JP2004007509A - Color conversion method provided with hue correction using a plurality of lookup tables and interpolation - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a model for converting an RGB signal into the CMKY signal of a printer. <P>SOLUTION: A color conversion method includes the following steps. A 1st color gamut input signal set having a plurality of input signals is prepared. The input signals in the 1st color gamut input signal set are sorted according to signal intensity. A plurality of one-dimensional lookup table sets corresponding to a color polyhedron are designed/formed. A set of lookup tables to be used for a specific color polyhedron is selected. The selection is a function of a section of the polyhedron determined as a function of the input signal set. Values in the lookup table set are looked up as a function of the input signal set. Weights are generated as a function of sorted signal intensities. Output values from the selected lookup table are interpolated as a function of the selected lookup table and the generated weights to generate a color gamut signal set to be converted into a desired color gamut signal set. <P>COPYRIGHT: (C)2004,JPO

Description

【０１０３】
図７についての説明を続ける。等式（４）の左手に見えるベクトル（Ｖ_１）は、ポイント「Ｃ」に対するＣＭＹ入力ポイントの位置付けを表す。等式（４）の右手に見える第１ベクトル（Ｖ_２）は、ポイント「Ｃ」に対するポイント「Ｐ」の位置付けを表す。そして、等式（４）の右手に見える第２ベクトル（Ｖ_３）は、ポイント「Ｃ」に対するポイント「Ｓ」の位置付けを表す。この等式の解は以下の式（５）のように求められる。
【０１０４】
【数２】

【０１０５】
これらの各重み係数によって、最終のＣＭＹＫ出力信号４０が次の式（６）のように求められる。
【０１０６】
【数３】

【０１０７】
ここで上付き添え字「（Ｃ）」、「（Ｐ）」、「（Ｓ）」をそれぞれ伴う各ＣＭＹＫ数値は各々、ポイント「Ｃ」、「Ｐ」、「Ｓ」における各ＣＭＹＫ中間信号にそれぞれ対応している。
【０１０８】
（上半分色相調節）
図５のブロック図に前処理ブロック５８（ここでは第１処理ブロックと呼ばれる）を追加する。この前処理ブロック５８は、各ＲＧＢ信号を各ＣＭＹ信号へと変換するだけであるが、この追加によって、各ＲＧＢ入力信号を各ＣＭＹＫ出力信号へと変換するためのモデルが得られる。中心を通る対角線上の各ＣＭＹＫルックアップテーブルは、カラーランプがニュートラルなグレーを再現し、かつＬ^＊出力応答がＲＧＢ入力信号に対し線形であるように設計される。
【０１０９】
また、６つの境界線分上の各ＣＭＹＫルックアップテーブルは、適度に大きな色域を再現し、純色からブラックまでの境界線分上のランプにおける色相のずれを補正するよう設計される。立方体内部の各ＣＭＹポイントに対する各ＣＭＹＫ出力信号は、中心を通る対角線上及び境界線上の各ＣＭＹＫ出力信号から補間され、この補間によって、内部のポイントの適正な色相及び線形性といった所望の特性がうまく保持される。上記構成・方法は、本明細書において図３のブロック３８との関連で「１ボックス構造」と説明されている。
【０１１０】
しかし、１ボックス構造は、ＲＧＢ立方体の上半分の面における、各ＣＭＹ入力ポイントに対応する各色相角度の出力には影響しない。なぜなら、これらの面における補間は、Ｒ，Ｍ，Ｂ，Ｃ，Ｇ，Ｙを結んでＲに戻るＲＧＢ立方体中のホワイトポイントと、多面体上で隣接する２つの純色ポイントとにのみ基づいているからである。純色ポイントとホワイトポイントの間に、この領域内にて色相のずれを補正するための補間格子ポイントは存在しない。
【０１１１】
上記影響しないことを改善するために、前述の計算構造には、上半分の面における色相のずれを補正するための「２ボックス構造」と呼ばれる計算構造が用いられる。上半分の色相のずれを処理するための図３のブロック３４は、各ＲＧＢ入力信号を各ＣＭＹ信号に変換するために、また、各ＲＧＢ信号の色相のずれを補正するために構築される。一方、下半分の色相調節及びブラック生成部としての処理ブロック３８は、中心を通る対角線上のグレーバランスを取るために、また、ＲＧＢ入力立方体の下半分の面における色相のずれの問題を解決するために設計される。
【０１１２】
そのように、上半分の色相調節部としての処理ブロック３４が設計・構築される時には、２次色領域におけるＣ_２Ｍ_２Ｙ_２信号は上記の所望の特性を既に所有している。つまりブロック３４の目的は、ＲＧＢ立方体の上半分の色相のずれの問題を補正する事にある。また、中心を通る対角線上のグレーバランスの問題は既に処理されているため、中心を通る対角線上のＣ_２Ｍ_２Ｙ_２信号は、ここでも等式（１）を使い、ＲＧＢ信号を変換することによって得られる。
【０１１３】
しかし、境界線上では、各ＲＧＢ信号を各ＣＭＹ信号に変換するには、各１次元ＲＧＢ−ＣＭＹルックアップテーブルが使用される。本発明の方法では、６セットの各１次元ＲＧＢ−ＣＭＹルックアップテーブルが、Ｒ，Ｇ，Ｂ，Ｃ，Ｍ，Ｙの各々からホワイトポイントまでの境界線上にそれぞれ配置される。これらの１次元ルックアップテーブルへのインデックスは各ＲＧＢ入力信号の最小値である。
【０１１４】
Ｗ_ｉ＝ｍｉｎ（Ｒ_ｉ，Ｇ_ｉ，Ｂ_ｉ）　　　　　　（７）
ブラックからホワイトへ中心を通って伸長する対角線上において、入力された各Ｒ，Ｇ，Ｂの各信号（ここではＲＧＢ入力信号と称する）は同等であり、等式（１）によるＲＧＢからＣＭＹへの変換が１次元線形関数によって、ブラックで１００％からホワイトで０％までインプリメントされる（図８（ａ））。
【０１１５】
Ｒからホワイトまでの境界線上では、入力されたＲ信号が１００％であり、入力されたＧ信号及びＢ信号（ここではＧＢ入力信号と称する）は同等で、０％から１００％まで推移する。図８（ｂ）のプロットは、Ｒからホワイトまでの境界線上における、ＲＧＢからＣＭＹへの各曲線の典型的なセットを表したものである。Ｃ曲線は０％で一定しているが、これは境界線上の色が最も純粋な色のままだからである。Ｍ曲線とＹ曲線は１００％から０％まで変動するが、降下の勾配は等式（１）が示すようには直線的ではない。
【０１１６】
これらの各曲線は、Ｒからホワイトまでの境界線上で、色素の混合作用又は、ドットが重なり合わない（ｄｏｔ−ｏｆｆ−ｄｏｔ）ハーフトーン効果によって生じうる色相のずれを補正するように形成されている。図５に示すように、２ボックス構造はブロック５８とブロック３８の組み合わせでもありうる。
【０１１７】
処理ブロックである、上半分色相調節部３４の詳細は図９に示す。これは、処理ブロックである、下半分色相調節及びブラック生成部３８と本質的に同一だが、各入力信号はＲＧＢであり、ソータブロック６２の出力は、順序付けされた各ＲＧＢ信号とその順序情報である。ブロック３４は重み生成器６４と、ＣＭＹルックアップテーブル選択器６６と、ルックアップテーブル６６と、ＣＭＹ補間器７０とを含む。
【０１１８】
この処理ブロックで考察すべきＫ色素は存在しない。両ブロックの違いは、上半分のブロックにブラック（Ｋ）出力信号が存在せず、計算において立方体の各頂点（Ｃ，Ｍ，Ｙ，Ｋ）及び（Ｒ，Ｇ，Ｂ，Ｗ）の役割が互いに逆転され、つまりＲとＣとが置換され、ＭとＧとが置換される点にある。「ＣＭＹルックアップテーブル選択器及び１次元テーブルルックアップ」ブロックのための７セットの各１次元ＲＧＢ−ＣＭＹルックアップテーブルの中で、境界線分上の６セットだけが柔軟に設計される。
【０１１９】
中心を通る対角線上のセットは、図８（ａ）のように固定される。実際には、Ｃ，Ｍ，Ｙからホワイトまでの境界線分上のルックアップテーブルは、知覚上の線形性を達成するよう設計されている。そして、ＲとＧとＢとからホワイトまでの各境界線分上の各ルックアップテーブルは、知覚上の線状性と、色素混合及び／又はドットが重なり合わないハーフトーン処理による色相のずれの補正とを、両方とも達成するように設計されている。
【０１２０】
処理ブロックである上半分色相調節部３４に入力されたパラメータは、Ｃ，Ｍ，Ｙ，Ｒ，Ｇ，Ｂの各々からホワイトまでの各線分上における、６セットの各ＣＭＹルックアップテーブルである。これらの各線分は図１０に太線で表されている。これらの各線分上の各カラー出力は、同線分上の各ＣＭＹルックアップテーブルによって直接決定される。
【０１２１】
これらの各ルックアップテーブルは、各２次色からホワイトまでの各カラーランプの各色相角度をほぼ一定に保持し、その諧調に対し、知覚上の均一性のような所望の特性を幾つか与えるために設計されている。中には、これらの各ルックアップテーブルを１次色の各諧調について使用する場合もある。
【０１２２】
図７に見る補間処理についての幾何学的説明もまた、処理ブロックである上半分色相調節部３４に対して有効である。しかし、各入力が各ＲＧＢ信号であるため、ＲＧＢ立方体については、各１次色がＲとＧとＢとであり、各２次色がＣとＭとＹとである。各重み係数を得るために、ここにも等式（５）が使用される。各ＣＭＹ信号は次の数式で求められる。
【０１２３】
【数４】

【０１２４】
下半分の色相調節に対応するＣＭＹ立方体の４面体区分と、上半分の色相調節に対応するＲＧＢ立方体の４面体区分とは互いに同一である。このため本発明の方法は、ＲＧＢ立方体における補間のために、前記ＣＭＹ立方体における補間に用いられるのと同じ計算を用いる。
【０１２５】
しかし、「下半分色相調節及びブラック生成部」のブロックによって、中心を通る対角線上のブラックからホワイトまでの各色のグレーバランスが既に取られているため、中心を通る対角線上にＣＭＹルックアップテーブルを求める必要はない。その代わりに、中心を通る対角線上に補間を目的として各ＣＭＹ数値を生成するには、各ＲＧＢ入力信号の座標を単に変換するだけでよい。
【０１２６】
本明細書で開示される技術は、ＲＧＢ、ＣＭＹ又はＣＭＹＫ以外の各出力色素にも適用される。例えば、４面体の境界線上に異なる各ルックアップテーブルを定めることで、ヘキサクローム（Ｈｅｘａｃｈｒｏｍｅ^ＴＭ）、ＣｃＭｍＹＫ、又は色素の他の設定法、もしくはＸＹＺ，Ｌａｂのような他の色空間を、信号から色へという単純な計算モデルとして扱う事ができる。
【０１２７】
（計算構造への発展）
これまでに述べた計算構造では、ＲＧＢ又はＣＭＹ立方体において中心を通る対角線上に、また各１次色及び各２次色をブラック及びホワイトポイントと結びつける各境界線分上に、各１次元ルックアップテーブルが位置付けられる。各１次元ルックアップテーブルが配置された各線分上において、得られた各色出力の特性は、正確にコントロールする事ができる。
【０１２８】
しかし、信号入力立方体の他の部分における色出力についてはこれほど正確ではない。というのは、これらが近傍の各ルックアップテーブルによって補間されるからである。
【０１２９】
ＣＭＹＫインクジェットプリンタを使った実験結果に基づき、各ルックアップテーブルが特定される各線分上の所望の特性を見出して、これを入力立方体の他の部分にうまく適用することもできる。
【０１３０】
しかし、時には、入力立方体の他の部分における色出力を正確にコントロールするのが望ましい場合がある。例えば、昔からあるプリンタのブルーポイントは、ＣとＭとが１００％でＹが０％だが、いつも紫がかった色相を有する。Ｃを１００％、Ｙを０％に保ちつつ、Ｍを減らすことで、より自然なブルーポイントを得ることができる。この自然なブルーポイントからブラック及びホワイトポイントまで、各カラーランプに沿った色相応答の出力を、正確にコントロールするのが望ましい場合もある。
【０１３１】
上記計算構造の一般的原理は、各１次色及び各２次色からホワイト及びブラックポイントまでの、中心を通る対角線上や、境界線分上にのみに各１次元ルックアップテーブルを配置することに限定されない。各ルックアップテーブルは、入力された、ＲＧＢ又はＣＭＹ立方体内部の他の線分上にも位置付けられ、そこでの色出力の特性を正確にコントロールしうる。
【０１３２】
しかし、もしも計算構造に対し、より多くの各ルックアップテーブルが追加されれば、補間に使用されるべきルックアップテーブルのセットを選択するための、各入力信号からの順序情報だけが不十分になってしまう。追加の各ルックアップテーブルを利用するためには、追加の処理ステップが必要である。
【０１３３】
選択された４面体内部における、追加の線分上での各ルックアップテーブルの配置を、図１１（ａ）に特に８０にて示す。この例では２本の太線８２、８４上に、追加的な２セットの各ルックアップテーブルが配置される。Ｖｓ軸に垂直な平面は、追加的な線分とポイント「Ｃ」、「Ｐ」、「Ｓ」で交差し、ポイント「Ａ」及び「Ｂ」でも交差する。入力（ｉｎｐｕｔ）ポイントを含む三角形８６は平面Ｖｓ＝０に投射される（図１１（ｂ）参照）。
【０１３４】
各中間出力信号は、これら５つの交差点における、直接的なテーブルルックアップによって得られる。その図解は図１１（ｂ）にも示されているが、ここでポイント「Ｃ」、「Ｐ」、「Ｓ」で囲まれた三角形８６は更に、４つの副次的な三角形（Ｉ〜ＩＶ）に分解される。上記△入力ポイントは、各ベクトルの適切なセット及び適切なセットの各ルックアップテーブルを選択するために定められる必要がある。
【０１３５】
上記入力ポイントは、行列（マトリクス）を転置することで代数的にテストされ、４つの三角形のうち何れが上記入力ポイントを含むのか確定される。最終の各出力信号は、入力ポイントを囲む副次的な三角形の３つの各頂点での中間信号から補間される。図１１（ｂ）の分割の図解は例示のためのものに過ぎず、最良の分割図解は特定の適用によって左右される。
【０１３６】
本発明の方法のもう１つの方式では、ＲＧＢ／ＣＭＹ信号立方体が６つ以上の各４面体に分割される。例えば、６つの上述された各４面体の１つ以上が、１次色と隣の２次色とを結ぶ４面体の境界線に追加的な頂点を導入することで分割される。中心を通る対角線や、上述された立方体表面の線分に加えて、他の線分を用いて立方体をもっと細かく分割することもできる。例えば、４面体の底辺に追加の頂点を導入してもよい（ここでＶｓ＝０である）。こうした場合でも、本明細書にて開示されている補間方法は本質的に同様に作用する。主な違いは、入力信号ベクトルを囲む４面体を識別するには、より複雑で高度なアルゴリズムが必要になるという点である。
【０１３７】
（実験結果）
計算構造の開発と発展から考えて、ＲＧＢからＣＭＹＫ、又はＲＧＢからＲＧＢなどの、変換処理の様々な側面をコントロールするのに、この構造を利用しうる事は明らかである。本発明の方法を用いた実験では、ＲＧＢからＣＭＹＫへの変換モデルの色相調節及び出力色域の問題が重視され、研究の焦点になっていた。図３に見るように、本発明では２ステップの方法が構築され、「下半分色相調節及びブラック生成部」モジュールのために７セットの各ＣＭＹＫルックアップテーブルが、「上半分色相調節部」モジュールのために６セットの各ＣＭＹルックアップテーブルが設計された。プリンタ色域はＣＩＥＬＡＢ空間で表される。色相調節のためには、ＣＩＥＬＵＶ空間における色相角度が補正される。ただし、他の色空間を用いる事もできる。
【０１３８】
ＣＭＹＫインクジェットプリンタの実験結果を、図１２（ａ）と図１２（ｂ）の９０、９６、及び図１３の１１０に示す。図１２（ａ）では、レッドの色相リーフにおける、単純なＵＣＲ及びＧＣＲインプリメンテーションの色域（線９２）と、本発明の方法に基づく計算構造の色域（線９４）とが比較されている。この実験結果から分かるのは、本発明の方法によって陰影領域に、より大きな色域を提供できることである。
【０１３９】
本発明で得られたレッドリーフにおける色域は更に、この色相角度にて、ＣＭＹＫの色域全体と比較される（図１２（ｂ）、９６）。ＣＭＹＫ全色域は線９８であり、本発明の方法の計算構造により得られた色域のリーフは線１００である。図１２からは、本発明の方法で得られた色域のリーフがＣＭＹＫ全色域に極めて近いことが分かる。
【０１４０】
この色相調節上の効果は図１３（ａ）、（ｂ）の１１０、１１６にそれぞれ示されている。どちらの図でも、補正された色相は実線で表される。図１３（ａ）では、グリーンからブラックまでの補正済みの色相線１１２が、従来のインプリメンテーションから得られた色相線１１４と比較されている。また、図１３（ｂ）では、グリーンからホワイトまでの補正済みの色相線１１８と、未補正の色相線１２０とが比較されている。
【０１４１】
各ＲＧＢ入力信号を各ＣＭＹＫプリンタ出力信号に変換するための効率的な計算構造が開発された。この構造はＣＭＹＫプリンタをＲＧＢプリンタとして製造するのに利用される。
【０１４２】
ＲＧＢプリンタの概略を述べるのは比較的簡単だが、それは、ＣＩＥＬＡＢ空間やｓＲＧＢ空間のような測色空間で特定される各色と、各ＲＧＢ信号との間に、１対１の対応関係が成立するからである。
【０１４３】
本発明の計算構造は、１次元ＢＧ及びＵＣＲの各ルックアップテーブルを用いた、従来のＵＣＲ及びＧＣＲ技術の単純なインプリメンテーションを発展させたものと考えられかもしれない。この構造では、ＲＧＢ又はＣＭＹの入力立方体の様々な部分に、複数セットの各１次元ルックアップテーブルが効果的に配置されて、製品化されたＲＧＢプリンタの出力応答をコントロールしている。
【０１４４】
各１次元ルックアップテーブルの配置は、ＲＧＢ又はＣＭＹの入力立方体を幾つかの４面体へと本来的に分割し、４面体の各境界線上の各ルックアップテーブルが、４面体内部の入力ポイントに対応するＣＭＹＫ出力信号の補間に利用される。
【０１４５】
本発明の計算構造は、ＲＧＢからＣＭＹＫへの変換のための２ステップの処理を構成するのに用いられて、充分に大きな色域を達成し、例えば各ハーフトーン又は各色素によって生じた色相のずれを補正する。実験結果からは、このモデルがＣＭＹＫ全色域とほぼ同じ大きさの色域を達成可能であり、色相のずれをうまく補正できることが分かる。
【０１４６】
この計算構造の応用は、ＲＧＢからＣＭＹＫへの変換を行うプリンタだけに限定される訳ではない。それは４つ以上のインク又は色素を備えたプリンタの製造にも応用されうる。また、プリンタ以外の装置の望ましくない作動の補正にも利用されうる。
【０１４７】
このように、複数の各ルックアップテーブル及び補間を用いた、色相調節による色変換方法が開示された。添付された各請求項で定義される発明の範囲内ならば、この方法を更に変化させ、修正できることも明らかである。
【図面の簡単な説明】
【図１】
下半分色相調節、及びブラック生成のためのＣＭＹ入力立方体を示すグラフである。
【図２】
ＢＧ及び各ＵＣＲの各曲線、また両曲線と１次元ＣＭＹＫ応答出力曲線との関係をそれぞれ示す各グラフであって、（ａ）はＢＧ及び各ＵＣＲの各曲線、（ｂ）は中心を通る対角線上のＣＭＹＫ応答曲線、（ｃ）はＣからブラックまでの境界線上におけるＣＭＹＫ応答曲線、（ｄ）はＧからブラックまでの境界線上におけるＣＭＹＫ応答曲線を示す。
【図３】
ＲＧＢからＣＭＹＫへの変換の構造を示すブロック図である。
【図４】
ＲＧＢからＲＧＢへの変換の構造を示すブロック図である。
【図５】
下半分の色相調節及びブラック生成に関する計算の構造を示すブロック図である。
【図６】
（ａ）ないし（ｆ）は６つの４面体に分割されたＣＭＹ入力立方体をそれぞれ示すグラフである。
【図７】
テーブルルックアップ及び補間処理の幾何学的説明のためのグラフである。
【図８】
（ａ）は固定されたブラックからホワイトまでの線における、１次元のＲＧＢからＣＭＹへの変換を示す曲線を示すグラフであり、（ｂ）は本発明の方法に従って設計されたレッドからホワイトまでの線における、１次元のＲＧＢからＣＭＹへの変換を示す曲線を示すグラフである。
【図９】
上半分色相調節に関する計算の構造を示すブロック図である。
【図１０】
上半分色相調節のためのＲＧＢ入力立方体を示すグラフである。
【図１１】
（ａ）は入力立方体の範囲内及びその表面上における追加的なルックアップテーブルと、（ｂ）は適切なルックアップテーブルを選択するための方法とを表すグラフである。
【図１２】
本発明の方法で得られたレッドリーフの色域の図形的比較をそれぞれ示すグラフであって、（ａ）は従来のＵＣＲ及びＧＣＲインプリメンテーションの色域との比較であり、（ｂ）はＣＭＹＫ色域全体との比較である。
【図１３】
（ａ）は従来のＵＣＲ及びＧＣＲインプリメンテーションの結果生じた色相線、及びグリーンからブラックまでの線上における本発明の方法から生じた色相線、（ｂ）はグリーンからホワイトまでの線上における補正済み及び未補正の色相との間の、ＣＩＥＬＵＶ空間における色相角度の図形的比較をそれぞれ示すグラフである。(Related application)
This application is related to US patent application Ser. No. 09 / 741,458, filed Dec. 19, 2000, entitled "A Black Generation Method for CMYK Color Printers Using Multiple Lookup Tables and Interpolation." I have.
[0001]
(Field of Invention)
The present invention belongs to the field of color conversion of digital images, and in particular, converts RGB input signals into CMYK corresponding to a printer having four dyes of cyan (C), magenta (M), yellow (Y), and black (K). It is intended for a method of converting to a printer signal, and for a general color conversion method such as color correction of an LCD display.
[0002]
(Background of the Invention)
Many color printing apparatuses use four dyes of cyan (C), magenta (M), yellow (Y), and black (K), collectively referred to as CMYK dyes. In a CMYK output device, many colors can be generated by combining one or more CMYK dyes. When the CMYK device is designed as an RGB device, it is necessary to form a combination unique to CMYK from each combination of RGB.
[0003]
The under color removal (UCR) technology and the gray component replacement (GCR) technology have been conventionally used to calculate these unique combinations. While these techniques are easy to implement, they do not fully exploit the color gamut available with the addition of the K dye.
[0004]
On the other hand, other powerful techniques for searching the entire CMYK signal space for the desired combination have yielded good results, but are not suitable for real-time implementation.
[0005]
The use of K dyes in addition to CMY dyes has numerous effects. For example, dark black or subtle shading is obtained, and control of the neutral color balance becomes easier. The outline of a CMYK printer suitable for color management is as follows. That is, in order to reproduce a color specified in a colorimetric space such as CIELAB or sRGB, a combination of C, Y, M, and K dyes is calculated. As described above, some colors are reproduced by a combination of a plurality of CMYKs.
[0006]
In UCR and GCR technology, the RGB signals are first converted to obtain a nominal CMY signal. The K dye is then used instead of a fixed amount of CMY dye based on the formulation of the CMY dye. The amount of K dye used and the amount of CMY dye removed usually depends on the minimum input amount of C, M, Y. In a typical implementation, one black generation (BG) curve and three UCR curves are used. These curves are implemented as one-dimensional LUTs (look-up tables), where the minimum value of the CMY signal is used as an index into the look-up table. This provides a model for converting the nominal RGB signals to printer CMYK signals.
[0007]
With such a model, the printer is considered to be an RGB printer. In the RGB printer, for all the colors in the color gamut, the RGB signals correspond to the colors specified in the colorimetric space in a one-to-one relationship.
[0008]
The outline of the RGB printer is as follows. An RGB printer target with color patches is formed to sample the RGB input cube over a wide area, and the CIELAB output value is measured. Then, based on the measurement data, a printer profile for converting the color specified in the colorimetric space into the printer RGB space is created. To reproduce colors outside the color gamut, a color gamut mapping technique is used. Obviously, the RGB printer model is very useful in a modular design of the printer profiling process.
[0009]
Such techniques do not expose the complexity of the RGB to CMYK conversion process and provide the user with a more intuitive RGB input color space. There is also an application such as Windows (registered trademark) Graphical Display Interface (GDI) printing. In such applications, the printer is only addressable as an RGB device, requiring the construction of an RGB printer model.
[0010]
The simple UCR / GCR technique described above does not provide enough flexibility to select the "best" CMYK combination to reproduce a particular color. A simple technique that uses a certain combination of CMYK numbers is less powerful, so the color gamut of an RGB printer obtained with it is also smaller.
[0011]
A more sophisticated way to control the use of CMYK is to search the full color gamut of a CMYK printer to obtain the desired CMYK signal. Consider one color specified in the colorimetric space. If the color is within the color gamut, the search will find one or more CMYK signal vectors that reproduce the input color. These CMYK signals are categorized by the amount of K dye used (minimum to maximum).
[0012]
The desired CMYK signal is obtained by specifying the relative amount of K dye used. One way to do this is to use a parameter to specify the usage of K relative to the minimum and maximum amount of K in the discovered CMYK signal vector. This parameter is set as a position function in the input color space to obtain the optimum output image quality. These methods make full use of the CMYK printer gamut.
[0013]
However, in order to widely sample the entire printer CMYK space, measure the target to be printed in a colorimetric space such as CIELAB, and find all CMYK signals that can correspond to the colors in each color gamut specified in the colorimetric space. Building a printer target that performs interpolation is a "powerful" method with intensive calculations.
[0014]
Further, the CMYK output signal is not associated with the input color in the RGB signal space, but rather with the color in the colorimetric space. Therefore, only these methods cannot be used for designing a CMYK printer as an RGB printer.
[0015]
Although these are useful for forming a three-dimensional color look-up table that directly converts each color in the colorimetric space into CMYK printer signals, the look-up table forming procedure also needs to incorporate gamut mapping technology. Needless to say.
[0016]
The use of black (K) dye for printing achieves higher densities than can be obtained by combining only CMY dyes. The problems that need to be solved here are as follows. That is, how to determine the amount of black dye used based on the RGB or CMY input values. Also, how to adjust other dyes once the black dye is introduced. As mentioned above, the prior art shows two main solutions to this problem. They are (1) UCR type technology and (2) search technology. The related patent application describes a method of converting an RGB input signal to a CMYK signal using a plurality of black generation look-up tables on a boundary line and a diagonal line passing through the center of a CMY cube, and interpolation. ing.
[0017]
U.S. Pat. No. 6,281,984 (Decker et al., Issued Aug. 28, 2001) "Externally defined four-dimensional dye (CMYK) is applied to four inks (C'M'Y) associated with a given printer. An improved system, method, and program for converting to a corresponding four-dimensional dye defined for 'K') describes the conversion of Lab numbers to CMYK numbers.
[0018]
U.S. Pat. No. 6,229,580 (Inoue, issued May 8, 2001) entitled "Image Color Correction Apparatus and Recording Medium Having Recorded Color Program," discloses a color correction of a specific color tone and the specific color tone. Are described for a plurality of color tones.
[0019]
U.S. Patent No. 6,191,874 (Yamada et al., Issued February 20, 2001) "Image Processing Apparatus and Method and Recording Medium" describes the extraction of a colorless color component and the function of the colorless color component as a function of the colorless color component. The processing of the CMY signal has been described.
[0020]
U.S. Pat. No. 6,140,997 (Tanaka, issued Oct. 31, 2000) entitled "Apparatus and method for extracting color characteristics for converting an RGB color space into a color space close to human senses" is disclosed in U.S. Pat. Describes the color processing performed by converting into a hue / saturation / lightness (HLS) value.
[0021]
U.S. Patent No. 6,137,596 (Decker et al., Issued October 24, 2000), "Systems, Methods, and Programs for Converting Three-Dimensional Dyes to More Than Three-Dimensional Dyes," and US Patent No. 6,137,594. No. (Decker et al., Oct. 24, 2000) "A system for converting externally defined dyes (CMYK) into corresponding dyes (C'M'Y'K ') associated with a given printer; US Patent No. 6,061,501 (Decker et al., Issued May 9, 2000), entitled "Externally Defined Four Dyes (CMYK), A system, method, and program for converting corresponding four-dimensional dyes defined for inks (C'M'Y'K ') "means that color patches in a color space are compared to patches in a black color space. Is engaged, based on the measured Lab figures are respectively described that converts a color point value as a function of the black color space.
[0022]
U.S. Pat. No. 6,057,931 (McConnell et al., Issued May 2, 2000) entitled "Color Image Copy Control Method and Apparatus" describes color correction of pixelated images using HSL numerical values.
[0023]
U.S. Patent No. 6,039,434 (Moloney, issued May 21, 2000), "Thresholded Undercolor Removal and Black Replacement in Thermal Inkjet Printers or Plotters," describes the conversion of RGB signals to reduced color regions. are doing.
[0024]
U.S. Pat. No. 5,987,168 (Decker et al., Issued Nov. 16, 1999) entitled "Systems, Methods, and Programs for Converting Three-Dimensional Dyes to More Than Three-Dimensional Dyes" The formation of a look-up table for converting to a space is described.
[0025]
U.S. Pat. No. 5,933,252 (Emori et al., Issued Aug. 3, 1999) entitled "Color Image Processing Method and Apparatus Therefor" converts a wide color space into a narrow color space while maintaining color continuity. And the conversion.
[0026]
U.S. Pat. No. 5,894,358 (Ebner et al., Issued Apr. 13, 1999) "Applicable Color Density Management System" describes UCR technology by adding all toner coverage and selectively subtracting toner. Explain.
[0027]
U.S. Pat. No. 5,887,124 (Iwasaki et al., Issued Mar. 23, 1999) entitled "Image Processing Apparatus and Method in Which Restriction Processing is Performed According to Color Component Values" describes limiting the use of dyes. ing.
[0028]
U.S. Pat. No. 5,828,816 (Kise et al., Issued Oct. 27, 1998) entitled "Image Processing Apparatus and Method" describes a technique for improving the reproduction of blue.
[0029]
U.S. Pat. No. 5,764,388 (Ueda et al., Issued Jun. 9, 1998), "Method and Apparatus for Converting Color Signal", converts a color space signal into a signal having a color space and a colorless space component. Is explained.
[0030]
U.S. Pat. No. 5,719,689 (Terada, issued Feb. 17, 1998) "Image Processing Apparatus" describes converting a color space signal into a color space and a black signal using a gray component extraction unit. are doing.
[0031]
U.S. Pat. No. 5,717,839 (Ichikawa, issued Feb. 10, 1998) "Image Processor and Printer Having Correction Table Data for External Sources Transferred to Printer" describes an image input device and an image printer. An image correction lookup table for correcting an image dependently is described.
[0032]
U.S. Patent No. 5,615,312 (Kohler, issued March 25, 1997) entitled "Color Management System with Business Graphics Representation Mode" describes a BGR technique for improving color images.
[0033]
U.S. Pat. No. 5,504,821 (Kanamori et al., Issued on Apr. 2, 1996), "A color conversion apparatus for performing three-dimensional color conversion on a color image in a color space using a small memory" Executing color space conversion using a lookup table and a color cube is described.
[0034]
U.S. Pat. No. 5,146,328 (Yamasaki et al., Issued Sep. 8, 1992) "Color Signal Network System" converts color signals into a compatible output format over a network with a variety of input and output devices. A system for conversion is described.
[0035]
U.S. Pat. No. 5,113,248 (Hibi et al., Issued May 12, 1992), "Method and Apparatus for Color Removal in Image Forming Apparatus," describes a UCR system that performs color correction.
[0036]
U.S. Pat. No. 4,977,448 (Murata et al., Issued Dec. 11, 1990), "Color Image Processing Apparatus with Accurate Color Reproduction Performance," describes a system for correcting various color characteristics.
[0037]
U.S. Pat. No. 4,965,664 (Udagawa et al., Issued Oct. 23, 1990) "A color image signal processing method for recording a color image from an input color image signal by converting individual color signal components. And apparatus "describes the conversion of luminance / hue / chromaticity (chromatic, chroma) signals into various output color space paradigms.
[0038]
U.S. Pat. No. 4,908,701 (Udagawa, issued Mar. 13, 1990) entitled "Color Image Processing and Apparatus for Color Adjustment During Image Processing" describes color correction as a function of the color component of the dark point. Explain.
[0039]
U.S. Pat. No. 4,649,423 (Hoffrichter et al., Issued Mar. 10, 1987) entitled "Method and Circuit Adjustment for Selective Hue and Color Correction" describes correction of color separation by processing HSL signals. Explain.
[0040]
U.S. Pat. No. 4,636,844 (Sasaki, issued Jan. 13, 1987) "Method of Processing a Color Image Signal" describes the processing of a black signal as a function of color separation.
[0041]
U.S. Pat. No. 4,553,835 (Morgan, Jr., issued Nov. 19, 1985) "Procedure for Making a Preprint Color Proof" creates a color separation proof as a function of the yellow content of the image. Explains things.
[0042]
U.S. Pat. No. 4,500,919 (Schreiber, issued Feb. 19, 1985) describes a color copying system that uses CRT tristimulus values to correct final print color values. I have.
[0043]
(Summary of the Invention)
The color conversion method is
Providing a first color area input signal set having a plurality of input signals;
Classifying the input signals of the first color region input signal set according to the signal strength;
Design and form a set of multiple one-dimensional lookup tables corresponding to color polyhedra,
Selecting a set of look-up tables for use with a particular color polyhedron, wherein the selection is a function of a section of the polyhedron determined as a function of the input signal set;
Look up the values in the lookup table set as a function of the input signal set,
Generate weights as a function of the classified signal strength,
Interpolating the output values from the selected look-up table as a function of the selected look-up table and the generated weights to produce a color gamut signal set that is converted to a desired color gamut signal set.
[0044]
It is an object of the present invention to provide a model for converting a nominal RGB signal to a printer CMYK signal.
[0045]
Another object of the present invention is to provide a color conversion method that enables local conversion control from RGB signals to CMYK signals.
[0046]
It is yet another object of the present invention to provide a color conversion method that controls the use of CMYK dyes using a plurality of one-dimensional LUTs (look-up tables).
[0047]
Still another object is to provide a color conversion method using a look-up table on a diagonal line and a boundary line passing through the center of the input color cube.
[0048]
Yet another object is to provide a color conversion method that uses most of the available CMYK gamut.
[0049]
Yet another object is to provide a method for correcting identifiable hue shifts.
[0050]
Yet another object is to achieve neutral gray scale, accurate hue angles, and proper perception in a color ramp (color gradient) from black to primary (primary) / black to secondary (mixed with primary). It is to provide a way to maintain the space.
[0051]
Yet another object is to perform hue correction on primary and secondary colors.
[0052]
The above summary and purpose of the invention is for a quick understanding of the nature of the invention. For a more thorough understanding of the present invention, reference is made to the following preferred embodiments of the invention, together with the drawings.
[0053]
(Detailed description of preferred embodiments)
The method of the present invention includes a flexible computing structure for converting an RGB (red, green, blue) or CMY (cyan, magenta, yellow) signal to a CMYK (cyan, magenta, yellow, black) signal. Is included. Although this computational structure may be considered an extension of conventional under color removal (UCR) and gray component replacement (GCR) techniques, multiple sets of one-dimensional CMYK look-up tables (LUTs) are used here. Thus, the use of CMYK dye is controlled. The look-up table is placed on the diagonal line passing through the center and on the boundary line of the input signal color cube to enhance the effect.
[0054]
By properly designing these look-up tables, one can take advantage of most of the available CMYK gamut and still have some non-ideal device response (eg, results of downstream halftoning and page marking processes). An RGB-to-CMYK conversion model is obtained that corrects for possible hue shifts along the straight line from pure color to black or white. For example, the look-up table may be constrained so that the hue angle at each ramp (ramps) from each pure color to white or black is constant.
[0055]
The present invention solves the problem of correcting sub-optimal color effects in "raw" (uncalibrated) output devices. The method of the present invention, when applied to color printing, converts RGB input signals commonly used in display monitors, digital cameras, and scanners into equivalents used in most color printers (eg, ink jet or laser printers). Used to convert amounts of CMYK dye. The method disclosed here also applies to the correction of the strong non-linear colorimetry of LCD displays. In the latter case, the invention calculates the RGB to RGB conversion, rather than the RGB to CMYK conversion. In this application, the computational structure will be slightly different. This is because only three channels need to be calculated, but the principle is the same.
[0056]
The method of the present invention is an efficient computational structure for determining the conversion from non-linear RGB to CMYK, RGB to RGB, or RGB to another color space, and is used to treat a CMYK printer as an RGB printer. The method of the present invention includes an efficient table lookup and interpolation technique that obtains an output signal based on the location of the RGB points entered in the RGB color cube. Here, a preferred embodiment of the method of the present invention when this calculation structure is applied to a CMYK printer will be described. Extensive application to color printers using four or more dyes (eg, Hexachrome ™ printers, ie, CMYK with bright cyan and bright magenta dyes) is fairly straightforward and the method of the present invention was understood. Deemed possible for engineers in the field
With additional background, a brief implementation of conventional UCR and GCR technologies will be reviewed. The method of the present invention extends this simple implementation to achieve an efficient computational structure that allows flexibility to control the use of output dyes.
[0057]
(Conventional UCR and GCR implementation)
As shown in FIG. 1, the RGB input signal space is conceptually considered as an RGB or CMY color cube 10. Assuming that the black point 12 (RGB signal is 0) is the origin and the three axes are respectively RGB, this cube is an RGB cube. Alternatively, if the white point 14 (CMY signal is 0) is set as the origin, this cube is a CMY cube. That is, the RGB cube and the CMY cube show the same input signal space. Here, the RGB and CMY signals originally have the relationship of the following equation (1).
[0058]
C = 1.0-R, M = 1.0-G, Y = 1.0-B (1)
The outlines of the black generation (BG) curve and the UCR curve are represented in FIG. Here, there are three UCR curves (C is shown by a two-dot chain line, M is shown by a broken line, and Y is shown by a one-dot chain line). These curves are usually formed slightly different from each other. This is to obtain a visually neutral generated color that exists on a diagonal line (straight line 16 in FIG. 1) extending through the center of the input signal cube from white to black. These curves are simply implemented as one-dimensional look-up tables, and the index into the look-up table is the minimum value of the input CMY signal, as shown in equation (2) below.
K _i = Min (C _i , M _i , Y _i ) (2)
An arbitrary CMY input signal and a CMYK output signal are obtained by the following equation (3).
[0059]
C _o = C _i -UCR _c (K _i ),
M _o = M _i -UCR _m (K _i ),
Y _o = Y _i -UCR _y (K _i ),
K _o = BG (K _i (3)
Here, “UCR” and “BG” in FIG. 2A represent functions of UCR and BG. In equation (3), the subscript “o” indicates an output, and the subscript “i” indicates an input.
[0060]
According to equation (3) and FIG. 2 (a), 100% of K is used at the black point, and the amount of CMY is greatly reduced. The reason why 100% K is used at the black point is that the K dye can reproduce neutral and deep black. The amount of CMY in black is reduced as needed to cover the full coverage of the dye in the printing process. As the color becomes lighter, the amount of K dye decreases at a relatively high rate. On the other hand, the decrease amounts of C, M, and Y are more gradual than those of K.
[0061]
On a diagonal line passing through the center of the input cube, the C, M, and Y signals are equivalent to each other and are called CMY input signals. The range of the signal is from 0% at the white point to 100% at the black point. Combining FIG. 2 (a) and equation (3) on a diagonal line 16 passing through the center results in a one-dimensional CMYK output curve on the diagonal line 16 passing through the center (FIG. 2 (b)).
[0062]
With a pure cyan to black boundary color segment 18 (C to black), the input signal for C is fixed at 100%. The M and Y input signals are equivalent and are called MY input signals. These signals increase from 0% at C to 100% at black. By applying equation (3) and FIG. 2 (a), the relationship between the CMYK output signal and the MY input signal on the color segment 18 from C to black (here called the colorless segment) Is obtained (FIG. 2C). Similarly, a color segment 20 from M to black, a color segment 22 from Y to black, a color segment 24 from R to black, a color segment 26 from G to black, and a color segment from B to black A one-dimensional CMYK response output is obtained with the color line segment 28 up to.
[0063]
These are indicated by the thick lines in FIG. Another specific example is FIG. 2 (d), which illustrates the CMYK response output in the color line segment 26 from G to black. The C and Y signals input here are fixed at 100%, and the M signal varies from 0% in M to 100% in black. The curves in FIG. 2 are shown for illustrative purposes only, and the relationship between FIG. 2 (a) and FIG. 2 (b) or FIG. 2 (d) represents only roughly.
[0064]
Thus, the BG and UCR curves are used to derive a one-dimensional CMYK response output curve on the diagonal through the center and on each of the six boundaries. Here, each of the six boundary lines is a color line segment extending from a pure color to a black point in the CMY input cube, or simply a line segment.
[0065]
This also illustrates why the implementation of the BG and UCR curves is inflexible. More specifically, if a CMYK response curve on the diagonal line passing through the center as shown in FIG. 2B is specified, each of the BG and UCR curves in FIG. 2A and CMYK on a plurality of boundary lines Response curves can also be derived.
[0066]
By properly designing the diagonal CMYK response curve through the center, the diagonal output color ramp is also controlled to remain neutral. These curves show the L of the output ramp, which is perceived as linear for a diagonal CMY input signal passing through the center. ^* (Equal brightness) is formed to respond.
[0067]
However, if the output response curve is formed to satisfy some constraints on the diagonal through the center, the response on the boundary is also fixed. Thus, the inability to independently identify different CMYK responses in different regions of the CMY input cube makes the conventional UCR and GCR approaches inflexible and reduces the color gamut of CMYK printers. This is a major reason for underutilization.
[0068]
The following description is expressed in the form of CMYK printing of an RGB image. If the CMYK response output curves on the diagonal line passing through the center and the CMYK response output curves on the six color segments from each of C, M, Y, R, G, and B to black are individually independent. If it can be specified, the use of CMYK can be controlled more flexibly. This is an important feature of the present invention.
[0069]
However, if the relationship in equation (3) is no longer valid, then conventional UCR and GCR implementations based on BG and UCR curves will no longer work.
[0070]
The computational structure of the method of the present invention embodies an efficient interpolation algorithm for converting each RGB input signal to each CMYK signal, utilizing an independently or locally specified CMYK response curve. ing. Other applications, such as LCD color correction, can be similarly described.
[0071]
As discussed above, and in the related applications described above, UCR-type techniques are not flexible enough to obtain optimal amounts of CMYK dye for all RGB color inputs. Other methods that require an expanded search require a large amount of calculation. While useful for off-line formation of three-dimensional color look-up tables, they are not suitable for independent computational structures for converting RGB signals to CMYK signals.
[0072]
The technique described in the aforementioned related application utilizes interpolation and multiple black generation look-up tables to provide more flexibility in using K than conventional UCR-type techniques. However, the use of CMY in the aforementioned related applications is still not very flexible.
[0073]
Referring again to FIG. 1, the method of the present invention, in addition to the black generation look-up table, provides a pure diagonal from black to white through the center of the CMY cube and from black to black on the boundaries of the cube. Lookup tables for C, M, and Y are also prepared on the trajectories leading to the primary colors and secondary colors. Thus, the present invention improves the flexibility of using CMY dyes.
[0074]
By properly designing each of these CMY look-up tables, neutral grayscale, accurate hue angles, and proper perceptual space for black to primary and black to secondary color ramps are maintained. You.
[0075]
In the method of the present invention, a look-up table is further defined on a locus from the primary color and the secondary color to white. By properly designing these look-up tables, the hue angle and the perceived space of the color ramp from white to primary and secondary colors are also controlled.
[0076]
The calculations required to realize the above advantages are not too complicated. This calculation is also applicable to embodiments in hardware or software. Each pure color trajectory is a closed (closed) polyhedron, and each of their vertices is R, Y, C, B, M (in circular order).
[0077]
As used herein, the terms "upper half" or "lower half" are used to roughly indicate each trajectory on the surface of the RGB / CMY color cube. "Upper half" refers to the surface portion between pure color and white. That is, it refers to the surfaces of three color cubes that intersect at the white point. "Lower half" refers to the surface portion from pure color to black. That is, it refers to the surfaces of three color cubes that intersect at the black point. Thus, those of ordinary skill in the art will appreciate that the methods of the present invention may be practiced with a particular focus on the upper or lower half of the cube. However, the color range of the entire cube is ascertained and changed by the balance of the upper half or the lower half.
[0078]
Next, the “color area” and the “color area signal set” will be described. The set of color gamut and the associated set of color gamut signals can be easily explained using an example. One color gamut signal set is selected for input, which is referred to herein as a first color gamut or first color gamut signal set.
[0079]
The final color gamut, final color gamut signal set, or final dye signal set will be referred to as a third color gamut. This third color gamut is selected to provide a signal set for a particular output device, such as a printer, copier, LCD, or the like. A neutral color gamut signal set of a neutral color gamut or a set of secondary color gamut is typically generated using the method of the present invention.
[0080]
The schematic structure of an RGB to CMYK conversion module according to the present invention is shown in FIG. In the first step, the path of each RGB signal 32, that is, the signal set from the first color area, is determined via the upper half hue adjustment unit 34, which is the first processing block, and the second set signal, ie, each C ₂ M ₂ Y ₂ A signal 36, and thus a second or intermediate color area, is obtained. Each C ₂ M ₂ Y ₂ The signal 36 is further processed by a second processing block, the lower half hue adjustment and black generator 38, to obtain a final set of each CMYK dye signal 40, the signal set provided by the third color gamut. Can be
[0081]
All colors are processed in the method of the present invention in the sense that one color gamut is converted to another color gamut. In turn, the term "processing" here refers to the transformation of some or most of the colors present in a cube.
[0082]
The schematic structure of an RGB to RGB conversion module according to the present invention is shown in FIG. In the first step, the path of the RGB signal 32 is determined by the upper half hue adjustment processing unit 34, and the second set signal 36 is obtained. The signal set 36 can be RGB or CMY signals. These signals are further processed by the lower half hue adjuster 44, which is a processing block, to obtain the final RGB dye signals 46, ie, the corrected first color area signal set, here.
[0083]
Next, processing from RGB to CMYK will be described. In the method of the present invention used for printing, first the conversion module 38 is designed and constructed. The CMY input cube of FIG. The parameters for this processing block are a total of 7 sets on a diagonal line extending from the white to the black through the center and a boundary segment extending from each of R, G, B, C, M and Y to the black. Are CMYK one-dimensional lookup tables. Here, the boundary line segment forms a polyhedron, particularly a tetrahedron inside the color cube, which is herein called a color tetrahedron or color polyhedron.
[0084]
Each line segment for which each one-dimensional lookup table of CMYK is defined is represented by a thick line in FIG. The positions where these one-dimensional lookup tables are defined are the same as the positions in the above-mentioned related application. However, in the related application, only one one-dimensional lookup table, namely, a K lookup table, was defined on these trajectories.
[0085]
On the other hand, in the present invention, each of the four one-dimensional lookup tables corresponding to CMYK is defined on these trajectories. By locating each CMYK lookup table, not only the K dye but also the output of each CMY dye can be flexibly controlled.
[0086]
Each CMYK look-up table on the diagonal and boundary segments passing through the center directly determines the output value of each CMYK on these segments. Those CMYK output numerical values that do not exist on these line segments corresponding to each CMY input point are obtained by triangular interpolation based on the output values on these line segments (see also FIG. 7).
[0087]
Adjustment of the gray balance is made possible by limiting the one-dimensional look-up table on a diagonal line through the center so that the dye output on the line segment from white to black creates a neutral grayscale ramp. Further, the hue adjustment in the lower half limits the one-dimensional lookup table from black to pure color, and outputs the dye output on the line segment from the primary color or the secondary color to black, such as CIELAB / CIELUV. This is made possible by forming a color lamp with a constant measured hue angle in space. Additional restrictions may be placed on the table design to enforce uniform gradation on gray lamps and lamps from black to primary and secondary colors.
[0088]
(Calculation structure corresponding to conversion from RGB to CMYK)
The structure of the method of the present invention is to obtain a model that converts the nominal RGB signal to a CMYK dye signal that can be used in a real device such as a printer or copier. As seen in FIG. 3, this structure has two parts. The upper half hue adjustment unit 34, which is a processing block, corrects a hue shift in the “upper half” plane of an RGB cube having three cubic surfaces intersecting at a white point. The processing block, lower half hue adjustment and black generator 38, controls the use of K to compensate for hue shifts in the "lower half" plane of an RGB cube with three cubic surfaces intersecting at the black point. I do.
[0089]
(Lower hue adjustment and black generation)
Here, the lower half hue adjustment and black generation unit 38, which is a processing block, will be described in detail. Block 38 is an extension of the conventional UCR and GCR implementation, which converts a nominal CMY signal to a printer CMYK signal. The parameters of this processing block are on a diagonal line passing through the center of the CMY cube and on the surface of the CMY cube, from C to black, M to black, Y to black, R to black, G to black, and B to black. It is a total of seven sets of each one-dimensional CMUK lookup table arranged on the extending line segment.
[0090]
Each thick line in FIG. 1 represents a location where these seven sets of CMYK lookup tables conceptually exist. Each of these look-up tables is specified independently of each other. The curves embodied in each of these look-up tables have the same general shape as the curves in FIGS. 2 (b)-(d). FIG. 5 shows a calculation structure for converting each of the nominal CMY signals into each of the CMYK printer signals using each of these one-dimensional lookup tables.
[0091]
It is well known in tetrahedral interpolation techniques that a unit signal cube can be divided into six tetrahedrons based on the relative intensities of the three signal components. These six tetrahedrons share a diagonal line passing through the center of the cube as a common side. In the CMY cube of FIG. 1, each vertex of the six tetrahedrons is represented by CB-black-white, CG-black-white, MB-black-white, MR-black-white, Y- G-black-white, YR-black-white.
[0092]
These vertices correspond to the following orders of CMY input signal components, CMY, CYM, MCY, MYC, YCM, and YMC, respectively. Here, the first component is the largest and the last component is the smallest. The first step in the conversion process is to sort the CMY input components by _l , V _m , V _s (Where V _l ≧ V _m ≧ V _s ).
[0093]
The signal V in FIG. 5 represents the order information. Each subscript l, m, s indicates the maximum value, intermediate value, and minimum value of each CMY input signal component. That is, V _l ≧ V _m ≧ V _s It becomes. This order information is transmitted to the look-up table selector 50 by a signal V, and is used for selecting a CMYK look-up table for interpolation.
[0094]
Once the tetrahedron is identified by the order signal V, three sets of each CMYK lookup table on three sides of the tetrahedron are selected by a CMYK look-up table selector (block 50).
[0095]
The weight generator 54 calculates w ₁ And w ₂ , Respectively, and these weights are input to the CMYK interpolator 56 together with each selected CMYK look-up table.
[0096]
The interpolation process of the method of the present invention is basically the same as the interpolation process of the above-mentioned related application. As shown in FIG. 6, the CMY input cube is divided into six tetrahedrons. For any CMY input point, the surrounding tetrahedron is determined by the order information of the CMY signals. Each CMYK output signal corresponding to each CMY input point is interpolated by a CMYK lookup table from three sides connecting white, primary color, and adjacent secondary colors to black on a tetrahedron surrounding the three sides. . For example, if the CMY input point is C _i ≧ M _i ≧ Y _i If the condition that i = 2 is satisfied, the tetrahedron surrounding the point is one whose vertices are cubic black, white, cyan, and blue (FIG. 6A).
[0097]
The CMYK output signal will be determined by interpolation from a CMYK lookup table on a diagonal line passing through the center from white to black, on a line segment connecting cyan and black, and on a line segment connecting blue and black. The sequence signal V is used to select a tetrahedron containing the CMY input points.
[0098]
Next, the minimum Vs of the CMY input signals is used as an index into each of these CMYK lookup table sets (LUTc, LUTp, LUTs), and three sets of each CMYK intermediate signal (CMYK). ^(C) , CMYK ^(P) And CMYK ^(S) ) Is looked up.
[0099]
That is, each CMYK look-up table on three sides of this tetrahedron is used to obtain each CMYK output printer signal. Finally, each CMYK output signal 40 is interpolated by the CMYK interpolator 56 from the three sets of each CMYK intermediate signal.
[0100]
The interpolation process includes a weight generator 54, and generates each weight coefficient for interpolation. Then, the CMYK interpolator 56 performs interpolation using each weight coefficient. The interpolation process is described in FIG. This is a tetrahedron selected at the coordinates of the reordered CMY input signal. In FIG. 7, the constant V including the CMY input points _s Are intersected with the sides of the tetrahedron where each CMYK look-up table exists. The three intersections "C", "P", and "S" each correspond to an index into LUTc, LUTp, and LUTs and form a section that penetrates a particular tetrahedron, which section is the input signal set. Is defined as a function of
[0101]
Within the scope of this geometric description, the method of the present invention provides a LUTc, LUTp, LUTs in a triangle connecting the three points of points "C" (center), "P" (primary), "S" (secondary). The final CMYK signal 40 is obtained by linear interpolation of the numerical values retrieved from. The relative positions of the CMY input points within the triangle define each weight coefficient for triangular interpolation. This is obtained by solving the following equation.
[0102]
(Equation 1)

[0103]
The description of FIG. 7 will be continued. The vector (V ₁ ) Represents the positioning of the CMY input point with respect to point "C". The first vector (V ₂ ) Represents the positioning of point “P” with respect to point “C”. Then, the second vector (V ₃ ) Represents the positioning of point “S” with respect to point “C”. The solution of this equation is obtained as in the following equation (5).
[0104]
(Equation 2)

[0105]
From these weighting factors, the final CMYK output signal 40 is obtained as in the following equation (6).
[0106]
[Equation 3]

[0107]
Here, each CMYK numerical value accompanied by a superscript “(C)”, “(P)”, “(S)” respectively corresponds to each CMYK intermediate signal at points “C”, “P”, “S”. Each corresponds.
[0108]
(Upper half hue adjustment)
A pre-processing block 58 (herein referred to as a first processing block) is added to the block diagram of FIG. This pre-processing block 58 only converts each RGB signal to each CMY signal, but this addition provides a model for converting each RGB input signal to each CMYK output signal. Each CMYK look-up table on the diagonal line passing through the center indicates that the color lamp reproduces neutral gray and L ^* The output response is designed to be linear with respect to the RGB input signal.
[0109]
Also, each CMYK look-up table on the six borders is designed to reproduce a moderately large color gamut and to correct the hue shift at the lamp on the border from pure color to black. Each CMYK output signal for each CMY point inside the cube is interpolated from each CMYK output signal on the diagonal and boundary lines passing through the center, which results in the desired characteristics such as proper hue and linearity of the points inside. Will be retained. The above configuration / method is described herein as "one box structure" in connection with block 38 in FIG.
[0110]
However, the one-box structure does not affect the output of each hue angle corresponding to each CMY input point on the upper half surface of the RGB cube. Because the interpolation in these planes is based only on the white points in the RGB cube connecting R, M, B, C, G, Y back to R, and two adjacent pure color points on the polyhedron. It is. There is no interpolation grid point between the pure color point and the white point to correct the hue shift in this area.
[0111]
In order to improve the above-mentioned influence, the above-mentioned calculation structure uses a calculation structure called “two-box structure” for correcting a hue shift in the upper half surface. The block 34 of FIG. 3 for handling the upper half hue shift is constructed to convert each RGB input signal to each CMY signal and to correct the hue shift of each RGB signal. On the other hand, the processing block 38 as the lower half hue adjustment and black generation unit solves the problem of hue shift in the lower half plane of the RGB input cube in order to balance diagonal gray passing through the center. Designed for.
[0112]
As such, when the processing block 34 as the upper half hue adjustment unit is designed and constructed, the C in the secondary color area is ₂ M ₂ Y ₂ The signal already possesses the desired characteristics described above. That is, the purpose of the block 34 is to correct the problem of hue shift in the upper half of the RGB cube. Also, since the problem of gray balance on the diagonal line passing through the center has already been dealt with, C ₂ M ₂ Y ₂ The signal is again obtained by transforming the RGB signals using equation (1).
[0113]
However, on the boundary line, each one-dimensional RGB-CMY lookup table is used to convert each RGB signal into each CMY signal. In the method of the present invention, six sets of each one-dimensional RGB-CMY look-up tables are respectively arranged on a boundary line from each of R, G, B, C, M, Y to the white point. The index into these one-dimensional lookup tables is the minimum value of each RGB input signal.
[0114]
W _i = Min (R _i , G _i , B _i ) (7)
On the diagonal line extending from black to white through the center, the input R, G, B signals (herein, referred to as RGB input signals) are equivalent, and from RGB to CMY according to equation (1). Is implemented by a one-dimensional linear function from 100% for black to 0% for white (FIG. 8 (a)).
[0115]
On the boundary line from R to white, the input R signal is 100%, and the input G signal and B signal (herein referred to as GB input signal) are equivalent and change from 0% to 100%. The plot in FIG. 8B represents a typical set of curves from RGB to CMY on the boundary line from R to white. The C curve is constant at 0%, because the color on the border remains the purest color. The M and Y curves vary from 100% to 0%, but the slope of the descent is not linear, as shown by equation (1).
[0116]
Each of these curves is formed to compensate for the hue shift that can be caused by the mixing action of the dyes or the dot-off-dot halftone effect on the boundary line from R to white. I have. As shown in FIG. 5, the two-box structure may be a combination of the blocks 58 and 38.
[0117]
FIG. 9 shows details of the upper half hue adjustment unit 34, which is a processing block. This is essentially the same as the processing block, lower half hue adjustment and black generator 38, but each input signal is RGB, and the output of sorter block 62 is the ordered RGB signals and their order information. is there. Block 34 includes a weight generator 64, a CMY look-up table selector 66, a look-up table 66, and a CMY interpolator 70.
[0118]
There are no K dyes to consider in this processing block. The difference between the two blocks is that there is no black (K) output signal in the upper half block, and the vertices (C, M, Y, K) and (R, G, B, W) of the cube have a role in the calculation. The point is that they are reversed, that is, R and C are replaced and M and G are replaced. Of the seven sets of each one-dimensional RGB-CMY look-up table for the "CMY look-up table selector and one-dimensional table look-up" block, only six sets on the boundary are flexibly designed.
[0119]
The diagonal set passing through the center is fixed as shown in FIG. In practice, the look-up table on the boundary from C, M, Y to white is designed to achieve perceptual linearity. Then, each look-up table on each boundary line segment from R, G, B to white indicates the perceived linearity and the hue shift due to the halftone processing in which the dye mixture and / or the dots do not overlap. The correction is designed to achieve both.
[0120]
The parameters input to the upper half hue adjustment unit 34, which is a processing block, are six sets of each CMY lookup table on each line segment from C, M, Y, R, G, B to white. Each of these line segments is represented by a thick line in FIG. Each color output on each of these lines is directly determined by each CMY look-up table on that line.
[0121]
Each of these look-up tables keeps each hue angle of each color ramp from each secondary color to white almost constant, and gives the tone some desired properties, such as perceptual uniformity. Designed for. In some cases, these look-up tables are used for each gradation of the primary color.
[0122]
The geometric description of the interpolation processing shown in FIG. 7 is also valid for the upper half hue adjustment unit 34 which is a processing block. However, since each input is each RGB signal, for the RGB cube, each primary color is R, G, and B, and each secondary color is C, M, and Y. Equation (5) is again used to obtain each weighting factor. Each CMY signal is obtained by the following equation.
[0123]
(Equation 4)

[0124]
The tetrahedral section of the CMY cube corresponding to the hue adjustment of the lower half and the tetrahedron section of the RGB cube corresponding to the hue adjustment of the upper half are identical to each other. Thus, the method of the present invention uses the same calculations for interpolation in the RGB cube as used for interpolation in the CMY cube.
[0125]
However, since the gray balance of each color from black to white on the diagonal line passing through the center has already been obtained by the block of “lower half hue adjustment and black generation unit”, the CMY lookup table is set on the diagonal line passing through the center. No need to ask. Instead, to generate each CMY numerical value on a diagonal line passing through the center for the purpose of interpolation, simply convert the coordinates of each RGB input signal.
[0126]
The techniques disclosed herein also apply to each output dye other than RGB, CMY or CMYK. For example, by defining different lookup tables on a tetrahedral boundary line, hexachrome (Hexachrome) can be used. ^TM ), CcMmYK, or other methods of setting dyes, or other color spaces such as XYZ, Lab, can be treated as a simple computational model from signal to color.
[0127]
(Development to computational structure)
In the computational structures described so far, each one-dimensional lookup is performed on a diagonal line passing through the center in an RGB or CMY cube, and on each boundary line connecting each primary color and each secondary color to black and white points. The table is positioned. The characteristics of each color output obtained on each line segment on which each one-dimensional lookup table is arranged can be accurately controlled.
[0128]
However, the color output in other parts of the signal input cube is less accurate. This is because they are interpolated by each nearby look-up table.
[0129]
Based on the results of experiments using a CMYK inkjet printer, each look-up table can also find the desired characteristic on each line segment specified and apply this successfully to other parts of the input cube.
[0130]
However, sometimes it is desirable to precisely control the color output in other parts of the input cube. For example, the blue point of a traditional printer has 100% C and M and 0% Y, but always has a purple hue. By reducing M while maintaining C at 100% and Y at 0%, a more natural blue point can be obtained. From this natural blue point to the black and white points, it may be desirable to precisely control the output of the hue response along each color ramp.
[0131]
The general principle of the above computational structure is that each one-dimensional lookup table is placed only on a diagonal line passing through the center or on a boundary line from each primary color and each secondary color to the white and black points. It is not limited to. Each look-up table is also located on another line segment inside the input RGB or CMY cube, and can precisely control the characteristics of the color output there.
[0132]
However, if more lookup tables were added to the computational structure, only the order information from each input signal was insufficient to select the set of lookup tables to be used for interpolation. turn into. To utilize each additional look-up table, additional processing steps are required.
[0133]
The arrangement of each look-up table on the additional line segment within the selected tetrahedron is shown in FIG. In this example, two additional sets of look-up tables are arranged on two thick lines 82 and 84. The plane perpendicular to the Vs axis intersects the additional line segment at points "C", "P", "S", and also at points "A" and "B". The triangle 86 including the input point is projected on the plane Vs = 0 (see FIG. 11B).
[0134]
Each intermediate output signal is obtained by a direct table lookup at these five intersections. The illustration is also shown in FIG. 11 (b), where the triangle 86 surrounded by points "C", "P" and "S" is further divided into four sub-triangles (I-IV). ). The △ input point needs to be defined to select the appropriate set of each vector and each look-up table in the appropriate set.
[0135]
The input points are algebraically tested by transposing a matrix to determine which of the four triangles contains the input point. Each final output signal is interpolated from the intermediate signal at each of the three vertices of the secondary triangle surrounding the input point. The split illustration in FIG. 11 (b) is for illustration only, and the best split illustration depends on the particular application.
[0136]
In another version of the method of the present invention, the RGB / CMY signal cube is divided into six or more tetrahedrons each. For example, one or more of each of the six aforementioned tetrahedrons is split by introducing additional vertices at the tetrahedron boundary connecting the primary color and the next secondary color. In addition to the diagonal line passing through the center and the line segment on the cube surface described above, other line segments can be used to further divide the cube. For example, additional vertices may be introduced at the base of the tetrahedron (where Vs = 0). In such a case, the interpolation method disclosed herein works essentially the same. The main difference is that a more complex and sophisticated algorithm is needed to identify the tetrahedron surrounding the input signal vector.
[0137]
(Experimental result)
Given the development and development of computational structures, it is clear that this structure can be used to control various aspects of the conversion process, such as RGB to CMYK or RGB to RGB. In experiments using the method of the present invention, the problems of the hue adjustment and output color gamut of the RGB-to-CMYK conversion model have been emphasized and have been the focus of research. As shown in FIG. 3, in the present invention, a two-step method is constructed, in which seven sets of each CMYK lookup table for the “lower half hue adjustment and black generator” module are replaced by the “upper half hue adjustment unit” module. For each of the six sets of CMY look-up tables were designed. The printer color gamut is represented by a CIELAB space. For hue adjustment, the hue angle in the CIELUV space is corrected. However, other color spaces can be used.
[0138]
The experimental results of the CMYK inkjet printer are shown in FIGS. 12A and 12B at 90 and 96, and at 110 in FIG. In FIG. 12 (a), the color gamut of a simple UCR and GCR implementation (line 92) and the color gamut of a computational structure based on the method of the present invention (line 94) in the red hue leaf are compared. I have. It can be seen from the experimental results that the method of the present invention can provide a larger color gamut in the shadow area.
[0139]
The color gamut of the red leaf obtained by the present invention is further compared with the entire CMYK color gamut at this hue angle (FIGS. 12B and 96). The CMYK gamut is line 98, and the gamut leaf obtained by the computational structure of the method of the present invention is line 100. It can be seen from FIG. 12 that the leaves of the color gamut obtained by the method of the present invention are very close to the CMYK full color gamut.
[0140]
The effect on the hue adjustment is shown by 110 and 116 in FIGS. 13 (a) and 13 (b), respectively. In both figures, the corrected hue is represented by a solid line. In FIG. 13A, a corrected hue line 112 from green to black is compared with a hue line 114 obtained from a conventional implementation. In FIG. 13B, the corrected hue line 118 from green to white and the uncorrected hue line 120 are compared.
[0141]
Efficient computational structures have been developed to convert each RGB input signal to each CMYK printer output signal. This structure is used to manufacture a CMYK printer as an RGB printer.
[0142]
It is relatively easy to outline an RGB printer, but it is a one-to-one correspondence between each color specified in a colorimetric space such as CIELAB space or sRGB space and each RGB signal. Because.
[0143]
The computational structure of the present invention may be considered as an evolution of a simple implementation of conventional UCR and GCR techniques using one-dimensional BG and UCR look-up tables. In this structure, multiple sets of each one-dimensional look-up table are effectively placed in various portions of the RGB or CMY input cube to control the output response of a commercialized RGB printer.
[0144]
The arrangement of each one-dimensional look-up table essentially divides the RGB or CMY input cube into several tetrahedra, and each look-up table on each tetrahedral boundary is located at an input point inside the tetrahedron. Used for interpolation of the corresponding CMYK output signal.
[0145]
The computational structure of the present invention can be used to construct a two-step process for the conversion from RGB to CMYK to achieve a sufficiently large color gamut, for example, for the hue produced by each halftone or each dye. Correct the misalignment. Experimental results show that this model can achieve a color gamut approximately the same size as the entire CMYK color gamut and can successfully correct hue shifts.
[0146]
The application of this computational structure is not limited to printers that convert RGB to CMYK. It can also be applied to the manufacture of printers with more than three inks or dyes. It can also be used to compensate for undesired operation of devices other than printers.
[0147]
Thus, a color conversion method based on hue adjustment using a plurality of lookup tables and interpolation has been disclosed. It will also be apparent that the method can be further varied and modified within the scope of the invention as defined in the appended claims.
[Brief description of the drawings]
FIG.
6 is a graph showing a CMY input cube for lower half hue adjustment and black generation.
FIG. 2
It is each graph which shows each curve of BG and each UCR, and each curve which shows the relationship between both curves and one-dimensional CMYK response output curve, (a) is each curve of BG and each UCR, (b) is a diagonal line passing through the center. The upper CMYK response curve, (c) shows the CMYK response curve on the boundary line from C to black, and (d) shows the CMYK response curve on the boundary line from G to black.
FIG. 3
It is a block diagram which shows the structure of conversion from RGB to CMYK.
FIG. 4
It is a block diagram which shows the structure of conversion from RGB to RGB.
FIG. 5
FIG. 4 is a block diagram showing a structure of calculation regarding hue adjustment and black generation of a lower half.
FIG. 6
(A) to (f) are graphs respectively showing CMY input cubes divided into six tetrahedrons.
FIG. 7
6 is a graph for explaining a table look-up and an interpolation process geometrically.
FIG. 8
(A) is a graph showing a curve showing a one-dimensional RGB to CMY conversion at a fixed black to white line, and (b) is a graph from red to white designed according to the method of the present invention. FIG. 4 is a graph showing a curve indicating a one-dimensional conversion from RGB to CMY in a line. FIG.
FIG. 9
It is a block diagram which shows the structure of the calculation regarding upper half hue adjustment.
FIG. 10
9 is a graph showing an RGB input cube for adjusting the upper half hue.
FIG. 11
(A) is a graph showing additional look-up tables within and on the surface of the input cube and (b) a method for selecting an appropriate look-up table.
FIG.
4A and 4B are graphs each showing a graphic comparison of the color gamut of a red leaf obtained by the method of the present invention, in which (a) is a comparison with the color gamut of a conventional UCR and GCR implementation, and (b) is a graph. This is a comparison with the entire CMYK color gamut.
FIG. 13
(A) Hue lines resulting from conventional UCR and GCR implementations, and hue lines resulting from the method of the present invention on green to black lines, (b) corrected on green to white lines 7 is a graph showing a graphical comparison of hue angles in CIELUV space between the uncorrected hue and the hue angle, respectively.

Claims (38)

Providing a first color area input signal set having a plurality of input signals;
Classifying each input signal of the first color gamut input signal set according to signal strength;
Design and form multiple one-dimensional lookup table sets corresponding to color polyhedrons,
Selecting a set of each look-up table for use with a particular color polyhedron,
The selection is
A function of a section of the polyhedron determined as a function of the input signal set,
Look up the values in the lookup table set as a function of the input signal set,
Generate weights as a function of the classified signal strength,
A color conversion that interpolates the output values from the selected look-up table as a function of the selected look-up table and the generated weights to produce a color gamut signal set that is converted to a desired color gamut signal set. Method. Classifying each input signal set into respective color region components V ₁ , V _m , V _s (V ₁ ≧ V _m ≧ V _s ),
Generate command signal,
Design and form a one-dimensional lookup table for the color area,
Generate the respective weights w ₁ , w ₂ as a function of V ₁ , V _m , V _s ,
Select a look-up table as a function of each classified component and command signal,
Interpolating each color region component using the respective weights and the selected look-up table to prepare a signal set corresponding to a desired color region,
The method of claim 1 including correcting for hue shifts in the first color region. The correction of the hue shift in the first color area is as follows:
Input RGB input signal,
Design and form each CMY one-dimensional lookup table,
3. The method of claim 2 including performing an interpolation to provide a set of CMY signals. The correction of the desired color area includes:
Input CMY input signal and black generation,
Design and form each CMYK one-dimensional lookup table,
3. The method of claim 2 including performing an interpolation to provide a CMYK signal set. 5. The method of claim 4, wherein designing and forming each of the CMYK one-dimensional look-up tables includes identifying independent look-up tables corresponding to each primary color, each secondary color, and each black. 6. The method of claim 5, wherein designing and forming each of the CMYK one-dimensional lookup tables includes controlling each hue angle. 6. The method of claim 5, wherein designing and forming each of the CMYK one-dimensional look-up tables includes controlling a colorimetric space of each color lamp. 5. The method of claim 4, wherein designing and forming each of the CMY one-dimensional look-up tables includes identifying independent look-up tables corresponding to each primary color and each secondary color. 9. The method of claim 8, wherein designing and forming each of the CMY one-dimensional lookup tables includes controlling a hue angle and a colorimetric space for each color lamp. The correction of the desired color area includes:
Input CMY input signal,
Design and form each CMY one-dimensional lookup table,
3. The method of claim 2 including performing an interpolation to provide a set of RGB signals. The method of claim 1 wherein processing the desired color gamut signal set comprises black generation. 12. The method of claim 11, wherein preparing the first color gamut input signal set includes preparing an RGB signal set and including generating a final dye signal set, including generating a CMYK signal set. The preparation of the first color area input signal set includes preparation of an RGB signal set, and generation of a final dye signal set including generation of a corrected first color area signal set as an RGB signal set. Method 1. Correcting the hue shift to generate a second color area signal set,
Processing a second color gamut signal set in a lower half hue adjustment module where colors between each pure color and black are processed;
Correcting for the hue shift to produce a final set of dye signals in the desired color gamut;
2. The method of claim 1 including processing the first color gamut input signal set in the upper half hue adjustment module where all colors are processed. The processing of the second color area input signal includes:
Classify each input signal according to signal strength,
Design and form each one-dimensional lookup table corresponding to each color line segment,
Select one specific lookup table,
Generate each weight as a function of each classified signal strength;
The method of claim 14, wherein each input signal is interpolated to generate a final set of dye signals. The interpolation of the hue shift is as follows:
The signal set is classified into each color region component V ₁ , V _m , V _s (V ₁ ≧ V _m ≧ V _s )
Generate a sequence signal,
Design and form a one-dimensional lookup table corresponding to the color area,
V _l, and generates a respective weight _w 1, _{w 2} as a function of _V m, _{V s,}
Select a look-up table set as a function of the classified components and the order signal,
15. The method of claim 14, including interpolating the color gamut components using each weight and the selected set of look-up tables to provide another set of color gamut signals. The correction of the first color area is as follows:
Input RGB input signal,
Design and form each CMY one-dimensional lookup table,
17. The method of claim 16, including performing an interpolation to provide a set of CMY signals. The correction of the second color area is as follows:
Input CMY input signal and black generation,
Design and form each CMYK one-dimensional lookup table,
18. The method of claim 17, including performing an interpolation to provide a CMYK signal set. 19. The method of claim 18, wherein designing and forming each of the CMYK one-dimensional look-up tables includes identifying independent look-up tables corresponding to primary colors, secondary colors, and black. 20. The method of claim 19, wherein designing and forming each of the CMYK one-dimensional look-up tables includes controlling a colorimetric space of each color lamp. 20. The method of claim 19, wherein designing and forming each of the CMYK one-dimensional look-up tables includes controlling each hue angle. The correction of the second color area is as follows:
Input CMY input signal,
Design and form each CMY one-dimensional lookup table,
17. The method of claim 16, including performing an interpolation to provide a set of RGB signals. 17. The method of claim 16, wherein designing and forming each of the CMY one-dimensional look-up tables includes identifying each look-up table independently from primary colors and secondary colors. 24. The method of claim 23, wherein designing and forming each of the CMY one-dimensional lookup tables includes controlling each hue angle. 24. The method of claim 23, wherein designing and forming each of the CMY one-dimensional look-up tables includes controlling a colorimetric space of each color lamp. The method of claim 14, wherein processing the second color gamut signal set comprises black generation. 27. The method of claim 26, wherein preparing the first color gamut input signal set comprises preparing an RGB signal set, and generating a final dye signal set includes generating a CMYK signal set. 15. The method of claim 14, wherein preparing the first color region input signal set includes preparing an RGB signal set, and generating a final dye signal set includes generating a corrected first color region signal set, which is an RGB signal set. Method. Prepare RGB input signal set,
The RGB input signal set is processed by the upper half hue adjustment module, which performs color processing including correction of hue shift, generates a second color area signal set,
Processing the second color gamut signal set in the lower half hue adjustment and black generation module, including processing all colors, including correction for hue shift, to generate a final set of dye signals. Color conversion method. The processing of the RGB input signal includes:
Classify each input signal according to signal strength,
Design and form each one-dimensional lookup table corresponding to the color line segment,
Select a specific set of lookup tables,
Generate each weight as a function of the classified signal strength,
30. The method of claim 29, comprising interpolating values from a set of look-up tables to generate a set of CMY signals. The processing of the CMY signal set includes:
Classify each input signal according to signal strength,
Design and form each one-dimensional lookup table corresponding to each colored line segment and each colorless line segment,
Select a specific set of lookup tables,
Generate each weight as a function of the classified signal strength,
31. The method of claim 30, including interpolating each look-up table signal to generate a CMYK dye signal set. The correction of the hue shift is as follows:
The signal set is classified into each color region component V ₁ , V _m , V _s (V ₁ ≧ V _m ≧ V _s )
Generate a sequence signal,
Design and form a one-dimensional lookup table corresponding to the color area,
V _l, and generates a respective weight _w 1, _{w 2} as a function of _V m, _{V s,}
Selecting a look-up table as a function of the sorted components and the order signal, interpolating each color gamut component using the weights and the selected look-up table, and providing another color gamut signal set. 30. The method of claim 29. The correction of the RGB signal set includes:
Design and form each one-dimensional lookup table for the second color area,
33. The method of claim 32, comprising performing an interpolation to provide a second color gamut signal set. The correction of the second color area signal set includes:
Generate black,
Design and form each one-dimensional lookup table for the final color area,
34. The method of claim 33, comprising performing an interpolation to provide a final set of dye signals. In designing and forming each one-dimensional lookup table and the final one-dimensional lookup table in the second color area, an independent lookup table is specified from each primary color, each secondary color, and black. 35. The method of claim 34, comprising: 31. The method of claim 30, wherein designing and forming each one-dimensional look-up table and final one-dimensional look-up table in the second color gamut includes controlling each hue angle. 31. The method of claim 30, wherein designing and forming each one-dimensional look-up table and the final one-dimensional look-up table in the second color gamut includes controlling a colorimetric space of each color lamp. 30. The method of claim 29, wherein the transposition preprocesses the RGB input signal to generate a CMY input signal.

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