JP2006086708A - Image processing method and image processor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processing method and an image processor which attain a high definition monochromatic photograph print by reducing color rolling which is considered as important in the field of monochromatic photograph. <P>SOLUTION: The image processing method in an image forming apparatus provided with a plurality of chromatic color recording materials, and one or more achromatic color recording material comprises a color separation process of at least two steps. In the second and subsequent steps of color separation process, available quantity of the chromatic color recording material is limited to one half or less of available quantity of the black recording material. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image processing method and apparatus for achieving high-quality printing. In particular, in the field of monochrome photography, color tone is regarded as important, and the present invention relates to high-precision printing technology that does not cause a color shift in one image.

  In the case of a color inkjet printer as an example of a color output device, an image can be expressed by three colors of cyan (C), magenta (M), and yellow (Y), or four colors including black (BK). Many. In recent years, for the purpose of higher image quality, a system capable of monochrome printing depending on settings has been proposed.

A monochrome printing technique in a color inkjet printer has been proposed (Patent Document 1). With this technology, BK recording materials are used predominantly, and one or two color recording materials are used as toning components, so that a system that can use both color printing and monochrome printing can be used in multiple colors. Even in an apparatus equipped with multi-gradation ink, a high-quality print can be obtained even when printing a monochrome photograph in which color tone is regarded as important.
Japanese Patent Application No. 2004-024841

  However, the above technique is divided into at least two or more stages (γ correction, post-processing) as shown in the flow chart of FIG. 1, and C, M, Y, lc (light C), lm (light M) ), When image processing is performed in a system that operates a recording material such as BK, the accuracy of processing for operating toning components C, M, and Y is low.

  The present invention has been made to solve the above problems, and provides an image processing method and apparatus capable of reducing color shift, which is important in the field of monochrome photography, and obtaining a high-quality monochrome photograph print. With the goal.

  In order to achieve the above object, in the present invention, image processing in an image forming apparatus comprising a plurality of chromatic recording materials and one or more achromatic recording materials including black and having at least two or more color separation processing steps. The method is characterized in that the usable amount of the chromatic recording material is limited to half or less of the usable amount of the black recording material after the second stage of the color separation process.

  As described above, according to the present invention, it is possible to control the recording material of the toning component more precisely, and it is possible to perform high-quality printing when printing a monochrome photograph in which color tone is regarded as important. Become.

  The above embodiments are examples for explaining the present invention, and are not described to limit the present invention.

  Examples of the prior art will be described below with reference to the drawings.

  FIG. 6 shows a flow of print mode selection and printing in the prior art example. First, in step 1, the user selects a print mode. In this example, there are two types, “color mode” and “monochrome mode”.

  "Color mode" is a print mode for printing normal color photographs, etc., and printing is performed using 6 colors of recording materials such as normal dark, light and black, and recently using 7 or 8 colors including special colors. I do.

  On the other hand, “monochrome mode” is a mode suitable for printing monochrome photographs, and at least in this example, is a mode for selecting a color separation table optimized for monochrome photograph printing.

  The printing mode selected in step 1 is subjected to color processing and quantization in steps 2 and 3 according to the flow shown in FIG. For each mode, the color conversion processing parameters are mode specific. Thereafter, printing is performed in step 4.

  FIG. 1 is a block diagram for explaining image processing. Input 8-bit (256 gradations) image data for each RGB color is converted into 1 bit for each color of C, M, Y, lc, lm, and BK (whether a dot is hit or not) It is a processing flow to output as data.

  Input an image at the beginning of the system (101). However, in the monochrome mode, a coefficient is calculated from the luminance of each color of R, G, and B by a known method, and the result is converted into data having luminance information such that R = G = B.

  The pre-stage color conversion processing (102) is a three-dimensional LUT containing the relationship of mapping the color gamut reproduced by the image data R, G, B of the sRGB standard into the color gamut reproduced by the printer of this printing system. In addition, using this together with a known interpolation operation, data conversion is performed to convert 8-bit image data R, G, and B into data R ′, G ′, and B ′ within the printer color gamut.

  The post-stage color conversion process (103) is based on the data R ′, G ′, and B ′ to which the color gamut is mapped, and the color separation data C, M, and C corresponding to the combination of inks that reproduce the color represented by the data. Processing for obtaining Y, K, lc, and lm is performed. This process is performed by using a three-dimensional LUT together with an interpolation operation as in the previous stage color conversion process. Hereinafter, this three-dimensional LUT is referred to as a “back table”.

  The γ correction (104) performs gradation value conversion for each color data of the color separation data obtained by the subsequent color conversion processing (103). Specifically, by using a one-dimensional LUT corresponding to the gradation characteristics of each color ink of the printer used in this system, conversion is performed so that the color separation data is linearly associated with the gradation characteristics of the printer. . This one-dimensional LUT is hereinafter referred to as a “γ correction table”.

  This color recording apparatus is a binary recording apparatus, and the data obtained by the γ correction is quantized into binary data for each color by the next quantization processing unit (105). As the quantization method, a conventionally known error diffusion method or dither method is used.

  Using the data thus obtained, printing is performed by the printing unit (106). In addition, if these processing flows use bit extension technology such as JP-A-11-339032, it is possible to perform printing with more excellent gradation.

  In the following, it is assumed that printing is performed in the monochrome mode. FIG. 4 is a post-processing table. Originally, the post-processing table is three-dimensional, but in order to show an example assuming a monochrome mode, a one-dimensional diagram in which R = G = B is shown. In the technique of Japanese Patent Application No. 2004-024841, the BK recording material is predominantly used in monochrome photography, and one or two of C, M, Y recording materials are used as the toning component to achieve high image quality printing. Has achieved. Therefore, the amount of C, M, and Y recording materials used is extremely small compared to black recording materials. In this example, BK is dominantly used and Y is used as a toning component.

  FIG. 2 is a graph showing the contents of the one-dimensional table of γ correction (104). The method for creating the one-dimensional table is described in detail in Japanese Patent Publication No. 8-2659 and Japanese Patent Application Laid-Open No. 2004-104436, and the details thereof are omitted.

  The horizontal axis of the graph of FIG. 2 is the color separation data output from the post-stage color conversion process (103) and input to the γ correction, and here it is data that can represent 256 gradations from 0 to 255.

  The vertical axis of the graph is the output of γ correction (104), which is data to be passed to the quantization process (105). Here, it is assumed that the output can express 4081 gradations from 0 to 4080.

  Incidentally, the design of the quantization table, the γ correction table, the subsequent table, the previous table, and the like possessed by each of the image processing flows in FIG. 1 is normally created in the opposite direction to the processing flow. In other words, the quantization table is designed first, and when completed, the γ correction table is designed next, and then the subsequent table and the previous table are designed in this order. This is because the matters determined in the later flow table cannot be overturned in the previous flow. For example, the signal value of γ correction is 0 to 4080, and up to 4080 can be passed to the quantization process. However, if the maximum value is set to 3968 in the γ correction table, how hard you do in the subsequent color conversion process However, the maximum value cannot be passed to the quantization process.

  FIG. 4 shows a post-processing table, and in this example, Y is used as the toning component because printing with BK alone is bluer than the target gray color. Since BK is dominantly used and Y is a simple toning component, Y is a signal value of the post-processing, and up to 70 is used.

  FIG. 2 shows a γ correction table. Here, the signal value that has passed through the subsequent processing flow of FIG. 4 corresponds to the horizontal axis of FIG. Since Y of the latter stage signal value is only used up to 70, the output of Y for γ correction is 810 at the maximum. At this time, although there are 256 gradations from 0 to 255 in the subsequent processing, only 71 gradations from 0 to 70 can be used.

  Embodiments of the present invention will be described below with reference to the drawings.

  This embodiment is performed after designing the quantization table, the γ correction table, and the subsequent table on the system of the above prior art example. Therefore, in this embodiment, as in the above-described prior art example, the printing mode selection and printing flow as shown in FIG. 6 and the image processing flow as shown in FIG. 1 are provided, and output in the monochrome mode is performed. Since the description of each processing unit is the same as that of the prior art example, a description thereof is omitted. In this embodiment, BK is dominantly used and Y is used as a toning component.

  FIG. 2 shows a γ correction table of the above prior art example, and FIG. 4 shows a subsequent table. Here, the combination of the γ correction table of FIG. 2 and the subsequent table of FIG. 4 is referred to as “conventional table combination”, and in the present embodiment, these tables have already been designed by conventional techniques and known methods. Assumes that.

  In this “conventional table combination”, since the maximum value of the latter stage of Y is only 70, the output of Y γ correction is 810 at the maximum. At this time, although there are 256 gradations from 0 to 255 in the subsequent processing, only 71 gradations from 0 to 70 can be used. Therefore, a γ correction table is newly created so that the maximum value of Y in the γ correction table (4080 in FIG. 2) becomes 810. Since the method for creating the γ correction table is described in detail in Japanese Patent Publication No. 8-2659 and Japanese Patent Application Laid-Open No. 2004-104436 as described above, the details thereof are omitted. Then, the γ correction table as shown in FIG. 3 is completed. The subsequent table is also changed accordingly. Specifically, in `` conventional table combination '', the relationship between the input to the subsequent color conversion process (horizontal axis in FIG. 4) and the output of the γ correction (vertical axis in FIG. 2) is not disrupted. Create a subsequent table that matches the correction table. The completed rear table is as shown in FIG. Here, the combination of the tables in FIG. 3 and FIG. 5 is referred to as a “table combination of the present technology”.

  For example, if the signal value input from the previous-stage color conversion process in the “conventional table combination” (the horizontal axis in FIG. 4) is 150, the output of the subsequent-stage color conversion process (the vertical axis in FIG. 4 and the horizontal line in FIG. (Axis) is 32, and the output of γ correction (vertical axis in FIG. 2) is 380.

  Similarly, if the signal value (horizontal axis in FIG. 5) input from the previous color conversion process is 150 in the “table combination of this technology”, the output of the subsequent color conversion process (vertical axis in FIG. The horizontal axis (3) is 128, the output of γ correction (vertical axis in FIG. 3) is 380, and the relationship that the input of the subsequent color conversion processing is 150 and the output of γ correction is 320 is not broken. If the γ correction table is re-created, if it is not convenient to have a numerical value of 380, it may be a subsequent table that is an approximate value. Here, the point of the present invention is that a recording material other than BK (Y in this embodiment) is remade, and γ is not changed in the γ correction table and the subsequent table.

  Explaining how to create the latter table as described above, first, the signal value (horizontal axis in FIG. 4) input from the previous stage color conversion process of `` conventional table combination '' and the output of γ correction (vertical axis in FIG. 2) ) As a two-dimensional matrix. Next, the output of the γ correction table (Fig. 3) newly created by changing the maximum value (Fig. 3 vertical axis) is the output of the γ correction of the `` conventional table combination '' (vertical axis of Fig. 2). A subsequent color conversion processing signal value that matches (or approximates) is searched from the matrix. In this way, the rear table as shown in FIG. 5 is completed.

  Based on the completed latter table shown in FIG. 5, the latter table is further redesigned. In the “conventional table combination”, only 71 gradations of 0 to 70 can be used for the latter stage signal value. However, if the newly created γ correction table (Fig. 3) is used, the latter stage signal is assigned to the 256th floor from 0 to 255. Can be used. That is, the change in the usage amount of the Y recording material when the signal value of the latter table is moved by 1 is reduced. That is, the post-stage color conversion processing unit can control the Y recording material finer than before, and can perform more precise monochrome tone design and color reproduction. Furthermore, there is almost no deviation in the color already designed in the subsequent stage table of the prior art because the relationship between the input to the subsequent stage color conversion process and the output of the γ correction is not disturbed. It became possible to make the control at the time of designing the latter table more precise.

  In this embodiment, the BK recording material is predominantly used, and the toning is performed only with the Y recording agent, but even if a plurality of toning components (for example, C, M, etc.) are used, a γ correction table and a subsequent table are provided for each color. If it is set by the above method, it is possible to cope with the same.

  In Example 1, the γ correction table was created so that the maximum value of Y in the γ correction table was 810. In the present embodiment, this is not set to 810 but is set to 972 with a margin of about 20%. By creating with sufficient margin in this way, it is possible to cope with the case where the amount of Y recording material used has to be increased when the latter table is designed again.

It is a figure which shows an image processing flow. It is a figure which shows the gamma table of a prior art. It is a figure which shows the (gamma) table used in 1st Embodiment. It is a figure which shows the back | latter stage table of a prior art. It is a figure which shows the back | latter stage table used by 1st Embodiment. It is a figure which shows the flow of printing mode selection and printing.

Claims (5)

An image processing method in an image forming apparatus comprising a plurality of chromatic recording materials and one or more achromatic recording materials including black, and having at least two or more color separation processing steps,
An image processing method characterized in that the usable amount of the chromatic recording material is limited to half or less of the usable amount of the black recording material in the second and subsequent stages of the color separation processing step. An image processing method in an image forming apparatus comprising a plurality of chromatic recording materials and one or more achromatic recording materials including black, and having at least two or more color separation processing steps,
The usable amount of the chromatic recording material is limited to half or less of the usable amount of the black recording material in the second and subsequent stages of the color separation process, and the usable amount of the chromatic recording material 2. The image processing method according to claim 1, wherein the image processing method is limited to 20% or less of the maximum amount used in the first decomposition processing step. An image processing method in an image forming apparatus comprising a plurality of chromatic recording materials and one or more achromatic recording materials including black, and having at least two or more color separation processing steps,
The usable amount of the chromatic recording material is limited to half or less of the usable amount of the black recording material in the second and subsequent steps of the color separation process, and the usable amount of the chromatic recording material is a color. An image processing method characterized by limiting to the maximum amount used in the first decomposition processing step.   2. The mode selection unit according to claim 1, further comprising mode selection means for selecting a color image or a monochrome mode of the output image, wherein the restriction is effective only when the monochrome mode is selected. Image processing method. An image forming apparatus comprising a plurality of chromatic recording materials and one or more achromatic recording materials including black, and comprising at least two or more color separation processing steps,
An image processing apparatus that limits the usable amount of the chromatic recording material to a half or less of the usable amount of the black recording material after the second stage of the color separation process.

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