JP2004064546A - Image processing apparatus and color reproduction method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable accurate color reproduction in a different observation environment by faithfully reproducing the spectral distribution characteristics of a target color in color conversion processing for reproducing the target color. <P>SOLUTION: A color sample searching unit 4 acquires the spectral reflectance of a designated color sample from a color sample database 3 storing the spectral reflectance of a plurality of colors. A printer model 5 estimates the spectral reflectance of each of the output colors obtained by various combinations of ejection quantities of ink of a plurality of colors used in forming an image. An error calculating section 6 determines output colors corresponding to the designated color sample, on the basis of the spectral reflectance of the color sample obtained in the section 4 and the spectral reflectance estimated by the printer model 5. A result displaying section 7 displays the determined output colors to a user by using a display device 8. <P>COPYRIGHT: (C)2004,JPO

Description

【００２１】
ステップＳ４０４では、ステップＳ４０３にて算出された分光反射率推定初期値に対して、インク重ね合わせ補正を行う（詳細は後述）。ステップＳ４０５では、用いるインクの打ち込み量の全ての組み合わせ（例えば０％から１００％まで１％間隔）について出力推定したかどうか判断し、全て推定していれば終了し、していなければステップＳ４０６に進む。ステップＳ４０６では、インクの打ち込み量を一定量変化させて新たなインク打ち込み量の組み合わせを設定し、ステップＳ４０２に戻る。なお、上記のようにして求めた分光反射率を、各インク打ち込み量の組み合わせに対応付けて格納しておくようにすれば、図４で説明した推定処理を繰り返す必要がなくなり、処理の高速化を図ることができる。
【００２２】
＜１次色ドットゲイン補正＞
次に、図５及び図６を用いて、ステップＳ４０２による１次色ドットゲイン補正の詳細を説明する。一般的には１次色ドットの分光反射率（ドットゲイン）が打ち込み量に対して線形に変化すると仮定しているのに対し、本実施形態ではドットゲインの非線形性の影響を考慮するために、１次色ドットゲイン補正を行ない、高精度な出力推定を行なう。
【００２３】
図５は本実施形態による１次色補正用パッチの例を示す図である。また、図６において、（ａ）はシアンインクの打ち込み量に対する分光反射率の測定結果を示す図、（ｂ）は（ａ）の測定結果から取得された１次色補正ＬＵＴを示す図である。
【００２４】
まず、予め色再現予測を行いたい対象のプリンタを用いて出力しておいた１次色補正用パッチを測色する。ここで用いる１次色補正用パッチとは、図５に示すような、各インクの打ち込み量を０％から１００％まで、２０％間隔というように各インクの打ち込み量を変化させたものである。このような１次色補正用パッチの分光反射率データは、図６（ａ）に示すような、各インクの離散的な打ち込み量に対する各波長の反射率である。これら各波長の反射率の測定データから、図６（ｂ）に示すような各インク、各波長での、打ち込み量と反射率との関係を示すＬＵＴに変換される。
【００２５】
ここで、インク打ち込み量に関しては２０％刻みの離散的な測定結果しか存在しないので、１次色補正ＬＵＴの作成には線形補間やスプライン補間等、一般的な補間法が用いられる。１次色ドットゲイン補正（ステップＳ４０２）では、このＬＵＴを用い、入力されたインク打ち込み量に対する、１次色ドットゲイン補正を行い、１次色の分光反射率を推定する。なお、図６（ｂ）には、簡単のため、４本のグラフしか描いていないが、実際には可視波長域においてサンプリングされた全ての波長（例えば、３８０ｎｍ〜７８０ｎｍまで１０ｎｍ刻みの４１波長）についてそれぞれテーブルが作成される。このようなＬＵＴを用い、設定されたインク打ち込み量における、１次色ドットゲイン補正された分光反射率を取得することができる。
【００２６】
＜インク重ね合わせ補正係数算出＞
次に図７を用いて、ステップＳ４０４によるインク重ね合わせ補正の詳細を説明する。
【００２７】
ステップＳ４０４では、予め色再現予測を行いたい対象のプリンタを用いて出力しておいたインク重ね合わせ補正用パッチを測色する。ここで用いるインク重ね合わせ補正用パッチとは、図７に示すような、各インクの打ち込み量を０％から１００％まで２０％間隔というように変化させ、さらに用いるインクを２色以上重ね合わせて印刷したものである。
【００２８】
次に、図７に示した重ね合わせ補正用パッチデータを記録するためのデータ（各パッチにおける各色の打ち込み量）を用いて、上記（１）〜（３）式により、すなわちステップＳ４０３と同様の処理により、重ね合わせ補正用パッチの分光反射率推定初期値を推定する。ここで算出された分光反射率推定初期値は、実際に図７の補正用パッチを測色して得られた実測データに対して誤差が生じている。そこで、該実測データとの誤差を修正するために、以下の（４）式を用いて、該誤差が最小となるように、最小二乗法等を用いて補正係数ａ_ｈ、λ、ｂ_{ｉ，ｊ， λ}、ｃ_{ｋ，ｌ，ｍ， λ}を決定する。
【００２９】
【数２】

【００３０】
なお、上記（４）式において、Ｒ_{ｐ， λ}は（１）式〜（３）式のＫＭ理論（Ｋｕｂｅｌｋａ−Ｍｕｎｋ理論）で求まる１次色補正後の推論値であり、Ｒ_{ｍｏｄ， λ}は、インク重ね合わせ補正後の補正された推論値を示している。そして、Ｒ_{ｍｏｄ， λ}とカラーパッチの実測値との誤差が小さくなるように係数ａ_{ｈ， λ}、ｂ_{ｉ，ｊ， λ}、ｃ_{ｋ，ｌ，ｍ， λ}を決定している。また、第２項のｉ，ｊと、第３項のｋ，ｌ，ｍは任意のインクを示しており、例えばｎ色のインクとしてＣ、Ｍ、Ｙ、Ｋの４色を用いるとした場合、ｉ　＝　Ｃ，Ｍ，Ｙ，Ｋ、ｊ　＝　Ｃ，Ｍ，Ｙ，Ｋ、…（ただし、ｉ≠ｊ，　ｋ≠ｌ≠ｍ）となる。また、（Ｋ／Ｓ）は（１）式に定義されたとおりである。
【００３１】
以上のようにして決定された補正係数は所定の記憶装置に記憶され、ステップＳ３０４によるインク重ね合わせ補正の実行時に読出される。即ち、ステップＳ３０４におけるインク重ね合わせ補正では、ステップＳ３０３で算出された分光反射率推定初期値に対して、上記インク重ね合わせ補正係数を用い、（４）式を適用してインク重ね合わせによる推定誤差を補正する。
【００３２】
＜誤差算出方法＞
次に、ステップＳ２０６による誤差算出方法の詳細を説明する。２つの色の誤差を算出する方法としては、一般にＣＩＥ色差式が知られている。しかしながら、このＣＩＥ色差式ではメタメリズムの影響を考慮していないため、本実施形態では、例えば、以下の（５）式で表すような、波長ごとの分光分布誤差の２乗平均（ＲＭＳ誤差）を用いる。
【００３３】
【数３】

【００３４】
ただし、上記ＲＭＳ以外でも、メタメリズムを考慮した誤差を算出できるものであれば、その種類は限定しない。例えば、（６）式のように、上記ＲＭＳ誤差において、
【００３５】
【数４】

で表されるＣＩＥ等色関数の和で与えられるような重み関数を用い、波長毎に重み付けしたものを用いても良い。
【００３６】
【数５】

【００３７】
以上のように、第１実施形態によれば目標とする色を再現するための色変換処理において、ユーザの指定した色見本帳などの色の分光分布特性を予め記憶させておき、その特性を出来るだけ忠実に再現することで、異なる観察環境下においても正確な色再現を実現することが出来る。
【００３８】
＜第２実施形態＞
次に第２実施形態について説明する。第２実施形態では、画像データに基づいて出力画像を推定するとともに、所望の色を所望の見本色に置換することを可能とする。
【００３９】
図８は第２実施形態による色再現装置の構成を示したブロック図である。図８において、８０１は本発明の実施形態である色再現装置を示している。なお、色再現装置８０１は汎用のコンピュータにおいて、後述する処理を実現する制御プログラムを実行させることで実現可能である。８０２は色指定情報入力部であり、マウス、キーボード等によってユーザが指定した色指定情報を入力する。８０３は色見本データベースであり、色見本名と分光反射率の対の形態で色見本を記憶する。８０４は色見本検索部であり、色指定情報入力部８０２で入力された色指定情報に基づき、色見本データベース８０３から色見本の分光反射率を検索、取得する。８０５は画像データベースであり、画像データを格納する。８０６は結果表示部であり、出力推定結果等を表示装置８０９に表示する。８０７はプリンタモデルであり、プリンタによる出力色の色（分光反射率）を推定する。８０８は画像出力部であり、画像出力装置８１０によって画像を出力させる。
【００４０】
８０９は表示装置であり、ＣＲＴやＬＣＤ等で構成され、各種ユーザインターフェースを提供したり、結果表示部８０６の制御によって処理結果を表示する。８１０は画像出力装置であり、インクジェット方式或いはレーザビーム方式等のカラープリンタである。８１１はキーボードやマウス等で構成され、色指定情報を入力するための色指定情報指定装置である。
【００４１】
＜全体処理＞
以下、第２実施形態による色再現装置の動作について詳細に説明する。図９は第２実施形態による色再現処理を説明するフローチャートである。図１０は第２実施形態の色再現処理に用いるユーザインターフェースの一例を示す図である。
【００４２】
まず、ステップＳ９０１において、結果表示部８０６は画像データベース８０５からユーザが画像指定部１００９にて指定した画像を読み込み、これを原画像表示部１００６に表示する。次に、ステップＳ９０２では、上記第１実施形態と同様の手順により、プリンタモデル８０７にて出力分光反射率を推定する。すなわち、画素データのＲＧＢ値から求まるＬａｂと各インク打ち込み量について推定された分光反射率から求まるＬａｂの比較で決定する（各画素のＲＧＢ値は、ＩＣＣプロファイル等でＬａｂ値に変換することができ、このＬａｂ値に最も近くなるように、各インクの打ち込み量を決定する）。このとき、各画素の推定された分光反射率から三刺激値Ｌａｂを算出し、ＩＣＣプロファイル等を用いて、表示装置８０９のデバイスＲＧＢ値に変換し、該デバイスＲＧＢ値を出力推定画像表示部１００７に表示する。
【００４３】
ステップＳ９０３では、ユーザが原画像表示部１００６にて、色指定したい画素をマウス等により色指定ポインタ１００８を操作して指定する。このとき、指定された画素のＲＧＢ値が指定色表示部１００３に表示される。ステップＳ９０４では、ユーザが指定した指定色を実際にどのような色で出力したいかを指定するために、色見本名入力部１００１にて色見本から所望の色を選択する。すなわち、色見本データベース８０３に記憶されている色見本の分光反射率中から、該色見本名選択部１００１にて指定された色見本の分光反射率が色見本検索部８０４によって読み込まれる。読み込まれた色見本の分光反射率は、分光反射率表示部１０１０に表示されるとともに、ＩＣＣプロファイル等を用いて表示装置８０９のデバイスＲＧＢ値に変換される。該デバイスＲＧＢ値は色見本確認部１００４に表示される。
【００４４】
ステップＳ９０５では、第１実施形態で説明したのと同様の手順で、プリンタモデル８０７にて出力推定を行い、当該色見本に最も近い色（分光反射率）となるインク打ち込み量を取得する。こうして、色見本に最も近いと推定された分光反射率を分光反射率表示部１０１０に表示する。また、この推定された分光反射率をＩＣＣプロファイル等を用いて表示装置８１０のデバイスＲＧＢ値に変換し、得られたデバイスＲＧＢ値を出力推定確認部１００５に表示する。そして、更新された出力推定画像を出力推定画像表示部１００７に表示する。
【００４５】
ユーザによって画像出力ボタン１０１１が押されると、ステップＳ９０６からステップＳ９０７へ進み、画像出力を行なう。すなわち、ユーザは、出力推定画像表示部１００７に表示された出力推定結果等を見て所望の画素に対して色指定をやり直したい場合、画像出力ボタン１０１１を押さずに指定色の選択を繰り返すことにより色修正を行なえる。また、出力推定結果が満足の行くものであれば、画像出力ボタン１０１１を押すことで、画像出力装置８１０から画像出力を得ることができる。すなわち、ステップＳ９０７において、画像出力部８０８が画像出力装置８１０から画像を出力させる。なお、上記において、指定された画素の色と同一の色を有する画素の全てについて見本色への置き換えが行われる。すなわち、指定された画素と同じＬａｂを有する画素は、特定の観察環境下では、全て同じ色に見える。ユーザはそのディスプレイ上の色を見て色補正を行うので、出力される色も、全て同じである必要がある。そこで、ある画素の分光反射率を更新した場合には、同じＬａｂの画素全てを更新する。
【００４６】
以上説明したように上記各実施形態によれば、目標とする色を再現するための色変換処理において、ユーザの指定した色の分光分布特性が忠実に再現され、異なる観察環境下においても正確な色再現を実現する色変換処理を行うことができる。
【００４７】
＜出力推定＞
なお、上記各実施形態では、プリンタモデル５および８０７における出力推定に適用できる方法は、上述した推定方法に限られるものではない。例えば、従来用いられているニューラルネットワークによる出力推定方法を用いても良いし、ユール‐ニールセンの修正式を用いたノイゲバウア式を用いても良い。すなわち、インクの分光反射率と打ち込み量を用いて出力予測を行う方法であれば、その方法は限定しない。
【００４８】
＜色見本データベース＞
図１１、図１２および図１３は、色見本データベース３、８０３のデータ構成例を示す図である。図１１では、色見本名と該色見本名に対応した分光反射率が記憶されているデータベースの初期状態である。さらに上記各実施形態において色再現予測結果をデータベースに追記した場合には、図１２のように、色見本に対して色再現予測結果にて得られたインク打ち込み量が追記される。また、インク打ち込み量の追記方法はこれに限られるものではなく、例えば、図１３に示すように、新たにユーザ出力として、該打ち込み量に加えて、実際に出力したパッチの分光反射率の測定値と共に追記するようにしても良い。また、色見本は一定の数に固定されるものではなくユーザが所望の時に、新たに測定した色見本データを追加してもよい。なお、上述のようにして追加登録されたユーザ出力、色見本は、上述の色見本検索部４、８０４による検索の対象となる。
【００４９】
＜ユーザインターフェース＞
また、上記各実施形態では、図３および図１０に示すユーザインターフェースの例を示したが、ユーザインターフェースの形態が図示のものに限定されないことは言うまでもない。例えば、光源情報選択部３０２および１００２において、ユーザが所望の光源を選択するとしたが、予め光源データを記述してあるファイルを読みこむ形式にしても構わない。つまり、ユーザの所望の設定ができるようなユーザインターフェース構成であればよい。
【００５０】
＜記憶媒体＞
なお、本発明は、複数の機器（例えばホストコンピュータ、インタフェイス機器、リーダ、プリンタなど）から構成されるシステムに適用しても、一つの機器からなる装置（例えば、複写機、ファクシミリ装置など）に適用しても良い。
【００５１】
また、本発明の目的は、前述した実施形態の機能を実現するソフトウェアのプログラムコードを記録した記憶媒体を、システムあるいは装置に供給し、そのシステムあるいは装置のコンピュータ（またはＣＰＵまたはＭＰＵ）が記憶媒体に格納されたプログラムコードを読み出し実行することによっても達成されることは言うまでもない。
【００５２】
この場合、記憶媒体から読み出されたプログラムコード自体が前述した実施形態の機能を実現することになり、そのプログラムコードを記憶した記憶媒体は本発明を構成することになる。
【００５３】
プログラムコードを供給するための記憶媒体としては、例えば、フレキシブルディスク、ハードディスク、光ディスク、光磁気ディスク、ＣＤ−ＲＯＭ、ＣＤ−Ｒ、磁気テープ、不揮発性のメモリカード、ＲＯＭなどを用いることが出来る。
【００５４】
また、コンピュータが読み出したプログラムコードを実行することにより、前述した実施形態の機能が実現されるだけでなく、そのプログラムコードの指示に基づき、コンピュータ上で稼動しているＯＳ（オペレーティングシステム）などが実際の処理の一部を行い、その処理によって前述した実施形態の機能が実現される場合も含まれることは言うまでもない。
【００５５】
さらに、記憶媒体から読み出されたプログラムコードが、コンピュータに挿入された機能拡張ボードやコンピュータに接続された機能拡張ユニットに備わるメモリに書き込まれた後、そのプログラムコードの指示に基づき、その機能拡張ボードや機能拡張ユニットに備わるＣＰＵなどが実際の処理の一部または全部を行い、その処理によって前述した実施形態の機能が実現される場合も含まれることは言うまでもない。
【００５６】
【発明の効果】
以上説明したように、本発明によれば、目標色を再現するための色変換処理において、目標色の分光分布特性を忠実に再現することが可能となり、異なる観察環境下においても正確な色再現が実現される。
【図面の簡単な説明】
【図１】第１実施形態による色再現装置の構成を示したブロック図である。
【図２Ａ】第１実施形態の色再現装置にて実行される色再現処理を示すフローチャートである。
【図２Ｂ】第１実施形態の色再現装置にて実行される色再現処理を示すフローチャートである。
【図３】色再現処理において用いられるユーザインターフェースの一例を示す図である。
【図４】本実施形態による出力推定処理を説明するフローチャートである。
【図５】本実施形態による１次色補正用パッチの例を示す図である。
【図６】（ａ）はシアンインクの打ち込み量に対する分光反射率の測定結果を示す図、
（ｂ）は（ａ）の測定結果から取得された１次色補正ＬＵＴを示す図である。
【図７】本実施形態によるインク重ね合わせ補正用パッチの例を示す図である。
【図８】第２実施形態による色再現装置の構成を示したブロック図である。
【図９】第２実施形態による色再現処理を説明するフローチャートである。
【図１０】第２実施形態の色再現処理に用いるユーザインターフェースの一例を示す図である。
【図１１】本実施形態による色見本データベースのデータ構成例を示す図である。
【図１２】本実施形態による色見本データベースのデータ構成例を示す図である。
【図１３】本実施形態による色見本データベースのデータ構成例を示す図である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image processing method and apparatus for accurately reproducing a target color in an image output device such as a color printer.
[0002]
[Prior art]
Conventionally, when a certain target color is accurately reproduced by a color printer or the like, first, an operator adjusts an image on a display such as a CRT or an LCD to obtain a desired print result, and actually prints the image. Looking at the result, the toning is performed by repeating trial and error of toning the image again on the display. For example, as disclosed in Japanese Patent Application Laid-Open No. 2000-333032, a method of displaying a color sample or an output image on a screen and performing color adjustment by reflecting the specified color on the output image so that the specified color becomes smooth on the output image. There is. There is also a method in which a color sample, which is a target color, is measured using a colorimeter, and an output color that is closest to the colorimetric value, that is, an output color with a minimum color difference is selected and output.
[0003]
[Problems to be solved by the invention]
However, the colors displayed on the display are generally composed of an additive color mixture of three phosphors of RGB, while the colors output by printing are the four color inks of cyan, magenta, yellow, and black, or the four color inks. It consists of subtractive color mixing of six color inks, including light cyan and light magenta. For this reason, the spectral reflectance may differ between the toning result displayed on the display and the actual printing result even if the tristimulus values such as XYZ match. In other words, since color matching is performed using conditionally equal colors, there is a problem that the color reproduction accuracy is reduced when the printed matter is observed in an environment different from the environment in which the toning is performed, for example, under a different illumination light source. . Also, in the method of minimizing the color difference between the color sample and the output color, even if the tristimulus values can be matched, since the spectral reflectance is different, the color sample and the output color under different illumination light sources are different. There was a problem that the appearance of the color was greatly different.
[0004]
SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and in a color conversion process for reproducing a target color, it is possible to reproduce a spectral distribution characteristic of a target color as faithfully as possible, and to realize different observation environments. It is an object of the present invention to enable accurate color reproduction even below.
[0005]
[Means for Solving the Problems]
An image processing apparatus according to the present invention for achieving the above object has the following configuration. That is,
Storage means for storing spectral reflectances of a plurality of colors;
Acquiring means for acquiring the spectral reflectance of the designated color from the storage means;
Estimating means for estimating the spectral reflectance of each output color obtained by combining and recording color materials used in image formation in various amounts,
Determining means for determining an output color corresponding to the specified color based on the spectral reflectance of the specified color obtained by the obtaining means and the spectral reflectance estimated by the estimating means;
Presentation means for presenting the output color determined by the determination means to the user.
[0006]
Further, the color reproduction method according to the present invention for achieving the above object,
A color reproduction method in an image processing apparatus having storage means for storing spectral reflectances of a plurality of colors,
An acquisition step of acquiring the spectral reflectance of a specified color from the storage unit,
An estimation step of estimating the spectral reflectance of each output color obtained by recording in combination with various amounts of color materials used during image formation,
Based on the spectral reflectance of the specified color obtained in the obtaining step and the spectral reflectance estimated in the estimating step, a determining step of determining an output color corresponding to the specified color,
A presenting step of presenting the output color determined in the determining step to the user.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments according to the present invention will be described in detail with reference to the accompanying drawings.
[0008]
<First embodiment>
FIG. 1 is a block diagram showing the configuration of the color reproduction device according to the first embodiment.
[0009]
In FIG. 1, reference numeral 1 denotes a color reproduction device according to an embodiment of the present invention. Note that the color reproduction device 1 can be realized by causing a general-purpose computer to execute a control program that realizes processing described later. A color designation information input unit 2 allows the user to input color designation information. Reference numeral 3 denotes a color sample database which stores color names and spectral reflectances in the color sample in association with each other. Reference numeral 4 denotes a color sample search unit that searches the color sample database 3 for the spectral reflectance of the color sample based on the color specification information input by the color specification information input unit 2. Reference numeral 5 denotes a printer model for estimating an output color (spectral reflectance of a printer output) based on the spectral reflectance of each ink and the amount of ejection.
[0010]
Reference numeral 6 denotes an error calculation unit that calculates an error between the spectral reflectance of the color sample searched by the color sample search unit 4 and the spectral reflectance estimated by the printer model 5. Reference numeral 7 denotes a result display unit, which displays the output estimation result of the printer model 5 on the display device 8. A display device 8 has a CRT, an LCD, and the like, and displays a result. The communication between the color sample database 3 and the result display unit 7 is for displaying the selected color sample on the result display unit. An image output unit 9 controls the image output device 10 to output a visible image. An image output device 10 outputs an image by a printer or the like. In the present embodiment, a description will be given assuming that the recording material is a color ink assuming an ink jet type color printer as an image output device. However, it is apparent that the present invention can be applied to other laser beam type color printers. . For example, in the case of a laser beam method, toner is used as a recording material. Reference numeral 11 denotes a color designation information input device, which includes a keyboard, a mouse, and the like.
[0011]
<Overall processing>
Next, a color reproduction process according to the first embodiment will be described. 2A and 2B are flowcharts showing a color reproduction process performed by the color reproduction device 1. FIG. 3 is a diagram illustrating an example of a user interface used in the color reproduction processing. The user interface shown in FIG. 3 is displayed on the display device 8, and an operation input to the user interface is performed by a keyboard and a mouse constituting the color designation information input device 11.
[0012]
First, in step S201, using the color designation information input device 11, the user can use the color sample name selection unit 301 to select a print color sample No. such as DIC or Pantone stored in the color sample database 3. (Hereinafter referred to as a color sample name), a desired color sample name is designated. In the processing described below, in step S202, the color sample search unit 4 reads the spectral reflectance of the color sample specified in step S201 from the color sample database 3. Then, in step S203, the color sample retrieval unit 4 calculates the tristimulus values (L * a * b *) of the read spectral reflectances, and displays the result on the color sample tristimulus value display unit 306. Further, the calculated tristimulus values are converted into device RGB values of the display device 8 using an ICC profile or the like, and the device RGB values are displayed on the color sample confirmation unit 303. At this time, the user can specify the light source information necessary for calculating the tristimulus value in the light source information selection unit 302. Note that the color sample name selection unit 301 and the light source information selection unit 302 may display a list of color samples and light source information registered in the apparatus, and allow the user to select a desired one from the list.
[0013]
In step S204, it is determined whether or not the color matching button 305 has been pressed (whether or not the button has been clicked with the mouse). If the button has been pressed, the color matching processing of steps S205 to S207 is executed. If not, the process proceeds to step S208. And skip. In the color matching process, first, in step S205, the spectral reflectance of the reproduced color output from the image output device 10 by the printer model 5 is estimated (the spectral reflectance estimating process will be described later). At this time, tristimulus values (L * a * b *) are calculated for the estimated spectral reflectance, and displayed on the output tristimulus value display unit 307. The calculated tristimulus values are converted into device RGB values of the display device 8 using an ICC profile or the like, and the device RGB values are displayed on the color sample confirmation unit 304.
[0014]
In step S206, the error calculator 6 calculates an error between each color (spectral reflectance) estimated by the printer model 5 and a color sample color (spectral reflectance) (the error calculation will be described later). The combination of the ink ejection amounts to obtain the estimated color with the minimum error from the color sample is obtained. In step S207, the result display unit 7 displays the obtained result on the display device 8. That is, of the errors calculated by the error calculation unit 6, the smallest one is displayed on the error display unit 308, and the amount of each ink hit at that time is displayed on the ink hit amount display unit 309, and the color sample and output estimation are performed. The spectral reflectance and Lab value of the value are displayed on the spectral reflectance display unit 310 and the tristimulus value display unit 311 respectively. In the spectral reflectance display section, the spectral reflectance of the color sample is indicated by a solid line, and the estimated spectral reflectance is indicated by a broken line. In the tristimulus value display unit 311, the value of the color sample is represented by a black circle, and the estimated value is represented by a white circle. Note that the white circles and the black circles displayed on the tristimulus value display unit 311 plot only the ab values of points having different Lab values. That is, the figure is obtained by projecting two points on the ab plane. This is to confirm the difference in chromaticity between the two points, and the brightness (L value) is confirmed on the color sample tristimulus value display unit 306 and the output tristimulus value display unit 307.
[0015]
In step S208, it is determined whether or not the patch output button 312 has been pressed. If the button has been pressed, the process proceeds to step S209 to execute patch output processing. If not, the process proceeds to step S210. However, since the patch output process is a process using the result of the color matching process in steps S205 to S207, the patch output button 312 is valid only after the color matching process has been performed. In step S209, the image output unit 9 outputs a patch using the image output device 10 using the amount of ejection displayed on the ink ejection amount display unit 309.
[0016]
In step S210, it is determined whether or not the file output button 313 has been pressed. If the button has been pressed, the process proceeds to step S211 to execute the file output process, and if not, the process proceeds to step S212. However, since the file output process is a process using the result of the color matching process in steps S205 to S207, the file output button 313 is effective only after the color matching process has been performed. In step S211, the ejection amount displayed on the ink ejection amount display unit 309 is output to a text file.
[0017]
In step S212, it is determined whether or not the database addition button 314 has been pressed. If the button has been pressed, the flow advances to step S213 to execute the database addition processing, and if not, the processing ends. However, since the database addition process is a process using the result of the color matching process in steps S205 to S207, the database addition button 314 is valid only after the color matching process has been performed. In step S213, the color sample name searched by the color sample search unit 4 and the shot amount displayed in the ink shot amount display unit 309 (estimated to reproduce a color having a spectral reflectance closest to the color sample name) Is added to the color sample database in association with each other.
[0018]
<Printer output estimation>
Next, the details of the output estimation processing in step S205 will be described with reference to FIG. FIG. 4 is a flowchart illustrating an output estimation process according to the present embodiment.
[0019]
In step S401, the amount of ink to be used is set to an initial value (for example, all 0%). In step S402, primary color dot gain correction is performed (details will be described later). In step S403, the spectral reflectance estimation initial value is calculated by the following equations (1) to (3) based on the KM theory (Kubelka-Munk theory) using the spectral reflectance of each ink whose primary color dot gain has been corrected. Do.
[0020]
(Equation 1)

[0021]
In step S404, ink overlay correction is performed on the spectral reflectance estimation initial value calculated in step S403 (details will be described later). In step S405, it is determined whether the output has been estimated for all combinations of the ink ejection amounts to be used (for example, 1% intervals from 0% to 100%). If all the outputs have been estimated, the process ends, and if not, the process proceeds to step S406. move on. In step S406, the ink ejection amount is changed by a fixed amount to set a new combination of ink ejection amounts, and the process returns to step S402. If the spectral reflectance determined as described above is stored in association with each combination of the ink ejection amounts, it is not necessary to repeat the estimation process described with reference to FIG. Can be achieved.
[0022]
<Primary color dot gain correction>
Next, the details of the primary color dot gain correction in step S402 will be described with reference to FIGS. In general, it is assumed that the spectral reflectance (dot gain) of the primary color dot changes linearly with respect to the amount of ejection, but in the present embodiment, in order to consider the effect of the dot gain nonlinearity, First, primary color dot gain correction is performed, and highly accurate output estimation is performed.
[0023]
FIG. 5 is a diagram illustrating an example of a primary color correction patch according to the present embodiment. 6A is a diagram illustrating a measurement result of the spectral reflectance with respect to the amount of cyan ink applied, and FIG. 6B is a diagram illustrating a primary color correction LUT acquired from the measurement result of FIG. .
[0024]
First, a primary color correction patch that has been output using a printer for which color reproduction prediction is desired is measured in advance. The primary color correction patch used here is one in which the amount of each ink applied is changed from 0% to 100%, such as at 20% intervals, as shown in FIG. . The spectral reflectance data of such a primary color correction patch is a reflectance of each wavelength with respect to a discrete ejection amount of each ink as shown in FIG. From the measurement data of the reflectance at each wavelength, the data is converted into an LUT indicating the relationship between the ejection amount and the reflectance at each ink and each wavelength as shown in FIG. 6B.
[0025]
Here, since there are only discrete measurement results of the ink ejection amount in increments of 20%, a general interpolation method such as linear interpolation or spline interpolation is used to create the primary color correction LUT. In the primary color dot gain correction (step S402), the LUT is used to perform primary color dot gain correction with respect to the input ink ejection amount, and the primary color spectral reflectance is estimated. Although only four graphs are drawn in FIG. 6B for simplicity, in practice, all the wavelengths sampled in the visible wavelength range (for example, 41 wavelengths from 380 nm to 780 nm in increments of 10 nm). Is created for each table. Using such an LUT, it is possible to acquire the spectral reflectance with the primary color dot gain corrected at the set ink ejection amount.
[0026]
<Calculation of ink overlay correction coefficient>
Next, the details of the ink overlay correction in step S404 will be described with reference to FIG.
[0027]
In step S404, the color of the ink overlay correction patch that has been output using the printer whose color reproduction prediction is to be performed in advance is measured. The ink overlay correction patch used here is such that as shown in FIG. 7, the ejection amount of each ink is changed from 0% to 100% at intervals of 20%, and two or more inks to be used are further overlaid. It was printed.
[0028]
Next, using the data for recording the overlay correction patch data shown in FIG. 7 (the amount of each color to be applied in each patch), the above equations (1) to (3) are used, that is, the same as step S403. The process estimates the spectral reflectance estimation initial value of the overlay correction patch. The calculated spectral reflectance estimation initial value has an error with respect to the actually measured data obtained by actually measuring the color of the correction patch in FIG. Then, in order to correct the error with the actual measurement data, the following equation (4) is used to correct the correction coefficient a _h , λ, bi, using the least square method or the like so as to minimize the error _{. j, λ} , _{ck, l, m, λ} are determined.
[0029]
(Equation 2)

[0030]
In the above equation (4), R _{p, λ} is an inference value after the primary color correction obtained by the KM theory (Kubelka-Munk theory) of the equations (1) to (3), and R _{mod, λ} is And the corrected inferred value after the ink overlay correction. Then, the coefficients _{ah, λ} , bi _{, j, λ} , _{ck, l, m, λ} are determined so that the error between R _{mod, λ} and the actually measured value of the color patch becomes small. Further, i, j of the second term and k, l, m of the third term indicate arbitrary inks. For example, when four colors of C, M, Y, and K are used as n-color inks , I = C, M, Y, K, j = C, M, Y, K,... (Where i ≠ j, k ≠ l ≠ m). Also, (K / S) is as defined in equation (1).
[0031]
The correction coefficient determined as described above is stored in a predetermined storage device, and is read when the ink overlay correction is performed in step S304. That is, in the ink overlay correction in step S304, an estimation error due to ink overlay is applied to the spectral reflectance estimation initial value calculated in step S303 using the above-described ink overlay correction coefficient and applying equation (4). Is corrected.
[0032]
<Error calculation method>
Next, details of the error calculation method in step S206 will be described. As a method of calculating an error between two colors, a CIE color difference equation is generally known. However, since the influence of metamerism is not taken into account in the CIE color difference equation, in the present embodiment, for example, the root mean square (RMS error) of the spectral distribution error for each wavelength as expressed by the following equation (5) is used. Used.
[0033]
[Equation 3]

[0034]
However, other than the above RMS, the type is not limited as long as the error can be calculated in consideration of metamerism. For example, as shown in equation (6), in the above RMS error,
[0035]
(Equation 4)

A weighting function given by the sum of the CIE color matching functions represented by the following equation may be used and weighted for each wavelength.
[0036]
(Equation 5)

[0037]
As described above, according to the first embodiment, in the color conversion processing for reproducing the target color, the spectral distribution characteristics of the color such as the color sample book specified by the user are stored in advance, and the characteristics are stored in the color conversion processing. By reproducing as faithfully as possible, accurate color reproduction can be realized even under different observation environments.
[0038]
<Second embodiment>
Next, a second embodiment will be described. In the second embodiment, an output image is estimated based on image data, and a desired color can be replaced with a desired sample color.
[0039]
FIG. 8 is a block diagram illustrating a configuration of a color reproduction device according to the second embodiment. In FIG. 8, reference numeral 801 denotes a color reproduction device according to an embodiment of the present invention. Note that the color reproduction device 801 can be realized by a general-purpose computer executing a control program that realizes processing described later. Reference numeral 802 denotes a color designation information input unit, which inputs color designation information designated by the user using a mouse, a keyboard, or the like. A color sample database 803 stores a color sample in the form of a pair of a color sample name and a spectral reflectance. Reference numeral 804 denotes a color sample search unit that searches and acquires the spectral reflectance of a color sample from the color sample database 803 based on the color specification information input by the color specification information input unit 802. An image database 805 stores image data. A result display unit 806 displays an output estimation result and the like on the display device 809. Reference numeral 807 denotes a printer model for estimating a color (spectral reflectance) of an output color by the printer. An image output unit 808 causes an image output device 810 to output an image.
[0040]
A display device 809 includes a CRT, an LCD, and the like, provides various user interfaces, and displays a processing result under the control of the result display unit 806. Reference numeral 810 denotes an image output device, which is a color printer of an ink jet system, a laser beam system, or the like. Reference numeral 811 denotes a color designation information designating device which includes a keyboard, a mouse, and the like, and is used to input color designation information.
[0041]
<Overall processing>
Hereinafter, the operation of the color reproduction device according to the second embodiment will be described in detail. FIG. 9 is a flowchart illustrating color reproduction processing according to the second embodiment. FIG. 10 is a diagram illustrating an example of a user interface used for color reproduction processing according to the second embodiment.
[0042]
First, in step S901, the result display unit 806 reads an image specified by the user with the image specifying unit 1009 from the image database 805, and displays the image on the original image display unit 1006. Next, in step S902, the output spectral reflectance is estimated by the printer model 807 in the same procedure as in the first embodiment. That is, it is determined by comparing the Lab obtained from the RGB values of the pixel data with the Lab obtained from the spectral reflectance estimated for each ink ejection amount. (The RGB values of each pixel can be converted into Lab values using an ICC profile or the like. The amount of each ink to be applied is determined so as to be closest to the Lab value). At this time, a tristimulus value Lab is calculated from the estimated spectral reflectance of each pixel, converted into a device RGB value of the display device 809 using an ICC profile or the like, and the device RGB value is output to the output estimation image display unit 1007. To be displayed.
[0043]
In step S903, the user operates the color designation pointer 1008 with the mouse or the like to designate a pixel whose color is to be designated on the original image display unit 1006. At this time, the RGB values of the designated pixel are displayed on the designated color display unit 1003. In step S904, a desired color is selected from the color sample in the color sample name input unit 1001 in order to specify what color the specified color specified by the user is actually output. That is, from among the spectral reflectances of the color samples stored in the color sample database 803, the spectral reflectance of the color sample specified by the color sample name selection unit 1001 is read by the color sample search unit 804. The read spectral reflectance of the color sample is displayed on the spectral reflectance display unit 1010, and is converted into a device RGB value of the display device 809 using an ICC profile or the like. The device RGB values are displayed on the color sample confirmation unit 1004.
[0044]
In step S905, the output is estimated by the printer model 807 in the same procedure as that described in the first embodiment, and the ink ejection amount that is the color (spectral reflectance) closest to the color sample is obtained. In this way, the spectral reflectance estimated to be closest to the color sample is displayed on the spectral reflectance display unit 1010. The estimated spectral reflectance is converted into a device RGB value of the display device 810 using an ICC profile or the like, and the obtained device RGB value is displayed on the output estimation confirmation unit 1005. Then, the updated output estimated image is displayed on the output estimated image display unit 1007.
[0045]
When the user presses the image output button 1011, the process advances from step S 906 to step S 907 to output an image. That is, when the user wants to redo the color designation for a desired pixel while viewing the output estimation result displayed on the output estimation image display unit 1007, the user repeatedly selects the designated color without pressing the image output button 1011. Allows color correction. If the output estimation result is satisfactory, an image output can be obtained from the image output device 810 by pressing the image output button 1011. That is, in step S907, the image output unit 808 causes the image output device 810 to output an image. In the above, all the pixels having the same color as the designated pixel are replaced with the sample colors. That is, all pixels having the same Lab as the designated pixel look the same color under a specific viewing environment. Since the user performs color correction by looking at the colors on the display, the colors to be output must all be the same. Therefore, when the spectral reflectance of a certain pixel is updated, all the pixels of the same Lab are updated.
[0046]
As described above, according to each of the above embodiments, in the color conversion process for reproducing the target color, the spectral distribution characteristics of the color specified by the user are faithfully reproduced, and accurate even under different observation environments. A color conversion process for realizing color reproduction can be performed.
[0047]
<Output estimation>
In each of the above embodiments, a method applicable to output estimation in the printer models 5 and 807 is not limited to the above-described estimation method. For example, a conventional output estimation method using a neural network may be used, or a Neugebauer equation using a Yule-Nielsen modified equation may be used. That is, the method is not limited as long as the output is predicted using the spectral reflectance of the ink and the ejection amount.
[0048]
<Color sample database>
FIGS. 11, 12 and 13 are diagrams showing examples of the data structure of the color sample databases 3 and 803. FIG. FIG. 11 shows an initial state of a database in which a color sample name and a spectral reflectance corresponding to the color sample name are stored. Further, when the color reproduction prediction result is additionally written in the database in each of the above embodiments, as shown in FIG. 12, the ink ejection amount obtained from the color reproduction prediction result is added to the color sample. Further, the method of additionally writing the ink ejection amount is not limited to this. For example, as shown in FIG. 13, in addition to the ejection amount, the measurement of the spectral reflectance of the actually output patch is performed as a new user output. It may be added together with the value. Further, the number of color samples is not fixed to a fixed number, and newly measured color sample data may be added when the user desires. The user output and color sample additionally registered as described above are to be searched by the color sample search units 4 and 804 described above.
[0049]
<User interface>
Further, in each of the above embodiments, the example of the user interface shown in FIGS. 3 and 10 has been described, but it goes without saying that the form of the user interface is not limited to the illustrated one. For example, in the light source information selection units 302 and 1002, the user selects a desired light source, but a format in which a file in which light source data is described in advance may be read. That is, any user interface configuration that allows the user to make desired settings may be used.
[0050]
<Storage medium>
The present invention can be applied to a system including a plurality of devices (for example, a host computer, an interface device, a reader, a printer, etc.), but may be a device including one device (for example, a copying machine, a facsimile machine, etc.). May be applied.
[0051]
Further, an object of the present invention is to provide a storage medium storing a program code of software for realizing the functions of the above-described embodiments to a system or an apparatus, and a computer (or CPU or MPU) of the system or apparatus to store the storage medium. Needless to say, this can also be achieved by reading out and executing the program code stored in the.
[0052]
In this case, the program code itself read from the storage medium realizes the function of the above-described embodiment, and the storage medium storing the program code constitutes the present invention.
[0053]
As a storage medium for supplying the program code, for example, a flexible disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a CD-R, a magnetic tape, a nonvolatile memory card, a ROM, and the like can be used.
[0054]
When the computer executes the readout program code, not only the functions of the above-described embodiments are realized, but also an OS (Operating System) running on the computer based on the instruction of the program code. It goes without saying that a case where a part of the actual processing is performed and the function of the above-described embodiment is realized by the processing is also included.
[0055]
Further, after the program code read from the storage medium is written into a memory provided on a function expansion board inserted into the computer or a function expansion unit connected to the computer, the function expansion is performed based on the instruction of the program code. It goes without saying that a CPU or the like provided in the board or the function expansion unit performs part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.
[0056]
【The invention's effect】
As described above, according to the present invention, in the color conversion processing for reproducing the target color, it is possible to faithfully reproduce the spectral distribution characteristics of the target color, and to achieve accurate color reproduction even in different observation environments. Is realized.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of a color reproduction device according to a first embodiment.
FIG. 2A is a flowchart illustrating a color reproduction process performed by the color reproduction device of the first embodiment.
FIG. 2B is a flowchart illustrating a color reproduction process performed by the color reproduction device of the first embodiment.
FIG. 3 is a diagram illustrating an example of a user interface used in a color reproduction process.
FIG. 4 is a flowchart illustrating an output estimation process according to the embodiment.
FIG. 5 is a diagram illustrating an example of a primary color correction patch according to the embodiment;
FIG. 6A is a diagram showing a measurement result of a spectral reflectance with respect to an ejection amount of cyan ink,
(B) is a diagram showing a primary color correction LUT obtained from the measurement result of (a).
FIG. 7 is a diagram illustrating an example of an ink overlay correction patch according to the present embodiment.
FIG. 8 is a block diagram illustrating a configuration of a color reproduction device according to a second embodiment.
FIG. 9 is a flowchart illustrating a color reproduction process according to a second embodiment.
FIG. 10 is a diagram illustrating an example of a user interface used for color reproduction processing according to the second embodiment.
FIG. 11 is a diagram illustrating a data configuration example of a color sample database according to the present embodiment.
FIG. 12 is a diagram illustrating a data configuration example of a color sample database according to the present embodiment.
FIG. 13 is a diagram illustrating a data configuration example of a color sample database according to the present embodiment.

Claims (17)

Storage means for storing spectral reflectances of a plurality of colors;
Acquisition means for acquiring the spectral reflectance of the designated color from the storage means;
Estimating means for estimating the spectral reflectance of each output color obtained by combining and recording color materials used in image formation in various amounts,
Determining means for determining an output color corresponding to the specified color based on the spectral reflectance of the specified color obtained by the obtaining means and the spectral reflectance estimated by the estimating means;
An image processing apparatus comprising: a presentation unit that presents the output color determined by the determination unit to a user. The said determination means determines the combination of the color material which minimizes the error between the reproduced color estimated by the estimation means and the set target color as the combination of the color materials to be used. Item 2. The information processing device according to item 1. The estimating means includes:
Primary color correction means for correcting the spectral reflectance of each color material included in the set combination of color materials based on the set shot amount;
Color mixture prediction means for predicting the spectral reflectance of mixed colors using the spectral reflectance corrected by the primary color correction means;
Using a correction coefficient determined from an error between the spectral reflectance actually measured for a predetermined sample and the spectral reflectance predicted by the color mixture prediction unit, the spectral reflectance of the mixed color predicted by the color mixture prediction unit is corrected. The information processing apparatus according to claim 1, further comprising a multi-order color correction unit that performs the correction. The storage unit stores a color sample name and a spectral reflectance in association with each other,
2. The image processing apparatus according to claim 1, wherein the acquisition unit acquires a spectral reflectance corresponding to a designated color sample name as a spectral reflectance of the designated color. 2. The image processing apparatus according to claim 1, wherein the presentation unit displays a color patch based on the estimated spectral reflectance of the output color determined by the determination unit. 2. The image according to claim 1, wherein the presenting unit displays an error between the estimated spectral reflectance of the output color determined by the determining unit and the spectral reflectance acquired by the acquiring unit. Processing equipment. 2. The image processing apparatus according to claim 1, wherein the presenting unit graphically displays the estimated spectral reflectance of the output color determined by the determining unit and the spectral reflectance acquired by the acquiring unit. . The presenting means obtains tristimulus values from each of the estimated spectral reflectance of the output color determined by the determining means and the spectral reflectance obtained by the obtaining means, and stores each tristimulus value in a tristimulus value space The image processing apparatus according to claim 1, wherein the image is displayed as a coordinate point. 2. The image processing apparatus according to claim 1, further comprising a registration unit that registers information on the output color determined by the determination unit so as to correspond to the designated color. 10. The registration unit according to claim 9, wherein the registration unit registers a combination of the used amounts of the color materials for obtaining the output color determined by the determination unit in the storage unit in association with the designated color. Image processing device. The image processing apparatus according to claim 9, wherein the registering unit registers the spectral reflectance of the output color determined by the determining unit in association with the designated color. Generating means for determining an output color for reproducing the color of each pixel based on the specified image data and generating an estimated image;
2. The image processing apparatus according to claim 1, further comprising an updating unit that replaces an output color of a pixel specified from an image represented by the image data with the output color determined by the determining unit. apparatus. A color reproduction method in an image processing apparatus having storage means for storing spectral reflectances of a plurality of colors,
An acquisition step of acquiring the spectral reflectance of a specified color from the storage unit,
An estimation step of estimating the spectral reflectance of each output color obtained by recording in combination with various amounts of color materials used during image formation,
Based on the spectral reflectance of the specified color obtained in the obtaining step and the spectral reflectance estimated in the estimating step, a determining step of determining an output color corresponding to the specified color,
A presentation step of presenting the output color determined in the determination step to a user. 14. The color reproduction method according to claim 13, further comprising a registration step of registering information on the output color determined in the determination step so as to correspond to the designated color in the storage unit. A generation step of determining an output color for reproducing the color of each pixel based on the specified image data and generating an estimated image,
14. The color reproduction according to claim 13, further comprising: an update step of replacing an output color of a pixel specified from an image represented by the image data with the output color determined in the determination step. Method. A control program for causing a computer to execute a color reproduction process using storage means storing spectral reflectances of a plurality of colors, wherein the acquisition means obtains the spectral reflectance of a designated color from the storage means.
Estimating means for estimating the spectral reflectance of each output color obtained by combining and recording color materials used in image formation in various amounts,
Determining means for determining an output color corresponding to the specified color based on the spectral reflectance of the specified color obtained by the obtaining means and the spectral reflectance estimated by the estimating means;
A control program for causing a computer to function as presentation means for presenting an output color determined by the determination means to a user. A storage medium storing the control program according to claim 16.

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