JP2004299171A - Process of dividing plate into a plurality of ink components including primary color ink and secondary color ink - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To expand the range of color reproduction and balance chroma when the primary color ink and the secondary color ink are usable. <P>SOLUTION: The plate division process has the process of setting an ink set including a plurality of primary color inks and at least one secondary color ink, the process of determining a plurality of reproduced colors in response to with a plurality of input colors when a color reproduced in response to one optional input color is called a reproduced color and the combination of quantities of inks of the ink set to reproduce the reproduced colors are called a plate division ink quantity set, and the process of determining a plurality of plate division ink quantity sets to reproduce a plurality of the reproduced colors. A plate division method to determine a plurality of reproduced colors is used so as to meet a predetermined chroma limitation in which the chroma of reproduced colors of the same hue as the secondary color ink has a range greater than the range of chroma reproducible by the primary color ink and smaller than the maximum range of the chroma reproducible by the ink set. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０１２５】
また、本実施例では、以下に示す条件を満たすように拡張有彩色ｅｍが算出される。
【０１２６】
（条件１）最外殻分版インク量セットがインクデューティ制限を満たす。
（条件２）拡張有彩色が彩度制限を満たす。
【０１２７】
インクデューティ制限としては、例えば、全種類のインク量の合計値の制限や、各色単独のインク量の制限、２色を混色するためのインク量の制限等を設定することができる。
【０１２８】
全種類のインク量の合計値の制限については、例えば、次式で表される。
【０１２９】
【数２】

【０１３０】
数式中、Ｃ、Ｍ、Ｙ、Ｒ、Ｖは、それぞれ、ＣＭＹＲＶ各色のインク量である（後述する他の数式でも同様である）。また、Ｄｕｔｙ＿Ｔは、インクや印刷媒体の種類に応じて予め設定された制限値である。
【０１３１】
各色単独のインク量の制限については、例えば、次式で表される。
【０１３２】
【数３】

【０１３３】
Ｄｕｔｙ＿Ｃ〜Ｄｕｔｙ＿Ｖは、インクや印刷媒体の種類に応じて各色のために予め設定された制限値である。
【０１３４】
２色を混色する際のインク量の制限については、例えば、次式で表される。
【０１３５】
【数４】

【０１３６】
なお、この制限においては、任意の２つのインクの組み合わせについて制限が課せられるが、その中の６つの組み合わせについて例示している。Ｄｕｔｙ＿ＣＭ〜Ｄｕｔｙ＿ＭＲは、インクや印刷媒体の種類に応じて各インクの組み合わせのために予め設定された制限値である。
【０１３７】
なお、インクデューティ制限としては、３色の混色、４色の混色等、任意の種類のインクの組み合わせに対する制限を設定しても良い。
【０１３８】
また、彩度制限については、例えば、ＣＭＹ各色の仮想的な階調値に対する制限を設定することができ、このような設定は次式で表される。
【０１３９】
【数５】

【０１４０】
数式中、ＣＤ、ＭＤ、ＹＤは、それぞれ、ＣＭＹ各色の仮想的な階調値である。また、Ｃ＿Ｌｉｍｉｔ、Ｍ＿Ｌｉｍｉｔ、Ｙ＿Ｌｉｍｉｔは、予め設定された制限値である。これらの制限値も、インクデューティ制限と同様に、インクや印刷媒体の種類に応じて変えれば、インクや印刷媒体の種類に応じて適切に彩度を制限することができる。
【０１４１】
以上のようなインクデューティ制限（条件１）と彩度制限（条件２）は、置換インク量を用いて得られるＣＭＹ各色の仮想的な階調値を用いて、図１２に示す１次色色空間において面で表現することができる（図示せず）。これらの面で囲まれた領域は、インクデューティ制限と彩度制限を満たす領域である。よって、ＣＭＹＲＶ各色のインク量で表された色のＣＭＹ各色の仮想的な階調値がこれらの面で囲まれた領域内にあれば、各インク量がインクデューティ制限と彩度制限とを満たすことができる。
【０１４２】
図１２（ｂ）には、拡張有彩色ｅｍが示されている。拡張有彩色ｅｍは、インクデューティ制限（条件１）と彩度制限（条件２）とを満たす領域の外殻面、すなわち、再現色外殻面（図示せず）に位置している。また、拡張有彩色ｅｍは、原点Ｗと最外殻有彩色ｍとを通る線分上に位置する。すなわち、拡張有彩色ｅｍは、原点Ｗと最外殻有彩色ｍとを通る線分と、再現色外殻面とが交わる位置にある色である。換言すれば、拡張有彩色ｅｍは、１次色色空間において最外殻有彩色ｍを表す最外殻有彩色ベクトルと同一の方向を有する最も長い拡張有彩色ベクトルで表される色であるとともに、彩度制限を満たし、拡張有彩色ｅｍを再現するための最外殻分版インク量セットがインクデューティ制限を満たす色である。
【０１４３】
このような拡張有彩色ｅｍは種々の方法を用いて算出することが可能である。例えば、１次色色空間において彩度制限（条件２）を満足する色を選択し、有彩１次色インクから有彩２次色インクへの置換を行って分版インク量セットを算出し、分版インク量セットがインクデューティ制限（条件１）を満足するか否かを判定する、という一連の処理を繰り返し実行することによって、逐次近似的に算出することができる。また、置換インク量やインクデューティ制限（条件１）、彩度制限（条件２）の各式等に基づき、いわゆる線形計画法を用いて算出することもできる。この場合には、一連のステップＳ１２０〜Ｓ１３０（図１１）が一度に実行されることとなる。
【０１４４】
以上のように、インクデューティ制限（条件１）と彩度制限（条件２）とを満たす拡張有彩色ｅｍ（最外殻分版インク量セット）を算出することによって、その色を印刷したときの画質が良好な範囲内で、色相が有彩２次色インクに近い場合であっても極端に彩度が高くなく、最外殻有彩色ｍと同じ方向に位置する最も階調値の大きい拡張有彩色ｅｍを得ることができる。
【０１４５】
図１１のステップＳ１４０では、入力色Ｉ（図１２）に対応する分版インク量セットＯの算出を行う。このステップＳ１４０では、まず、拡張有彩色ｅｍに対する最外殻分版インク量セットｅｍｐの算出を行う。最外殻分版インク量セットｅｍｐは、上述のステップＳ１３０において拡張有彩色ｅｍを算出する際に、インクデューティ制限（条件１）を満たすか否かの判断のために既に算出されている値である。ただし、利用可能なインクの種類が多い場合には、有彩１次色インクと有彩２次色インクとの置換の自由度が高くなる。そのため、拡張有彩色ｅｍに対応する最外殻分版インク量セットｅｍｐとして、インクデューティ制限（条件１）を満たす範囲において複数種類のインク量の組み合わせを選択することができる場合がある。このような場合には、本実施例では、複数の組み合わせの中から、各インク量の合計値が最も小さい組み合わせを選択して最外殻分版インク量セットｅｍｐとして用いている。
【０１４６】
次に、最外殻分版インク量セットに基づいて分版インク量セットＯの算出を行う。図１２（ｃ）は、入力色Ｉと分版インク量セットＯとの関係の概略を示す説明図である。本実施例では、入力色Ｉが示すベクトルの長さＬＬＩと、最外殻有彩色ｍが示すベクトルの長さＬＬｍの比を、最外殻分版インク量セットｅｍｐに乗じることによって算出した比例分版インク量セットを、分版インク量セットＯとして用いる。このとき、最外殻有彩色ｍに対応する分版インク量セットは最外殻分版インク量セットｅｍｐとなる。原点Ｗと最外殻分版インク量セットｅｍｐとの間の色はインクデューティ制限を満たすことが可能であるので、印刷媒体とインクセットの特定の組み合わせで再現可能である。また、原点Ｗと最外殻分版インク量セットｅｍｐとの間の色は彩度制限を満たすので、色相が有彩２次色インクに近いときであっても、その彩度が極端に高くなることを抑制することができる。よって、印刷媒体とインクセットの特定の組み合わせで再現可能な色の範囲を有効に利用することができる。また、このように長さＬＬＩに比例するように分版インク量セットＯを算出することによって、入力色Ｉに対する分版インク量セットＯを容易に算出することができる。
【０１４７】
こうして、ステップＳ１００〜Ｓ１４０の処理を順次実行することによって、１次色表色系で表された入力色Ｉに対応する再現色表色系で表された分版インク量セットＯが算出される。また、分版インク量セットＯは、入力色Ｉや長さＬＬＩ、ＬＬｍとの関係に加えて、置換インク量やインクデューティ制限（条件１）、彩度制限（条件２）の各式等に基づき、線形計画法を用いて直接算出することもできる。この場合には、一連のステップＳ１２０〜Ｓ１４０が一度に実行されることとなる。このようにして得られた分版インク量セットＯは、図６のステップＳ２０における第２の階調値セットとして用いることができる。なお、分版インク量セットＯで再現される色が、入力色Ｉに対応付けられた再現色（印刷媒体上に再現される色）に相当する。
【０１４８】
図１１のステップＳ１５０では、全ての入力色に対する分版インク量セットが算出されたか否かの判断がされる。すべての分版インク量セット算出が完了していない場合には、ステップＳ１２０〜Ｓ１４０の処理が繰り返され、完了している場合には処理を終了する。
【０１４９】
なお、分版処理に必要な時間をより短くするためには、一連の処理を実行するための最外殻有彩色の数を制限することが好ましい。このとき、分版処理を行いたい入力色に対応する最外殻有彩色が無い場合には、その入力色に近い複数の色の分版インク量セットを補間して、対応する分版インク量セットを求めることができる。また、このとき、最外殻有彩色を、最外殻有彩色と原点Ｗとを結ぶ直線が色立体中の全範囲に分布するように、予め複数準備するのが好ましい。こうすることによって、色立体中の特定の領域において、分版インク量セットの補間誤差が大きくなることを抑制することができる。
【０１５０】
以上のように、本実施例では、拡張有彩色ｅｍおよび最外殻分版インク量セットの決定が、以下の３つの条件、
（ｉ）最外殻分版インク量セットがインクデューティ制限内である、
（ｉｉ）拡張有彩色が彩度制限内である、
（ｉｉｉ）インクセットで再現可能な範囲で拡張有彩色ベクトルの長さが最も長くなる、
（ｉｖ）拡張有彩色ｅｍを再現するための最外殻分版インク量セットのインク量の合計が最も少なくなる、
を満たすように実行されている。なお、これら全ての条件を満たしていなくても、拡張有彩色ｅｍが最外殻有彩色ｍよりも彩度が高い色であれば、色再現範囲を拡張することができる。例えば、条件（ｉｉｉ）を満たしておらず、拡張有彩色ベクトルが最長でない場合でも、最外殻有彩色ベクトルよりも長くなるように構成されていれば、色再現範囲を拡張することができる。
【０１５１】
また、色再現範囲をより広い色相範囲において拡張するためには、より広い色相範囲において、拡張有彩色ベクトルが最外殻有彩色ベクトルよりも長くなるようにすることが好ましい。ここで、拡張有彩色ベクトルを延長することができる色相の範囲は、使用可能な有彩２次色インクの色相に応じて変わる範囲である。有彩２次色インクは、そのインクの色相に近い色相を有する領域の色再現範囲を拡張することができる。そのため、互いに色相の異なるより多くの種類の有彩２次色インクを使用可能とすることによって、より広い色相範囲において、拡張有彩色ベクトルが最外殻有彩色ベクトルよりも長くなるようにすることができる。また、このときも、彩度制限を満たすように拡張有彩色を設定することによって、拡張有彩色の色相が有彩２次色インクに近い場合でも、極端に彩度の高い拡張有彩色を設定することを抑制することができる。
【０１５２】
以上説明したように、本実施例では、有彩１次色インクと有彩２次色インクとを用いて再現することが可能な色彩の範囲を有効に利用した分版処理を行っている。そのため、色再現範囲を拡張させた印刷を行うことができる。また、原点と最外殻有彩色とを結ぶ直線と再現色外殻面との交点に位置する拡張有彩色に基づいた分版処理を行っているので、使用可能なインクの種類が増えた場合でも、容易に分版処理結果を得ることができる。また、彩度制限を満たす範囲内に再現色が設定されるので、色相が有彩２次色インクに近いときに彩度の極端に高い色が発生することを抑制することができる。その結果、印刷画像の中の一部の領域を不自然に目立たせることなく、色の再現範囲を拡張することができる。
【０１５３】
Ｄ．分版処理の第３実施例：
図１４は、分版処理の第３実施例の処理手順を示すフローチャートである。上述の図１１の分版処理実施例との差異は、ブラックインクＫを用いた下色除去（ＵＣＲ：Ｕｎｄｅｒ Ｃｏｌｏｒ Ｒｅｍｏｖａｌ）処理Ｓ２２０を実行している点である。本実施例のＵＣＲ処理は、有彩１次色インクＣ、Ｍ、Ｙの階調値の一部をブラックインクＫの階調値に置換する処理である。ＵＣＲ処理は、周知の種々の方法によって実現可能であるため、ここでは詳細な説明を省略する。
【０１５４】
ステップＳ２００では、使用可能なインクセットとして、有彩１次色インクＣ、Ｍ、Ｙと有彩２次色インクＲ、ＶとブラックインクＫからなるインクセットを設定している。
【０１５５】
次に、ステップＳ２１０では、インクセットの各色のインク量の制限であるインクデューティ制限を設定する。上述の図１１に示す実施例におけるインクデューティ制限との差異は、ブラックインクＫのインク量を考慮して設定されている点である（詳細は後述）。
【０１５６】
次に、ステップＳ２２０では、分版処理の対象となる入力色（例えば、図６のステップＳ２０では１次色階調値セットで表現されている）に対し、ＵＣＲ処理を実行する。その結果、ＣＭＹＫ各色の階調値Ｃｉ、Ｍｉ、Ｙｉ、Ｋｉで表現された入力色Ｉが得られる。本実施例では、これらの階調値のうちのＣＭＹ各色の階調値Ｃｉ、Ｍｉ、Ｙｉに対して、拡張有彩色ｅｍを用いた分版処理を実行する。一連の処理Ｓ２３０〜Ｓ２６０は、図１１に示す実施例の処理Ｓ１２０〜Ｓ１５０と同じ処理である。その結果、ＣＭＹ各色の階調値Ｃｉ、Ｍｉ、Ｙｉに対する分版インク量Ｃｏ、Ｍｏ、Ｙｏ、Ｒｏ、Ｖｏが得られる。ブラックインクＫについては、ＵＣＲ処理Ｓ２２０の結果得られる階調値Ｋｉが分版インク量Ｋｏとして用いられる。
【０１５７】
このように、第３実施例の分版処理では、有彩１次色インクＣＭＹと有彩２次色インクＲＶに加えて、ブラックインクＫを用いて再現することが可能な色彩の範囲を有効に利用した分版処理を行っている。そのため、色再現範囲をさらに拡張させた印刷を行うことが可能である。
【０１５８】
また、この実施例においては、上述のインクデューティ制限（条件１）において、ブラックインクＫのインク量を考慮した制限を設けるのが好ましい。例えば、数式２に示す全種類のインク量の合計値の制限については、ＣＭＹＲＶ各色のインク量に、ステップＳ２２０で得られたブラックインクＫのインク量Ｋｉを合わせた合計値が、Ｄｕｔｙ＿Ｔ以下となるように設定することができる。こうすることによって、印刷媒体のインク吸収量の制限を越えた量のインクを吐出することを抑制することができる。また、複数色を混色する場合のインク量の制限についても、ブラックインクＫのインク量Ｋｉを用いて制限を設定することができる。ブラックインクＫ単独のインク量の制限についてはＵＣＲ処理Ｓ２２０においてインク量Ｋｉを算出する際に考慮するのが好ましい。
【０１５９】
なお、本実施例の分版処理を図６に示す色変換ルックアップテーブルの作成処理のステップＳ２０に適用したときには、第２の階調値セットは、有彩１次色インクＣＭＹと有彩２次色インクＲＶとブラックインクＫの各色インク量で表された階調値となる。よって、ステップＳ３０では、ＣＭＹＲＶＫ各色を用いて再現されたカラーパッチが作成される。
【０１６０】
Ｅ．インクセットの変形例：
上述の各実施例には、図５に示すインクセット以外にも様々な種類のインクセットを適用することができる。図１５〜２２は、いずれも、適用可能なインクセットの実施例の各インク成分を示す説明図である。ブラックインクＫの成分と色材以外の成分については、図５と同様であるので、図示を省略している。図５に示すインクセットとの差異は、色材の種類と濃度が一部異なる点である。その結果、これらのインクセットは、互いに少しずつ異なる色彩の再現性を向上させることが可能である。よって、印刷したい画像に適したインクセットを選択して用いることによって、より高画質な印刷結果を得ることができる。
【０１６１】
図１５〜２０のインクセットには、カラーパッチを測色して得られた、レッドインクＲとバイオレットインクＶのそれぞれの置換インク量が示されている。このように、これらのインクセットでは、置換インク量の合計値がいずれも１．７以上である。その結果、有彩２次色インクは、有彩１次色インクの混色と同程度のインク量を用いることによって、より高い彩度を再現することが可能である。その結果、有彩１次色インクと有彩２次色インクとを利用することによって、有彩１次色インクのみで再現可能な領域よりも広い範囲の色彩を再現することが可能となる。
【０１６２】
また、各インクとしては、上述の図５、図１５〜２２に示す組成に限定されることなく、その他の組成に従った適切なインクを用いても良い。さらに、用いるインクの色や数についても、この組み合わせに限定されることなく、例えば、有彩２次色インクとしてレッドインクＲのみを利用可能な構成としても良く、また、有彩２次色インクとして、グリーンインクやブルーインクを用いる構成としてもよい。但し、互いに組み合わせて無彩色を再現可能なインクを有彩１次色インクとして用い、有彩１次色インクのいずれとも色相が異なるインクを有彩２次色インクとして用いることが好ましい。このようなインクで構成されたインクセットを用いることによって、色再現範囲の拡張を考慮した分版処理を実行することができる。
【０１６３】
Ｆ．印刷システムの第２実施例：
図２３は、印刷システムの第２実施例を説明する説明図である。第２実施例と上述の印刷システムとの差異は、同じインクと同じ印刷媒体を利用可能であるとともに再現色の彩度の範囲が互いに異なる２つの色変換ルックアップテーブルＬＵＴ１、ＬＵＴ２を備えている点である。
【０１６４】
図２３には、本実施例のプリンタドライバ９６ａの概略が示されている。色変換ルックアップテーブル以外の構成は、図１に示す印刷システムと同じである。すなわち、９７ａ〜１０１ａの各機能部の動作は、図１に示す９７〜１０１の各機能部の動作とそれぞれ同じである。
【０１６５】
図２３の例では、プリンタドライバ９６は、自然画用色変換ルックアップテーブルＬＵＴ１と、ポスター用色変換ルックアップテーブルＬＵＴ２とを備えている。自然画用色変換ルックアップテーブルＬＵＴ１は、印刷媒体上に再現可能な彩度の範囲が比較的狭く、ポスター用色変換ルックアップテーブルＬＵＴ２は、印刷媒体上に再現可能な彩度の範囲が比較的広くなるように、それぞれ構成されている。
【０１６６】
このような、彩度の範囲が互いに異なる２つのルックアップテーブルＬＵＴ１、ＬＵＴ２を用いる利点は、以下のように説明することができる。例えば、人の注目を集めることを目的とするポスターを印刷するために、敢えて彩度の高い色を用いる場合がある。このようなときに、彩度の範囲が比較的広いポスター用色変換ルックアップテーブルＬＵＴ２を利用して印刷すれば、再現される色の彩度を高めることが可能となる。一方、写真画像などの自然画を印刷するときには、特定の色相を有する色についてのみ極端に彩度が高くなることを抑制することが好ましい。このようなときに、彩度の範囲が比較的狭い自然画用色変換ルックアップテーブルＬＵＴ１を利用すれば、彩度の均衡のとれた自然な印刷画像を得ることができる。このように、再現される彩度の範囲が異なる複数の色変換ルックアップテーブルを利用可能とすれば、印刷画像の種類に応じた好ましい彩度の範囲を利用して印刷を行うことができる。
【０１６７】
このような、彩度の範囲が互いに異なる色変換ルックアップテーブルＬＵＴ１、ＬＵＴ２は、上述の分版処理の各実施例において、制限値が互いに異なる複数の彩度制限を使い分けることによって作成することができる。例えば、図１１〜１３に示す実施例において、彩度の拡張される割合を比較的小さい値に制限する彩度制限を用いれば、自然画の印刷に適した自然画用色変換ルックアップテーブルＬＵＴ１を作成することができる。また、彩度の拡張される割合を比較的大きい値に制限する彩度制限を用いれば、より広い彩度の範囲を利用可能なポスター用色変換ルックアップテーブルＬＵＴ２を作成することができる。特に、彩度制限を課さずにインクデューティ制限を満足する色変換ルックアップテーブルを作成すれば、印刷画像の画質を印刷媒体の種類に応じて向上させるとともに、インクセットで実現可能な色の再現範囲を十分に活用するポスター用色変換ルックアップテーブルＬＵＴ２を準備することができる。
【０１６８】
本実施例では、このようにして準備された２つの色変換ルックアップテーブルＬＵＴ１、ＬＵＴ２のそれぞれに対応する「自然画印刷モード」と「ポスター印刷モード」が利用可能である。色変換モジュール９８ａは、印刷モード選択部１０１ａで選択された印刷モードに対応した色変換ルックアップテーブルを選択して参照する。ここで、印刷モードの選択をユーザに許容することが好ましい。本実施例では、ユーザは、プリンタドライバ９６ａの印刷条件設定のための画面（図示せず）を介して、印刷モード選択部１０１ａに対する印刷モードの選択指示を行うことができる。こうすることによって、意図しない彩度の範囲を用いて画像が印刷されることを抑制することができる。また、印刷に用いる画像データの形式に応じ、印刷モード選択部１０１ａが自動的に印刷モードを選択する構成とすることも好ましい。自然画の画像データを生成する画像生成装置（デジタルスチルカメラ、デジタルビデオカメラなど）は、ＪＰＥＧ形式の画像データを生成することが一般的である。そこで、ＪＰＥＧ形式の画像データに基づいて印刷を行うときに、印刷モード選択部１０１ａが「自然画像印刷モード」を自動的に選択すれば、ユーザが指示することなく好ましい彩度の範囲を用いて印刷を行うことができる。
【０１６９】
なお、複数種類のインクセットと印刷媒体の組み合わせが利用可能であるときには、組み合わせ毎に、彩度の範囲が異なる複数の色変換ルックアップテーブルをそれぞれ準備することが好ましい。こうすれば、インクセットや印刷媒体の種類に係わらず、印刷画像の種類に応じた好ましい彩度の範囲を利用して印刷を行うことができる。また、利用可能な彩度の範囲は２種類に限らず、より多くの種類の彩度の範囲を利用可能とすることが好ましい。こうすることによって、印刷画像の種類に応じて、彩度の範囲をよりきめ細かく使い分けることができる。また、印刷画像の種類に応じて印刷媒体を使い分ける場合には、それぞれの印刷媒体に対し、色変換ルックアップテーブルを１つずつ準備することも好ましい。このとき、各色変換ルックアップテーブルの彩度の範囲は、対応する印刷画像の種類に合わせて設定される。こうすることによって、使用する印刷媒体に対応する印刷モード（色変換ルックアップテーブル）を選択することによって、印刷画像の種類に応じた好ましい彩度の範囲を利用して印刷を行うことができる。
【０１７０】
以上、説明したように、上述の各実施例では、有彩２次色インクを利用することによって色の再現範囲を拡張することができる。また、分版インク量セットを、彩度制限を満足するように算出しているので、色相が有彩２次色インクに近いときでも極端に彩度が高い色を再現することを抑制することができる。その結果、印刷画像において、極端に彩度が高い色が目立つことを抑制し、彩度の均衡をとることができる。また、階調値の大きい拡張有彩色に基づいた分版処理を行えば、色再現範囲の拡張を考慮した分版処理を容易に実行することができる。さらに、再現される彩度の範囲の異なる複数の色変換ルックアップテーブルＬＵＴを利用可能とすることによって、印刷画像の種類に応じた彩度の範囲を用いて印刷を実行することができる。
【０１７１】
ところで、色変換ルックアップテーブルＬＵＴを用いた色変換の補間精度を向上させるためには、入力色の変化に対する再現色の見た目の変化を考慮して色変換ルックアップテーブルＬＵＴを作成することが好ましい。例えば、図６のステップＳ２０では、１次色階調値セット（入力色）が、その階調値の取り得る範囲内に複数準備される。ここで、入力色の階調値の変化に対する再現色の見た目の変化が大きい階調値範囲ほど、入力色をより細かく設定すれば、補間の精度を向上させることができる。ところが、入力色の階調値の変化に対する再現色の階調値の変化が色によって大きく異なるときには、再現色の見た目の変化を予測することが難しくなる場合がある。その結果、複数の入力値の設定を行うために、非常な労力を必要とする場合があった。上述の分版処理の各実施例では、入力色の階調値の変化に対する再現色の階調値の変化が、有彩２次色インクに近い色相を有する領域において極端に大きくなることを抑制することができる。従って、複数の入力色の設定を容易に行うことができるので、補間精度を向上させた色変換ルックアップテーブルＬＵＴを容易に作成することができる。
【０１７２】
なお、この発明は上記の実施例や実施形態に限られるものではなく、その要旨を逸脱しない範囲において種々の態様において実施することが可能であり、例えば次のような変形も可能である。
【０１７３】
Ｇ．変形例：
Ｇ１．変形例１：
上述の各実施例において、彩度制限を印刷媒体の種類に応じて設定することが好ましい。印刷物の色の再現性は、同じインクセットを用いる場合でも、印刷媒体の種類によって異なる場合がある。そこで、同じインクセットを用いる場合であっても、複数の彩度制限を印刷媒体の種類に応じて使い分ければ、再現される色の彩度を印刷媒体に応じて適切に制限することができる。
【０１７４】
Ｇ２．変形例２：
彩度制限としては、有彩１次色インクの各色成分の仮想的な階調値に対する制限に限定されるものではなく、再現色の彩度に相関のある種々の値に対する制限を用いることができる。例えば、図１２に示す１次色色空間において、原点Ｗと点Ｋとを結ぶ直線を無彩色線と呼ぶときに、再現色を１次色色空間に表現したときの座標と無彩色線との距離を制限してもよい。また、彩度制限の度合いは、画像の出力結果の官能評価に基づいて設定することができる。例えば、色相が滑らかに変化するグラデーションパターンを印刷し、不自然に目立つ部分が生じない値に設定すればよい。
【０１７５】
Ｇ３．変形例３：
上述の各実施例において、入力色Ｉに対する分版インク量セットＯとして、有彩１次色インクと有彩２次色インクとの置換可能な範囲において、複数のインク量の組み合わせをとることができる場合がある。このような場合には、複数のインク量の組み合わせの中から、インクデューティ制限を満たす範囲において、各インク量の合計値が最小となる組み合わせを、分版インク量セットＯとして用いることが好ましい。こうすることによって、印刷画像の画質を向上させるとともに、インクの使用量を節約することができる。また、再現色の明度が高い（明るい）ときには、有彩１次色インクを積極的に用いるような組み合わせを用いることも好ましい。有彩１次色インクを積極的に用いると、置換インク量に従って複数の有彩１次色インクのインク量が増えるため、印刷媒体に記録されるインクドット数の合計が増加する。その結果、明るい領域で目立ちやすい粒状性（画像のざらつき）を目立ちにくくすることができる。また、再現色の彩度が低いときに、有彩１次色インクを積極的に用いるような組み合わせを用いることも好ましい。彩度の低い色は有彩１次色インクのみを用いて再現することが可能である。従って、このような彩度の低い色を有彩１次色インクを積極的に用いて再現すれば、有彩２次色インクを節約することができる。
【０１７６】
Ｇ４．変形例４：
上述の各実施例では、使用可能なインクセットの各インクの色相が互いに異なっているが、色相がほぼ同じで濃度の異なる複数種類のインクを使用可能な構成としても良い。この場合、各色相の階調値に応じて濃度の異なるインクを使い分けることによって、インクドットの数が少ないほど目立ちやすい粒状性（画像のざらつき）を向上し、インクドットの数が多い場合に目立ちやすいバンディング（筋状の模様）を抑制することができる。このとき、各インクのインク量は、上述のインクデューティ制限や彩度制限、置換インク量等の条件設定を、全てのインクのインク量を考慮した設定とし、いわゆる線形計画法を用いて算出することができる。また、各色相ごとに分版インク量を算出し、得られた分版インク量を、ほぼ同じ色相を有し濃度の異なる複数のインクに再分配する方法を用いても良い。この場合も、インクデューティ制限と彩度制限とにおいて全てのインクのインク量を考慮した制限を設け、さらに、最終的な各インクのインク量がインクデューティ制限と彩度制限とを満たすようにすることが好ましい。
【０１７７】
なお、上記各実施例においては、「インク量」は、ベタ領域を再現するときのインク量を１００％としたときの、０％〜１００％の範囲を表す各インクの階調値であり、色変換ルックアップテーブルＬＵＴの出力を意味している。色相がほぼ同じで濃度の異なる複数種類のインクを使用可能な場合には、同じ色相を有する濃淡インクの色材の合計値を「インク量」に対応させることによって、分版処理を行うことができる。このとき、得られた「インク量」を、濃淡インクのそれぞれに分配することによって、適切な色彩を再現することができる。
【０１７８】
Ｇ５．変形例５：
この発明は熱転写プリンタやドラムスキャンプリンタにも適用可能である。この発明は、いわゆるインクジェットプリンタのみではなく、一般に、複数色のインク色の混色によって色を再現する印刷装置に適用することができる。このような印刷装置としては、例えばファクシミリ装置や、コピー装置がある。
【０１７９】
Ｇ６．変形例６：
上記実施例において、ハードウェアによって実現されていた構成の一部をソフトウェアに置き換えるようにしてもよく、逆に、ソフトウェアによって実現されていた構成の一部をハードウェアに置き換えるようにしてもよい。例えば、プリンタドライバ９６（図１）の機能の一部を、プリンタ２０内の制御回路４０（図３）が実行するようにすることも可能である。
【図面の簡単な説明】
【図１】印刷システムの構成を示すブロック図
【図２】プリンタ２０の概略構成図
【図３】プリンタ２０の構成を示すブロック図
【図４】印刷ヘッド２８の下面におけるノズル配列を示す説明図
【図５】インクセットを示す説明図
【図６】色再現の処理手順を示すフローチャート
【図７】カラーパッチを示す説明図
【図８】分版処理の処理手順を示すフローチャート
【図９】再現色を設定する様子の概略を示す説明図
【図１０】色の再現範囲の拡張される割合を説明する説明図
【図１１】分版処理の処理手順を示すフローチャート
【図１２】１次色色空間を示す説明図
【図１３】拡張有彩色を算出する様子の概略を示す説明図
【図１４】分版処理の処理手順を示すフローチャート
【図１５】インク成分の別の例を示した説明図
【図１６】インク成分の別の例を示した説明図
【図１７】インク成分の別の例を示した説明図
【図１８】インク成分の別の例を示した説明図
【図１９】インク成分の別の例を示した説明図
【図２０】インク成分の別の例を示した説明図
【図２１】インク成分の別の例を示した説明図
【図２２】インク成分の別の例を示した説明図
【図２３】印刷システムの別の例を示すブロック図
【符号の説明】
２０…プリンタ
２１…ＣＲＴ
２２…紙送りモータ
２４…キャリッジモータ
２６…プラテン
２８…印刷ヘッド
３０…キャリッジ
３２…操作パネル
３４…摺動軸
３６…駆動ベルト
３８…プーリ
３９…位置センサ
４０…制御回路
４１…ＣＰＵ
４３…Ｐ−ＲＯＭ
４４…ＲＡＭ
４５…ＣＧ
５０…Ｉ／Ｆ専用回路
５２…ヘッド駆動回路
５４…モータ駆動回路
５６…コネクタ
６０…印刷ヘッドユニット
９０…コンピュータ
９１…ビデオドライバ
９５…アプリケーションプログラム
９６、９６ａ…プリンタドライバ
９７、９７ａ…解像度変換モジュール
９８、９８ａ…色変換モジュール
９９、９９ａ…ハーフトーンモジュール
１００、１００ａ…ラスタライザ
１０１、１０１ａ…印刷モード選択部
ＬＵＴ、ＬＵＴ１、ＬＵＴ２…色変換ルックアップテーブル
ＰＰ…印刷用紙
ＰＤ…印刷データ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a color printing technique using a plurality of types of ink.
[0002]
[Prior art]
2. Description of the Related Art In recent years, color inkjet printers have become widespread as image output devices. An ordinary color inkjet printer uses a plurality of types of inks having hues of cyan C, magenta M, and yellow Y in addition to black (K) ink. Any color of the color image can be reproduced using these plural kinds of inks.
[0003]
In such a printer, the ink amount of each usable ink is determined according to an arbitrary color of a color image. In the present specification, the process of determining the ink amount of each ink used at the time of printing for such color reproduction is called “separation process” or “ink color separation process”. The relationship between the color data of the color image and the amount of each color ink is stored in advance as a color conversion look-up table (LUT: Look Up Table), and the amount of ink of each color at each pixel position is determined according to the LUT during printing. (For example, refer to Patent Document 1).
[0004]
[Patent Document 1]
JP-A-10-19089
[0005]
[Problems to be solved by the invention]
By the way, the color reproducibility of a printer is determined by the type of ink that can be used by the printer. Typically, an arbitrary color can be reproduced by combining three chromatic primary color inks (for example, cyan C, magenta M, and yellow Y inks). A chromatic secondary color ink having a hue different from each of the chromatic primary color inks may be used. Here, the “chromatic secondary color” means a color that can be separated into two chromatic primary color components. When the chromatic secondary color ink is used, the color reproduction range of an image region having a hue close to the hue of the chromatic secondary color ink, in particular, the saturation range can be extended. However, in the prior art, no attempt has been made to balance the saturation.
[0006]
The present invention has been made to solve the above-described conventional problems, and when the chromatic primary color ink and the chromatic secondary color ink can be used, the reproduction range of the reproduced color is expanded. The aim is to balance the saturation.
[0007]
[Means for Solving the Problems and Their Functions and Effects]
In order to solve at least a part of the above problems, a color separation method according to the present invention includes a color separation method for determining an ink amount of each ink to reproduce an arbitrary color using a plurality of color inks on a print medium. (A) as a usable ink, a plurality of chromatic primary color inks capable of reproducing an achromatic color when used in combination with each other, and a hue of any of the plurality of chromatic primary color inks. Setting an ink set including at least one different chromatic secondary color ink; and (b) a color reproduced on the print medium in response to any one input color is called a reproduction color, A combination of each ink amount of the ink set for reproducing a color on the print medium is referred to as a color separation ink amount set, and a color represented by each ink amount of the plurality of chromatic primary color inks as a reference vector. Primary space Determining a plurality of reproduction colors to be reproduced on the print medium according to a plurality of input colors in the primary color space, when called a color space; and (c) reproducing the plurality of reproduction colors. And determining a plurality of color separation ink amount sets for the chromatic primary color ink. In the step (b), the saturation of a reproduced color having the same hue as the chromatic secondary color ink is adjusted to the chromatic primary color ink. The plurality of reproduction colors are determined so as to satisfy a predetermined saturation limit wider than a range of saturation reproducible by the color ink and narrower than a maximum range of saturation reproducible by the ink set. You.
[0008]
According to this separation method, the saturation of the reproduced color having the same hue as the chromatic secondary color ink is wider than the range of the chroma that can be reproduced by the chromatic primary color ink, and can be reproduced by the ink set. Since the setting is made so as to satisfy the saturation limit narrower than the maximum range of the saturation, the color reproduction range can be extended and the color separation processing can be performed with the saturation balanced.
[0009]
In the color separation method, a color expression area reproducible by the ink set in the primary color space and located in a shell of a color expression area satisfying a predetermined restriction including the saturation restriction. A vector representing one type of chromatic color is referred to as a first type vector, and is located in the outer shell of a color expression area reproducible by the chromatic primary color ink and in the same direction as the first type vector. When the vector representing the second type chromatic color is referred to as a second type vector, the saturation restriction is a predetermined ratio of the length of the first type vector to the length of the second type vector. It is preferable to limit the value to the limit value or less.
[0010]
By doing so, it is possible to suppress the range of reproducible saturation from being extremely expanded only for colors having a part of the hue. Can be.
[0011]
In each of the color separation methods, it is preferable that the limit value is constant irrespective of the hue of the reproduced color.
[0012]
By doing so, it is possible to suppress a change in the range of reproducible saturation due to a change in the limit value, so that it is possible to perform a color separation process that balances saturation.
[0013]
In each of the color separation methods, it is preferable that the saturation limit restricts the size of each color component of the chromatic primary color ink when the reproduced color is expressed in the primary color space.
[0014]
This makes it possible to easily set the saturation limit.
[0015]
In each of the color separation methods, the step (b) includes: (b1) locating a chromatic color at an outermost shell position of a color expression area reproducible by the chromatic primary color ink in the primary color space. When referred to as an outer shell chromatic color, it is an outermost shell separation ink amount set corresponding to the outermost shell chromatic color, and can be reproduced by the ink set and has a higher saturation than the outermost shell chromatic color. Determining an outermost shell separation ink amount set for reproducing a high expanded chromatic color; and (b2) determining the outermost shell separation ink amount set based on a relationship between the outermost shell chromatic color and the outermost shell separation ink amount set. Determining the plurality of reproduction colors respectively associated with the plurality of input colors in a primary color space, wherein the step (b1) comprises the steps of: Set the upper limit of the amount as the ink duty limit And determining the extended chromatic color as a color represented by a longer extended chromatic color vector having the same direction as the outermost chromatic color vector representing the outermost chromatic color in the primary color space. Determining the outermost shell color separation ink amount set for reproducing the expanded chromatic color, wherein the determination of the expanded chromatic color and the outermost color separation ink amount set is performed under the following conditions: It is preferable that (i) the outermost color separation ink amount set is within the ink duty limit, and (ii) the extended chromatic color is within the saturation limit.
[0016]
By doing so, the outermost shell color separation ink amount is reproduced so as to reproduce an extended chromatic color having higher chroma than the outermost chromatic color having the highest chroma that can be reproduced only with the chromatic primary color ink. Since the set is determined, the color separation process can be performed in consideration of the expansion of the color reproduction range. Further, since the ink amount is limited by the ink duty limit and the saturation limit, the color separation process can be performed in accordance with the characteristics of the print medium and the saturation can be balanced.
[0017]
In each of the above separation methods, the determination of the extended chromatic color and the outermost shell separation ink amount set may further include the following conditions: (iii) the length of the extended chromatic color vector within a range reproducible by the ink set. Is the longest.
[0018]
By doing so, it is possible to perform a separation process that effectively utilizes the color reproduction range that can be reproduced by the ink set.
[0019]
In each of the above separation methods, the determination of the expanded chromatic color and the outermost shell separation ink amount set is further performed under the following conditions: (iv) the outermost shell separation ink for reproducing the expanded chromatic color. It is preferable to perform the process so that the total of the ink amounts of the amount set is minimized.
[0020]
In this way, the amount of ink used can be saved.
[0021]
In each of the separation methods described above, the reproduced color is the outermost shell separation ink amount set for the outermost chromatic color having the same vector direction as the input color in the primary color space, and the vector length of the input color and The color is preferably reproduced by a proportional color separation ink amount set obtained by multiplying the ratio of the outermost chromatic color to the vector length.
[0022]
This makes it possible to easily set the reproduction color associated with the input color.
[0023]
In each of the above separation methods, it is preferable that the chromatic secondary color ink contains a color material different from the plurality of chromatic primary color inks.
[0024]
By doing so, color reproducibility can be improved.
[0025]
In each of the color separation methods, the chromatic secondary color ink may be used when the hue reproducible by the chromatic secondary color ink is reproduced by mixing the plurality of chromatic primary color inks. It is preferable to be able to reproduce a higher saturation than that which can be reproduced by mixing the next color ink.
[0026]
By doing so, it is possible to reproduce a color having a saturation higher than the saturation that can be reproduced only with the chromatic primary color ink.
[0027]
In each of the color separation methods, the ink set includes first and second chromatic secondary color inks having different hues from each other, and the chromatic secondary color ink is replaced with the plurality of chromatic primary color inks. When the same hues and saturations are reproduced by replacing the chromatic primary color inks with each other, the respective ink amounts of the plurality of chromatic primary color inks with respect to the ink amounts of the chromatic secondary color inks are replaced ink amounts. For each of the first and second chromatic secondary color inks, when the two inks having the largest values among the replacement ink amounts are set as the main component primary color inks, the first chromatic secondary color ink is used. It is preferable that one of the two main component primary color inks of the ink and one of the two main component primary color inks of the second chromatic secondary color ink are different inks.
[0028]
By doing so, the color reproduction range can be further extended.
[0029]
In each of the above separation methods, the ink set includes a black ink, and in the step (b), a black component is removed by performing an undercolor removal process of the black color on the input color, so that a plurality of the color components are removed. It is preferable that the method includes a step of obtaining a corrected input color composed of a primary color component of chromaticity, wherein the reproduced color is determined according to the corrected input color.
[0030]
By doing so, the color reproduction range can be further extended.
[0031]
According to another aspect of the present invention, there is provided a printing apparatus that prints an image by ejecting ink onto a printing medium. Each ink of an ink set composed of a plurality of chromatic primary color inks capable of reproducing a color and at least one chromatic secondary color ink having a hue different from any of the plurality of chromatic primary color inks is ejected. A print head, and an adjustment unit for adjusting the ejection amount of each ink of the ink set, wherein the adjustment unit has a relatively narrow range of chroma reproducible on the print medium. One type of color printing mode, and a second type of color printing that can use the same ink as the first type of color printing mode and has a relatively wide range of reproducible saturation on the print medium And an over-de.
[0032]
According to this printing apparatus, it is possible to use the first type color print mode and the second type color print mode in which the reproduced range of the saturation is different, so that the range of the saturation according to the type of the print image can be used. Can be used to execute printing.
[0033]
In the above printing apparatus, it is preferable that the first type color print mode and the second type color print mode are print modes that can use the same print medium.
[0034]
In this way, even when the same print medium is used, printing can be performed using the saturation range according to the type of the print image.
[0035]
In the above-described printing apparatus, the adjustment unit may be configured to convert the input color image data represented by the first color system into a second color system represented by a reproduced color system composed of ink amounts of the respective inks of the ink set. It is preferable to include a color conversion module that performs conversion into color image data using a color conversion lookup table.
[0036]
By doing so, the process of converting the image data into the ink amount data can be quickly performed by referring to the lookup table.
[0037]
In each of the printing apparatuses, the adjustment unit includes a plurality of color conversion lookup tables prepared in advance corresponding to a plurality of print modes included in the adjustment unit, and the color conversion module is used by the adjustment unit. It is preferable to use a color conversion lookup table corresponding to the print mode.
[0038]
By doing so, conversion processing corresponding to the print mode to be used can be performed quickly.
[0039]
The present invention can be realized in various forms. For example, an image data conversion method and apparatus using the above separation method, a printing method and a printing apparatus, a method and apparatus for creating a color conversion lookup table , A computer program for realizing the functions of these methods or apparatuses, a recording medium on which the computer program is recorded, a data signal including the computer program and embodied in a carrier wave, and the like.
[0040]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, embodiments of the present invention will be described in the following order based on examples.
A. Equipment configuration:
B. First embodiment of separation processing:
C. Second Embodiment of Separation Processing:
D. Third Embodiment of Separation Processing:
E. FIG. Modification of ink set:
F. Second embodiment of the printing system:
G. FIG. Modification:
[0041]
A. Equipment configuration:
FIG. 1 is a block diagram showing a configuration of a printing system as one embodiment of the present invention. This printing system includes a computer 90 as an image data processing device and a color printer 20 as a printing unit. Note that the printer 20 and the computer 90 can be called a “printing device” in a broad sense.
[0042]
In the computer 90, an application program 95 operates under a predetermined operating system. The operating system incorporates a video driver 91 and a printer driver 96 as an adjustment unit, and the application program 95 outputs print data PD to be transferred to the printer 20 via these drivers. Will be. An application program 95 for performing image retouching and the like performs desired processing on an image to be processed, and displays an image on the CRT 21 via a video driver 91.
[0043]
When the application program 95 issues a print command, the printer driver 96 of the computer 90 receives image data from the application program 95 and converts it into print data PD to be supplied to the printer 20. In the example shown in FIG. 1, inside the printer driver 96, a resolution conversion module 97, a color conversion module 98, a halftone module 99, a rasterizer 100, a color conversion lookup table LUT, a print mode selection unit 101 are provided.
[0044]
The resolution conversion module 97 plays a role of converting the resolution (that is, the number of pixels per unit length) of the color image data formed by the application program 95 into a print resolution. The image data whose resolution has been converted in this way is still image information composed of three color components of RGB. The color conversion module 98 converts the RGB image data (input color image data) for each pixel into multi-tone data of a plurality of ink colors (second color data) that can be used by the printer 20 while referring to the color conversion lookup table LUT. 2 color image data).
[0045]
The color conversion lookup table LUT is prepared corresponding to the available print mode. In the present embodiment, available print modes are set according to a combination of a print medium and an ink set used for printing (details will be described later).
[0046]
When there are a plurality of available print modes, the user can select a print mode to be used by giving an instruction to the print mode selection unit 101. The instruction to the print mode selection unit 101 can be given via a screen (not shown) for setting print conditions of the printer driver 96. The color conversion module 98 selects and refers to the color conversion look-up table LUT corresponding to the print mode selected by the print mode selection unit 101.
[0047]
The color-converted multi-tone data has, for example, 256 tone values. The halftone module 99 generates a halftone image data by executing a so-called halftone process. The halftone image data is rearranged by the rasterizer 100 in the order of data to be transferred to the printer 20, and output as final print data PD. Note that the print data PD includes raster data indicating a dot recording state during each main scan and data indicating a sub-scan feed amount.
[0048]
Note that the printer driver 96 corresponds to a program for realizing a function of generating the print data PD. A program for realizing the function of the printer driver 96 is supplied in a form recorded on a computer-readable recording medium. Examples of such a recording medium include a flexible disk, a CD-ROM, a magneto-optical disk, an IC card, a ROM cartridge, a punched card, a printed matter on which a code such as a bar code is printed, and a computer internal storage device (such as a RAM or ROM). Various computer readable media, such as memory and external storage, can be used.
[0049]
FIG. 2 is a schematic configuration diagram of the printer 20. The printer 20 includes a sub-scan feed mechanism that conveys the printing paper PP in the sub-scan direction by the paper feed motor 22 and a main scan feed mechanism that reciprocates the carriage 30 in the axial direction (main scan direction) of the platen 26 by the carriage motor 24. A head driving mechanism for driving a print head unit 60 mounted on the carriage 30 to control ink ejection and dot formation; and a paper feed motor 22, a carriage motor 24, a print head unit 60, and an operation panel 32. And a control circuit 40 that controls the exchange of signals. The control circuit 40 is connected to the computer 90 via the connector 56.
[0050]
The sub-scan feed mechanism that transports the print paper PP includes a gear train (not shown) that transmits the rotation of the paper feed motor 22 to the platen 26 and a paper transport roller (not shown). A main scanning feed mechanism for reciprocating the carriage 30 includes an endless drive belt 36 provided between the carriage motor 24 and a slide shaft 34 laid parallel to the axis of the platen 26 and slidably holding the carriage 30. And a position sensor 39 for detecting the origin position of the carriage 30.
[0051]
FIG. 3 is a block diagram illustrating the configuration of the printer 20 with the control circuit 40 at the center. The control circuit 40 is configured as an arithmetic logic operation circuit including a CPU 41, a programmable ROM (PROM) 43, a RAM 44, and a character generator (CG) 45 storing a dot matrix of characters. The control circuit 40 further includes an I / F dedicated circuit 50 dedicated to interface with an external motor or the like, and a head connected to the I / F dedicated circuit 50 to drive the print head unit 60 to eject ink. A drive circuit 52 and a motor drive circuit 54 for driving the paper feed motor 22 and the carriage motor 24 are provided. The I / F dedicated circuit 50 has a built-in parallel interface circuit and can receive print data PD supplied from the computer 90 via the connector 56. The circuit included in the I / F dedicated circuit 50 is not limited to the parallel interface circuit, but can be determined in consideration of the ease of connection with the computer 90 such as a universal serial bus interface circuit and the communication speed. The printer 20 performs printing according to the print data PD. The RAM 44 functions as a buffer memory for temporarily storing raster data.
[0052]
The print head unit 60 has the print head 28, and can mount an ink cartridge. The print head unit 60 is attached to and detached from the printer 20 as one component. That is, when the print head 28 is to be replaced, the print head unit 60 is replaced.
[0053]
FIG. 4 is an explanatory diagram showing the nozzle arrangement on the lower surface of the print head 28. On the lower surface of the print head 28, a nozzle group for discharging cyan ink C, a nozzle group for discharging magenta ink M, a nozzle group for discharging black ink K, and a red ink R are discharged. Nozzle group for discharging the violet ink V, and a nozzle group for discharging the yellow ink Y. In this embodiment, an ink set including six inks C, M, Y, R, V, and K can be used. In the example of FIG. 4, the plurality of nozzles Nz of one nozzle group are arranged in a straight line along the sub-scanning direction SS, but may be arranged in a staggered manner.
[0054]
FIG. 5A is an explanatory diagram illustrating the ink components of the CMYRVK color inks of the ink set. The ink of each color is a mixed solution based on ion-exchanged water to which an appropriate amount of a coloring material composed of various dyes or pigments for giving a desired color, ethylene glycol for viscosity adjustment, and the like are added. The type of the color material is indicated by the color index (CI) of the color material.
[0055]
The cyan ink C, the magenta ink M, and the yellow ink Y can reproduce gray (achromatic color) by being used in combination with each other, and correspond to a chromatic primary color ink. The red ink R and the violet ink V have different hues from the chromatic primary color inks (CMY) and correspond to the chromatic secondary color inks. The red ink R has a hue between the yellow ink Y and the magenta ink M, and the violet ink V has a hue between the magenta ink M and the cyan ink C.
[0056]
The mixed color of the chromatic primary color inks C, M, and Y can reproduce substantially the same hue and saturation as the respective colors of the chromatic secondary color inks R and V. Here, each ink amount of the mixed color of the chromatic primary color ink with respect to the ink amount of the chromatic secondary color ink, that is, the chromatic primary color ink when the ink amount of the chromatic secondary color ink is 1 Are referred to as replacement ink amounts. At this time, it is possible to reproduce substantially the same color even if the CMY inks and the RV inks are replaced based on the replacement ink amount.
[0057]
FIGS. 5B and 5C show experimental results obtained by measuring the replacement ink amount using the ink set shown in FIG. 5A, respectively. The experimental results were obtained by measuring and comparing the color patches of the mixed color of the chromatic primary color inks C, M and Y with the color patches of the chromatic secondary color inks R and V. is there. FIG. 5B shows the replacement ink amount for the red ink R, and the replacement ink amounts of the respective CMY colors are written with the signs of wCR, wMR, and wYR in order. FIG. 5C shows the replacement ink amount with respect to the violet ink V, and the replacement ink amounts of the respective CMY colors are written with the symbols wCV, wMV, and wYV in order. In the right column of each table, the total value of each replacement ink amount is described.
[0058]
As described above, the replacement ink amount of each of the chromatic secondary color inks R and V is such that two of the three ink amounts are larger than zero, and one ink amount is zero. That is, the chromatic secondary color inks R and V can be decomposed into two chromatic primary color components. Further, in the ink set shown in FIG. 5, it is possible to replace the mixed color of the chromatic primary color inks with the chromatic secondary color inks in an amount smaller than the total value of the respective ink amounts. As a result, it is possible to reproduce substantially the same hue and saturation with a smaller amount of ink by actively using the chromatic secondary color ink. Further, by reducing the amount of ink, higher brightness can be reproduced. Further, by using the chromatic secondary color ink having the same amount of ink as the mixed color of the chromatic primary color ink, it is possible to reproduce higher chroma. Therefore, even when a limit (ink duty limit) is imposed on the total amount of ink used (details will be described later), by using the chromatic secondary color ink, the chromatic primary color ink can be mixed. It is possible to reproduce a higher saturation than can be reproduced. As described above, by using the chromatic primary color ink and the chromatic secondary color ink, it is possible to reproduce colors in a wider range than the range that can be reproduced only with the chromatic primary color ink.
[0059]
The two chromatic secondary color inks R and V are inks having different hues. Further, the primary color inks of the main components of these inks R and V, that is, the two inks having the largest values among the replacement ink amounts of the CMY colors are different from each other. In the example of FIG. 5, the primary color inks of the red ink R are the magenta ink M and the yellow ink Y. The primary color inks of the violet ink V are a cyan ink C and a magenta ink M. In this example, the yellow ink Y and the cyan ink C are different. As a result, the two chromatic secondary color inks R and V can extend the color reproduction range of the regions having different hues. Therefore, a wider color reproduction range can be reproduced as compared with the case where chromatic secondary color inks having similar hues are used.
[0060]
Further, in the ink set shown in FIG. 5A, the chromatic secondary color inks R and V contain different color materials from the chromatic primary color inks C, M and Y. Therefore, by using the chromatic secondary color ink instead of the mixed color of the chromatic primary color inks C, M, and Y, the reproducibility of the hue close to that of the chromatic secondary color ink can be improved.
[0061]
In the printer 20 having the hardware configuration described above, the carriage 30 is reciprocated by the carriage motor 24 while the paper PP is being conveyed by the paper feed motor 22, and at the same time, the piezo elements of the print head 28 are driven, and the ink droplets of each color are To form an ink dot to form a multi-color and multi-tone image on the paper PP.
[0062]
B. First embodiment of separation processing:
B1. How to create a color conversion lookup table:
FIG. 6 is a flowchart showing a color reproduction processing procedure in this embodiment. In steps S10 to S70, a color conversion lookup table LUT (FIG. 1) for performing color reproduction is created.
[0063]
First, in step S10, one combination of a print medium and an ink set used for printing is selected. An ordinary printer is assumed to use one print medium selected by the user from a plurality of types of print media (plain paper, glossy paper, matte paper, etc.). In some types of printers, the ink set to be used may be selected from a plurality of types of ink sets (for example, a dye ink set and a pigment ink set). The color reproducibility of the printed matter depends on the printing medium and the ink set. Therefore, in this embodiment, the processing of steps S10 to S60 is executed for each combination of the print medium and the ink set, and a color conversion lookup table LUT suitable for the combination is created. Note that the type of print medium and the type of ink set that are assumed to be used in the printer 20 are generally displayed on a screen (not shown) for setting print conditions of the printer driver 96.
[0064]
In step S20, a color separation process of converting a primary color tone value set represented by a primary color system into a second tone value set represented by a reproduced color system is executed. The primary color system is a color system represented by the amount of each color ink of the chromatic primary color ink CMY, and the reproduction color system is a color system represented by the amount of each color ink used at the time of printing. System. This primary color tone value set is composed of a plurality of chromatic primary color inks C, M, and Y. The ink amount of each of the chromatic primary color inks C, M, and Y ranges from a possible minimum value (zero) to a maximum value (ink amount when reproducing a solid area), for example, 256 from 0 to 255. This is a value expressed in gradation. In this embodiment, the solid area is reproduced by ejecting ink to all pixels. Therefore, the ink amount when reproducing such a solid area can be set to 100%.
[0065]
In step S20, first, a plurality of primary color tone value sets are prepared. It is preferable that the ink amounts of the chromatic primary color inks C, M, and Y of the plurality of primary color tone value sets are distributed over the entire possible range (0% to 100%). It is particularly preferred that the particles are uniformly distributed throughout. As the plurality of values of the ink amount, for example, eleven values of “0, 25, 50, 75, 100, 125, 150, 175, 200, 225, 255” can be used. It should be noted that the apparent change in the reproduced color with respect to the change in the gradation value of each ink amount may differ depending on the gradation value of each ink. In such a case, it is preferable to prepare the ink amounts of the respective inks at finer intervals in the range of the gradation value in which the change in the color appearance is large. By doing so, it is possible to create a color conversion look-up table LUT that precisely corresponds to a change in the apparent color.
[0066]
Next, the plurality of primary color tone value sets are converted into a second tone value set expressed in a reproduction color system. The reproduced color color system is a color system represented by each ink amount of an ink set used at the time of printing, for example, each color ink amount of a chromatic primary color ink CMY and a chromatic secondary color ink RV. The second gradation value set is a value expressing the range of the minimum (0%) to the maximum (100%) of the ink amount of each color of CMYRV by, for example, 256 gradations from 0 to 255. is there. Details of the color separation processing from the primary color system to the reproduced color system will be described later.
[0067]
In step S30, a plurality of types of color patches corresponding to a plurality of primary color tone value sets are created. FIG. 7 is an explanatory diagram illustrating an example of a color patch created in the present embodiment. The vertical axis represents the tone value of the magenta ink M of the primary color tone value set prepared in step S20, and the horizontal axis represents the tone value of the yellow ink Y. Each color patch is reproduced with each ink amount of the ink set obtained by converting each gradation value according to the color separation process in step S20. Note that the example of FIG. 7 shows a case where the tone value of the cyan ink C in the primary color tone value set is set to zero. Actually, a plurality of types of color patches corresponding to a plurality of tone values of the cyan ink C are created, but are not shown. Thus, in step S30, a plurality of types of color patches corresponding to the plurality of primary color tone value sets prepared in step S20 described above are created.
[0068]
In step S40 (FIG. 6), colorimetry of the plurality of color patches created in step 30 is performed using a colorimeter. The data obtained as a result of the color measurement is data represented by a color system that does not depend on devices such as a printer and a monitor, for example, an L * a * b * color system and an XYZ color system. As described above, in step S40, the colorimetry of each color patch is performed, and thus the “primary color / device-independent color system correspondence relationship” between the primary color system and the device-independent color system. Can be determined. As a result of the color measurement, the range of colors that can be reproduced by the printer 20 in the device-independent color system can also be confirmed.
[0069]
In step S50, the correspondence between an arbitrary first color system and the primary color system is determined based on the "primary color / device-independent color system" obtained in step S40. To set. The first color system is a color system of the input color image data of the color conversion look-up table LUT. For example, the sRGB color system can be used. Such a "first color system / device-independent color system correspondence relationship" between the first color system and the device-independent color system is set in advance. Therefore, by using the “correspondence relationship between the first color system / device-independent color system” and the “correspondence relationship between primary color / device-independent color system” obtained in step S40, The correspondence between the color system 1 and the primary color system can be set. Note that the color reproduction range of the first color system and the color reproduction range of the printer may have portions that do not overlap with each other. In such a case, it is preferable to appropriately use the entirety of the color regions by appropriately setting the enlarged or reduced correspondence.
[0070]
Thus, the first correspondence between the first color system and the primary color system (step S50), and the second correspondence between the primary color system and the reproduced color system (step S20). Is set, a color conversion look-up table LUT (FIG. 1) for reproducing the set correspondence is created in step S60. The color conversion look-up table LUT in the present embodiment receives RGB image data as input and outputs multi-tone image data for six ink colors shown in FIG. Therefore, when creating the color conversion look-up table LUT, first, a primary color tone value set expressed in CMY corresponding to the tone value of the RGB image data is calculated. Next, a second tone value set corresponding to the primary color tone value set, that is, an ink amount of each ink is determined according to a separation process described later. Then, a correspondence relationship in which the values of the RGB image data are input and the ink amounts of the respective inks are output is stored in the lookup table LUT.
[0071]
In step S70 of FIG. 6, it is determined whether or not the processing of steps S10 to S60 has been completed for all combinations of the print medium and the ink set that are assumed to be used in the printer 20. If all the processes have not been completed, the processes of steps S10 to S60 are repeated, and if completed, the process proceeds to the next step S80.
[0072]
In step S80, the created plural types of color conversion look-up tables LUT are incorporated in the printer driver 96 (FIG. 1). The printer driver 96 is a computer program for causing the computer 90 to realize a function of creating the print data PD supplied to the printer 20. The color conversion lookup table LUT is installed in the computer 90 together with the printer driver 96 as data referred to by the printer driver 96. Note that the printer driver 96 in which the color conversion lookup table LUT is incorporated is usually supplied by the manufacturer of the printer 20.
[0073]
In step S90 of FIG. 6, the user executes printing using the printer 20. At this time, a look-up table suitable for the combination of the print medium and the ink set used for actual printing is selected from the color conversion look-up tables LUT for all combinations of the print medium and the ink set, and printing is executed. Is done. A set of a print medium and an ink set used for actual printing is selected by a user on a screen (not shown) for setting printing conditions of the printer driver 96.
[0074]
B2. Details of the separation process in the first embodiment:
FIG. 8 is a flowchart illustrating a processing procedure of the color separation processing. In the color separation process, a conversion process from the primary color system to the reproduced color system is performed. In step S500 in FIG. 8, an ink set including chromatic primary color inks C, M, and Y and chromatic secondary color inks R and V is set as usable ink.
[0075]
Next, in step S510, a reproduction color REC corresponding to the input color I (Ci, Mi, Yi) is determined (details will be described later).
[0076]
Next, in step S520, the separation ink amount set O (Co, Mo, Yo, Ro, Yo) is determined based on the reproduced color REC (details will be described later). In step S530, it is determined whether or not the processing in steps S510 and S520 has been completed for all reproduction colors required to create the lookup table. Then, the processing of steps S510 and S520 is repeated until the processing for all reproduced colors is completed.
[0077]
FIG. 9 is an explanatory diagram showing an outline of setting a reproduction color in step S510 in FIG. In the example of FIG. 9, for simplification of description, two types of cyan ink C and magenta ink M are available as chromatic primary color inks, and one of violet ink V is used as chromatic secondary color ink. The type is assumed to be available.
[0078]
FIG. 9A is an explanatory diagram showing a primary color space in which the ink amount of each CM color is represented as a reference vector. The horizontal axis indicates the gradation value of the cyan ink C, and the vertical axis indicates the gradation value of the magenta ink M. In this example, the gradation value of each color of the CMV can take a value in the range of 0 to 100. A gradation value = 0 means that the ink amount is zero, and a gradation value = 100 means the ink amount when reproducing the solid area. Therefore, the input color I represented in the primary color system is represented as one point in a square having a side length of 100 in the primary color space. Hereinafter, an area in the primary color space in which the input color I is expressed is referred to as an input color expression area. In FIG. 9A, the input color expression area INA is indicated by hatching. In addition, the first type outer shell line OL10 of the input color expression area INA is indicated by a thick line.
[0079]
FIG. 9B is an explanatory diagram illustrating how to set a color reproduction range for a reproduction color using a primary color space. The reproduced color is a color set according to the input color, and is a color reproduced using the chromatic primary color ink CM and the chromatic secondary color ink V.
[0080]
Here, it is assumed that the 1: 2 mixed color of the cyan ink C and the magenta ink M can reproduce almost the same hue and saturation as the violet ink V having the same ink amount as the cyan ink C. That is, the replacement ink amounts for the violet ink V are cyan ink C = 1 and magenta ink M = 2. For example, the color P10 in FIG. 9B is a color that can be reproduced by setting C = 50 and M = 100. Further, even if at least a part of the gradation values of each color of the CM is replaced with the gradation value of V according to the replacement ink amount, it is possible to reproduce substantially the same color. For example, even if “C = 25, M = 50, V = 25” or “C = 0, M = 0, V = 50”, almost the same color can be reproduced. Here, the gradation values obtained by replacing all the gradation values of the chromatic secondary color ink V with the gradation values of the chromatic primary color ink CM (C = 50, M = 100 in this example) Can be used as virtual gradation values for expressing a color reproduced using each CMV color in a primary color space.
[0081]
The area MAXA in the figure indicates the maximum area of colors that can be reproduced using the CMV colors (hereinafter, referred to as the maximum color expression area MAXA). For example, the color P20 in the figure is a color reproduced by setting “C = 100, M = 100, V = 100”, and has a virtual gradation value “C = 200, M = 300”. Is expressed. An outer shell line OL20 indicates the outer shell of the maximum color expression area MAXA.
[0082]
The maximum color expression area MAXA is wider than the input color expression area INA. The chromatic secondary color ink V has a feature that the saturation is higher than that of the chromatic primary color ink CM. Therefore, by using the chromatic secondary color ink V, the reproducible color reproduction range can be extended to a higher saturation range.
[0083]
In the present embodiment, a reproduction color is set in an area that satisfies the following restrictions in such a maximum color expression area MAXA.
[0084]
(Condition a10) CD ≦ C_Limit1
(Condition a20) MD ≦ M_Limit1
[0085]
CD and MD are the tone values of the C and M color components in the reproduced color, respectively. C_Limit1 and M_Limit1 are limit values of CD and MD, respectively, and are preset values. Here, the two limit values C_Limit1 and M_Limit1 are set to values larger than the maximum value (100 in this example) of the actual gradation values of the C and M color components. Further, these limit values C_Limit1 and M_Limit1 are set to values smaller than the maximum values of the gradation values of C and M in the maximum color expression area MAXA surrounded by the outer shell line OL20.
[0086]
In the figure, the outer shell line OL30 of the area satisfying the above-described conditions (conditions a10 and a20) in the maximum color expression area MAXA is indicated by a thick line. In the present embodiment, a reproduction color is set in an area surrounded by the outer shell line OL30 (hereinafter, an area in which a reproduction color is set is referred to as a reproduction color expression area). In the drawing, the reproduced color expression area REA is indicated by hatching. The reproduction color expression area REA set in this way is wider than the input color expression area INA (FIG. 9A) in the primary color space, and further, the maximum maximum color that can be reproduced by the three inks CMV. The area is smaller than the expression area MAXA. By the way, when the same ink set is used, a color with higher saturation is reproduced using more ink. In FIG. 9, a point of a color having higher saturation is represented by a point having a larger gradation value, that is, a point far from the origin W. Therefore, it can be considered that the reproduced color expression area REA has a wider range of saturation than the input color expression area INA, and has a narrower range of saturation than the maximum color expression area MAXA.
[0087]
As described above, in the present embodiment, the saturation of the reproduced color is limited to the range of saturation wider than the input color expression area INA and narrower than the maximum color expression area MAXA by the above conditions a10 and a20. . Therefore, the conditions a10 and a20 can be considered as saturation limits in the present invention. As described above, when the color reproduction range is expanded in the direction of higher saturation by the chromatic secondary color ink, a condition for restricting the expansion of the reproduction range can be used as the saturation restriction.
[0088]
FIG. 10 is an explanatory diagram for explaining a rate at which the color reproduction range is extended. FIG. 10A is an explanatory diagram showing the same primary color space as that of FIG. 9B, and outer shell lines OL10 to OL30 are shown in the drawing. In the figure, distances L10 to L30 between the colors on the outer shell lines OL10 to OL30 and the origin W are shown. These distances L10 to L30 are distances related to colors represented by vectors having the same direction. FIG. 10A shows an angle θ between the direction of the vector and the direction of the C-axis.
[0089]
FIG. 10B is a graph showing a relationship between the distances L10 to L30 and the angle θ. The horizontal axis represents the angle θ, and the vertical axis represents the ratio LR of each of the distances L10 to L30 to the distance L10.
[0090]
Is defined as 0 ° when the vector is oriented in the C-axis direction and 90 ° when oriented in the M-axis direction, and is a value determined by the ratio of each color component of the CM. Also, as the angle θ is closer to 0 °, the hue of the color approaches the hue of the cyan ink C, and as the angle θ is closer to 90 °, the hue of the color approaches the hue of the magenta ink M. Therefore, the angle θ can be considered as an index representing the hue.
[0091]
The distance L10 is a distance from the origin W to the first kind of outer shell line OL10 (FIG. 10A), and corresponds to the outer shell of the color expression area when only the chromatic primary color ink CM is used. Is the distance to do. Therefore, the ratio LR2 of the distance L20 to the distance L10 (= L20 / L10) can be considered to mean the expansion ratio of the saturation for the maximum color expression area MAXA (FIG. 9B). Similarly, the ratio LR3 of the distance L30 to the distance L10 (= L30 / L10) can be considered to mean the expansion ratio of the saturation for the reproduced color expression area REA (FIG. 9B).
[0092]
The points P50 to P56 shown in FIG. 10B show the correspondence with the points on the outer line OL20 in FIG. 10A, and the outer line OL20 in FIG. The points correspond to the points P50 to P56 described above.
[0093]
In the example of FIG. 10B, the expansion ratio LR2 of the saturation for the maximum color expression area MAXA (FIG. 9B) increases as the hue is closer to the hue of the chromatic secondary color ink V. On the other hand, the expansion ratio LR3 of the saturation for the reproduction color expression area REA (FIG. 9B) is configured not to become extremely large even when the hue is close to the hue of the chromatic secondary color ink V. Therefore, if the reproduction color REC is set in the reproduction color expression area REA surrounded by the outer line OL30, even if the color is close to the hue of the chromatic secondary color ink V, the saturation is different from that of other colors. It can be suppressed from becoming extremely high in comparison.
[0094]
The reason why the reproduced color REC is set in the reproduced color expression area REA (FIG. 9B) satisfying the saturation limit (conditions a10 and a20) is as follows. The chromatic secondary color ink V has a feature that the saturation is higher than that of the chromatic primary color ink. Therefore, by using the chromatic secondary color ink V, it becomes possible to expand the color reproduction range in the direction of higher saturation as the hue is closer to the hue of the chromatic secondary color ink V. By the way, printed images include images expressed using various colors such as natural images. When such an image is output using the entire maximum color expression area MAXA, the saturation of an area having a hue close to the chromatic secondary color ink becomes extremely high, and the area may be unnaturally conspicuous. . Further, in a gradation region where the hue changes smoothly, the saturation of a portion having a hue close to the chromatic secondary color ink becomes extremely high, and the boundary with other portions may be conspicuous. Therefore, when expanding the color reproduction range using the chromatic secondary color ink, it is preferable to limit the rate at which the saturation is expanded. Therefore, in the examples of FIGS. 9 and 10, even if the hue is close to the chromatic secondary color ink V, the saturation limit is such that the reproduced color expression region is not extended to an extremely high saturation region. Conditions a10 and a20) are imposed. By doing so, it is possible to extend the color reproduction range without unnaturally conspicuous some areas in the print image.
[0095]
Here, it is preferable to limit the ratio LR3 at which the saturation is expanded so as not to become excessively large. For a color whose hue is far from the chromatic secondary color ink, the saturation is hardly expanded even when the chromatic secondary color ink is used. Therefore, by limiting the saturation expansion ratio LR3 to a value that is not excessively large, it is possible to prevent the difference in saturation between colors near and far from the chromatic secondary color ink from becoming extremely large. it can. For example, the expansion ratio LR3 of the saturation is preferably 2.5 or less, particularly preferably 2 or less, and most preferably 1.5 or less. On the other hand, in order to extend the color reproduction range, it is preferable to set the value as large as possible. In the examples of FIGS. 9 and 10, the limit on the expansion ratio LR3 of the saturation is determined according to the limit values C_Limit1 and M_Limit1 of each color component of the chromatic primary color ink CM. For example, if the limit values C_Limit1 and M_Limit1 are set to 1.5 times the maximum value (100 in this example) of the actual tone value of each CM color component, the limit value for the ratio is set to 1.5. be able to.
[0096]
Further, it is preferable that the limit value for the ratio be constant regardless of the hue. By doing so, it is possible to suppress a portion where the saturation changes with a change in the limit value from unnaturally conspicuous. 9 and 10, since the limit values C_Limit1 and M_Limit1 are set to the same value, the limit value for the ratio is constant regardless of the hue.
[0097]
The reproduced color expression area REA described above can be similarly set even when the number of ink types increases. For example, when three kinds of CMY inks as chromatic primary color inks and two kinds of RV inks as chromatic secondary color inks can be used, the gradation value of the chromatic secondary color ink RV is set to chromatic primary color ink. A limit value for each virtual tone value of each CMY color obtained by replacing the tone value of the color ink CMY can be used as a saturation limit. By doing so, it is possible to prevent the virtual tone value of each of the CMY colors from becoming extremely large only for colors having a hue close to the chromatic secondary color ink. As a result, the saturation of a color having a hue close to that of the chromatic secondary color ink is prevented from becoming extremely high, and the color reproduction range can be reduced without unnaturally conspicuous in a part of the print image. Can be extended.
[0098]
The reproduction color REC corresponding to the input color I is set in the reproduction color expression area REA set as described above. Usually, the correspondence between the plurality of representative input colors I and the plurality of reproduction colors REC is determined first, and the reproduction colors REC corresponding to the other input colors I correspond to the representative input colors. It can be set by interpolation. Here, as the plurality of correspondences prepared in advance, the plurality of input colors I are distributed over substantially the entire area of the input color expression area INA, and the plurality of reproduction colors REC respectively corresponding to the plurality of input colors I are provided. Is preferably distributed almost over the entire reproduction color expression area REA. By doing so, the reproduced color REC can be accurately obtained regardless of the color of the input color I, and the reproduced color expression area REA can be effectively used. Further, it is preferable to set the hues of the input color I and the reproduction color REC so as to be substantially the same. As the index indicating the hue, for example, the ratio of the gradation values of each color of the chromatic primary color ink can be used. In addition, a virtual tone value ratio can be used as an index indicating the hue of the reproduced color.
[0099]
In step S520 of FIG. 8, the separation ink amount set O (Co, Mo, Yo, Ro, Vo) for reproducing the reproduction color REC set in the reproduction color expression area REA on the print medium as described above. Is calculated. Since there can be an infinite number of color separation ink sets for an arbitrary reproduced color REC, the color separation ink amount set is determined by setting specific conditions. For example, in the present embodiment, the separation ink amount set O (Co, Mo, Yo, Ro, Vo) is determined so that the total ink amount is minimized.
[0100]
As described above, in the first embodiment, the region corresponding to the hue close to the chromatic secondary color ink in the reproduction color expression region REA is not extended to the extremely high saturation range by the saturation restriction. Is set to As a result, it is possible to extend the color reproduction range without unnaturally conspicuous in some areas in the print image.
[0101]
C. Second Embodiment of Separation Processing:
FIG. 11 is a flowchart illustrating the processing procedure of the second embodiment. In this embodiment, in addition to the saturation limit, the reproduced color is set so as to satisfy the ink duty limit corresponding to the limit on the amount of ink absorbed per unit area of the print medium.
[0102]
In step S100 of FIG. 11, an ink set including chromatic primary color inks C, M, and Y and chromatic secondary color inks R and V is set as a usable ink set.
[0103]
Next, in step S110, an ink duty limit, which is a limit on the ink amount of each color of the ink set, is set. The ink duty limit is set according to the type of ink or print medium (details will be described later).
[0104]
By the way, the input color represented by the primary color system represents a gradation value (primary color) in which the possible range (0% to 100%) of the ink amount of each CMY color is represented by 256 gradations of 0 to 255. (Gradation value set). Further, the color separation ink amount set expressed in the reproduction color system uses a gradation value expressing a possible range (0% to 100%) of the ink amount of each color of CMYRV in 256 gradations of 0 to 255. Is expressed.
[0105]
FIGS. 12A and 12B are explanatory diagrams illustrating a primary color space represented by using the ink amounts of the respective CMY colors as reference vectors. A color represented by the primary color system is represented as one point in a cube represented by CMY gradation values 0 to 255 in the primary color space. The cube is an area where the ink amount of each of the CMY colors of the chromatic primary color ink can take a value. Hereinafter, this cube is called a color solid, and among the six surfaces of the color solid, three surfaces (three surfaces surrounding K (C = M = Y = 100%)) facing the origin W are the first. Called the outer shell surface of the seed. In other words, the first type of outer shell surface has an ink amount of at least one chromatic primary color of 100% and an ink amount of at least one chromatic primary color ink of less than 100%. It consists of color points that have values. When a straight line connecting the origin W and the point K is called an achromatic line, the distance between one point in the primary color space and the achromatic line can be used as an index of saturation. Further, when a point obtained by projecting one point in the primary color space vertically onto the achromatic line is called a projection point, the distance between the origin W and the projection point can be used as an index of lightness. The direction from the projection point to one point in the primary color space can be used as a hue index.
[0106]
In FIGS. 12A and 12B, hatching is given to the first type outer shell surface where Y is maximum (Y = 255). Further, one color m is marked on the hatched first type outer shell surface. This color m is set as the outermost shell chromatic color m in step S120 in FIG. In the examples of FIGS. 12A and 12B, the outermost chromatic color m is set on the outermost surface where the Y component is the maximum, and the gradation values of the CMY colors are Cm and Mm in the order of CMY. , Ym (in this example, Ym = 255).
[0107]
In the color separation process of the present embodiment, the color separation associated with the input color I on the line segment connecting the origin W and the outermost chromatic color m by sequentially executing the processes of steps S130 to S140 described later. An ink amount set (gradation values of each color of CMYRV in this embodiment) can be obtained. In the present embodiment, a plurality of outermost shell chromatic colors are prepared in order to execute the color separation processing for a plurality of input colors I, and a series of processes (S130 to S140) are performed on each outermost shell chromatic color. Is executed.
[0108]
In step S130 of FIG. 11, an extended chromatic color em located in the outer shell of a color region that can be reproduced by using the inks of the respective colors of CMYRV in the ink set is obtained (FIG. 12B).
[0109]
FIG. 13 is an explanatory diagram showing an outline of calculating an extended chromatic color em. In the example of FIG. 13, it is described that the same two chromatic primary color inks CM and one chromatic secondary color ink V as in the example of FIG. 9 can be used.
[0110]
FIG. 13A is an explanatory diagram showing a primary color space similar to FIG. 9A. The input color I represented in the primary color system is represented as one point in a square having a side length of 100. This square corresponds to the color solid described above. In the figure, the first type outer shell line OL1 having a square shape is indicated by a thick line. The first type outer shell line OL1 corresponds to the above-described first type outer shell surface. The outermost shell chromatic color m is set on the line where C of the first type outer shell line OL1 is the maximum (C = 100).
[0111]
FIG. 13B is an explanatory diagram illustrating how to set a reproduction color expression area A for a reproduction color using a primary color space. The reproduced color is a color that can be reproduced by using the chromatic secondary color ink V in addition to the chromatic primary color ink CM. The extended chromatic color em is set at the outer shell position of the reproduction color expression area A. In the example of FIG. 13B, the reproduced color expression area A is limited to an area satisfying the following conditions.
[0112]
(Condition a1) CD ≦ C_Limit2
(Condition a2) MD ≦ M_Limit2
(Condition b1) The gradation value of each ink is 100 or less.
(Condition b2) The total value of the gradation values of each ink is 200 or less.
[0113]
The two conditions a1 and a2 are the same as the conditions a10 and a20 in the example of FIG. 9 and correspond to the saturation limit in the present invention.
[0114]
The limitation of the gradation value by the remaining two conditions b1 and b2 can be explained as follows. That is, the print medium has a limit on the amount of ink absorbed per unit area. When an amount of ink that exceeds this limit is ejected, bleeding may occur due to the ink that has not been completely absorbed, or the print medium may be wavy. Therefore, it is preferable to limit the amount of ink used. Such an upper limit of the ink amount, that is, an upper limit of the gradation value is called an ink duty limit. Further, an appropriate value of the ink duty limit may be different depending on the type of ink. In such a case, the image quality of the print image can be further improved by setting different limit values for each color. In addition, by providing a limit value for the total value of the gradation values of each color (that is, the total value of the ink amount) as in the condition b2, it is possible to eject ink in an amount exceeding the ink absorption amount limit of the print medium. Can be suppressed. Further, it is preferable to provide a limit value for the total value of the two types of ink amounts for an area where two colors are to be reproduced, and to set a limit value for the total value of many types of ink amounts. It is also preferable to do so. Further, if these limit values are changed according to the type of the print medium, the image quality of the print image can be improved according to the type of the print medium.
[0115]
Such an ink duty limit is expressed by the gradation value of each color of the usable ink CMV, and by using the virtual gradation value of each CM color obtained by using the replacement ink amount, the primary color space Can be expressed as In the present embodiment, the ink duty limit is represented by a first-order inequality using the gradation values of each color of the CMV (FIG. 13B). Therefore, the ink duty limit is expressed using a straight line in the primary color space.
[0116]
The reproduced color expression area A is represented by an area surrounded by a straight line corresponding to the ink duty limit and a straight line corresponding to the saturation limit. In FIG. 13B, a straight line LC indicates a straight line where C = 100. The reason for the inclination with respect to the C axis is that by using the violet ink V, the virtual gradation value of each CM color can be further increased. Therefore, the region satisfying C ≦ 100 is inside this straight line LC. Further, the straight line LCV is a straight line where C + V = 200. This straight line corresponds to the limit of C + V ≦ 200 derived from the two limits of C ≦ 100 and V ≦ 100. The region satisfying C + V ≦ 200 is inside this straight line LCV.
[0117]
Further, FIG. 13B shows the following straight line corresponding to the ink duty limit. That is, the straight line LCMV is a straight line where C + M + V = 200, the straight line LMV is a straight line where M + V = 200, and the straight line LM is a straight line where M = 100. The straight line LCLim is a straight line corresponding to the saturation limit a1, and the straight line LMlim is a straight line corresponding to the saturation limit a2.
[0118]
As a result, the color in the reproduction color expression area A surrounded by these straight lines is a color that satisfies the ink duty limit and the saturation limit, and can be reproduced by using the chromatic secondary color ink V.
[0119]
The distance between the straight line LCV, LCMV, LMV corresponding to the ink duty limit and the origin W is a value that changes according to the replacement ink amount of the chromatic secondary color ink. That is, as the replacement ink amount increases, the distance between the straight line corresponding to each ink duty limit and the origin W increases. As a result, the larger the replacement ink amount, the wider the area that can be reproduced by using the chromatic primary color ink and the chromatic secondary color ink. Therefore, from the viewpoint of reproducible region expansion, the total value of the replacement ink amount is preferably larger than 1, and particularly preferably 1.5 or more. In the example of FIG. 13, the replacement ink amount of the violet ink V is set to 1 for the cyan ink C and 2 for the magenta ink M, so that the total value of the replacement ink amounts is 3. In the example of the ink set of FIG. 5, the replacement ink amount of the red ink R is 0.0, 0.71, 2.86 in the order of CMY, and the total value is 3.57. The replacement ink amount of the violet ink V is 0.68, 2.89, and 0.0 in the order of CMY, and the total value is 3.57. Since the total value of the replacement ink amounts of the two inks RV is 1.5 or more, a wider color reproduction range can be obtained by using these inks R and V. If the total replacement ink amount of each chromatic primary color ink is larger than 1, the chromatic secondary color ink should use the same amount of ink as the mixed color of the chromatic primary color inks. Thus, higher saturation can be reproduced. In this case, by using the chromatic primary color ink and the chromatic secondary color ink, it is possible to reproduce a color in a wider range than a region that can be reproduced only with the chromatic primary color ink. .
[0120]
In the present specification, such an outer shell of the reproduction color expression area is referred to as a reproduction color outer surface. The reproduced color outer surface is represented by a reproduced color system for each ink amount of the ink set, and each ink amount of the chromatic secondary color ink is changed according to the replacement ink amount. Can be mapped in the primary color system. In the example of FIG. 13B, the outer shell line OL3 constituting the outer shell of the reproduced color expression area A corresponds to the reproduced color outer shell surface mapped to the primary color space (hereinafter, the outer shell line OL3 is referred to as the outer shell line OL3). Reproduced color outer line OL3). Note that the condition of V ≦ 100 is satisfied in the reproduction color expression region A, and therefore, the corresponding straight line is not shown.
[0121]
In FIG. 13, the reproduced color expression area A is hatched, and the reproduced color outer line OL3 is displayed thick. By setting the reproduction color in the reproduction color expression area A that satisfies the saturation limit and the ink duty limit, a wider color reproduction range can be realized as compared with the case where only the chromatic primary color ink is used. Can suppress the generation of reproduced colors having extremely high saturation even when the color is close to the chromatic secondary color ink, and can also suppress the occurrence of bleeding and waving of the print medium.
[0122]
An extended chromatic color em is set on the reproduction color outer line OL3. The extended chromatic color em is a color located at the intersection of a line segment passing through the origin W and the outermost chromatic color m and the reproduced color outer line OL3. That is, in the present embodiment, the extended chromatic color em is a color represented by the longest extended chromatic color vector having the same direction as the outermost chromatic color vector representing the outermost chromatic color m in the primary color space. In addition, the outermost color separation ink amount set for satisfying the saturation limit and for reproducing the extended chromatic color em is a color satisfying the ink duty limit.
[0123]
As described above, the extended chromatic colors described above can be similarly set even when the types of inks are increased. Here, virtual gradation values for expressing the extended chromatic color em in the primary color space are CDem, MDem, and YDem in the order of CMY colors. Further, the ink amounts of the color separation ink amount set corresponding to the extended chromatic color em (corresponding to the outermost shell color separation ink amount set) are Cem, Mem, Yem, Rem, and Vem in the order of CMYRV. Then, the gradation values CDem, MDem, and YDem of each virtual CMY color are expressed by the following equations using the replacement ink amounts shown in FIGS.
[0124]
(Equation 1)

[0125]
In this embodiment, the extended chromatic color em is calculated so as to satisfy the following condition.
[0126]
(Condition 1) The outermost shell separation ink amount set satisfies the ink duty limit.
(Condition 2) The extended chromatic color satisfies the saturation limit.
[0127]
As the ink duty limit, for example, a limit on a total value of ink amounts of all types, a limit on an ink amount of each color alone, and a limit on an ink amount for mixing two colors can be set.
[0128]
The limitation on the total value of the ink amounts of all types is expressed by the following equation, for example.
[0129]
(Equation 2)

[0130]
In the formulas, C, M, Y, R, and V are the ink amounts of the respective colors of CMYRV (the same applies to other formulas described later). Duty_T is a limit value set in advance according to the type of ink or print medium.
[0131]
The limitation of the ink amount of each color alone is represented by the following equation, for example.
[0132]
[Equation 3]

[0133]
Duty_C to Duty_V are limit values preset for each color according to the type of ink or print medium.
[0134]
The limitation on the amount of ink when two colors are mixed is expressed, for example, by the following equation.
[0135]
(Equation 4)

[0136]
In addition, in this restriction, a restriction is imposed on a combination of any two inks, but six combinations are exemplified. Duty_CM to Duty_MR are limit values preset for combinations of inks according to the type of ink or print medium.
[0137]
As the ink duty limit, a limit for an arbitrary combination of inks, such as a mixture of three colors and a mixture of four colors, may be set.
[0138]
As for the saturation limit, for example, it is possible to set a limit on a virtual gradation value of each color of CMY, and such a setting is expressed by the following equation.
[0139]
(Equation 5)

[0140]
In the formulas, CD, MD, and YD are virtual gradation values of each of the CMY colors. C_Limit, M_Limit, and Y_Limit are preset limit values. If these limit values are changed according to the type of ink or print medium, similarly to the ink duty limit, the saturation can be appropriately limited according to the type of ink or print medium.
[0141]
The above-described ink duty limit (condition 1) and saturation limit (condition 2) are based on the primary color space shown in FIG. 12 using the virtual gradation values of each of the CMY colors obtained using the replacement ink amount. Can be represented by a plane (not shown). The area surrounded by these planes is an area that satisfies the ink duty limit and the saturation limit. Therefore, if the virtual gradation values of the CMY colors of the colors represented by the ink amounts of the CMYRV colors are within the area surrounded by these surfaces, each ink amount satisfies the ink duty limit and the saturation limit. be able to.
[0142]
FIG. 12B shows an extended chromatic color em. The extended chromatic color em is located on the outer shell surface of an area that satisfies the ink duty limit (condition 1) and the saturation limit (condition 2), that is, the reproduced color outer surface (not shown). The extended chromatic color em is located on a line segment passing through the origin W and the outermost chromatic color m. That is, the extended chromatic color em is a color at a position where a line segment passing through the origin W and the outermost chromatic color m intersects with the reproduction color outer surface. In other words, the extended chromatic color em is a color represented by the longest extended chromatic vector having the same direction as the outermost chromatic vector representing the outermost chromatic color m in the primary color space, The outermost shell separation ink amount set for satisfying the saturation limit and reproducing the extended chromatic color em is a color satisfying the ink duty limit.
[0143]
Such an extended chromatic color em can be calculated using various methods. For example, a color that satisfies the saturation limit (condition 2) in the primary color space is selected, a chromatic primary color ink is replaced with a chromatic secondary color ink, and a color separation ink amount set is calculated. By repeatedly executing a series of processes of determining whether the color separation ink amount set satisfies the ink duty limit (condition 1), it is possible to successively and approximately calculate. Further, it can also be calculated using a so-called linear programming method based on the expressions of the replacement ink amount, the ink duty limit (condition 1), the saturation limit (condition 2), and the like. In this case, a series of steps S120 to S130 (FIG. 11) are executed at once.
[0144]
As described above, by calculating the extended chromatic color em (the outermost color separation ink amount set) that satisfies the ink duty limit (condition 1) and the saturation limit (condition 2), the color when printing that color is obtained. Within the range where the image quality is good, even if the hue is close to the chromatic secondary color ink, the saturation is not extremely high, and is located in the same direction as the outermost chromatic color m. A chromatic color em can be obtained.
[0145]
In step S140 of FIG. 11, a color separation ink amount set O corresponding to the input color I (FIG. 12) is calculated. In this step S140, first, the outermost shell separation ink amount set emp for the extended chromatic color em is calculated. The outermost shell separation ink amount set emp is a value that has already been calculated to determine whether or not the ink duty limit (condition 1) is satisfied when calculating the extended chromatic color em in step S130. is there. However, when there are many types of ink that can be used, the degree of freedom of replacement between the chromatic primary color ink and the chromatic secondary color ink increases. Therefore, in some cases, a combination of a plurality of types of ink amounts can be selected as the outermost color separation ink amount set emp corresponding to the extended chromatic color em within a range that satisfies the ink duty limit (condition 1). In such a case, in the present embodiment, the combination having the smallest total value of each ink amount is selected from the plurality of combinations and used as the outermost shell separation ink amount set emp.
[0146]
Next, a color separation ink amount set O is calculated based on the outermost shell color separation ink amount set. FIG. 12C is an explanatory diagram schematically showing the relationship between the input color I and the color separation ink amount set O. In this embodiment, the proportionality calculated by multiplying the ratio of the length LLI of the vector indicated by the input color I to the length LLm of the vector indicated by the outermost chromatic color m by the outermost color separation ink amount set emp. The separation ink amount set is used as the separation ink amount set O. At this time, the color separation ink amount set corresponding to the outermost shell chromatic color m is the outermost color separation ink amount set emp. Since the color between the origin W and the outermost shell separation ink amount set emp can satisfy the ink duty limit, it can be reproduced with a specific combination of the print medium and the ink set. Further, since the color between the origin W and the outermost shell separation ink amount set emp satisfies the saturation limit, the saturation is extremely high even when the hue is close to the chromatic secondary color ink. Can be suppressed. Therefore, it is possible to effectively use a range of colors that can be reproduced by a specific combination of a print medium and an ink set. By calculating the color separation ink amount set O in such a manner as to be proportional to the length LLI, the color separation ink amount set O for the input color I can be easily calculated.
[0147]
In this way, by sequentially executing the processing of steps S100 to S140, the color separation ink amount set O expressed in the reproduced color system corresponding to the input color I expressed in the primary color system is calculated. . In addition to the relationship between the input color I and the lengths LLI and LLm, the color separation ink amount set O includes the replacement ink amount, the ink duty limit (condition 1), the saturation limit (condition 2), and the like. And can be directly calculated using linear programming. In this case, a series of steps S120 to S140 are executed at once. The color separation ink amount set O thus obtained can be used as the second gradation value set in step S20 in FIG. The color reproduced by the color separation ink amount set O corresponds to a reproduced color (a color reproduced on a print medium) associated with the input color I.
[0148]
In step S150 in FIG. 11, it is determined whether the color separation ink amount sets for all input colors have been calculated. If the calculation of all the separated ink amount sets has not been completed, the processing of steps S120 to S140 is repeated, and if completed, the processing is terminated.
[0149]
In order to further reduce the time required for the separation processing, it is preferable to limit the number of outermost chromatic colors for executing a series of processing. At this time, if there is no outermost chromatic color corresponding to the input color to be subjected to the color separation process, the color separation ink amount set of a plurality of colors close to the input color is interpolated to obtain the corresponding color separation ink amount. You can ask for a set. At this time, it is preferable to prepare a plurality of outermost shell chromatic colors in advance so that a straight line connecting the outermost shell chromatic color and the origin W is distributed over the entire range in the color solid. By doing so, it is possible to suppress an increase in the interpolation error of the color separation ink amount set in a specific area in the color solid.
[0150]
As described above, in the present embodiment, the determination of the extended chromatic color em and the outermost shell separation ink amount set is performed under the following three conditions:
(I) the outermost shell separation ink amount set is within the ink duty limit,
(Ii) the extended chromatic color is within the saturation limit;
(Iii) the length of the extended chromatic color vector is the longest in a range that can be reproduced by the ink set;
(Iv) the sum of the ink amounts of the outermost color separation ink amount set for reproducing the extended chromatic color em is the smallest;
Running to meet. Even if all of these conditions are not satisfied, the color reproduction range can be extended as long as the extended chromatic color em has a higher saturation than the outermost chromatic color m. For example, even when the condition (iii) is not satisfied and the extended chromatic color vector is not the longest, the color reproduction range can be extended if the extended chromatic color vector is configured to be longer than the outermost chromatic color vector.
[0151]
In order to extend the color reproduction range in a wider hue range, it is preferable that the extended chromatic color vector be longer than the outermost chromatic color vector in a wider hue range. Here, the hue range in which the extended chromatic color vector can be extended is a range that changes according to the hue of the usable chromatic secondary color ink. The chromatic secondary color ink can extend the color reproduction range of an area having a hue close to the hue of the ink. Therefore, by using more types of chromatic secondary color inks having different hues from each other, the extended chromatic color vector is made longer than the outermost chromatic color vector in a wider hue range. Can be. Also at this time, by setting the extended chromatic color so as to satisfy the saturation limit, even when the hue of the extended chromatic color is close to the chromatic secondary color ink, the extended chromatic color with extremely high saturation is set. Can be suppressed.
[0152]
As described above, in the present embodiment, the color separation processing is performed by effectively using the range of colors that can be reproduced using the chromatic primary color ink and the chromatic secondary color ink. Therefore, printing in which the color reproduction range is extended can be performed. Separation processing is performed based on the extended chromatic color located at the intersection of the straight line connecting the origin and the outermost chromatic color and the outer surface of the reproduced color. However, the separation processing result can be easily obtained. In addition, since the reproduction color is set within a range that satisfies the saturation limit, it is possible to suppress the occurrence of a color having extremely high saturation when the hue is close to the chromatic secondary color ink. As a result, it is possible to extend the color reproduction range without unnaturally conspicuous in some areas in the print image.
[0153]
D. Third Embodiment of Separation Processing:
FIG. 14 is a flowchart showing a processing procedure of the third embodiment of the color separation processing. The difference from the above-described color separation processing example of FIG. 11 is that undercolor removal (UCR: Under Color Removal) processing S220 using black ink K is executed. The UCR process of the present embodiment is a process of replacing a part of the gradation values of the chromatic primary color inks C, M, and Y with the gradation value of the black ink K. Since the UCR process can be realized by various known methods, a detailed description is omitted here.
[0154]
In step S200, an ink set including chromatic primary color inks C, M, and Y, chromatic secondary color inks R and V, and black ink K is set as a usable ink set.
[0155]
Next, in step S210, an ink duty limit, which is a limit on the ink amount of each color of the ink set, is set. The difference from the ink duty limit in the embodiment shown in FIG. 11 described above is that it is set in consideration of the ink amount of the black ink K (details will be described later).
[0156]
Next, in step S220, the UCR process is performed on the input color to be subjected to the color separation process (for example, represented by the primary color tone value set in step S20 in FIG. 6). As a result, the input color I expressed by the gradation values Ci, Mi, Yi, Ki of each of the CMYK colors is obtained. In the present embodiment, the color separation process using the extended chromatic color em is performed on the gradation values Ci, Mi, and Yi of the CMY colors among these gradation values. A series of processes S230 to S260 are the same processes as the processes S120 to S150 of the embodiment shown in FIG. As a result, the separation ink amounts Co, Mo, Yo, Ro, and Vo for the gradation values Ci, Mi, and Yi of each of the CMY colors are obtained. For the black ink K, the gradation value Ki obtained as a result of the UCR process S220 is used as the color separation ink amount Ko.
[0157]
As described above, in the color separation processing of the third embodiment, in addition to the chromatic primary color ink CMY and the chromatic secondary color ink RV, the color range that can be reproduced using the black ink K is effective. Separation processing is used. Therefore, it is possible to perform printing in which the color reproduction range is further extended.
[0158]
Further, in this embodiment, it is preferable to set a limit in consideration of the amount of the black ink K in the above-described ink duty limit (condition 1). For example, regarding the limitation on the total value of the ink amounts of all types shown in Expression 2, the total value obtained by adding the ink amount Ki of the black ink K obtained in step S220 to the ink amount of each color of CMYRV is Duty_T or less. It can be set as follows. By doing so, it is possible to suppress ejection of an amount of ink that exceeds the limit on the amount of ink absorbed by the print medium. In addition, the limitation of the ink amount when a plurality of colors are mixed can be set using the ink amount Ki of the black ink K. It is preferable to consider the limitation of the ink amount of the black ink K alone when calculating the ink amount Ki in the UCR process S220.
[0159]
When the color separation processing of the present embodiment is applied to step S20 of the color conversion lookup table creation processing shown in FIG. 6, the second gradation value set includes the chromatic primary color inks CMY and chromatic 2 The gradation value is represented by the amount of each color ink of the next color ink RV and the black ink K. Therefore, in step S30, a color patch reproduced using each color of CMYRVK is created.
[0160]
E. FIG. Modification of ink set:
Various kinds of ink sets other than the ink set shown in FIG. 5 can be applied to each of the above-described embodiments. 15 to 22 are explanatory diagrams showing each ink component of an example of an applicable ink set. The components of the black ink K and the components other than the coloring material are the same as in FIG. 5, and are not illustrated. The difference from the ink set shown in FIG. 5 is that the types and densities of the color materials are partially different. As a result, these ink sets can improve the reproducibility of colors slightly different from each other. Therefore, by selecting and using an ink set suitable for an image to be printed, a higher quality print result can be obtained.
[0161]
The ink sets in FIGS. 15 to 20 show the respective replacement ink amounts of the red ink R and the violet ink V obtained by measuring the color patches. Thus, in these ink sets, the total value of the replacement ink amount is 1.7 or more. As a result, the chromatic secondary color ink can reproduce higher saturation by using the same amount of ink as the mixed color of the chromatic primary color ink. As a result, by using the chromatic primary color ink and the chromatic secondary color ink, it is possible to reproduce a wider range of colors than the area that can be reproduced only with the chromatic primary color ink.
[0162]
Further, as each ink, the ink is not limited to the composition shown in FIGS. 5 and 15 to 22 described above, and an appropriate ink according to another composition may be used. Further, the color and number of inks used are not limited to this combination. For example, a configuration may be used in which only red ink R can be used as a chromatic secondary color ink. Alternatively, a configuration using green ink or blue ink may be used. However, it is preferable to use inks that can reproduce achromatic colors in combination with each other as chromatic primary color inks, and use inks having a hue different from any of the chromatic primary color inks as chromatic secondary color inks. By using an ink set composed of such inks, it is possible to execute a color separation process in consideration of expansion of the color reproduction range.
[0163]
F. Second embodiment of the printing system:
FIG. 23 is an explanatory diagram illustrating a second embodiment of the printing system. The difference between the second embodiment and the above-described printing system is that the printing system includes two color conversion look-up tables LUT1 and LUT2 that can use the same ink and the same printing medium and have different saturation ranges of reproduced colors. Is a point.
[0164]
FIG. 23 shows an outline of the printer driver 96a of this embodiment. The configuration other than the color conversion lookup table is the same as that of the printing system shown in FIG. That is, the operation of each of the functional units 97a to 101a is the same as the operation of each of the functional units 97 to 101 shown in FIG.
[0165]
In the example of FIG. 23, the printer driver 96 includes a natural image color conversion lookup table LUT1 and a poster color conversion lookup table LUT2. The natural image color conversion look-up table LUT1 has a relatively narrow range of chroma reproducible on a print medium, and the poster color conversion look-up table LUT2 compares the range of chroma reproducible on a print medium. Each is configured to be as wide as possible.
[0166]
The advantage of using the two look-up tables LUT1 and LUT2 having different saturation ranges can be explained as follows. For example, in order to print a poster intended to attract the attention of a person, a color with high saturation may be used. In such a case, if printing is performed using the poster color conversion look-up table LUT2 having a relatively wide range of saturation, the saturation of the reproduced color can be increased. On the other hand, when printing a natural image such as a photographic image, it is preferable to suppress an extremely high saturation only for a color having a specific hue. In such a case, if the natural image color conversion look-up table LUT1 having a relatively narrow range of saturation is used, a natural print image with balanced saturation can be obtained. As described above, if a plurality of color conversion look-up tables having different reproduced saturation ranges can be used, printing can be performed using a preferable saturation range according to the type of print image.
[0167]
Such color conversion look-up tables LUT1 and LUT2 having different saturation ranges can be created by appropriately using a plurality of saturation limits having different limit values in each embodiment of the above-described separation processing. it can. For example, in the embodiment illustrated in FIGS. 11 to 13, if a saturation limit that limits the rate of expansion of the saturation to a relatively small value is used, the natural image color conversion lookup table LUT1 suitable for printing a natural image is used. Can be created. In addition, by using a saturation limit that limits the rate of expansion of the saturation to a relatively large value, a poster color conversion lookup table LUT2 that can use a wider range of saturation can be created. In particular, if a color conversion look-up table that satisfies the ink duty limit without imposing the saturation limit is created, the image quality of the printed image can be improved according to the type of print medium, and the color reproduction that can be realized with the ink set The poster color conversion lookup table LUT2 that makes full use of the range can be prepared.
[0168]
In the present embodiment, the “natural image print mode” and the “poster print mode” corresponding to each of the two color conversion look-up tables LUT1 and LUT2 prepared in this way can be used. The color conversion module 98a selects and refers to a color conversion lookup table corresponding to the print mode selected by the print mode selection unit 101a. Here, it is preferable to allow the user to select the print mode. In this embodiment, the user can instruct the print mode selection unit 101a to select a print mode via a screen (not shown) for setting print conditions of the printer driver 96a. By doing so, it is possible to suppress printing of an image using an unintended saturation range. It is also preferable that the print mode selection unit 101a automatically selects a print mode according to the format of image data used for printing. An image generating apparatus (digital still camera, digital video camera, etc.) that generates image data of a natural image generally generates JPEG format image data. Thus, when printing is performed based on JPEG format image data, if the print mode selection unit 101a automatically selects the “natural image print mode”, the user can use the preferred range of saturation without instructing. Printing can be performed.
[0169]
When a combination of a plurality of types of ink sets and print media is available, it is preferable to prepare a plurality of color conversion lookup tables having different saturation ranges for each combination. In this way, printing can be performed using a preferable range of saturation according to the type of the print image, regardless of the type of the ink set or the print medium. Further, the available saturation range is not limited to two types, and it is preferable that more types of saturation ranges can be used. By doing so, the range of saturation can be used more finely depending on the type of print image. Further, in the case where the print medium is properly used according to the type of the print image, it is also preferable to prepare one color conversion lookup table for each print medium. At this time, the saturation range of each color conversion lookup table is set according to the type of the corresponding print image. In this way, by selecting a print mode (color conversion lookup table) corresponding to the print medium to be used, printing can be performed using a preferable range of saturation according to the type of print image.
[0170]
As described above, in each of the embodiments described above, the color reproduction range can be extended by using the chromatic secondary color ink. In addition, since the color separation ink amount set is calculated so as to satisfy the saturation limit, it is possible to suppress reproduction of a color having extremely high saturation even when the hue is close to the chromatic secondary color ink. Can be. As a result, it is possible to suppress a color with extremely high saturation from being conspicuous in the print image, and to balance the saturation. Further, if the color separation processing based on the extended chromatic color having a large gradation value is performed, the color separation processing in consideration of the expansion of the color reproduction range can be easily performed. Further, by making available a plurality of color conversion look-up tables LUT having different reproduced saturation ranges, printing can be performed using the saturation range according to the type of the print image.
[0171]
By the way, in order to improve the interpolation accuracy of the color conversion using the color conversion lookup table LUT, it is preferable to create the color conversion lookup table LUT in consideration of the appearance change of the reproduced color with respect to the change of the input color. . For example, in step S20 of FIG. 6, a plurality of primary color tone value sets (input colors) are prepared within a range where the tone values can be taken. Here, if the input color is set more finely in the gradation value range in which the apparent change in the reproduced color with respect to the change in the gradation value of the input color, the accuracy of the interpolation can be improved. However, when the change in the tone value of the reproduced color with respect to the change in the tone value of the input color greatly differs depending on the color, it may be difficult to predict the apparent change in the reproduced color. As a result, in some cases, setting a plurality of input values requires a great deal of labor. In each embodiment of the color separation processing described above, the change in the gradation value of the reproduced color with respect to the change in the gradation value of the input color is prevented from becoming extremely large in a region having a hue close to the chromatic secondary color ink. can do. Therefore, since a plurality of input colors can be easily set, a color conversion look-up table LUT with improved interpolation accuracy can be easily created.
[0172]
The present invention is not limited to the above-described examples and embodiments, but can be implemented in various modes without departing from the gist of the invention, and for example, the following modifications are possible.
[0173]
G. FIG. Modification:
G1. Modification 1
In each of the above embodiments, it is preferable that the saturation limit is set according to the type of the print medium. The color reproducibility of the printed matter may differ depending on the type of print medium even when the same ink set is used. Therefore, even when the same ink set is used, the saturation of reproduced colors can be appropriately limited according to the print medium by using a plurality of saturation limits depending on the type of print medium. .
[0174]
G2. Modified example 2:
The saturation limitation is not limited to the limitation on the virtual gradation value of each color component of the chromatic primary color ink, and the limitation on various values correlated with the saturation of the reproduced color may be used. it can. For example, in the primary color space shown in FIG. 12, when a straight line connecting the origin W and the point K is called an achromatic line, the distance between the coordinates when the reproduced color is expressed in the primary color space and the achromatic line May be restricted. Further, the degree of saturation restriction can be set based on a sensory evaluation of an image output result. For example, a gradation pattern whose hue changes smoothly may be printed and set to a value that does not cause an unnaturally noticeable portion.
[0175]
G3. Modification 3:
In each of the above-described embodiments, the color separation ink amount set O for the input color I may be a combination of a plurality of ink amounts within a range where the chromatic primary color ink and the chromatic secondary color ink can be replaced. May be possible. In such a case, it is preferable to use, as the color separation ink amount set O, the combination that minimizes the total value of the respective ink amounts within the range that satisfies the ink duty limit, among the combinations of the plurality of ink amounts. By doing so, it is possible to improve the quality of the printed image and to save the amount of ink used. Further, when the lightness of the reproduced color is high (bright), it is also preferable to use a combination that actively uses the chromatic primary color ink. When the chromatic primary color ink is actively used, the ink amount of the plurality of chromatic primary color inks increases according to the replacement ink amount, so that the total number of ink dots recorded on the print medium increases. As a result, it is possible to make the graininess (roughness of an image) that is conspicuous in a bright area less noticeable. It is also preferable to use a combination in which the chromatic primary color ink is actively used when the saturation of the reproduced color is low. A low-saturation color can be reproduced using only the chromatic primary color ink. Therefore, if such low-saturation colors are positively reproduced using the chromatic primary color ink, the chromatic secondary color ink can be saved.
[0176]
G4. Modification 4:
In each of the above embodiments, the hue of each ink of the usable ink set is different from each other. However, a configuration may be used in which a plurality of types of inks having substantially the same hue and different densities can be used. In this case, by using inks having different densities in accordance with the tone values of the respective hues, the granularity (roughness of an image) that is more conspicuous as the number of ink dots is smaller is improved. Easy banding (streak-like pattern) can be suppressed. At this time, the ink amount of each ink is calculated using a so-called linear programming method by setting the above-described conditions such as the ink duty limit, the saturation limit, and the replacement ink amount in consideration of the ink amounts of all the inks. be able to. Alternatively, a method of calculating the color separation ink amount for each hue and redistributing the obtained color separation ink amount to a plurality of inks having substantially the same hue and different densities may be used. In this case as well, the ink duty limit and the saturation limit are limited in consideration of the ink amounts of all the inks, and the final ink amount of each ink satisfies the ink duty limit and the saturation limit. Is preferred.
[0177]
In each of the above embodiments, the “ink amount” is a tone value of each ink that represents a range of 0% to 100% when the ink amount when reproducing the solid area is 100%, This means the output of the color conversion lookup table LUT. When a plurality of types of inks having substantially the same hue and different densities can be used, the color separation processing can be performed by associating the total value of the color materials of the dark and light inks having the same hue with the “ink amount”. it can. At this time, an appropriate color can be reproduced by distributing the obtained “ink amount” to each of the dark and light inks.
[0178]
G5. Modification 5:
The present invention is also applicable to a thermal transfer printer and a drum scan printer. The present invention can be applied not only to a so-called ink-jet printer but also to a printing apparatus that generally reproduces colors by mixing a plurality of ink colors. Such printing apparatuses include, for example, facsimile machines and copy machines.
[0179]
G6. Modification 6:
In the above embodiment, a part of the configuration realized by hardware may be replaced by software, and conversely, a part of the configuration realized by software may be replaced by hardware. For example, a part of the functions of the printer driver 96 (FIG. 1) may be executed by the control circuit 40 (FIG. 3) in the printer 20.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of a printing system.
FIG. 2 is a schematic configuration diagram of a printer 20.
FIG. 3 is a block diagram illustrating a configuration of a printer 20.
FIG. 4 is an explanatory diagram showing a nozzle arrangement on the lower surface of the print head 28.
FIG. 5 is an explanatory diagram showing an ink set.
FIG. 6 is a flowchart showing a color reproduction processing procedure;
FIG. 7 is an explanatory diagram showing a color patch.
FIG. 8 is a flowchart showing a processing procedure of a separation process;
FIG. 9 is an explanatory diagram showing an outline of setting a reproduction color.
FIG. 10 is an explanatory diagram illustrating a rate at which a color reproduction range is extended.
FIG. 11 is a flowchart illustrating a processing procedure of a separation process;
FIG. 12 is an explanatory diagram showing a primary color space.
FIG. 13 is an explanatory diagram showing an outline of calculating an extended chromatic color;
FIG. 14 is a flowchart showing the procedure of a color separation process;
FIG. 15 is an explanatory diagram showing another example of an ink component.
FIG. 16 is an explanatory diagram showing another example of an ink component.
FIG. 17 is an explanatory diagram showing another example of an ink component.
FIG. 18 is an explanatory diagram showing another example of an ink component.
FIG. 19 is an explanatory diagram showing another example of an ink component.
FIG. 20 is an explanatory diagram showing another example of an ink component.
FIG. 21 is an explanatory diagram showing another example of an ink component.
FIG. 22 is an explanatory diagram showing another example of an ink component.
FIG. 23 is a block diagram showing another example of the printing system.
[Explanation of symbols]
20 ... Printer
21 ... CRT
22 ... Paper feed motor
24 ... Carriage motor
26 ... Platen
28 ... Print head
30 ... carriage
32 Operation panel
34 ... Sliding shaft
36 ... Drive belt
38 ... Pulley
39… Position sensor
40 ... Control circuit
41 ... CPU
43 ... P-ROM
44 ... RAM
45 ... CG
50 ... I / F dedicated circuit
52 ... Head drive circuit
54 ... Motor drive circuit
56… Connector
60 print head unit
90 ... Computer
91 ... Video driver
95 ... Application program
96, 96a: Printer driver
97, 97a ... resolution conversion module
98, 98a ... color conversion module
99,99a ... Halftone module
100, 100a ... rasterizer
101, 101a ... print mode selection unit
LUT, LUT1, LUT2 ... Color conversion lookup table
PP: printing paper
PD… Print data

Claims (21)

A color separation method for determining an ink amount of each ink in order to reproduce an arbitrary color using a plurality of color inks on a print medium,
(A) As a usable ink, a plurality of chromatic primary color inks capable of reproducing an achromatic color when used in combination with each other, and at least one chromatic primary color ink having a hue different from any of the plurality of chromatic primary color inks. Setting an ink set including a secondary color ink; and
(B) A color reproduced on the printing medium according to any one input color is called a reproduction color, and a combination of the respective ink amounts of the ink set for reproducing the reproduction color on the printing medium is referred to as a reproduction color. When a color space in which each ink amount of the plurality of chromatic primary color inks is referred to as a reference vector is referred to as a primary color space, a plurality of inputs in the primary color space are referred to. Determining a plurality of reproduction colors to be reproduced on the print medium according to the color,
(C) determining a plurality of color separation ink amount sets for reproducing the plurality of reproduction colors,
In the step (b),
The saturation of a reproduction color having the same hue as that of the chromatic secondary color ink is wider than the range of saturation that can be reproduced by the chromatic primary color ink, and the maximum of the saturation that can be reproduced by the ink set is maximum. The plurality of reproduction colors are determined so as to satisfy a predetermined saturation limit narrower than the limit range.
Separation method. The separation method according to claim 1, wherein
A first type chromatic color, which is a color expression region reproducible by the ink set in the primary color space and is located in a shell of a color expression region satisfying a predetermined restriction including the saturation restriction. The vector is referred to as a first-type vector, and a second-type chromatic color located in the outer shell of a color expression area reproducible by the chromatic primary color ink and located in the same direction as the first-type vector is referred to as a first-type vector. When a vector to be represented is called a second kind vector,
In the color separation method, the saturation restriction may limit a ratio of a length of the first type vector to a length of the second type vector to a predetermined limit value or less. The separation method according to claim 2, wherein
The separation method, wherein the limit value is constant irrespective of the hue of the reproduced color. The separation method according to claim 1, wherein the separation method includes:
The color separation method is a color separation method that limits the size of each color component of the chromatic primary color ink when the reproduced color is expressed in the primary color space. A separation method according to any one of claims 1 to 4, wherein
The step (b) comprises:
(B1) In the primary color space, a chromatic color at the outermost shell position of a color expression area reproducible by the chromatic primary color ink is referred to as an outermost chromatic color. An outermost shell separation ink amount set associated with a coloring, wherein the outermost shell separation for reproducing an extended chromatic color that is reproducible by the ink set and has higher saturation than the outermost chromatic color. Determining an ink amount set;
(B2) the plurality of reproduced colors respectively associated with the plurality of input colors in the primary color space based on a relationship between the outermost chromatic color and the outermost color separation ink amount set. The step of determining;
Including
The step (b1) comprises:
Setting an upper limit of the amount of ink that can be used per unit area of the print medium as an ink duty limit,
Determining the extended chromatic color as a color represented by a longer extended chromatic color vector having the same direction as the outermost chromatic color vector representing the outermost chromatic color in the primary color space; Determining the outermost shell separation ink amount set for reproducing a chromatic color;
With
The determination of the extended chromatic color and the outermost color separation ink amount set is based on the following conditions:
(I) the outermost shell separation ink amount set is within the ink duty limit,
(Ii) the extended chromatic color is within the saturation limit;
Done to satisfy the
Separation method. The separation method according to claim 5, wherein
The determination of the extended chromatic color and the outermost hull separation ink amount set further includes the following conditions:
(Iii) the length of the extended chromatic color vector is the longest in a range reproducible by the ink set;
Separation method is performed to satisfy. A separation method according to claim 5 or claim 6, wherein
The determination of the extended chromatic color and the outermost hull separation ink amount set further includes the following conditions:
(Iv) the total amount of ink in the outermost shell separation ink amount set for reproducing the extended chromatic color is the smallest;
Separation method is performed to satisfy. A separation method according to any one of claims 5 to 7, wherein
The reproduced color includes the vector length of the input color and the outermost shell chromatic color in the outermost shell separation ink amount set for the outermost shell chromatic color having the same vector direction as the input color in the primary color space. A separation method that is a color reproduced by a proportional separation ink amount set obtained by multiplying by a ratio with a vector length. A separation method according to any one of claims 1 to 8, wherein
The color separation method, wherein the chromatic secondary color ink contains a color material different from the plurality of chromatic primary color inks. A separation method according to any one of claims 1 to 9, wherein
The chromatic secondary color ink is reproduced as a mixed color of the chromatic primary color ink when a hue reproducible by the chromatic secondary color ink is reproduced by a mixed color of the plurality of chromatic primary color inks. A separation method that can reproduce higher saturation than is possible. A separation method according to any one of claims 1 to 10, wherein
The ink set includes first and second chromatic secondary color inks having different hues from each other,
By replacing the chromatic secondary color ink with a combination of the plurality of chromatic primary color inks, the plurality of chromatic secondary color inks are reproduced with substantially the same hue and saturation. Each ink amount of the primary color ink is defined as a replacement ink amount,
For each of the first and second chromatic secondary color inks, when the two inks having the largest values among the replacement ink amounts are set as the main component primary color inks,
One of the two main component primary color inks of the first chromatic secondary color ink is different from the one of the two main component primary color inks of the second chromatic secondary color ink. Separation method that is ink. A separation method according to any one of claims 1 to 11, wherein
The ink set includes black ink,
The step (b) comprises:
Performing a process of removing the under color of the black ink on the input color to remove a black component to obtain a corrected input color composed of a plurality of chromatic primary color components; Determined according to the input color,
Separation method. A method for creating a color conversion lookup table for converting input color image data represented by a first color system into second color image data represented by a reproduced color system,
The reproducible color system includes a plurality of chromatic primary color inks capable of reproducing an achromatic color when used in combination with each other, and at least one chromatic color having a hue different from any of the plurality of chromatic primary color inks. A color system for reproducing colors using an ink set containing secondary color inks,
The method of creating the color conversion lookup table includes:
Converting a first set of tone values represented by the first color system into a primary color scale represented by a primary color system for each ink amount of the plurality of chromatic primary color inks; Setting a first correspondence to convert to a set of tonal values;
2. A second correspondence relationship for converting the primary color tone value set for a plurality of input colors in the primary color system into each ink amount of the ink set according to the color separation method of claim 1. Setting step;
The first and second correspondences are used to determine the correspondence between the first tone value set represented by the first color system and the respective ink amounts of the ink set, Storing in a conversion lookup table;
Comprising,
How to create a color conversion lookup table. An image data processing device for converting input color image data represented by a first color system into second color image data represented by a reproduced color system,
A color conversion look-up table created according to the method of claim 13;
A color conversion module that performs the conversion process with reference to the color conversion lookup table;
An image data processing device comprising: A printing apparatus that prints an image by discharging ink onto a print medium,
A plurality of chromatic primary color inks capable of reproducing an achromatic color when used in combination with each other, and at least one chromatic secondary color ink having a hue different from any of the plurality of chromatic primary color inks. A print head capable of discharging each ink of the ink set,
An adjustment unit that adjusts the ejection amount of each ink of the ink set,
The adjustment unit is capable of using the same ink as the first type color print mode and the first type color print mode having a relatively narrow range of chroma reproducible on the print medium, A second type of color print mode having a relatively wide range of chroma reproducible on a print medium,
Printing device. The printing device according to claim 15, wherein
The printing apparatus, wherein the first type color print mode and the second type color print mode are print modes that can use the same print medium. A printing device according to claim 15 or claim 16,
The adjustment unit is
The conversion from the input color image data represented by the first color system to the second color image data represented by the reproduced color system composed of the ink amounts of the respective inks of the ink set is performed by color conversion. A printing device comprising a color conversion module that performs conversion using a conversion lookup table. The printing device according to claim 17,
The adjustment unit includes a plurality of color conversion look-up tables prepared in advance corresponding to a plurality of print modes that the adjustment unit has,
The color conversion module uses a color conversion lookup table corresponding to a print mode used by the adjustment unit,
Printing device. A plurality of chromatic primary color inks capable of reproducing an achromatic color when used in combination with each other, and at least one chromatic secondary color ink having a hue different from any of the plurality of chromatic primary color inks. A printing method for printing an image by ejecting each ink of an ink set on a printing medium,
(A) selecting one of a plurality of print modes including a first type print mode having a relatively narrow range of saturation reproducible on the print medium and a second type print mode having a relatively wide range. When,
(B) adjusting the ejection amount of each ink of the ink set according to the selected print mode;
A printing method comprising: A plurality of chromatic primary color inks capable of reproducing an achromatic color when used in combination with each other, and at least one chromatic secondary color ink having a hue different from any of the plurality of chromatic primary color inks. A computer program for generating print data to be supplied to a printing unit that prints an image by discharging each ink of an ink set to be printed on a print medium,
(A) a function of selecting one of a plurality of print modes including a first type print mode having a relatively narrow range of saturation reproducible on the print medium and a second type print mode having a relatively wide range When,
(B) a function of adjusting the ejection amount of each ink of the ink set according to the selected print mode;
(C) a function of generating print data representing the ejection state of each ink at each pixel on the print medium according to the adjusted ejection amount of each ink;
Computer program to make a computer realize. A computer-readable recording medium on which the computer program according to claim 20 is recorded.

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