Corresponding to the input device and / or the output device, a definition storage unit is provided for storing definition designation information for designating one second color conversion definition from a plurality of types of the second color conversion definitions. The color conversion apparatus according to claim 5, wherein: It has a specification part that specifies the input device and output device,
The data conversion unit specifies the input device and output device specified by the specification unit from the first, second, and third color conversion definitions stored in the definition storage unit, and specified by the specification unit The input color data is output using the first, second, and third color conversion definitions selected one by one based on the definition designation information corresponding to the input device and / or the output device. The color conversion apparatus according to claim 9 , wherein the color conversion apparatus converts the color data.

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