JP4033019B2 - Color conversion apparatus, image forming apparatus, and color conversion program - Google Patents

Description

【００４５】
同様に、特定点Ｐ６は格子点Ｐ４と格子点Ｐ１１とを結ぶ線の中点に位置するため、Ｐ特定点Ｐ６におけるＣＭＹＫ色空間パラメータ（Ｃ６，Ｍ６，Ｙ６，Ｋ６）はそれぞれ下記の式（５）,（６）,（７）,（８）により算出される。
【００４６】
【数２】

【００４７】
この後に処理をＳ２５に移す。ここでは、変換点ＸにおけるＣＭＹＫ色空間パラメータ（Ｃｘ，Ｍｘ，Ｙｘ，Ｋｘ）を求めるための、点Ｐ１,Ｐ２,Ｐ３,Ｐ４,Ｐ５,Ｐ６における重み係数を算出する。図５は、補間多面体Ｈ１において重み係数を算出する方法を説明する図である。
【００４８】
まず、変換点Ｘから補間多面体Ｈ１の各辺におろした垂線が各辺に交わる位置を求める（図５における点Ａ,Ｂ,Ｃ,Ｄ,Ｅ,Ｆ,Ｇ,Ｈ,Ｉ，Ｊ,Ｋ,Ｌ）。
図５における点Ａは、点Ｐ２と点５とを結ぶ線分Ｐ２−Ｐ５上の点である。同様に、点Ｂは線分Ｐ１−Ｐ５, 点Ｃは線分Ｐ４−Ｐ５, 点Ｄは線分Ｐ３−Ｐ５, 点Ｅは線分Ｐ４−Ｐ６, 点Ｆは線分Ｐ３−Ｐ６, 点Ｇは線分Ｐ２−Ｐ６, 点Ｈは線分Ｐ１−Ｐ６, 点Ｉは線分Ｐ２−Ｐ４, 点Ｊは線分Ｐ１−Ｐ３, 点Ｋは線分Ｐ１−Ｐ２, 点Ｌは線分Ｐ３−Ｐ４上の点である。
【００４９】
点Ｐ１における重み係数Ｗ１は、点Ｐ４,Ｃ,Ｌ,Ｉ,Ｅ,Ｘの６点により形成される多面体の体積を基に算出される。
同様に、点Ｐ２における重み係数Ｗ２は点Ｐ３,Ｄ,Ｌ,Ｊ,Ｆ,Ｘの６点、点Ｐ３における重み係数Ｗ３は点Ｐ２,Ａ,Ｋ,Ｇ,Ｉ,Ｘの６点、点Ｐ４における重み係数Ｗ４は点Ｐ１,Ｂ,Ｊ,Ｈ,Ｋ,Ｘの６点、点Ｐ５における重み係数Ｗ５は点Ｐ６,Ｆ,Ｅ,Ｇ,Ｈ,Ｘの６点、点Ｐ６における重み係数Ｗ６は点Ｐ５,Ｂ,Ｄ,Ｃ,Ａ,Ｘの６点により形成される多面体の体積を基に算出される。例えば、点Ｐ６における重み係数Ｗ６を算出するための多面体は、図５に示す多面体Ｓ１である。
【００５０】
そして、点Ａ,Ｂ,Ｃ,Ｄ,Ｅ,Ｆの６点により形成される多面体の体積をＶ（Ａ,Ｂ,Ｃ,Ｄ,Ｅ,Ｆ）と表記すると、重み係数Ｗ１, Ｗ２,Ｗ３,Ｗ４,Ｗ５,Ｗ６はそれぞれ下記の式（９）,（１０）,（１１）,（１２）,（１３）,（１４）により算出される。
【００５１】
【数３】

【００５２】
この後に処理をＳ２６に移す。ここでは、変換点ＸにおけるＣＭＹＫ色空間パラメータ（Ｃｘ，Ｍｘ，Ｙｘ，Ｋｘ）を、重み係数Ｗ１, Ｗ２,Ｗ３,Ｗ４,Ｗ５,Ｗ６と点Ｐ１,Ｐ２,Ｐ３,Ｐ４,Ｐ５,Ｐ６におけるＣＭＹＫ色空間パラメータ（Ｃｎ，Ｍｎ，Ｙｎ，Ｋｎ）を用いて下記の式（１５）,（１６）,（１７）,（１８）により算出する。
【００５３】
【数４】

【００５４】
そして、Ｓ２６の処理を終了すると、当該補間処理を終了する。
当該補間処理を終了すると、図２の色変換処理に戻り、Ｓ０６にて、Ｘをインクリメントする。その後、Ｓ０７に処理を移し、Ｘの値がＸ＿ＳＩＺＥより大きいか否か判断する。ここで、Ｘの値がＸ＿ＳＩＺＥ以下であると判断すると（Ｓ０７：ＮＯ）、Ｓ０４に処理を移し上記の処理を繰り返す。一方、Ｘの値がＸ＿ＳＩＺＥより大きいと判断すると（Ｓ０７：ＹＥＳ）、Ｓ０８に処理を移し、Ｘを０にセットするとともにＹをインクリメントする。その後、Ｓ０９に処理を移し、Ｙの値がＹ＿ＳＩＺＥより大きいか否か判断する。ここで、Ｙの値がＹ＿ＳＩＺＥ以下であると判断すると（Ｓ０９：ＮＯ）、Ｓ０４に処理を移し上記の処理を繰り返す。一方、Ｙの値がＹ＿ＳＩＺＥより大きいと判断すると（Ｓ０９：ＹＥＳ）、Ｓ１０に処理を移し、色変換処理されたデータをプリンタ２００に出力する。そして、当該色変換処理を終了する。
【００５５】
以上の処理により、Ｘ＿ＳＩＺＥ×Ｙ＿ＳＩＺＥ個の全ての画素データＰ（Ｘ，Ｙ）＝（Ｒ，Ｇ，Ｂ）をＣＭＹＫ色空間パラメータに変換する。
［本発明との対応関係］
以上説明した実施形態において、ＰＣ１００は本発明における色変換装置である。
【００５６】
また、色変換プログラム１０２ａは本発明における色変換プログラムである。また、図３におけるＳ０４の処理は本発明における位置検出手段、図４におけるＳ２１の処理およびＳ２２の処理は本発明における補間点抽出手段、図４におけるＳ２３の処理およびＳ２４の処理は本発明における補間点色変換値算出手段、図４におけるＳ２５の処理は本発明における重み係数算出手段、図４におけるＳ２６の処理は本発明における補間演算手段として機能している。
【００５７】
［効果］
このように構成されたＰＣ１００によれば、格子点Ｐ１,Ｐ２,Ｐ３,Ｐ４で形成される基準単位格子面Ｍ１を補間多面体Ｈ１の内部に含むことができる。
このため、基準単位格子面Ｍ１上の位置にある画素データＰ（Ｘ，Ｙ）＝（Ｒ，Ｇ，Ｂ）をＣＭＹＫ色空間パラメータに変換する際は、基準単位格子面Ｍ１を構成する格子点Ｐ１,Ｐ２,Ｐ３,Ｐ４だけでなく特定点Ｐ５,Ｐ６における色変換値も用いて補間を行うことができる。即ち、基準単位格子面Ｍ１を構成する格子点の１点のみＫ成分の値がｋで、その他の３点のＫ成分の値が０になっているような場合において、特定点Ｐ５,Ｐ６におけるＫ成分の値も用いて補間を行うことができるため、幾何学模様の発生を低減するＣＭＹＫ色空間パラメータを生成することができる。
【００５８】
また、補間多面体Ｈ１の辺にグレー軸を含むことができる。このため、グレー軸上の位置にある画素データＰ（Ｘ，Ｙ）＝（Ｒ，Ｇ，Ｂ）をＣＭＹＫ色空間パラメータに変換する際には、補間多面体Ｈ１を形成する点の中で有彩色を表す画像データを用いずにグレー軸上にある点のみを用いて補間を行うことができるので、グレーを表す画素データＰ（Ｘ，Ｙ）は、グレーを表すＣＭＹＫ色空間パラメータに変換することができる。
【００５９】
また、特定点Ｐ５,Ｐ６はそれぞれ単位補間立方体Ｔ１，Ｔ２の中心点であるため、格子点Ｐ１,Ｐ２,Ｐ３,Ｐ４の夫々と特定点Ｐ５,Ｐ６との距離が等しい。このため、図４におけるＳ２５の処理において、６つの八面体の体積を求める計算を簡便にすることができるので、図４におけるＳ２５の処理を速く行うことができる。
【００６０】
（実施の形態２）
以下、本発明の実施の形態２について図面を参照しながら説明する。
まず、プリンタ２００の構成を図７に基づいて説明する。
プリンタ２００は、図７に示すように、所定の処理プログラムに基づいて処理を実行するＣＰＵ２０１，種々の制御プログラムが格納されたＲＯＭ２０３，外部装置から入力したデータ等を格納する各種メモリが設けられたＲＡＭ２０４，入出力Ｉ／Ｆ２０５，利用者により操作可能な複数の操作キー２０６ａおよび各種情報を表示する表示パネル２０６ｂからなるユーザＩ／Ｆ２０６と，プリンタエンジン用インターフェース（以降、プリンタエンジン用Ｉ／Ｆとする）２０７とプリンタエンジン２０８を備えている。
【００６１】
ＲＯＭ２０３には、ＣＰＵ２０１が色変換処理を実行するための色変換プログラム２０３ａと、色変換処理で用いる色変換特性が記載されている色変換テーブル２０３ｂの記憶領域が確保されている。
上記入出力Ｉ／Ｆ２０５は、上記各要素を相互に接続しているとともにＰＣ等２１０の外部機器と接続しており、画像データがＰＣ等２１０からプリンタ２００に入力される。
【００６２】
実施の形態１では色変換処理（図２参照）および補間処理（図３参照）をＣＰＵ１０１が実行するが、本発明の実施の形態２ではプリンタ２００内のＣＰＵ２０１が実行する。色変換処理および補間処理の方法は実施の形態１と同様であるので、色変換処理および補間処理の説明は省略する。
【００６３】
［効果］
このように構成されたプリンタ２００によれば、実施の形態１と同様にして生成したＣＭＹＫ色空間パラメータを用いて画像を形成することができる。
【００６４】
このため、画像を形成する際に幾何学模様の発生を低減することができる。
［変形例］
以上、本発明の実施の形態について説明したが、本発明の実施の形態は上記実施の形態に何ら限定されることなく、本発明の技術的範囲に属する限り種々の形態をとり得ることはいうまでもない。
【００６５】
例えば、上記実施形態においては、プリンタ２００に画像形成装置としての構成を適用したものを例示した。しかし、画像形成の機能を有していれば、コピー機，ファクシミリ等についても同様に適用可能である。
例えば、上記実施形態においては、ＲＧＢ色空間からＣＭＹＫ色空間に変換するものを例示した。しかし、ＲＧＢ色空間からＲＧＢ色空間に変換するについても同様に適用可能である。
【００６６】
また、上記実施形態においては、特定点Ｐ５,Ｐ６が夫々、単位補間立方体Ｔ１,Ｔ２の中心点であるものを例示した。しかし、特定点Ｐ５はＰ１とＰ１０とを結ぶ線分であるグレー軸上であれば線分Ｐ１Ｐ１０の中立になくてもよい。同様に特定点Ｐ６はＰ１１とＰ４とを結ぶ線分であるグレー軸上であれば線分Ｐ１１Ｐ４の中立になくてもよい。さらに、特定点Ｐ５,Ｐ６は夫々、単位補間立方体Ｔ１,Ｔ２内の点であればどこでもよく、必ずしもグレー軸上に設定する必要はない。また単位補間多面体の形状は、立方体に限定されず長方体とすることもできる。
【図面の簡単な説明】
【図１】実施の形態１における色変換装置の構成を表すブロック図。
【図２】実施の形態における色変換処理手順を示すフローチャート。
【図３】実施の形態における補間処理手順を示すフローチャート。
【図４】実施の形態における補間演算の概念を説明する図。
【図５】実施の形態における補間演算の重み係数算出の概念を説明する図。
【図６】実施の形態における色変換テーブルの構成説明図である。
【図７】実施の形態２におけるプリンタの構成を表すブロック図。
【図８】幾何学模様を説明する図。
【符号の説明】
１０…スキャナ１０、２０…デジタルカメラ、３０…携帯電話、１００…ＰＣ、１０１…ＣＰＵ、１０２…ＨＤＤ、１０３…ＲＯＭ、１０４…ＲＡＭ、１０５…入出力インターフェース、１０６…ユーザインターフェース、１０６ａ…操作キー、１０６ｂ…表示パネル、１０７…通信用インターフェース、２００…プリンタ、２０１…ＣＰＵ、２０３…ＲＯＭ、２０４…ＲＡＭ、２０５…入出力インターフェース、２０６…ユーザインターフェース、２０６ａ…操作キー、２０６ｂ…表示パネル、２０７…プリンタエンジン用インターフェース、２０８…プリンタエンジン、２１０…ＰＣ等。[0001]
BACKGROUND OF THE INVENTION
The present invention is used in a color printer or the like, and a first color signal in a first color space (for example, RGB) defined by a combination of three different color signals is converted into a second color space (same as or different from the first color space). For example, the present invention relates to a color conversion apparatus that converts a second color signal (for example, CMYK), an image forming apparatus including the color conversion apparatus, and a color conversion program.
[0002]
[Prior art]
For example, when an image displayed on a color CRT is printed by a color printer, the color signals for the color CRT are RGB signals (red, green, blue), and the color signals for the color printer are CMYK signals (cyan, magenta). (Yellow / Black), it is necessary to convert RGB signals into CMYK signals.
[0003]
As such a color signal conversion method, a method using a color conversion table is currently widely used.
This is because, for example, CMYK values that reproduce RGB values on grid points arranged in a grid pattern in the RGB color space are stored in the color conversion table, and for CMYK values that reproduce RGB values that are not on grid points, This is a method of obtaining by using interpolation calculation based on CMYK values on points.
[0004]
For interpolation using a color conversion table, a method of selecting and interpolating 4 to 8 grid points around a point to be color converted (hereinafter also referred to as a conversion point) is generally used. There are known a method of interpolating using a method (for example, see Patent Document 1) and a method of performing an interpolation using a pyramid polyhedron (for example, see Patent Document 2).
[0005]
[Patent Document 1]
Japanese Patent Laid-Open No. 2000-165691 (FIG. 2)
[Patent Document 2]
Japanese Patent Laid-Open No. 56-14237 (FIG. 2)
[0006]
[Problems to be solved by the invention]
However, in such an interpolation method, for example, from the RGB color space (R: red, G: green, B: blue) to the CMYK color space (C: cyan, M: magenta, Y: yellow, K: black). When converting, there is a problem that a geometric pattern having a right or circular outline is generated. The reason is as follows.
In the triangular pyramid interpolation, when the conversion point is inside the triangular pyramid, the interpolation is performed using four lattice points forming the triangular pyramid. On the other hand, when the conversion point is on the surface of the triangular pyramid, interpolation is performed using three lattice points on the surface.
[0007]
When the K (black) component is interpolated when there is a conversion point on the surface of the triangular pyramid, the value of the K component is k for only one lattice on the lattice surface as shown in FIG. Consider a case where the value of the K component at three points is zero.
At this time, if the point at which the value of the K component is 0.5 × k is obtained by interpolation, the position is indicated by a broken line, and if the point at which the value of the K component is 0.2 × k is obtained, one point is obtained. When a point where the value of the K component is, for example, 0.8 × k is obtained, the position indicated by the two-dot chain line is obtained.
[0008]
In other words, the K component is reproduced as a gradation having a right-angled contour in the unit cell plane, causing a geometric pattern to be generated.
Further, in the pyramid polyhedron, when the conversion point is inside the pyramid polyhedron, interpolation is performed using five lattice points forming the pyramid polyhedron. On the other hand, when the transformation point is on the bottom surface of the pyramidal polyhedron, interpolation is performed using four lattice points on the bottom surface.
[0009]
When the transformation point is on the bottom surface of the pyramidal polyhedron, when interpolation of the K (black) component is performed, the value of the K component is k for only one lattice on the lattice plane as shown in FIG. Consider the case where the values of the other three K components are zero.
At this time, if a point where the value of the K component is 0.5 × k, for example, is obtained by interpolation, the position shown by the broken line is obtained, and if a point where the value of the K component is 0.2 × k is obtained, for example, Further, when the point at which the value of the K component becomes, for example, 0.8 × k is obtained, the position indicated by the two-dot chain line is obtained.
[0010]
That is, the K component is reproduced as a gradation having a circular outline in the unit lattice plane, and causes a geometric pattern.
In particular, in the CMYK color space, when gray is reproduced, a method is generally used in which light gray is reproduced by a mixed color of CMY, and when it becomes dark gray, it is reproduced using K for the first time. Therefore, as shown in FIG. 8, there is a tendency that only one grid point has a K component and the other three grid points have a K component of 0, and a geometric pattern is generated in the CMYK color space. It is an easy cause.
[0011]
SUMMARY An advantage of some aspects of the invention is that it provides a color conversion apparatus, an image forming apparatus, and a color conversion program that reduce the occurrence of a geometric pattern.
[0012]
[Means for Solving the Problems and Effects of the Invention]
In order to solve the above problem, the color conversion device according to claim 1 is:
The first color signal in the first color space defined by the combination of three different color signals is the same as the first color space using a color conversion table using each color component value of the first color space as a parameter, or A color conversion device for converting to a second color signal of a different second color space,
Position detecting means for detecting a position of the first color signal in a color space having each color component of the first color space as a coordinate axis based on each color component value representing the first color signal;
Among the discrete lattice points in the color space specified by the color component values of the first color space corresponding respectively to the color conversion values to the second color signal described in the color conversion table, Selecting four lattice points constituting the reference unit lattice plane closest to the position of the first color signal detected by the position detection means, and facing the reference unit lattice plane and the reference unit lattice plane; A specific point having a predetermined position from the reference unit lattice plane is selected within each of two unit interpolation spaces formed by two adjacent unit lattice planes, and an interpolation polyhedron is selected from these points. Interpolation point extraction means to be set;
Interpolation point color conversion for extracting the color conversion values at the positions of four lattice points constituting the reference unit lattice plane from the color conversion table and calculating the color conversion values at the specific points based on the color conversion table A value calculating means;
Weight coefficient calculation means for calculating weight coefficients of the four grid points and the specific point based on the positions of the four grid points and the specific point with respect to the position of the first color signal in the interpolation polyhedron;
Interpolation calculation means for obtaining a second color signal of the second color space by interpolation calculation using a color conversion value at the point forming the interpolation polyhedron and the weighting coefficient is provided.
[0013]
According to the color conversion apparatus configured as described above, the reference unit lattice plane formed by the four lattice points can be included in the interpolation polyhedron formed by the four lattice points and the specific point.
For this reason, when converting the first color signal at the position on the reference unit grid surface into the second color signal, not only the four grid points constituting the reference unit grid surface but also the color conversion values at specific points are used. Can be interpolated.
[0014]
That is, even when only one of the lattice points constituting the reference unit lattice surface has a K component value of k and the other three points have K component values of 0, the reference unit lattice surface is formed. Since interpolation can be performed using the value of the K component at the specific point in addition to the value of the K component at the four grid points, a second color signal that reduces the occurrence of a geometric pattern can be generated.
[0015]
Further, in the color conversion device according to claim 1, as described in claim 2,
The unit interpolation space is a cube;
The first color space is a color space whose diagonal can be defined as a gray axis,
The interpolation point extracting means may select a point on a diagonal line in the unit interpolation space whose direction is defined by a vector of a gray axis in the first color space.
[0016]
According to the color conversion device configured as described above, the side of the interpolation polyhedron can include the gray axis.
For this reason, when the first color signal at the position on the gray axis is converted to the second color signal, interpolation is performed using only the points on the gray axis among the points forming the interpolation polyhedron. Therefore, it is possible to prevent chromatic color components from being mixed in the conversion from the first color signal to the first color signal on the gray axis.
[0017]
Further, in the color conversion device according to claim 2, as described in claim 3,
The selected interpolation point may be a center point of the unit interpolation space, that is, a midpoint of the diagonal line.
[0018]
According to the color conversion device configured as described above, the distance between each of the four lattice points constituting the reference unit lattice plane and the specific point becomes equal.
For this reason, when the weighting coefficient calculating means calculates the weighting coefficient, it is possible to simplify the calculation of the positions of the four grid points and the specific points with respect to the position of the first color signal, so that the color conversion processing is performed quickly. Can do.
[0019]
In addition, the color conversion device according to claim 4 is:
The first color signal in the first color space defined by the combination of three different color signals is the same as the first color space using a color conversion table using each color component value of the first color space as a parameter, or A color conversion device for converting to a second color signal of a different second color space,
Position detecting means for detecting a position of the first color signal in a color space having each color component of the first color space as a coordinate axis based on each color component value representing the first color signal;
Among the discrete lattice points in the color space specified by the color component values of the first color space corresponding respectively to the color conversion values to the second color signal described in the color conversion table, Selecting four lattice points constituting the reference unit lattice plane closest to the position of the first color signal detected by the position detection means, and facing the reference unit lattice plane and the reference unit lattice plane; An interpolation point extracting means for selecting a center point of each of the two unit interpolation spaces constituted by each of two adjacent unit grid surfaces adjacent to each other, and setting an interpolation octahedron from these points;
Interpolation point color conversion for extracting the color conversion values at the positions of the four lattice points constituting the reference unit lattice plane from the color conversion table and calculating the color conversion values at the center point based on the color conversion table A value calculating means;
Weight coefficient calculation means for calculating weight coefficients of the four grid points and the center point based on the positions of the four grid points and the center point with respect to the position of the first color signal in the interpolation octahedron;
Interpolation calculation means for obtaining a second color signal of the second color space by interpolation calculation using a color conversion value at the point forming the interpolation octahedron and the weighting factor is provided.
[0020]
According to the color conversion device configured as described above, the reference unit lattice plane formed by the four lattice points can be included in the interpolation polyhedron formed by the four lattice points and the center point.
For this reason, when converting the first color signal at the position on the reference unit grid surface to the second color signal, not only the four grid points constituting the reference unit grid surface but also the color conversion values at the center point are used. Can be interpolated.
[0021]
That is, even when only one of the lattice points constituting the reference unit lattice surface has a K component value of k and the other three points have K component values of 0, the reference unit lattice surface is formed. Since interpolation can be performed using the value of the K component at the center point in addition to the value of the K component at the four grid points, a second color signal that reduces the occurrence of a geometric pattern can be generated.
[0022]
Further, the distance between each of the four lattice points constituting the reference unit lattice plane and the center point becomes equal. For this reason, when the weighting coefficient calculating means calculates the weighting coefficient, it is possible to simplify the calculation of the positions of the four grid points and the center point with respect to the position of the first color signal. Can do.
[0023]
An image forming apparatus according to claim 5 is provided.
A color conversion device according to any one of claims 1 to 4 is provided.
According to the image forming apparatus configured as described above, an image can be formed using the second color signal generated by the color conversion apparatus according to any one of claims 1 to 4.
[0024]
For this reason, generation | occurrence | production of a geometric pattern can be reduced when forming an image.
Further, the color conversion program according to claim 6 is:
A computer is caused to function as each means of the color conversion device according to any one of claims 1 to 4.
[0025]
A computer system controlled by such a program can constitute a part of the color conversion device according to claims 1 to 4, and can obtain the same operations and effects as the color conversion device.
The color conversion program described above is provided to the color conversion device itself, the image forming apparatus, and users who use these devices via, for example, a recording medium such as an FD or CD-ROM, or a communication network such as the Internet. Is.
[0026]
Examples of the computer system that executes the above-described color conversion device include, for example, a computer system built in the color conversion device, a computer system built in the image forming device, or a color conversion device and a wireless or wired connection to the image forming device. A computer system or the like connected to be able to perform data communication via a communication path can be used.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
(Embodiment 1)
Hereinafter, a personal computer in which the configuration of the color conversion apparatus of the present invention is applied will be described as a first embodiment of the present invention.
[0028]
First, the configuration of the personal computer 100 will be described with reference to FIG.
As shown in FIG. 1, a personal computer (hereinafter referred to as a PC) 100 includes a CPU 101 that executes processing based on a predetermined processing program, a hard disk (hereinafter referred to as HDD) 102 as a storage device, and various control programs. ROM 103 storing data, RAM 104 provided with various memories for storing data input from an external device, input / output interface (hereinafter referred to as input / output I / F) 105, a plurality of operation keys operable by a user A user interface (hereinafter referred to as a user I / F) 106 and a communication interface (hereinafter referred to as a communication I / F) 107 including a display panel 106b that displays 106a and various types of information are provided.
[0029]
The HDD 102 has a storage area for a color conversion program 102a for the CPU 101 to execute color conversion processing and a color conversion table 102b in which color conversion characteristics used in the color conversion processing are described.
The input / output I / F 105 connects the above elements to each other and is connected to the scanner 10, the digital camera 20, and the mobile phone 30. Image data having image color information as data is stored in the scanner 10, digital Input from the camera 20 and the mobile phone 30 to the PC 100. Further, the input / output I / F 105 is connected to the printer 200, and the image data color-converted by the PC 100 is output to the printer 200.
[0030]
The user I / F 106 outputs a print start command to the CPU 101 when an operation for starting printing is performed using the operation key 106a.
The communication I / F 107 is connected to the network 40, and image data is input from the network 40 to the PC 100.
[0031]
In the PC 100 configured as described above, first, the CPU 101 acquires image data input from the scanner 10, the digital camera 20, the mobile phone 30, or the network 40 according to a predetermined processing program and stores the image data in, for example, the HDD 102. When a print start command is input from the user I / F 106 to the CPU 101, the CPU 101 stores image data from the HDD 102 to the RAM 104. Thereafter, the CPU 101 reads image data from the RAM 104 and performs color conversion processing based on the color conversion program 102a. Then, the color-converted image data is output to the printer 200 via the input / output I / F 105.
[0032]
Next, color conversion processing executed by the CPU 101 of the PC 100 will be described with reference to FIG.
FIG. 2 is a flowchart showing the color conversion process. This color conversion process is a process repeatedly executed while the PC 100 is activated (powered on).
[0033]
When this color conversion process is executed, the CPU 101 first determines in S01 whether or not a print start command has been input. If it is determined that a print start command has been input (S01: YES), the process proceeds to S02. On the other hand, if it is determined that the print start command has not been input (S01: NO), the process of S01 is repeated.
[0034]
The image data input to the PC 100 includes X_SIZE pixel data in the horizontal direction and Y_SIZE pixel data in the vertical direction (X_SIZE: input data horizontal size (Pixel): Y_SIZE: input data vertical size (Pixel)). That is, it is composed of X_SIZE × Y_SIZE pixel data P (X, Y). X is a horizontal coordinate value of the pixel, Y is a vertical coordinate value, and 0, 1, 2,..., X_SIZE for X, 0, 1, 2,. A value of Y_SIZE is attached. X_SIZE and Y_SIZE differ depending on the image data.
[0035]
The pixel data P (X, Y) is composed of three types of color components defined by R (red), G (green), and B (blue), and each component is 8 bits from 0 to 255. It has 256 gradations, and normally 0 indicates the darkest part and 255 indicates the highest brightness.
When the process proceeds from S01 to S02, for example, the pixel data P (X, Y) at all (X, Y) coordinates is read from the HDD 102 and stored in the RAM 104.
[0036]
Thereafter, X and Y are set to 0 as the initial setting of the coordinate value of the pixel data in S03.
Then, the processing is shifted to S04, and the pixel data P (X, Y) corresponding to the values of X and Y is RGB based on the RGB values in P (X, Y) and having R, G, and B as axes, respectively. A position in the color space is obtained (this position is referred to as a conversion point).
[0037]
Here, in a three-dimensional space such as an RGB color space, lattice points arranged in a lattice shape are set, and each lattice point has an RGB value as a coordinate value in the three-dimensional space. The color conversion table stores CMYK values as control signals for the output device that reproduces the RGB values. That is, in this case, as shown in FIG. 6, the color conversion table includes a combination of three identification numbers (0, 0, 0), (0 , 0, 1),..., (M, m, m) and four parameters (C, M, Y, K) of the CMYK color space corresponding to the combination.
[0038]
At this time, the grid point indicated by the identification number (0, 0, 0) is the origin of the RGB color space, and each identification number is one in the positive direction of each of the R, G, and B axes with respect to the origin. Each value is set to increase, and there is a grid point indicated by each identification number.
Further, as can be seen from the fact that grid points arranged in a grid pattern in the three-dimensional space are set, the data represented in the color conversion table is distributed discretely in the RGB color space. Therefore, in the process of S04, a position (hereinafter referred to as a conversion point) in the RGB color space of the pixel data P (X, Y) = (R, G, B) to be converted is specified.
[0039]
Thereafter, interpolation processing is executed in S05. The interpolation process is a process of converting to a CMYK color space using a color conversion table stored in the HDD 102.
This interpolation processing is executed according to the procedure shown in FIG. That is, in this interpolation processing, first, in S21, the reference unit cell surface closest to the conversion point in the RGB orthogonal coordinate space is obtained.
[0040]
For example, when the conversion point X = (Rx, Gx, Bx) exists at the position shown in FIG. 4, the surface formed by the lattice points P1, P2, P3, and P4 is selected as the reference unit lattice surface M1. The FIG. 4 is a diagram for explaining a method of extracting a reference unit cell surface.
Thereafter, the process proceeds to S22. Here, first, two adjacent unit cell surfaces that are opposed to and adjacent to the reference unit cell surface M1 are selected. In FIG. 4, a surface M2 formed by lattice points P7, P8, P9, and P10 and a surface M3 formed by lattice points P11, P12, P13, and P14 are selected as adjacent unit lattice surfaces.
[0041]
Then, a unit interpolation cube T1 composed of the reference unit lattice plane M1 and the adjacent unit lattice plane M2 and a unit interpolation cube T2 composed of the reference unit lattice plane M1 and the adjacent unit lattice plane M3 are set. A center point P5 of the interpolation cube T1 and a center point P6 of the unit interpolation cube T2 are selected (hereinafter, points P5 and P6 are also referred to as specific points). Thus, the interpolation polyhedron H1 including the conversion point X therein is constituted by the lattice points P1, P2, P3, P4 and the specific points P5, P6.
[0042]
Thereafter, the process proceeds to S23. Here, the CMYK color space parameters (C, M, Y, K) at the lattice points P1, P2, P3, P4 forming the reference unit lattice plane M1 are extracted from the color conversion table.
Thereafter, the CMYK color space parameter at the point P1 is (C1, M1, Y1, K1), the CMYK color space parameter at the point P2 is (C2, M2, Y2, K2), and the CMYK at the point Pn (n: integer). The color space parameter is described as (Cn, Mn, Yn, Kn).
[0043]
Thereafter, the process proceeds to S24. Here, first, CMYK color space parameters (C10, M10, Y10, K10) and (C11, M11, Y11, K11) in P10 and P11 are extracted from the color conversion table.
Then, the CMYK color space parameters (C5, M5, Y5, K5) at the specific point P5 are calculated based on the CMYK color space parameters at P1 and P10. That is, since the specific point P5 is located at the midpoint of the line connecting the lattice point P1 and the lattice point P10, the CMYK color space parameters at the specific point P5 are represented by the following equations (1), (2), (3), Calculated by (4).
[0044]
[Expression 1]

[0045]
Similarly, since the specific point P6 is positioned at the midpoint of the line connecting the lattice point P4 and the lattice point P11, the CMYK color space parameters (C6, M6, Y6, K6) at the P specific point P6 are respectively expressed by the following formulas ( 5), (6), (7), and (8).
[0046]
[Expression 2]

[0047]
Thereafter, the process proceeds to S25. Here, the weighting coefficients at points P1, P2, P3, P4, P5, and P6 for calculating CMYK color space parameters (Cx, Mx, Yx, Kx) at the conversion point X are calculated. FIG. 5 is a diagram for explaining a method of calculating a weighting coefficient in the interpolation polyhedron H1.
[0048]
First, a position where a perpendicular line extending from the transformation point X to each side of the interpolation polyhedron H1 intersects each side is obtained (points A, B, C, D, E, F, G, H, I, J, K in FIG. 5). , L).
A point A in FIG. 5 is a point on a line segment P2-P5 connecting the point P2 and the point 5. Similarly, point B is line segment P1-P5, point C is line segment P4-P5, point D is line segment P3-P5, point E is line segment P4-P6, point F is line segment P3-P6, point G Is a line segment P2-P6, point H is a line segment P1-P6, point I is a line segment P2-P4, point J is a line segment P1-P3, point K is a line segment P1-P2, and point L is a line segment P3- It is a point on P4.
[0049]
The weighting factor W1 at the point P1 is calculated based on the volume of the polyhedron formed by the six points P4, C, L, I, E, and X.
Similarly, the weighting factor W2 at the point P2 is six points P3, D, L, J, F, and X, and the weighting factor W3 at the point P3 is six points P2, A, K, G, I, and X, The weighting factor W4 at P4 is six points P1, B, J, H, K, and X, the weighting factor W5 at point P5 is the six points at points P6, F, E, G, H, and X, and the weighting factor at point P6 W6 is calculated based on the volume of the polyhedron formed by the six points P5, B, D, C, A, and X. For example, the polyhedron for calculating the weighting factor W6 at the point P6 is the polyhedron S1 shown in FIG.
[0050]
If the volume of the polyhedron formed by the six points A, B, C, D, E, and F is expressed as V (A, B, C, D, E, F), the weighting factors W1, W2, and W3 , W4, W5, W6 are calculated by the following equations (9), (10), (11), (12), (13), (14), respectively.
[0051]
[Equation 3]

[0052]
Thereafter, the process proceeds to S26. Here, the CMYK color space parameters (Cx, Mx, Yx, Kx) at the transformation point X are set to CMYK at the weighting factors W1, W2, W3, W4, W5, W6 and the points P1, P2, P3, P4, P5, P6. The color space parameters (Cn, Mn, Yn, Kn) are used to calculate the following equations (15), (16), (17), (18).
[0053]
[Expression 4]

[0054]
Then, when the process of S26 is finished, the interpolation process is finished.
When the interpolation process ends, the process returns to the color conversion process of FIG. 2, and X is incremented in S06. Thereafter, the process proceeds to S07, and it is determined whether or not the value of X is greater than X_SIZE. If it is determined that the value of X is less than or equal to X_SIZE (S07: NO), the process proceeds to S04 and the above process is repeated. On the other hand, if it is determined that the value of X is greater than X_SIZE (S07: YES), the process proceeds to S08, where X is set to 0 and Y is incremented. Thereafter, the process proceeds to S09, and it is determined whether or not the value of Y is larger than Y_SIZE. If it is determined that the value of Y is equal to or less than Y_SIZE (S09: NO), the process proceeds to S04 and the above process is repeated. On the other hand, if it is determined that the value of Y is greater than Y_SIZE (S09: YES), the process proceeds to S10, and the color-converted data is output to the printer 200. Then, the color conversion process ends.
[0055]
Through the above processing, all the X_SIZE × Y_SIZE pixel data P (X, Y) = (R, G, B) are converted into CMYK color space parameters.
[Correspondence with the present invention]
In the embodiment described above, the PC 100 is the color conversion apparatus according to the present invention.
[0056]
The color conversion program 102a is a color conversion program in the present invention. 3 is the position detecting means in the present invention, the processes in S21 and S22 in FIG. 4 are the interpolation point extracting means in the present invention, the processes in S23 and S24 in FIG. 4 are the interpolation in the present invention. The point color conversion value calculation means, the process of S25 in FIG. 4 functions as the weighting coefficient calculation means in the present invention, and the process of S26 in FIG. 4 functions as the interpolation calculation means in the present invention.
[0057]
[effect]
According to the PC 100 configured as described above, the reference unit lattice plane M1 formed by the lattice points P1, P2, P3, and P4 can be included in the interpolation polyhedron H1.
Therefore, when the pixel data P (X, Y) = (R, G, B) at the position on the reference unit lattice plane M1 is converted into CMYK color space parameters, the lattice points constituting the reference unit lattice plane M1. Interpolation can be performed using not only P1, P2, P3 and P4 but also color conversion values at specific points P5 and P6. That is, in the case where the value of the K component is k only at one of the lattice points constituting the reference unit lattice plane M1, and the values of the K components of the other three points are 0, the specific points P5 and P6 Since interpolation can also be performed using the value of the K component, it is possible to generate CMYK color space parameters that reduce the occurrence of geometric patterns.
[0058]
Further, a gray axis can be included in the side of the interpolation polyhedron H1. For this reason, when the pixel data P (X, Y) = (R, G, B) on the gray axis is converted into the CMYK color space parameter, the chromatic color among the points forming the interpolation polyhedron H1. Since interpolation can be performed using only points on the gray axis without using image data representing, pixel data P (X, Y) representing gray is converted into CMYK color space parameters representing gray. Can do.
[0059]
Since the specific points P5 and P6 are the center points of the unit interpolation cubes T1 and T2, respectively, the distances between the lattice points P1, P2, P3, and P4 and the specific points P5 and P6 are equal. For this reason, in the process of S25 in FIG. 4, since the calculation which calculates | requires the volume of six octahedrons can be simplified, the process of S25 in FIG. 4 can be performed quickly.
[0060]
(Embodiment 2)
Embodiment 2 of the present invention will be described below with reference to the drawings.
First, the configuration of the printer 200 will be described with reference to FIG.
As shown in FIG. 7, the printer 200 is provided with a CPU 201 that executes processing based on a predetermined processing program, a ROM 203 that stores various control programs, and various memories that store data input from an external device. A user interface 206 including a RAM 204, an input / output I / F 205, a plurality of operation keys 206a that can be operated by a user and a display panel 206b for displaying various information, a printer engine interface (hereinafter referred to as a printer engine I / F). 207) and a printer engine 208.
[0061]
The ROM 203 has a storage area for a color conversion program 203a for the CPU 201 to execute color conversion processing and a color conversion table 203b in which color conversion characteristics used in the color conversion processing are described.
The input / output I / F 205 connects the above elements to each other and is connected to an external device such as a PC 210, and image data is input from the PC 210 to the printer 200.
[0062]
In the first embodiment, the CPU 101 executes color conversion processing (see FIG. 2) and interpolation processing (see FIG. 3), but in the second embodiment of the present invention, the CPU 201 in the printer 200 executes. Since the color conversion process and the interpolation process are the same as in the first embodiment, description of the color conversion process and the interpolation process is omitted.
[0063]
[effect]
According to the printer 200 configured as described above, an image can be formed using CMYK color space parameters generated in the same manner as in the first embodiment.
[0064]
For this reason, generation | occurrence | production of a geometric pattern can be reduced when forming an image.
[Modification]
Although the embodiments of the present invention have been described above, the embodiments of the present invention are not limited to the above-described embodiments, and various forms can be taken as long as they belong to the technical scope of the present invention. Not too long.
[0065]
For example, in the above embodiment, the printer 200 is applied as a configuration as an image forming apparatus. However, as long as it has an image forming function, it can be similarly applied to a copying machine, a facsimile, and the like.
For example, in the above embodiment, the conversion from the RGB color space to the CMYK color space is exemplified. However, the same applies to conversion from the RGB color space to the RGB color space.
[0066]
In the above embodiment, the specific points P5 and P6 are the center points of the unit interpolation cubes T1 and T2, respectively. However, the specific point P5 does not have to be neutral in the line segment P1P10 as long as it is on the gray axis that is a line segment connecting P1 and P10. Similarly, the specific point P6 does not have to be neutral in the line segment P11P4 as long as it is on the gray axis that is a line segment connecting P11 and P4. Furthermore, the specific points P5 and P6 may be any points within the unit interpolation cubes T1 and T2, respectively, and need not necessarily be set on the gray axis. The shape of the unit interpolation polyhedron is not limited to a cube, and may be a rectangular parallelepiped.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of a color conversion device according to Embodiment 1. FIG.
FIG. 2 is a flowchart showing a color conversion processing procedure in the embodiment.
FIG. 3 is a flowchart showing an interpolation processing procedure in the embodiment.
FIG. 4 is a diagram illustrating the concept of interpolation calculation in the embodiment.
FIG. 5 is a diagram for explaining the concept of calculating a weighting factor for interpolation in the embodiment.
FIG. 6 is a configuration explanatory diagram of a color conversion table in the embodiment.
FIG. 7 is a block diagram illustrating a configuration of a printer according to a second embodiment.
FIG. 8 is a diagram illustrating a geometric pattern.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Scanner 10, 20 ... Digital camera, 30 ... Mobile phone, 100 ... PC, 101 ... CPU, 102 ... HDD, 103 ... ROM, 104 ... RAM, 105 ... I / O interface, 106 ... User interface, 106a ... Operation key 106b ... display panel, 107 ... communication interface, 200 ... printer, 201 ... CPU, 203 ... ROM, 204 ... RAM, 205 ... input / output interface, 206 ... user interface, 206a ... operation keys, 206b ... display panel, 207 ... printer engine interface, 208 ... printer engine, 210 ... PC, etc.

Claims (6)

The first color signal in the first color space defined by the combination of three different color signals is the same as the first color space using a color conversion table using each color component value of the first color space as a parameter, or A color conversion device for converting to a second color signal of a different second color space,
Position detecting means for detecting a position of the first color signal in a color space having each color component of the first color space as a coordinate axis based on each color component value representing the first color signal;
Among the discrete lattice points in the color space specified by the color component values of the first color space corresponding respectively to the color conversion values to the second color signal described in the color conversion table, Selecting four lattice points constituting the reference unit lattice plane closest to the position of the first color signal detected by the position detection means, and facing the reference unit lattice plane and the reference unit lattice plane; A specific point having a predetermined position from the reference unit lattice plane is selected within each of two unit interpolation spaces formed by two adjacent unit lattice planes, and an interpolation polyhedron is selected from these points. Interpolation point extraction means to be set;
Interpolation point color conversion for extracting the color conversion values at the positions of four lattice points constituting the reference unit lattice plane from the color conversion table and calculating the color conversion values at the specific points based on the color conversion table A value calculating means;
Weight coefficient calculation means for calculating weight coefficients of the four grid points and the specific point based on the positions of the four grid points and the specific point with respect to the position of the first color signal in the interpolation polyhedron;
Using a color conversion value at the point forming the interpolated polyhedron and the weighting factor, and an interpolation calculation means for obtaining a second color signal of the second color space by interpolation calculation,
A color conversion device characterized by that. The unit interpolation space is a cube;
The first color space is a color space whose diagonal can be defined as a gray axis,
2. The color conversion according to claim 1, wherein the interpolation point extracting unit selects a point on a diagonal line in the unit interpolation space whose direction is defined by a vector of a gray axis in the first color space. apparatus. The color conversion apparatus according to claim 2, wherein the selected interpolation point is a center point of the unit interpolation space, that is, a midpoint of the diagonal line. The first color signal in the first color space defined by the combination of three different color signals is the same as the first color space using a color conversion table using each color component value of the first color space as a parameter, or A color conversion device for converting to a second color signal of a different second color space,
Position detecting means for detecting a position of the first color signal in a color space having each color component of the first color space as a coordinate axis based on each color component value representing the first color signal;
Among the discrete lattice points in the color space specified by the color component values of the first color space corresponding respectively to the color conversion values to the second color signal described in the color conversion table, Selecting four lattice points constituting the reference unit lattice plane closest to the position of the first color signal detected by the position detection means, and facing the reference unit lattice plane and the reference unit lattice plane; An interpolation point extracting means for selecting a center point of each of the two unit interpolation spaces constituted by each of two adjacent unit grid surfaces adjacent to each other, and setting an interpolation octahedron from these points;
Interpolation point color conversion for extracting the color conversion values at the positions of the four lattice points constituting the reference unit lattice plane from the color conversion table and calculating the color conversion values at the center point based on the color conversion table A value calculating means;
Weight coefficient calculation means for calculating weight coefficients of the four grid points and the center point based on the positions of the four grid points and the center point with respect to the position of the first color signal in the interpolation octahedron;
Using a color conversion value at the point forming the interpolation octahedron and the weighting factor, and interpolation calculation means for obtaining a second color signal of the second color space by interpolation calculation,
A color conversion device characterized by that. An image forming apparatus comprising the color conversion device according to claim 1. The program for functioning a computer as said each means of the color conversion apparatus in any one of Claims 1-4.

Images