JP2007038578A - Apparatus and method of image processing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem wherein, when an allowable ink hit amount is two times lower than the maximum ink hit amount of a primary color, the ratio of the primary color constituting the maximum amount of a secondary color can not be uniquely decided, not to reproduce a hue intended at the maximum amount of the secondary color. <P>SOLUTION: A secondary color chart, which comprises a plurality of patches with the ratio of the primary color constituting the secondary color changed, is printed, allowing a user to select one chart from the printed secondary color charts, to constitute the secondary color based on the primary color ratio of the chart thus selected. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image output method, particularly an image processing apparatus, an image processing method, an image processing program, and a computer-readable recording medium that are meaningful in an inkjet printer.

Conventionally, printing on a recording medium (media) with an inkjet printer has been performed with image processing adjusted to achieve optimal color reproduction without causing ink bleeding or overflow to the medium. (For example, refer to Patent Document 1).
JP 2003-334934 A

  However, when the ink shot amount is less than twice the maximum primary color amount depending on the type of media, the ratio of the primary color in the maximum secondary color amount cannot be determined uniquely, and the maximum secondary color amount There was a problem that the intended hue could not be reproduced.

The present invention
An ink ejection amount input means for inputting the ink ejection amount of the recording medium;
A secondary color chart generating means for generating a secondary color chart composed of a plurality of patches in which the ratio of the primary color constituting the secondary color is changed from the ink ejection amount of the recording medium;
Secondary color component value input means for inputting a proportion of primary colors constituting the secondary color;
Providing a color separation table generating means for generating a color separation table for converting an image signal into an ink signal from a ratio of the primary color constituting the secondary color and the amount of ink applied to the recording medium,
Enter the maximum ink ejection amount of the recording medium,
Secondary color chart generation and output,
Input the ratio of the primary color constituting the secondary color selected by visual judgment from the secondary color chart,
A color separation table is generated from the maximum ink ejection amount of the recording medium and the ratio of the primary colors constituting the secondary colors.

  According to the present invention, when the ink shot amount is less than twice the maximum primary color amount depending on the type of media, a color separation table in which the ratio of the primary colors constituting the maximum secondary color amount is changed is generated. By doing so, it becomes possible to express the secondary color with the maximum saturation obtained with the hue desired by the user, and it is possible to reproduce the intended color.

(First embodiment)
An embodiment of the present invention is shown below.

  FIG. 1 is a diagram illustrating an example of a hardware configuration of an image forming system according to the present embodiment. The image processing apparatus 100 is a personal computer or the like. The CPU 101 is a central processing unit that integrally controls each unit of the image processing apparatus 100 by executing an operating system, application programs, a devise driver, and the like. The RAM 102 is a memory that provides a work area for the CPU 100. The ROM 103 is a memory that stores a boot program such as BIOS. The HDD 104 is a fixed storage device such as a hard disk drive, and stores image data such as a test pattern image in addition to computer programs such as an application program, an operating system, and various driver programs. The communication IF 105 is an interface for performing data communication with an external device such as USB, IEEE 1394, wired LAN, or wireless LAN. The display IF 106 is a control unit for controlling display of image information and the like on a display device 109 connected to the outside or the inside. The operation unit 107 is an input device such as a pointing device or a key input device. The printer 108 is an image forming apparatus that forms an image on a medium by an inkjet method or a laser beam method. The display device 109 is a liquid crystal display for displaying image data and the like.

  FIG. 2 is a diagram illustrating an example of a software configuration of the image processing apparatus 100. With reference to FIG. 1 and FIG. 2, a flow when printing out will be described. As the printer 108 that performs print output, a generally popular inkjet printer or the like can be used. When printing the output image data, the application 202 issues a print output request to the OS 201. For example, the graphics data portion is composed of a graphics rendering command, and the image image data portion issues a rendering command group indicating an output image composed of an image rendering command to the OS 201.

  The OS 201 receives an application output request and issues a drawing command group to the printer driver 208 corresponding to the output printer. The printer driver 208 processes a print request and a drawing command group input from the OS 201, creates print data that can be printed by the printer 108, and transfers the print data to the printer 108. When the printer 108 is a raster printer, the printer driver 208 sequentially performs image correction processing on the drawing commands from the OS 201, and sequentially rasterizes the drawing commands in the RGB 24-bit page memory, and rasterizes all the drawing commands. After that, the contents of the RGB 24-bit page memory are converted into a data format that the printer 108 can print, for example, CMYK data, and transferred to the printer 108.

  Next, processing performed by the printer driver 208 will be described with reference to FIG. The image correction processing unit 301 performs image correction processing on color information included in the drawing command group input from the OS 201. As the image correction processing, for example, RGB color information is converted into luminance / color difference signals, exposure correction processing is performed on the luminance signals, and the corrected luminance / color difference signals are inversely converted into RGB color information.

  The printer correction processing unit 302 first rasterizes a rendering command based on RGB color information subjected to image correction processing, generates a raster image on an RGB 24-bit page memory, and performs color reproduction space mapping, color matching to CMYK, and color to CMYK The separation process, the gamma correction process, and the halftone process are performed to generate CMYK data depending on the color reproducibility of the printer for each pixel, and the printable image data is transferred to the printer 108.

1. Printer Correction Processing FIG. 3 is a diagram schematically showing the internal processing configuration of the printer driver 208. Processing in the printer correction processing unit 302 will be described in detail. FIG. 4 is a diagram illustrating an example of a detailed block configuration of the printer correction processing unit 302. In the following, for simplicity of explanation, it is assumed that a color space usually represented in three dimensions is schematically represented in two dimensions (FIG. 5 and the like).

  First, RGB 8-bit image data whose brightness, contrast, and color tone are adjusted by the image correction processing unit 301 is input to the image signal input unit 401 in the printer correction processing unit 302. The RGB 8-bit image data input to the image signal input unit 401 corresponds to the color reproduced on the display device 109. For example, in the coordinate values of the CIE L * a * b * color system which is a uniform color space, the image data represents a color (L_Monitor, a_Monitor, b_Monitor).

However, as can be seen from FIG. 5, the color reproduction space of the display device 109 and the color reproduction space of the printer 108 do not coincide with each other in a uniform color space such as an L * a * b * space. This means that the printer cannot form an image outside the color reproduction space of the printer shown in FIG. 5 and in an area (shaded area) in the color reproduction space of the display device. More specifically, the subsequent color separation processing unit 403 performs RGB-CMYK conversion on the image data expressed on the display device 109, and the output γ correction processing unit 404 performs gradation correction processing. Even if the halftone processing unit 405 executes binarization processing and then outputs the image to the image output unit 406, an area where image formation is impossible, that is, an area on the color space that cannot be expressed by the printer 108 (shaded area) Will occur.
Therefore, on the printer 108 side, a pseudo color (L * a * b * value), that is, a display for an area (shaded portion) in the color space that can be reproduced by the display device 109 but cannot be reproduced by the printer 108. It is necessary to print by generating a pseudo color different from the color of the device 109.

  Hereinafter, the L * a * b * space as a uniform color space is copied to the cylindrical coordinates H (= atan (b / a)), S (= sqrt (a * 2 + b * 2)), and V (= L *). Considering HSV space, a case where color space compression is performed for the entire space will be described. Here, atan (x) is a function for obtaining the arc tangent of x. Further, sqrt (x) is a function for obtaining √x.

2. Color Matching Processing Unit The color matching processing unit 402 in the printer correction processing unit 302 compresses an area that cannot be reproduced by the printer 108 in the color reproduction space (monitor gamut) of the display device 109, so that the printer 108. Are associated with points in the color reproduction space (printer gamut). That is, the RGB 8-bit data processed by the color matching processing unit 402 is converted into R′G′B ′ 8-bit data corresponding to points on the printer color reproduction space.

  Specifically, the color matching processing unit 402 performs conversion from the RGB color signal space of the display device 109 to the R′G′B ′ color signal space of the printer 108 according to the following procedure.

  In the color matching processing unit 402 shown in FIG. 4, for example, the color L is maintained while maintaining the lightness L * so that the monitor RGB gamut is inside the printer R′G′B ′ gamut in the L * a * b * space. Compression is performed by performing processing such as lowering the degree S (= sqrt (a ** a * + b ** b *)). An example of this compression processing is shown in FIG.

  FIG. 6 is a diagram conceptually showing gamut compression in the saturation (S) direction on the SV plane. That is, the set of L * a * b * values in the printer gamut corresponding to the monitor RGB values is obtained. When the monitor gamut after compression fits in the printer gamut, for example, the color difference ΔE (= sqrt ((L * ′ − L *) 2+ (a * ′ − a *) 2+ (b * ′ − b *) 2 )) Is minimized so that a set of monitor (R, G, B) and printer (R ′, G ′, B ′) is determined by using L * a * b * value as a key. The printer R′G′B ′ value corresponding to the value can be determined. Of course, the color matching processing unit 402 can be realized by using a LUT (Look Up Table).

  In this embodiment, since the size of the printer gamut differs depending on the type of recording medium (medium), a plurality of matching tables are held in the matching table unit 407 as LUTs for each medium.

3. Color Separation Processing Unit Next, processing in the color separation processing unit 403 in the printer correction processing unit 302 will be described.

  In the color separation processing unit 403, the 8-bit signal of each color converted into R′G′B ′ for the printer by the color matching processing unit 402 is converted into an 8-bit signal value of CMYK corresponding to the ink color of the printer. Convert. As a method for converting a color signal from R′G′B ′ to CMYK, for example, a method by color masking is known. The color conversion method by this color masking is shown in the following formula.

これら数式を演算することにより、ＣＭＹ値が得られる。尚、Ｋ（ブラック）の信号値の決定方法としては様々な方法がある。例えば、上記行列式における最右辺を、そのベクトル要素のそれぞれからＫ値を引いたベクトル［Ｄｒ−ＫＤｇ−Ｋ Ｄｂ−Ｋ］ｔに置き換え、インク量に対応する各色信号値ＣＭＹが常に正または０であるという条件を利用してＫ値に拘束を加えつつ、試行鎖誤的にマスキングマトリクスを求めることにより、Ｋ値を決定することができる。尚、色分解処理部４０３をＬＵＴを使用して実現することももちろん可能である。

By calculating these mathematical formulas, CMY values can be obtained. There are various methods for determining the K (black) signal value. For example, the rightmost side in the determinant is replaced with a vector [Dr-KDg-K Db-K] t obtained by subtracting the K value from each of the vector elements, and each color signal value CMY corresponding to the ink amount is always positive or 0. The K value can be determined by obtaining the masking matrix erroneously in the trial chain while constraining the K value using the condition that Of course, the color separation processing unit 403 can be realized by using an LUT.

  In the present embodiment, since the appropriate ink amount varies depending on the type of media, the color separation table unit 408 holds a plurality of color separation tables as LUTs for each medium.

4). Output Gamma Correction Processing Unit Next, processing in the output gamma correction processing unit 404 in the printer correction processing unit 302 will be described.

  In the output gamma correction processing unit 404, CMYK 8-bit data output by sequentially converting the color signal of the input image in the color matching processing unit 402 and the color separation processing unit 403 is processed in the subsequent halftone processing unit 405. The data is converted into data, and C′M′Y′K ′ 8-bit data is output. The halftone processing unit 405 performs adjustment using a one-dimensional LUT for each ink in order to compensate for nonlinear characteristics with respect to lightness.

  In the present embodiment, since the non-linear characteristic of brightness varies depending on the type of media, the gamma correction table unit 409 holds a plurality of gamma correction tables as LUTs for each medium.

5. Halftone Processing Unit Next, processing in the halftone processing unit 405 in the printer correction processing unit 302 will be described.

  In the halftone processing unit 405, C′M′Y′K ′ each of 8 bits, which is sequentially converted by the color matching processing unit 402, the color separation processing unit 403, and the output gamma correction processing unit 404 from the color signal of the input image, is output. Data is converted into 2-bit data for each of C "M" Y "K" that can be printed by the printer.

  In this halftone processing method, for example, a Bayer-type 16 × 16 matrix is assigned to the input C′M′Y′K ′ image, and pixel values on the image corresponding to the elements of the matrix are assigned. This is realized by setting 1 when the value is large and 0 when the pixel value is equal to or less than the element of the matrix. In addition, an error diffusion method or the like can be used as another halftone processing method.

  The 2-bit data of C "M" Y "K" that can be printed by the printer thus obtained is sent to the printer 108 and an image is formed on the medium.

6). Table by Media The tables prepared for each type of media are stored in the matching table unit 407, the color separation table unit 408, and the gamma correction table unit 409, respectively. In the matching table unit 407, a table is prepared for each size and shape of the media color reproduction space (gamut). In the color separation table unit 408, a table is prepared for each ink ejection amount of media. In the gamma correction table unit 409, a table is prepared for each media characteristic.

  A table corresponding to the media type specified at the time of printing is selected by the paper type input unit 410 from the plurality of tables.

7. Addition of Secondary Color Editing Color Separation Table Processing for adding the secondary color editing color separation table in the above-described image forming system will be described with reference to FIG.

  Step S701: The maximum ink hit amount of the target medium is input by the ink hit amount input unit 414.

  Step S702: The secondary color chart generation unit 415 generates image data of the secondary color chart (FIG. 8) from the ink ejection amount input in step S701, and passes through the halftone processing unit 405 and the image signal output unit 406. The printer 108 forms an image on the target medium. When the maximum ink ejection amount is 180% (when the maximum primary color amount is 100%), the primary color configuration of each patch in the secondary color chart is set in a table as shown in FIG.

  Step S703: The target medium on which the secondary color chart is formed is visually checked, and the ratio of primary colors constituting the secondary colors of RGB is determined. FIG. 10 conceptually shows the change of the hue of the secondary color depending on the ratio of the primary color of R on the a * b * plane. To make the hue of R more than M, select R1, and to make it more Y, select R5.

Step S704: The secondary color component value input unit 412 inputs the ratio of the primary color that constitutes the secondary color determined in step S703. Specifically, the patch number of the secondary color chart (FIG. 8) is input to each of RGB, and the ratio of each color is obtained from the table of FIG. Example (R2, G3, B5)
Step S705: The color separation table generation unit 413 generates a secondary color edit color separation table from the maximum ink ejection amount of the target medium and the ratio of the primary colors constituting the secondary color. As an example of the generation method, it is obtained by performing interpolation calculation at a ratio of a new secondary color based on a color separation table of 200% printing.

  Step S706: The secondary color edit color separation table generated in step S705 is registered in the color separation table unit 408.

  Through the above steps, processing for adding a secondary color edit color separation table is performed.

(Other embodiments)
In the above-described embodiment, the case where ink is used as a color material has been described as an example. However, it goes without saying that the present invention can be similarly applied to other color materials such as toner.

  A storage medium storing software program codes for realizing the functions of the above-described embodiments is supplied to a system or apparatus, and a program code stored in the storage medium by a computer (or CPU or MPU) of the system or apparatus It goes without saying that the object of the present invention can also be achieved by reading and executing. In this case, the program code itself read from the storage medium realizes the novel function of the present invention, and the storage medium storing the program code constitutes the present invention.

  As a storage medium for supplying the program code, for example, a flexible disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a CD-R, a magnetic tape, a nonvolatile memory card, a ROM, or the like can be used.

  In addition, the functions of the above-described embodiments are realized by executing the program code read by the computer, and the OS running on the computer is part of the actual processing based on the instruction of the program code. Alternatively, the functions of the above-described embodiment can be realized by performing all of them and performing the processing.

  Further, after the program code read from the storage medium is written to a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, the function expansion is performed based on the instruction of the program code. The CPU or the like provided in the board or the function expansion unit performs part or all of the actual processing, and the functions of the above-described embodiments can be realized by the processing.

  The invention of the present application is also applied to a case where the program is distributed to a requester via a communication line such as personal computer communication from a storage medium in which the program code of the software realizing the functions of the above-described embodiments is recorded. Needless to say, you can.

1 is a diagram illustrating an example of a hardware configuration of an image forming system according to an embodiment. 2 is a diagram illustrating an example of a software configuration of an image processing apparatus 100. FIG. 3 is a diagram schematically illustrating an internal processing configuration of a printer driver 208. FIG. 3 is a diagram illustrating an example of a detailed block configuration of a printer correction processing unit 302. FIG. It is a figure for demonstrating the difference of the color reproduction space of a printer, and the color reproduction space of a display apparatus. It is a figure which shows notionally the gamut compression to a saturation (S) direction in SV plane. It is a flowchart explaining the flow of a secondary color edit color separation table addition process. It is a figure which shows an example of a secondary color chart. FIG. 9 is a diagram illustrating a primary color configuration table for each patch in the secondary color chart of FIG. 8. It is a figure which shows notionally the change of the hue of the secondary color by the ratio of a primary color in an a * b * plane.

Claims (4)

An ink ejection amount input means for inputting the ink ejection amount of the recording medium;
A secondary color chart generating means for generating a secondary color chart composed of a plurality of patches in which the ratio of the primary color constituting the secondary color is changed from the ink shot amount of the recording medium;
Secondary color component value input means for inputting a proportion of primary colors constituting the secondary color;
An image comprising: a color separation table generating unit configured to generate a color separation table for converting an image signal into an ink signal from an ink ejection amount of the recording medium and a ratio of a primary color constituting the secondary color. Processing equipment.   The image processing apparatus according to claim 1, wherein an ink ejection amount of the recording medium is less than twice a maximum amount of primary colors.   2. The image processing according to claim 1, wherein the secondary color chart patches are numbered, and the secondary color component value input means sets the primary color ratio by designating the number. apparatus. Inputting the amount of ink to be printed on the recording medium;
Generating and printing a secondary color chart composed of a plurality of patches in which the ratio of the primary color constituting the secondary color is changed from the ink ejection amount of the recording medium;
A step of visually determining a ratio of a primary color constituting the secondary color from the secondary color chart; a step of inputting a ratio of the primary color constituting the secondary color; an ink ejection amount of the recording medium; And a step of generating a color separation table for converting an image signal into an ink signal from a ratio of primary colors constituting a secondary color.

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