JP2006237992A - Image processor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that transformation with color correction parameters created in an image processor causes such a phenomenon that primary RGBCMY is not transformed into primary RGBCMY after transformation, and RGB isochromatic gray is not transformed into RGB isochromatic gray. <P>SOLUTION: Conditions for restricting primary RGBCMY to become primary RGBCMY similarly even after transformation and for restricting isochromatic gray to become RGB isochromatic gray similarly even after transformation are added to color correction parameters, thereby performing color correction for compensating them conveniently. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image processing apparatus for managing color reproduction.

  In recent years, with the spread of personal computers / workstations, color document creation using DTP (desktop publishing) and CAD (computer-aided design) using these has become widely used. Under such circumstances, a highly accurate and simple color reproduction management technique is required in order to keep the color reproduction of color printing constant in the presence of various color printers.

  First, in the sense of highly accurate color reproduction management, there is a demand for stable and constant color reproduction that does not depend on the printing device, and stable color reproduction that does not depend on changes over time of the printing device or environmental changes.

  On the other hand, in terms of simple color reproduction management technology, there is a need for color reproduction management technology that can be used even by beginners regarding color reproduction management. Now that inexpensive color printing equipment has become widespread, examples of performing color catalog printing in offices and the like are increasing. Therefore, there is a need for a color reproduction management technique that allows users who have not been involved in color reproduction management to easily manage color reproduction.

  As such a high-precision and simple color reproduction management technique, an image processing apparatus using polynomial approximation is known, and a color to be color-managed is specified in relation to this image processing apparatus, and the color An attempt has been made to examine an apparatus that calculates color correction parameters and performs color reproduction management only by giving a reproduction color and specifying an importance level (more precisely, a weight).

  The above examination example is intended to provide a technique that enables even a person who does not particularly have skills related to color reproduction management to easily and accurately manage color reproduction. Based on the above, intuitive and easy control is realized by setting physical values that are color reproduction targets for a plurality of colors and performing color reproduction management, and nonlinear color correction processing is automatically performed based on the settings. Therefore, highly accurate color reproduction management becomes easy.

As a conventional example, for example, Patent Document 1 can be cited.
JP 2002-344755 A

  However, when conversion is performed using the color correction parameter created by the image processing apparatus, a phenomenon may occur in which the primary RGBCMY is not converted to the primary RGBCMY after the conversion, or the RGB color gray is not converted to the RGB color gray after the conversion. There was a problem. At this time, if the primary CMY is not converted to the primary CMY, there arises a problem that the maximum density in printer printing is not stored. In addition, when the same color gray is not converted to the equivalent color gray, the impression of the image may be different.

  In the present invention, the primary RGBCMY becomes the primary RGBCMY similarly after the conversion, and the constraint condition for the same color gray to become the RGB equal color gray after the conversion is added to the color correction parameter. The purpose is to perform color correction to compensate for these.

In order to solve the above problems, the present invention provides:
An image processing apparatus comprising image output means for outputting an image and conversion characteristic calculation means for calculating conversion characteristics in the image output apparatus,
An image processing apparatus comprising image output means for outputting an image and conversion characteristic calculation means for calculating conversion characteristics in the image output apparatus,
The image output means includes
Color signal conversion means for converting color signal values expressed in the first color system into color signal values in the same or different third color system;
Color signal conversion means for converting the converted color signal value of the third color system into a color signal value expressed in the second color system;
Image output means for outputting an image based on the converted color signal value of the second color system;
And having
Further, a correction unit that corrects the conversion value of the second color signal value with respect to the first color signal value based on the conversion characteristic calculated by the conversion characteristic calculation device;
Have
The conversion characteristic calculation means calculates the conversion characteristic,
Correction color estimation means for estimating a color when the color signal of the third color system is subjected to color signal correction and output as an image, using the fourth color system;
Color reproduction target setting means for giving a color reproduction target for the color signal of the third color system in the fourth color system;
And
When the color signal values of the third color system before correction are equal to each other, the conversion characteristics are maintained so that the estimated value is close to the target value while the color retains the value after correction. calculate,
Take measures characterized by that.

  As is clear from the above description, according to the present invention, the color to be color-managed is designated by the RGB value, the reproduction color of the color is given by L * a * b * and the importance (more accurately, Color reproduction can be managed simply by specifying (weight). In addition, since a constraint condition is added to the color correction parameter to be created, a specific conversion desired by the user can be compensated. For this reason, even a beginner who does not particularly have the skills related to color reproduction management can easily and accurately manage color reproduction.

  In addition, as described above, by fixing the target color reproduction information to one with a specific printing device and applying the present invention periodically, calibration of color reproduction against changes over time and environmental fluctuations is possible. Can be applied. That is, the color reproduction management means of the present invention can be applied to various uses and can flexibly cope with various color reproduction management systems.

<First embodiment>
FIG. 1 is a block diagram showing an image processing apparatus as a first embodiment of the present invention. In the above configuration, 101 is a CPU, 102 is a main memory, 103 is a SCSI interface, 104 is a network interface, 105 is an HDD, 106 is a graphic accelerator, 107 is a color monitor, 108 is a USB controller, 109 is a color printer, and 110 is a keyboard. / Mouse controller, 111 is a keyboard, 112 is a mouse, 113 is a local area network, and 114 is a PCI bus.

  A digital image printer output operation in the above configuration will be described. First, an image application stored in the HDD 105 is activated by the CPU 101 based on an OS program that has received a user instruction. Subsequently, the digital image data stored in the HDD 105 is transferred to the main memory 102 via the PCI bus 114 via the SCSII / F 103 based on a command from the CPU 101 in accordance with processing in the image application according to a user instruction. Alternatively, image data stored in a server connected to the LAN or digital image data on the Internet is transferred to the main memory 102 via the PCI bus 114 via the network I / F 104 according to a command from the CPU 101. Hereinafter, an embodiment will be described assuming that the digital image data held in the main memory 102 is image data in which each RGB color signal is expressed by 8 bits without a sign. The digital image data held in the main memory 102 is transferred to the graphic accelerator 106 via the PCI bus 114 in response to a command from the CPU 101. The graphic accelerator 106 performs D / A conversion on the digital image data and then displays the color monitor through the display cable. To 107. As a result, an image is displayed on the color monitor 107. When the user instructs the image application to output the digital image stored in the main memory 102 from the printer 109, the image application transfers the digital image data to the printer driver. The CPU 101 converts the digital image data into CMYK digital image data based on a later-described process flowchart of the printer driver, and transmits the CMYK image data to the printer 109 via the USB controller 108. As a result of the series of operations described above, a CMYK image is printed by the printer 109.

  Hereinafter, the printer driver operation in the above configuration will be described with reference to the flowchart of FIG. The printer driver in this embodiment performs color conversion using a color correction LUT for converting colors according to user preferences, color correction conversion for correcting RGB values to obtain a desired color reproduction, and RGB color. The RGB 24-bit image data is converted into CMYK 32-bit image data using the conversion using the color conversion LUT for converting the signal into the CMYK color signal and the above three color conversions.

  First, in step 201, a pointer to RGB 24-bit image data (each color signal is unsigned 8-bit image data) held in the main memory 102 is acquired, and a memory area for holding image data after CMYK conversion is secured. At the same time, other initialization operations are performed.

  In step 202, parameters used for color correction are acquired from the HDD 105. Details of the color correction parameters and the color correction conversion will be described in step 205.

  In step 203, one RGB value, which is a pixel value, is acquired from the RGB 24-bit image data in the main memory 102 in the raster scan order.

  In step 204, RGB 24-bit → RGB 24-bit conversion is performed by tetrahedral interpolation calculation using the color correction LUT. The color correction LUT has a data structure as shown in FIG. 16 in which the correspondence between the color coordinate data of the grid points in the RGB color space and the coordinate values of the RGB color space reproduced by the grid points is described. An R / G / B value step is described at the head of the data structure, and thereafter, RGB color coordinates corresponding to each grid point are described by being nested in the order of R, G, and B. This data structure is schematically represented in the RGB color space as shown in FIG. In the tetrahedral interpolation, a hexahedral area surrounded by eight adjacent lattice points is subjected to interpolation calculation for each tetrahedral area divided into six as shown in the schematic diagram of FIG.

  In step 205, the second-order nonlinear transformation for the three-dimensional vector and the γ transformation for each element are combined to perform color correction transformation as shown in the equation of FIG. Here, the matrix element mij and the γ conversion coefficient γi in FIG. 5 are color correction parameters. The calculation is performed by floating point calculation, but after the conversion according to the equation of FIG. 5 is completed, each color signal is rounded to unsigned 8-bit data. At this time, a value exceeding 255 is clipped to 255, and a value below 0 is clipped to 0.

  In step 206, RGB 24-bit data is converted into CMYK 32-bit image data (CMYK color signals are unsigned 8-bit image data) by tetrahedral interpolation according to the color conversion LUT. Here, in the following description, this RGB color space before the conversion is particularly called Private RGB. That is, the color correction calculation in step 205 after RGB24bit → RGB24bit conversion in step 204 is calculation on Private RGB.

  In step 207, this CMYK 32-bit value is written in an appropriate memory address according to the pixel position.

  In step 208, it is determined whether or not conversion has been performed on all necessary pixels, and if so, the process jumps to step 209, and if not, the process jumps to step 203.

  In step 209, the CMYK 32-bit image data stored in the main memory is transmitted to the printer 109 via the USB controller 108, and the operation ends in step 210.

  Hereinafter, a parameter creation operation using the color correction parameter creation application in the configuration of FIG. 1 will be described.

  First, a color correction parameter creation application stored in the HDD 105 is activated by the CPU 101 based on an OS program that has received a user instruction. When the color correction parameter creation application is activated, a dialog window shown in FIG. 6 is displayed. The dialog and the operation flow of the application will be described in detail later, but the user uses the window of FIG. 6 to display the Private RGB value (see the description of step 206) and the L * a * Confirm and specify b * value. Here, the user has determined that there is no problem with the correspondence set (hereinafter referred to as target color reproduction information) of the private RGB value and the L * a * b * value that is the color reproduction target when the image is output with this RGB value. When the user presses a parameter creation button, a color correction parameter is generated and stored in the HDD 105.

  In the following, the dialog window of FIG. 6 will be described. A window 601 displays a list of target color reproduction information. The private RGB value of the target color on the left side of the window is the L * a * b * value that is the color reproduction target when the image is output on the right side. Is displayed. In addition, the selected target color reproduction information is displayed in reverse video. Reference numeral 602 denotes a slider bar. By controlling this bar, the target color reproduction information displayed is scrolled and selected. Reference numeral 603 denotes a reproduction color designation button. When this button is pressed, a setting dialog shown in FIG. 7 is displayed, and the user sets target color reproduction information from the dialog shown in FIG. Reference numeral 604 denotes a parameter creation button. When this button is pressed, the color correction parameter creation application creates a color correction parameter and stores it in the HDD 105. Reference numeral 605 denotes an end button. When this button is pressed, the color correction parameter creation application is ended.

  Hereinafter, the color correction parameter creation application operation will be described with reference to the state diagram of FIG.

  In state 801, an initialization operation such as reading an initial setting value of target color reproduction information is performed.

  Next, in the state 802, a user operation determination waiting state in the window of FIG. 6 is entered. Here, when the slider bar 602 is operated, the process proceeds to the state 803. When the reproduction color designation button 603 is pressed, the process proceeds to the state 804, and when the parameter creation button 604 is pressed, the process proceeds to the state 805. When the button 605 is pressed, the state 806 is entered.

  In state 803, the display of the target color reproduction information on the window 601 is scrolled and the selected target color reproduction information is changed according to the control amount of the slider bar.

  In state 804, the dialog shown in FIG. 6 is displayed, and the target color reproduction information editing state is entered. Here, the Private RGB value of the color to be edited is changed in the edit box 701, and the L * a * b * value that is the color reproduction target is edited in the edit box 702. In the edit box 703, the importance of the color to be edited is set as a positive number. This value is used as a weight at the time of evaluation value calculation in step 1008 of the evaluation value calculation process described later. When the correction button 704 is pressed, the currently selected target color reproduction information is overwritten. When the add button 705 is pressed, new target color reproduction information is added. When the delete button 706 is pressed, the currently selected target color reproduction information is deleted. When these buttons 704, 705, 706 and buttons are pressed, the respective operations are performed and stored in the target color reproduction information, and the dialog shown in FIG. 6 is closed.

  In the state 805, color correction parameters are created according to the flowchart of FIG.

  In state 805, after performing an end operation such as memory release, the color correction parameter creation application operation ends.

  Hereinafter, the color correction parameter creation processing in the state 805 will be described with reference to the flowchart of FIG.

  In step 901, initialization such as initial setting of a color correction parameter (matrix element mij and γ conversion coefficient γi in the equation shown in FIG. 5) and securing of a memory area is performed.

  In step 902, first, an evaluation value sum for the current color correction parameter is calculated. The calculation of the evaluation value sum will be described later with reference to the flowchart of FIG.

  In step 903, it is determined whether or not the calculated evaluation value sum is equal to or smaller than a predetermined value. If the calculated evaluation value sum is equal to or smaller than the predetermined value, the process jumps to step 906, and if larger, the process jumps to step 904.

  In step 904, the number of times that the loop calculation from step 905 to step 904 has been performed is acquired. If this number is greater than the predetermined number, the process jumps to step 907;

  In step 905, a color correction parameter is calculated based on an algorithm described later.

  In step 906, the current color correction parameter is stored in the memory, and the color correction parameter creation process is terminated.

  Hereinafter, the evaluation value calculation process used in step 902 will be described with reference to the flowchart of FIG. In this flow, the evaluation value fi for the i-th color reproduction target color and the evaluation value sum by the sum of fi are calculated. The rough process is also used in the color correction parameter update described later.

  In step 1001, first, a color correction parameter to be evaluated is acquired and set.

  In step 1002, i, which is a variable indicating the number of loops, is set to 1 as an initialization operation. Also, the color estimation LUT necessary for color estimation in step 1006 is read. The LUT has a data structure as shown in FIG. 17. When this data structure is schematically represented in the RGB color space, it is represented as shown in FIG. Since this configuration has the same format as the data structure shown in FIG. 3 and FIG. 16 described in the description of step 204, details are omitted. Note that this LUT is prepared by measuring the color of the private RGB values actually measured in the L * a * b * color system and prepared in advance.

  In step 1003, the i-th target color reproduction information, which is a corresponding set of Private RGB values and L * a * b * values that are color reproduction targets when an image is output with these RGB values, is read from the memory. .

  In step 1004, a pair of correspondence between the private RGB value Corg and the L * a * b * value Drep is acquired from the target color reproduction information read from the memory. Also, the weight w for the color is acquired at the same time.

In step 1005, the private RGB value Corg is converted into Ccmp using the same formula of FIG. 5 used in step 205. In step 1007, the L * a * b * value Dcal is read from the private RGB value Ccmp in step 1002. Estimation is performed using the estimation LUT. Tetrahedral interpolation is used for the estimation calculation, and interpolation calculation is performed for each of the tetrahedral areas divided into six as shown in the schematic diagram of FIG.

In step 1008, the color difference between the L * a * b * value Drep, which is the target color reproduction value, and the estimated L * a * b * value Dcal is calculated by CIEΔE94 and multiplied by the weight w to obtain the evaluation value fi. .
In step 1009, it is determined whether or not the operations from steps 1004 to 1008 have been performed on the correspondence relationship between all Private RGB values Corg and L * a * b * values Drep in the target color reproduction information. If it is not applied to step 1010, 1 is added to the variable i indicating the number of loops, and then the process jumps to step 1004.

  In step 1010, an end operation of the evaluation value calculation process is performed.

  Hereinafter, the color correction parameter update processing in step 905 will be described with reference to the flowchart of FIG. The flowchart in FIG. 12 performs color correction parameter updating based on the D.L.S. method (attenuating least square method) in order to sequentially reduce the evaluation value sum.

  Here, in the following description, the matrix element mij and the γ conversion coefficient γi are arranged in a line and treated as a vector x, and each element of the color correction parameter is represented by a vector element xk (l = 0 to l). Further, the amount of change to be updated of the color correction parameter kl-th parameter xk is represented by Δxk.

  In step 1201, the color correction parameters to be updated, the evaluation values of all target color reproduction information based on the parameters, the minute fluctuation width necessary for calculating the gradient of the evaluation value space and the column vector x, and the damping factor (ρ) are calculated. Get and set. The damping factor is defined by the following expression 12-1.

また微小変動幅の詳細に関しては、ステップ１２０６の説明にて述べる。
ステップ１２０２では、更新すべき色補正パラメータの各要素を次に示す式１２−２によってベクトル要素ｘiに変換する。

Details of the minute fluctuation range will be described in the description of step 1206.
In step 1202, each element of the color correction parameter to be updated is converted into a vector element xi according to the following expression 12-2.

このときの列ベクトルｘをベクトルの初期値とする。また初期化動作としてループ回数を示す変数であるsを１に設定する。

The column vector x at this time is set as the initial value of the vector. Also, s, which is a variable indicating the number of loops, is set to 1 as an initialization operation.

  In step 1203, the l-th parameter xl of the column vector x is added and changed by the minute fluctuation width set in step 1201.

  In step 1204, based on the column vector x changed in step 1203, an evaluation value is calculated using the processing described in the flowchart of FIG.

  In step 1205, the column vector x changed in step 1203 is restored to the initial value of the vector.

  In step 1206, the initial evaluation value of all target color reproduction information set in step 1202, the post-change evaluation value calculated in step 1204, and the fluctuation range set in step 1201 are used, and Expression 12-3 shown below is used. From the evaluation value space and the gradient of the column vector x.

gradientは目標色再現情報n（n＝０〜p）に対して算出し、ａknとしてメモリに格納する。ここで微小変動幅は偏微分における変数の差分に相当する。

The gradient is calculated for the target color reproduction information n (n = 0 to p) and stored in the memory as akn. Here, the minute fluctuation width corresponds to a variable difference in partial differentiation.

  In step 1207, it is determined whether the operations from step 1203 to step 1206 have been performed on all the parameters of the column vector x. If so, the process proceeds to step 1208. If not, a variable indicating the number of loops. After adding 1 to i, the process jumps to step 1203.

  In step 1208, the DLS method is applied from the damping factor set in step 1201, the step and the initial evaluation value, and the gradient calculated in step 1206, and from the following equation 12-4, xi which is a parameter of the column vector x A fluctuation amount Δxi is calculated.

その後、算出した変動分によって式１２−５、式１２−６から色補正パラメータを更新する。

Thereafter, the color correction parameter is updated from Equations 12-5 and 12-6 according to the calculated variation.

ステップ１２０９では、後述のプライマリＲＧＢＣＭＹが変換後においても同様にプライマリＲＧＢＣＭＹとなる、並びに等色グレーが変換後においても同様にＲＧＢ等色グレーになるための拘束条件を色補正パラメータに付加する。

In step 1209, a constraint condition for causing primary RGBCMY, which will be described later, to be the primary RGBCMY after conversion, and for the same color gray to be the same RGB color after conversion, is added to the color correction parameter.

  In step 1210, an end operation of the color processing parameter update process is performed.

  In the following, a description will be given of a constraint condition in which the primary RGBCMY in step 1210 becomes the primary RGBCMY in the same way after conversion, and the same color gray becomes the RGB same color gray after conversion.

  However, in the following description, regarding the RGB value represented by 8 bits, it is assumed that 255 is normalized to 1. Further, the relationship between the input Private RGB and the conversion destination Private R'G'B 'at the time of conversion by the color correction parameter is as shown in Expression 13-1 from FIG.

次に、ＲＧＢ色空間におけるプライマリＲＧＢが、変換後においても同様にプライマリＲＧＢとなるための拘束条件について説明する。ここでプライマリＲＧＢのＲＧＢ色空間における色座標と変換後に補償されるべき色座標について式１３−２に示す。

Next, a constraint condition for the primary RGB in the RGB color space to become the primary RGB similarly after conversion will be described. Here, the color coordinates in the RGB color space of the primary RGB and the color coordinates to be compensated after conversion are shown in Expression 13-2.

ここで上記変換は式１３−１から以下の式１３−３のように表せる。

Here, the above conversion can be expressed from Equation 13-1 to Equation 13-3 below.

すなわち、式１３−３から、

That is, from Equation 13-3,

となる。よって一次色の補償は色補正パラメータの項ｍ14、ｍ24、ｍ34を式１３−４、ｍ15、ｍ25、ｍ35を式１３−５、ｍ16、ｍ26、ｍ36を式１３−６のように拘束する。

It becomes. Therefore, in the primary color compensation, the terms m14, m24, and m34 of the color correction parameter are constrained to Equations 13-4, m15, m25, and m35 as Equations 13-5, and m16, m26, and m36 as Equation 13-6.

  Next, a constraint condition for the primary CMY in the RGB color space to become the primary CMY after conversion will be described. Here, the color coordinates in the RGB color space of the primary CMY and the color coordinates to be compensated after conversion are shown in Expression 13-7.

ここで上記変換は式１３−１から以下の式１３−８のように表せる。

Here, the above conversion can be expressed by the following equation 13-8 from equation 13-1.

すなわち、式１３−８から、

That is, from Equation 13-8,

となる。よって二次色の補償は色補正パラメータの項ｍ19、ｍ29、ｍ39を式１３−９、ｍ18、ｍ28、ｍ38を式１３−１０、ｍ17、ｍ27、ｍ37を式１３−１１のように拘束する。

It becomes. Therefore, in the secondary color compensation, the terms m19, m29, and m39 of the color correction parameter are constrained to the expressions 13-9, m18, m28, and m38, and the expressions 13-10, m17, m27, and m37 are constrained as the expression 13-11.

  Next, a description will be given of a constraint condition for causing RGB equal color gray in the RGB color space to become the same color gray after conversion. Here, the color coordinates in the RGB color space of equal color gray and the color coordinates to be compensated after conversion are shown in Expression 13-2. Here, the uniform color gray is defined as satisfying Expression 13-13. Α is a constant.

ここで上記変換は式１３−１から以下の式１３−１４のように表せる。

Here, the above conversion can be expressed by the following equation 13-14 from equation 13-1.

このとき等色グレーから同等色グレーが補償される為には、式１３−１５が必要となる。

At this time, in order to compensate for the equivalent color gray from the equal color gray, Expression 13-15 is required.

よって等色グレーの補償は色補正パラメータの項ｍ11、ｍ21、ｍ31、およびｍ19、ｍ29、ｍ39を式１３−１5のように拘束する。

Therefore, the compensation of the equal color gray constrains the color correction parameter terms m11, m21, m31, and m19, m29, m39 as shown in Expression 13-15.

  When constraint conditions for compensating all primary colors, secondary colors, and equal grays are added to the color correction parameters, Expressions 13-4 to 13-6, Expressions 13-9 to Expressions 13-11, From 13 to 15, the color correction parameter is expressed by Equation 13-16.

本実施例に依れば、簡便な操作で色再現管理を行うことが可能である。

According to this embodiment, it is possible to perform color reproduction management with a simple operation.

  Here, by fixing the target color reproduction information to one and applying the present invention periodically with a specific printing device, color reproduction calibration can be performed with respect to changes over time and environmental fluctuations. . In particular, regarding the creation of the color correction parameter, it is possible to compensate for converted RGB primary color, secondary color, and equal color gray by applying constraint conditions.

<Second embodiment>
In the present embodiment, with respect to the processing of FIG. 2 in the first embodiment, the color correction conversion based on the color correction parameter in step 205 is superimposed on the RGB → RGB conversion using the color correction LUT in step 204 to obtain one color correction. This is a summary of RGB → RGB conversion processing using an LUT. Only the differences from the first embodiment will be described below.

  First, the printer driver operation in the second embodiment in the configuration of FIG. 1 will be described with reference to the flowchart of FIG. The printer driver in the present embodiment uses the color conversion using the color conversion LUT from the RGB color signal to the RGB color signal, the conversion using the color conversion LUT from the RGB color signal to the CMYK color signal, and the above two color conversions. The RGB 24-bit image data is converted into CMYK 32-bit image data.

  First, in step 1301, a pointer to RGB 24-bit image data (each color signal is unsigned 8-bit image data) held in the main memory 102 and a memory area for holding the image data after CMYK conversion are secured. At the same time, other initialization operations are performed.

  In step 1302, the color correction LUT used in the processing in step 1304 and the color conversion LUT used in the processing in step 1305 are acquired from the HDD 105.

  In step 1303, one RGB value as a pixel value is acquired from the RGB 24-bit image data in the main memory 102 in the raster scan order.

  In step 1304, RGB 24-bit → RGB 24-bit conversion is performed by tetrahedral interpolation calculation using the color correction LUT. The data structure of the color correction LUT is the same as that used in step 204. Further, the converted RGB color space is referred to as a private RGB color space as in the first embodiment.

  In step 1305, RGB 24-bit data is converted into CMYK 32-bit image data (CMYK color signals are unsigned 8-bit image data) by tetrahedral interpolation according to the color conversion LUT.

  In step 1306, the CMYK 32-bit value is written in an appropriate memory address according to the pixel position.

  In step 1307, it is determined whether or not conversion has been performed on all necessary pixels. If it has been performed, the process jumps to step 1308, and if not, the process jumps to step 1303.

  In step 1308, the CMYK 32-bit image data stored in the main memory is transmitted to the printer 109 via the USB controller 108, and the operation ends in step 1309.

  Hereinafter, in the color correction parameter creation application based on the operation of FIG. 8, only the end process in the state 805, which is different from the operation of the first embodiment, will be described with reference to the flowchart of FIG. In the second embodiment, the color correction conversion based on the color correction parameter is superimposed on the RGB → RGB conversion color correction LUT in the state 805 to newly generate the RGB → RGB conversion color correction LUT used in step 1304.

  In step 1401, an RGB → RGB conversion color correction LUT without basic color correction is acquired from the HDD.

  In step 1402, one RGB value on the LUT lattice point is acquired according to an appropriate order.

  In step 1403, color correction is performed on the acquired RGB values based on the calculated color correction parameter, the equation of FIG. 5 that combines the second-order nonlinear transformation for the three-dimensional vector and the γ transformation independent of each element. Perform conversion.

  In step 1404, the calculated RGB value is written to the same LUT lattice point as the acquired position.

  In step 1405, it is confirmed whether or not the processing in steps 1403 to 1404 has been performed on all grid points. If not completed, the process jumps to step 1402, and if completed, the process jumps to step 1406.

  In step 1406, the creation of the conversion LUT used in step 1304 ends.

  According to the present embodiment, since the color conversion processing at the time of printer output is one less than that of the first embodiment, high-speed processing is possible.

<Third embodiment>
This embodiment superimposes the color correction conversion based on the color correction parameters in step 205 and the RGB → CMYK conversion using the color conversion LUT in step 206 on the processing of FIG. This is a summary of RGB → CMYK conversion processing using a color correction LUT. Only the differences from the first embodiment will be described below.

  The printer driver operation in the third embodiment in the configuration of FIG. 1 operates like the flowchart of FIG. 13 as in the second embodiment. The description of this flowchart is omitted.

  Hereinafter, in the color correction parameter creation application based on the operation of FIG. 8, only the end process in the state 805, which is different from the operation of the first embodiment, will be described with reference to the flowchart of FIG. In the third embodiment, the color correction conversion based on the color correction parameter and the RGB → CMYK conversion color conversion LUT are superimposed in the state 805 to newly generate the RGB → CMYK color conversion LUT used in step 1305.

  In step 1501, an RGB → CMYK color conversion LUT without basic color correction is acquired from the HDD.

  In step 1502, RGB values corresponding to LUT lattice points are acquired.

  In step 1503, color correction is performed on the acquired RGB values based on the calculated color correction parameter, the equation of FIG. 5 that combines the second-order nonlinear transformation for the three-dimensional vector and the γ transformation for each element independently. Perform conversion.

  In step 1504, the converted RGB values are converted from RGB to CMYK by tetrahedral interpolation according to the color conversion LUT.

  In step 1505, the calculated CMYK value is written to the appropriate grid point of the new LUT.

  In step 1506, it is confirmed whether or not the processing in steps 1503 to 1505 has been performed on all grid points. If not completed, the process jumps to step 1502, and if completed, the process jumps to step 1507.

  In step 1505, the generated new RGB → CMYK color conversion LUT is stored in the HDD.

  In step 1508, the creation of the conversion LUT used in step 1305 ends.

  According to the present embodiment, since the color conversion processing at the time of printer output is one less than that of the first embodiment, high-speed processing is possible.

(Other embodiments)
<Color correction conversion type>
Although the second-order nonlinear conversion is used as the color correction conversion in the above-described embodiment, it is also possible to use a third-order or higher-order nonlinear conversion. It is also possible to combine various operations such as logarithmic operations.

<Color correction conversion>
In the above embodiment, second-order nonlinear conversion and γ conversion are used as the color correction conversion in step 205. However, in order to shorten the calculation time, it is also possible to use approximate calculation using LUT for color correction conversion.

<Color estimation method>
Although the second-order nonlinear conversion is used as the color correction conversion in the above-described embodiment, it is also possible to use a third-order or higher-order nonlinear conversion. It is also possible to combine various operations such as logarithmic operations.

<Parameter update>
The DLS method is applied to update the color correction parameters, but other optimization methods such as an orthogonalization method and a quasi-Newton method can be applied.

<Color reproduction target setting>
The target color reproduction information only needs to clearly indicate the correspondence between RGB and L * a * b *. Therefore, for example, the color estimation LUT used in step 1007 can be used.

<Other color spaces>
In this embodiment, the constraint condition when performing color correction in the RGB color space has been described. However, for example, even when the color space for performing color correction is the CMY color space, the primary color (RGBCMY) can be set by setting similar conditions. ) As well as gray.

1 is a block diagram showing a system configuration of an image processing apparatus as a first embodiment of the present invention. FIG. 6 is a flowchart illustrating an image output operation in the printer driver according to the first exemplary embodiment of the present invention. It is a schematic diagram showing the grid point arrangement | positioning in RGB color space. It is a schematic diagram showing area division in tetrahedral interpolation. It is a formula showing conversion for color correction. It is a figure which shows the user interface of a color correction parameter creation application. It is a figure which shows the user interface for a reproduction color setting. It is a state diagram which shows operation | movement of a color correction parameter creation application. It is a flowchart figure which shows the operation | movement of a color correction parameter calculation process. It is a flowchart figure which shows the operation | movement of evaluation value calculation. It is a schematic diagram showing the grid point arrangement | positioning in RGB color space. It is a flowchart figure which shows the color correction parameter update process using a DLS method. FIG. 10 is a flowchart illustrating an image output operation by a printer driver according to a second exemplary embodiment of the present invention. It is a flowchart figure which shows the production | generation operation | movement of the color correction LUT for RGB-> RGB conversion in step 806 in the 2nd Example of this invention. It is a flowchart figure which shows the production | generation operation | movement of RGB-> CMYK color conversion LUT in step 806 in the 3rd Example of this invention. It is a figure showing the data structure of LUT. It is a figure showing the data structure of LUT.

Explanation of symbols

101 CPU
102 Main memory
103 SCSI I / F
104 Network I / F
105 HDD
106 graphics accelerator
107 color monitor
108 USB controller
109 Color printer
110 Keyboard / Mouse Controller
111 keyboard
112 mice
113 LAN
114 PCI bus

Claims (8)

An image processing apparatus comprising image output means for outputting an image and conversion characteristic calculation means for calculating conversion characteristics in the image output apparatus,
The image output means includes
Color signal conversion means for converting color signal values expressed in the first color system into color signal values in the same or different third color system;
Color signal conversion means for converting the converted color signal value of the third color system into a color signal value expressed in the second color system;
Image output means for outputting an image based on the converted color signal value of the second color system;
And having
Further, a correction unit that corrects the conversion value of the second color signal value with respect to the first color signal value based on the conversion characteristic calculated by the conversion characteristic calculation device;
Have
The conversion characteristic calculation means calculates the conversion characteristic,
Correction color estimation means for estimating a color when the color signal of the third color system is subjected to color signal correction and output as an image, using the fourth color system;
Color reproduction target setting means for giving a color reproduction target for the color signal of the third color system in the fourth color system;
And
When the color signal values of the third color system before correction are equal to each other, the conversion characteristics are maintained so that the estimated value is close to the target value while the color retains the value after correction. calculate,
An image processing apparatus. An image processing apparatus comprising image output means for outputting an image and conversion characteristic calculation means for calculating conversion characteristics in the image output apparatus,
The image output means includes
Color signal conversion means for converting color signal values expressed in the first color system into color signal values in the same or different third color system;
Color signal conversion means for converting the converted color signal value of the third color system into a color signal value expressed in the second color system;
Image output means for outputting an image based on the converted color signal value of the second color system;
And having
Further, a correction unit that corrects the conversion value of the second color signal value with respect to the first color signal value based on the conversion characteristic calculated by the conversion characteristic calculation device;
Have
The conversion characteristic calculation means calculates the conversion characteristic,
Correction color estimation means for estimating a color when the color signal of the third color system is subjected to color signal correction and output as an image, using the fourth color system;
Color reproduction target setting means for giving a color reproduction target for the color signal of the third color system in the fourth color system;
And
Alternatively, when the color signal value of the third color system before correction is either the maximum signal value or the minimum signal value for each signal value, the estimated value is the target while the color retains the value after correction. Calculate the conversion characteristics so that it is close to the value,
An image processing apparatus. The image processing apparatus according to claim 2, wherein the conversion characteristic calculation unit calculates the conversion characteristic,
When the color signal value of the third color system before correction indicates one of the RGBCMY primary colors, the conversion characteristic is calculated so that the estimated value is close to the target value while retaining the value after correction.
An image processing apparatus.   4. The image processing apparatus according to claim 1, wherein the third color system is an RGB color system or a CMY color system. 5. The image processing apparatus according to claim 1, wherein the correction unit in the image output unit includes:
The color signal conversion unit configured to convert the converted color signal value of the third color system into the color signal value of the third color system according to the calculated conversion characteristic.
Image processing apparatus The image processing apparatus according to claim 1, wherein the correction unit in the image output unit includes:
In the conversion from the color signal value of the first color system to the color signal value of the third color system, the same third color signal value is obtained from the color signal value of the third color system based on the calculated conversion characteristic. Means for superimposing the conversion to the color system of the first color system, and setting again as the conversion from the color signal value of the first color system to the color signal value of the third color system,
Based on the calculated conversion characteristic, the color signal value of the third color system is converted to the same third color system, and the color signal value of the third color system is converted to the second color system. Means for superimposing the conversion of the color signal value of the second color system into a color signal value of the fourth color system from the second color system value;
Composed of either
An image processing apparatus. The image processing apparatus according to claim 1, wherein the conversion characteristic calculation unit calculates the conversion characteristic so that the estimated value is close to a target value.
For each of the plurality of colors set by the target color reproduction setting means, a difference between the estimated color and the target color in the fourth color system is calculated as an evaluation value, and conversion characteristics are used so that the sum of the evaluation values is reduced. By calculating the conversion characteristics,
An image processing apparatus.   8. The image processing apparatus according to claim 7, wherein when the conversion characteristic is calculated so that the estimated value is close to a target value in the conversion characteristic calculation apparatus, DLS, or Newton method, quasi-Newton method, or steepest descent method is used. An image processing apparatus characterized by calculating conversion characteristics asymptotically.

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