JP2014072860A - Image processing apparatus and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent reduction in color saturation and deterioration of level difference in gradation, even when the total amount of color materials becomes large.SOLUTION: A total amount calculation unit 20 determines, on the basis of an input color signal comprising a plurality of color components including a black component, the total amount of toner by adding the plurality of color components for every pixel. A color component limiting unit 22, when the total amount of toner becomes equal to or more than a limit value TAC, limits the black component constituting the input color signal together with a plurality of other non-black components (CMYOV), and increasingly limits the black component as the total amount of toner becomes larger.

Description

  The present invention relates to an image processing apparatus and a program.

  In an image forming apparatus using a color material (recording material) such as toner or ink, if the total color material amount per pixel exceeds a limit value (for example, 300%), poor fixing of the color material or scattering of the color material may occur. May occur, resulting in degradation of image quality, damage to the apparatus body, and the like. Therefore, the total color material amount is calculated in units of one pixel, and when the total color material amount exceeds the limit value, a process of reducing the total color material amount may be performed.

  For example, in Patent Document 1 below, in an image forming apparatus using four color materials of cyan (C), magenta (M), yellow (Y), and black (K), a decrease in lightness due to a reduction in the total amount of color materials. In order to prevent this, an image forming apparatus that reduces the amount of CMY color material while maintaining the ratio of the amount of CMY color material without changing the amount of black (K) color material is disclosed.

JP 2004-21202 A

  By the way, in order to expand the color gamut, in addition to the basic colors CMYK, for example, special color materials such as orange (O), green (G), violet (V), etc. are used, and 6 colors (CMYKOV) and 7 colors are used. An image may be formed with a color material of (CMYKOGV). When 6-color (CMYKOV) or 7-color (CMYKOGV) color materials are used, the total color material amount per pixel is larger than when using 4-color (CMYK) color materials and easily exceeds the limit value. As the number of color components increases, the amount of color material to be reduced also increases.

  For example, when the color material amount of color components other than black (K) is reduced with respect to 6 color (CMYKOV) or 7 color (CMYKOGV) color materials, the reduction amount of the color material increases, and a special color such as OGV Despite the use of color materials, there is a risk that the saturation will decrease. Further, if the amount of the color material other than black (K) is reduced, the gradation step near the limit value becomes large, and the gradation smoothness may be reduced.

  An object of the present invention is to provide an image processing apparatus and program capable of preventing a decrease in saturation and a deterioration in gradation level even when the total amount of color materials is limited.

  The invention according to claim 1 is a total amount calculating means for obtaining a total amount of color material by adding the plurality of color components for each pixel based on an input color signal composed of a plurality of color components including a black component; A color component that restricts the black component that constitutes the input color signal together with a plurality of other non-black components when the total amount of material exceeds a total amount limit value, and restricts the black component to a greater extent as the total amount of color material increases And an restricting unit.

  The invention according to claim 2 is the image processing apparatus according to claim 1, wherein the color component limiting means limits each color component while maintaining a ratio of non-black components.

  The invention according to claim 3 is the image processing apparatus according to claim 1 or 2, wherein the plurality of color components include a basic color component including a black component and one or a plurality of spot color components. It is characterized by that.

  The invention according to claim 4 is the image processing apparatus according to any one of claims 1 to 3, wherein the black component is not limited when the total amount of the color material is equal to or greater than the total amount limit value. A lightness priority restriction mode for restricting a plurality of non-black components, and a saturation priority restriction mode for restricting both the black component and the plurality of non-black components when the total amount of the color material is equal to or greater than the total amount restriction value. It further has mode selection means for selecting.

  The invention according to claim 5 is a computer for obtaining a total amount of color material by adding the plurality of color components for each pixel based on an input color signal composed of a plurality of color components including a black component; A step of restricting the black component constituting the input color signal together with a plurality of other non-black components when the total amount of color material exceeds a total amount limit value, and restricting the black component to a greater extent as the total amount of color material increases And a program for executing the above.

  According to the first and fifth aspects of the invention, even when the total amount of the color material is limited, a decrease in saturation and a deterioration in gradation level are prevented as compared with the case where the configuration of the present invention is not provided. It becomes possible.

  According to the second aspect of the present invention, changes in color reproducibility such as color balance and hue are reduced as compared with the case where the configuration of the present invention is not provided.

  According to the third aspect of the present invention, even when the input color signal includes a special color in addition to the basic color, the saturation and the gradation level difference are reduced as compared with the case where the input color signal does not have the configuration of the present invention. Deterioration can be prevented.

  According to the invention which concerns on Claim 4, it becomes possible to perform the process according to the case where priority is given to the reproducibility of saturation or brightness.

It is a block diagram which shows an example of the image processing apparatus which concerns on embodiment of this invention. 6 is a flowchart illustrating an example of toner total amount adjustment processing. 6 is a graph illustrating an example of a black amount adjustment rate α with respect to a total toner amount. It is a graph for demonstrating color reproducibility. 6 is a graph for explaining gradation with respect to the total amount of toner.

  FIG. 1 shows an example of an image processing apparatus according to an embodiment of the present invention. The image processing apparatus 10 receives the image data, performs image processing, and outputs the image data subjected to the image processing to the image forming apparatus 30.

  The image forming apparatus 30 has a function of forming and outputting an image corresponding to image data on a recording medium such as recording paper using a color material (recording material) such as toner or ink. For example, the image forming apparatus 30 forms an image by applying an electrophotographic process using toners of basic colors and special colors. As an example, the image forming apparatus 30 forms an image using toner of each color of cyan (C), magenta (M), yellow (Y), black (K), orange (O), and violet (V). Specifically, the image forming apparatus 30 receives the data of each color component of CMYKOV as print data, and scans and exposes the photosensitive drum, which is an image carrier, in accordance with each data. Then, an electrostatic latent image is formed and developed using each color toner of CMYKOV to form each color toner image. Then, the image forming apparatus 30 transfers the toner image while superimposing the toner image on the recording medium, and melts and fixes the toner image on the recording medium by performing heating and pressurizing processes. As a result, an image corresponding to the image data is formed on the recording medium. In this embodiment, as an example, a case where an image is formed using CMYKOV six-color toners will be described. However, as another example, green (G) may be used as a special color, or CMYKOGV, CMYKRGB, or the like. An image may be formed using seven colors of toner.

  The image processing apparatus 10 includes an image receiving unit 12, a color conversion unit 14, a limit value setting unit 16, and a total toner amount limiting unit 18. The total toner amount limiting unit 18 includes a total amount calculating unit 20 and a color component limiting unit 22.

  The image reception unit 12 receives input of image data to be printed. For example, image data represented by a combination of RGB (red, green, blue), image data represented by a combination of CMYK (cyan, magenta, yellow, black), and the like are input to the image receiving unit 12. The The image receiving unit 12 may be input with image data represented by a combination of CMYKOGV (cyan, magenta, yellow, black, orange, green, violet), image data represented by CMYKOV, and the like.

  The color conversion unit 14 functions as a color management system (CMS), and converts the image data received from the image receiving unit 12 into data of a device color space that is a color space depending on the image forming apparatus 30. As an example, when the device color space of the image forming apparatus 30 is a CMYKOV color space, the color conversion unit 14 converts the image data received from the image reception unit 12 into CMYKOV color space data (hereinafter referred to as a CMYKOV color signal). To be converted). For example, when the image data received by the image receiving unit 12 is RGB color space data (RGB color signal), the color conversion unit 14 performs a multidimensional lookup table (multidimensional LUT) on the RGB color signal. Are converted into CMYKOV color signals, which are data in the device color space. When the image data received by the image receiving unit 12 is CMYK color space data (C ″ M ″ Y ″ K ″ color signal), or CMYKOV space data (C ″ M ″ Y ″). K "O" V "color signal), the color conversion unit 14 performs C" M "Y" K "color signal and C" M "Y" K. The “O” V ”color signal is converted into a CMYKOV color signal which is data in the device color space. Then, the color conversion unit 14 outputs the CMYKOV color signal after color conversion to the total toner amount limiting unit 18. The CMYKOV color signal input to the total toner amount limiting unit 18 corresponds to an example of the input color signal.

  As another example, the color conversion unit 14 converts image data such as RGB color signals into data in a device-independent color space (eg, L * a * b * color space) such as CIELAB using a multidimensional LUT. (L * a * b * signal), and the L * a * b * signal may be converted into a CMYKOV color signal, which is image data in the device color space, using a multidimensional LUT.

  The limit value setting unit 16 outputs the limit value TAC for the total amount of toner in one pixel unit to the total toner amount limiting unit 18. The limit value TAC of the total toner amount is a predetermined value. For example, when the maximum toner output value of each color of CMYKOV is 100%, it is set to 240% to 280%. Note that the value of the limit value TAC is an example, and a value of about 300% may be set.

  The total amount calculation unit 20 calculates a total toner amount H (H = C + M + Y + K + O + V) that is the sum of the CMYKOV color signals output from the color conversion unit 14 for each pixel.

  When the total toner amount H is equal to or greater than the limit value TAC, the color component limiting unit 22 limits the toner amount of black (K) and limits the toner amount of color components (CMYOV) other than black (K). For example, the color component limiting unit 22 adjusts the K color signal so that the toner amount of black (K) decreases as the total toner amount H increases (the signal sum increases). Further, the color component limiting unit 22 maintains the toner amount ratio of the color components (CMYOV) other than black (K) based on the adjusted K color signal and the limit value TAC, and the sum of the CMYKOV color signals ( The CMYOV color signal is adjusted so that the total toner amount is less than the limit value TAC.

  The detailed processing of the total toner amount restriction unit 18 will be described with reference to the flowchart shown in FIG.

  First, the total amount calculation unit 20 receives the CMYKOV color signal from the color conversion unit 14, and obtains the total toner amount H (H = C + M + Y + K + O + V) that is the sum of the CMYKOV color signals for each pixel (S01).

  Next, the color component limiting unit 22 determines the black amount adjustment rate α (≦ 100%) (black adjustment rate α) for adjusting the black (K) toner amount based on the total toner amount H (S02). .

  Here, the relationship between the total toner amount H and the black amount adjustment rate α will be described with reference to FIG. As an example, the black amount adjustment rate α is expressed by a function using the total toner amount H as a variable. Graphs 100 and 110 shown in FIG. 3 show the black amount adjustment rate α according to the present embodiment, and a graph 120 shows the black amount adjustment rate α as a comparative example. As shown in the graphs 100 and 110, when the total toner amount H is less than the limit value TAC (for example, 250%), the black amount adjustment rate α is set to 100%, and when the total toner amount H is equal to or greater than the limit value TAC, it is determined in advance. In accordance with the negative inclination, the black amount adjustment rate α is set to be smaller as the total toner amount H increases. In the comparative example, as shown in the graph 120, the black amount adjustment rate α is maintained constant (100%) regardless of the total toner amount H. For example, information indicating the correspondence between the total toner amount H and the black amount adjustment rate α is stored in advance in a storage device (not shown), and the color component limiting unit 22 adjusts the black amount with respect to the total toner amount H based on the information. Determine the rate α.

Then, the color component limiting unit 22 obtains the K ′ color signal after the toner amount adjustment by multiplying the K color signal received from the color conversion unit 14 by the black amount adjustment rate α according to the following equation (1). (S03).
K ′ = (α / 100) × K (1)

  Thus, when the total toner amount H is less than the limit value TAC, the K ′ color signal after toner amount adjustment is equal to the K color signal after color conversion, and when the total toner amount H is equal to or greater than the limit value TAC, the total toner amount H As the amount of toner increases, the K ′ color signal after toner adjustment becomes smaller and the amount of black (K) toner is further reduced.

Next, the color component limiting unit 22 maintains the ratio of CMYOV color signals other than black (K) (the ratio of the CMYOV toner amount) based on the K ′ color signal after the toner amount adjustment and the limit value TAC. Meanwhile, the CMYOV color signal is obtained so that the sum of the CMYKOV color signals is less than the limit value TAC (S04). Specifically, the color component limiting unit 22 obtains an adjustment coefficient n by subtracting the K ′ color signal after toner adjustment from the limit value TAC according to the following equation (2), and each color signal for the sum of the CMYOV signals: Is multiplied by an adjustment coefficient n to obtain a C′M′Y′O′V ′ color signal after toner amount adjustment.
Formula (2):
n = TAC-K ′
C ′ = n × C / (C + M + Y + O + V)
M ′ = n × M / (C + M + Y + O + V)
Y ′ = n × Y / (C + M + Y + O + V)
O ′ = n × O / (C + M + Y + O + V)
V ′ = n × V / (C + M + Y + O + V)
As a result, the ratio of the C′M′Y′O′V ′ color signal becomes the same as the ratio of the CMYOV color signal, and the sum of the C′M′Y′K′O′V ′ color signal is less than the limit value TAC. The C′M′Y′K′O′V ′ color signal is determined so that

  Then, the total toner amount limiting unit 18 outputs the C′M′Y′K′O′V ′ color signal after the toner amount adjustment to the image forming apparatus 30 (S05).

  The image forming apparatus 30 receives the C′M′Y′K′O′V ′ color signal after adjusting the toner amount, and displays an image with the toner amount corresponding to the C′M′Y′K′O′V ′ color signal. It is formed on a recording medium.

  As described above, when the total toner amount H is equal to or greater than the limit value TAC, the K color signal is adjusted so that the black toner amount decreases as the total toner amount H increases. The reduction amount of the color component (CMYOV) toner amount is reduced. Since the reduction amount of the toner amount of the special color (OV) is reduced, even when the total toner amount H is limited to less than the limit value TAC, the saturation is compared with the case where the configuration according to the present embodiment is not provided. Is prevented and the color gamut is prevented from being narrowed. That is, the color gamut expansion effect when the special color is used is fully utilized.

  In addition, according to the image processing apparatus 10 according to the present embodiment, it is possible to prevent a gradation step near the limit value TAC from increasing compared to the case where the configuration according to the present embodiment is not provided. The level difference is improved.

  In addition, since the ratio of the toner amount of CMYOV colors other than black (K) is maintained, there is less change in color reproducibility such as color balance and hue compared to the case where the configuration according to the present embodiment is not provided. Become.

  Note that the slope of the black amount adjustment rate α in the range where the total toner amount H is equal to or greater than the limit value TAC may be changed according to the number of toners used in the image forming apparatus 30. For example, the larger the number of toners used, the larger the negative slope of the black amount adjustment rate α, so that the black amount adjustment rate α becomes smaller. Referring to FIG. 3, as an example, when an image is formed using six colors of toner, the black amount adjustment rate α is determined according to the graph 110, and when an image is formed using seven colors of toner, The black amount adjustment rate α is determined according to the graph 120 having a larger slope than the graph 110. Since the total toner amount H is likely to increase as the number of toners used increases, the color component other than black (K) can be reduced by reducing the black amount adjustment rate α to reduce the amount of black (K) toner. The amount of toner is reduced, thereby suppressing the reduction in saturation.

  Next, referring to FIG. 4, color reproducibility according to an example and a comparative example of the present embodiment will be described. As an example, a case where a YOMK color signal is used as an input color signal and a case where a YGCK color signal is used will be described. FIG. 4 shows the lightness L * and saturation C * of the input color signal, and the results (lightness L *, saturation C *) when the processing according to the example and the comparative example is performed on the input color signal.

Here, a comparative example will be described. In the comparative example, as shown in the graph 120 of FIG. 3, the black (K) toner amount is maintained without changing the black amount adjustment rate α according to the total toner amount H. Then, while maintaining the ratio of the color components other than black (K), the signals of the color components other than black (K) are adjusted so that the total toner amount becomes less than the limit value TAC. In the comparative example, the C′M′Y′K′O′V ′ color signal after toner amount adjustment is obtained according to the following formula (3).
Formula (3):
K '= K
n = TAC-K ′
C ′ = n × C / (C + M + Y + O + V)
M ′ = n × M / (C + M + Y + O + V)
Y ′ = n × Y / (C + M + Y + O + V)
O ′ = n × O / (C + M + Y + O + V)
V ′ = n × V / (C + M + Y + O + V)

  In the comparative example, when the YOMK color signal or the YGCK color signal is used, the total toner amount is maintained while maintaining the ratio of the color components other than black (K) without changing the toner amount of black (K). The YOM color signal or the YGC color signal is adjusted so as to be less than the limit value TAC.

  Referring to the graph shown in FIG. 4, the black (K) toner amount is reduced in the embodiment, whereas the black (K) toner amount is not reduced in the comparative example. Therefore, the YOMK color signal and the YGCK color signal are not reduced. In either case, the difference in the lightness L * with respect to the input color signal is greater in the example than in the comparative example. On the other hand, the difference of the saturation C * with respect to the input color signal is smaller in the embodiment than in the comparative example in both the YOMK signal and the YGCK signal, and the reproducibility of the saturation C * is in the comparative example. The example is better than that. In this way, by reducing the toner amount of black (K) according to the total toner amount H and reducing the reduction amount of the toner amount of the color components other than black (K), the saturation C is compared with the comparative example. * High reproducibility is obtained.

  Next, with reference to FIG. 5, the gradation of the example of this embodiment and the comparative example will be described. FIG. 5 shows the coverage (halftone dot area ratio) (%) with respect to the total toner amount H (%). As an example, black (K) and orange (O) coverage is shown. According to the embodiment, in the range where the total toner amount H is not less than the limit value TAC, the difference in gradation is smaller than that in the comparative example. That is, according to the present embodiment, the difference between the black (K) and the orange (O) according to the embodiment is smaller than the difference between the black (K) and the orange (O) according to the comparative example. Becomes smaller and the gradation step is improved.

  As a modified example, the method for adjusting the amount of black (K) toner may be switched between a case where priority is given to the reproducibility of the saturation for the input color signal and a case where priority is given to the reproducibility of the lightness. As described with reference to FIG. 4, when the total toner amount H is increased, the reduction amount of the toner amount of black (K) is increased, and the reduction amount of the toner amount of color components other than black (K) is decreased. Compared to the case where the amount of black (K) toner is not reduced, the difference in saturation C * with respect to the input color signal is reduced. That is, by executing the processing according to the present embodiment, the reproducibility of the saturation C * with respect to the input color signal becomes higher than that of the comparative example. On the other hand, when the amount of black (K) toner is not reduced as in the comparative example, the difference in lightness L * with respect to the input color signal is smaller than when the amount of black (K) toner is reduced. That is, by performing the processing according to the comparative example, the reproducibility of the lightness L * with respect to the input signal becomes higher than that of the present embodiment.

  Therefore, in the modification, when priority is given to the reproducibility of the saturation with respect to the input color signal over the reproducibility of the lightness, the color component restriction unit 22 increases in accordance with the graph 100 or the graph 110 shown in FIG. The K color signal is adjusted so that the amount of black (K) toner decreases. On the other hand, when priority is given to the lightness reproducibility with respect to the input color signal over the chroma reproducibility, the color component limiting unit 22 maintains the toner amount of black (K) without reducing it according to the graph 120 shown in FIG. To do. The color component limiting unit 22 adjusts signals of color components (CMYOV) other than black (K) according to the above equation (2) based on the K ′ color signal with or without the toner amount being reduced. Accordingly, when priority is given to the reproducibility of saturation, the reduction amount of the toner amount of the color components (CMYOV) other than black (K) is reduced, and the reproducibility of the saturation is improved. On the other hand, when priority is given to lightness reproducibility, the toner amount of black (K) is maintained, the toner amount of color components other than black (CMYOV) is further reduced, and lightness reproducibility is improved.

  For example, when the total toner amount exceeds the limit value TAC, the brightness priority limit mode for limiting the toner amount of other color components (CMYOV) without limiting the toner amount of black (K), and the total toner amount is the limit value A saturation priority restriction mode for restricting the toner amounts of black (K) and other color components (CMYOV) in the case of TAC or higher is set in the image processing apparatus 10 in advance. In addition, a user interface unit (UI unit) (not shown) is provided in the image processing apparatus 10 as a mode selection unit, and the UI unit displays a selection screen for selecting a lightness priority restriction mode or a saturation priority restriction mode. The lightness priority restriction mode or the saturation priority restriction mode may be selected using the UI unit. The color component restriction unit 22 executes the process according to the present embodiment when the saturation priority restriction mode is selected, and executes the process according to the comparative example when the lightness priority restriction mode is selected.

  As described above, by switching the method of adjusting the amount of black (K) toner depending on whether reproducibility of saturation or lightness is given priority, an image that matches the user preference and the type of input color signal is formed. obtain.

  In the above-described embodiment, the case of using six-color (CMYKOV) toner has been described. However, even when five-color or seven-color toner is used, the same effect as the above-described embodiment can be obtained. Further, the image processing apparatus 10 may be included in the image forming apparatus 30.

  Note that the image processing apparatus 10 is realized by cooperation of hardware resources and software, for example. Specifically, the image processing apparatus 10 includes a processor such as a CPU (not shown). The processor reads out and executes a program stored in a storage device (not shown), thereby executing the functions of the color conversion unit 14 and the total toner amount limiting unit 18 described above. The program is stored in a storage device such as a hard disk drive (HDD) via a recording medium such as a CD or DVD, or via communication means such as a network. Note that the program may be stored in advance in a storage device such as a hard disk drive. Programs stored in a storage device such as a hard disk drive are read into a memory such as a RAM and executed by a processor, thereby realizing the functions of the color conversion unit 14 and the total toner amount limiting unit 18 described above. . Note that the functions of the color conversion unit 14 and the total toner amount limiting unit 18 may be realized only by hardware.

  DESCRIPTION OF SYMBOLS 10 Image processing apparatus, 12 Image reception part, 14 Color conversion part, 16 Limit value setting part, 18 Toner total amount restriction | limiting part, 20 Total amount calculation part, 22 Color component restriction | limiting part, 30 Image forming apparatus.

Claims (5)

A total amount calculating means for obtaining a total amount of color material by adding the plurality of color components for each pixel based on an input color signal composed of a plurality of color components including a black component;
When the total color material amount exceeds the total amount limit value, the black component constituting the input color signal is limited together with a plurality of other non-black components, and the black component is more largely limited as the total color material amount increases. Color component limiting means;
An image processing apparatus comprising: The image processing apparatus according to claim 1,
The color component limiting means limits each color component while maintaining the ratio of non-black components.
An image processing apparatus. The image processing apparatus according to claim 1 or 2,
The plurality of color components includes a basic color component including a black component and one or a plurality of spot color components.
An image processing apparatus. An image processing apparatus according to any one of claims 1 to 3, wherein
When the color material total amount is equal to or greater than the total amount limit value, the brightness priority limit mode for limiting a plurality of non-black components without limiting the black component, and the color material total amount is equal to or greater than the total amount limit value Further comprising mode selection means for selecting a saturation priority restriction mode for restricting both the black component and the plurality of non-black components.
An image processing apparatus. On the computer,
Obtaining a total amount of color material by adding the plurality of color components for each pixel based on an input color signal composed of a plurality of color components including a black component;
When the total color material amount exceeds the total amount limit value, the black component constituting the input color signal is limited together with a plurality of other non-black components, and the black component is more largely limited as the total color material amount increases. Steps,
A program characterized by having executed.

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