JP2009071695A - Image processor, image processing method, program, and storage medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the consumption of color materials during image output while preventing undesired deterioration in picture quality. <P>SOLUTION: A histogram information acquiring means 351 calculates a luminance histogram of an input RGB image and sends a dynamic range as histogram information thereupon to a color material saving processing means 352. The color material saving processing means 352 performs color material saving processing on a CMYK image after conversion by a color conversion means 350 such that as the dynamic range is larger, the color material saving processing is performed more intensely. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a device having an image output function, such as a printer or a copying machine, and more particularly to a technique for saving consumption of color materials during image output.

  In devices with image output functions such as printers and copiers, consumption of color materials such as toner and ink is saved (saved) in addition to the normal mode in which images are output with standard color material consumption. In many cases, the color material save mode for outputting an image can be selected.

  For such color material saving, for example, an image forming apparatus disclosed in Patent Document 1 is known. In this image forming apparatus, the first toner saving process is performed in which the area of the image data to be output is determined, and the calculation for halving the maximum density is applied to the character / line image area, and the photographic area is applied. A second toner saving process using dot thinning is applied. Further, the edge portion of the image data is detected, and the second toner saving process is applied to the character / line drawing area, but the application is suppressed to the edge portion.

  Further, an ink consumption reduction method and apparatus disclosed in Patent Document 2 are known. This creates a histogram of brightness (for black and white printing) or a histogram of color density for each primary color (for color printing) from the bitmap image developed from the print data, and uses this histogram to reduce ink consumption. To determine whether or not to perform density reversal processing, or use a histogram to select a color paper that requires the least amount of ink consumption, and match each primary color to the selected paper color. That is, density conversion is performed.

Japanese Patent Laid-Open No. 11-151833 JP 2004-146914 A

  Color material save mode such as printer is used mainly for the purpose of not requiring high image quality, such as checking the layout of the output image, but the image quality may cause inconvenient image quality degradation, for example, hindering the confirmation of the image content. Deterioration must be prevented. However, in the color material saving process as in Patent Document 1, depending on the characteristics of the image, the contrast may be lost, and it may be difficult to recognize what the image is.

  Therefore, an object of the present invention is to provide an image processing apparatus and method having a novel configuration capable of performing effective color material saving while suppressing image quality deterioration by performing appropriate color material saving processing according to an image. There is to do.

  The technique of Patent Document 2 uses a histogram to determine whether to implement a special color material saving method such as density reversal processing or using an output paper other than white, and controls the strength of the color material saving process. I can't do that.

  Therefore, by controlling the intensity of the color material saving process using the histogram information of the input image, it is one of the problems to be solved by the present invention to save the color material without significantly degrading the image. It is.

The invention described in claim 1
Color conversion means for converting input image data into image data of a color material signal;
Color material save processing means for performing color material save processing on the image data converted by the color conversion means;
Histogram information acquisition means for acquiring histogram information about the brightness or brightness of the input image data,
The color material saving processing means controls the intensity of color material saving processing according to the histogram information.

  Note that the strength of the color material saving process corresponds to a color material saving rate (a reduction degree of the color material consumption amount) described later. Therefore, increasing the strength of the color material saving process means increasing the color material saving rate.

According to a second aspect of the present invention, there is provided an image processing apparatus according to the first aspect of the present invention.
The histogram information is a dynamic range,
The color material saving process means is to increase the strength of the color material saving process as the dynamic range is larger.

According to a third aspect of the present invention, there is provided an image processing apparatus according to the first aspect of the present invention.
The strogram information is a dynamic range and an average or median value,
When the average value or median value is less than a predetermined value, the color material saving processing means increases the strength of the color material saving processing as the dynamic range is larger, and the average value or median value is greater than or equal to the predetermined value. The purpose is to make the color material saving process the weakest.

  The weakest color material saving process is to minimize the color material saving rate within the control range, and no color material saving is performed as described later (substantially the color material saving process is not performed). Not included).

According to a fourth aspect of the present invention, in the image processing apparatus according to the second or third aspect of the present invention,
The input image data is divided for each object,
The histogram information acquisition means acquires histogram information for an image object,
The color material saving processing means controls the intensity of the color material saving processing for the image object according to the histogram information.

A feature of the invention described in claim 5 is an image processing apparatus according to the invention described in claim 2 or 3, wherein
An image area separating means for separating the input image data into an image area and an area other than the image area;
The histogram information acquisition means acquires histogram information for an image area,
The color material saving processing means controls the intensity of the color material saving processing for the image area according to the histogram information.

According to a sixth aspect of the present invention, in the image processing apparatus according to any one of the second to fifth aspects,
The histogram information acquisition means acquires histogram information about color difference or chromaticity in addition to histogram information about luminance or brightness,
The color material saving process means controls the intensity of the color material saving process in accordance with the histogram information acquired by the histogram information acquisition means.

The invention described in claim 7
A color conversion step of converting input image data into image data of a color material signal;
A color material saving process for applying a color material saving process to the image data converted by the color conversion process;
A histogram information acquisition step of acquiring histogram information about luminance or brightness of the input image data,
In the color material saving process, the intensity of the color material saving process is controlled according to the histogram information.

A feature of the invention described in claim 8 is the image processing method according to the invention described in claim 7,
The histogram information is a dynamic range,
The color material saving process is to increase the strength of the color material saving process as the dynamic range is larger.

According to a ninth aspect of the present invention, in the image processing method according to the seventh aspect of the present invention,
The strogram information is a dynamic range and an average or median value,
When the average value or median value is less than a predetermined value, the color material saving process step increases the strength of the color material saving process as the dynamic range is larger, and the average value or median value is greater than or equal to the predetermined value. The purpose is to make the color material saving process the weakest.

According to a tenth aspect of the present invention, in the image processing method according to the eighth or ninth aspect,
The input image data is divided for each object,
The histogram information acquisition step acquires histogram information about the image object,
The color material saving process is to control the intensity of the color material saving process for the image object according to the histogram information.

A feature of the invention described in claim 11 is an image processing method according to the invention described in claim 8 or 9, wherein
An image area separation step for separating the input image data into an image area and an area other than the image area;
The histogram information acquisition step acquires histogram information for an image area,
The color material saving process includes controlling the intensity of the color material saving process for the image area according to the histogram information.

According to a twelfth aspect of the present invention, in the image processing method according to any one of the eighth to eleventh aspects,
The histogram information acquisition step acquires histogram information about color difference or chromaticity in addition to histogram information about luminance or brightness,
The color material saving process includes controlling the intensity of the color material saving process according to the histogram information acquired by the histogram information acquisition process.

  A thirteenth aspect of the invention is a program that causes a computer to execute each step of the image processing method according to any one of the eighth to twelfth aspects of the invention.

  A fourteenth aspect of the invention is a computer-readable storage medium in which a program for causing a computer to execute each step of the image processing method according to any one of the eighth to twelfth aspects is recorded.

  The influence of the color material saving process on the image quality differs depending on the distribution state of brightness or brightness in the image to be processed. Since the invention according to claims 1 and 7 controls the intensity of the color material saving process according to the histogram information about the brightness or brightness of the image, the influence on the image quality is considered for images with various brightness or brightness distributions. The color material saving process can be performed.

  Assume that the color material saving process is performed with the same intensity for an image with a large luminance or brightness dynamic range and an image with a small dynamic range. In the case of an image with a small dynamic range, there is a possibility that the color material saving process lowers the overall density and the contrast is crushed, making it impossible to recognize what the image is. On the other hand, in the case of an image with a large dynamic range, such extreme image quality deterioration is unlikely to occur, but conversely, there is a possibility that a sufficient color material saving effect cannot be obtained. Since the invention according to claims 2 and 8 increases the strength of the color material saving process as the dynamic range is larger, image quality deterioration is suppressed for an image with a small dynamic range, and sufficient color material saving effect is achieved for an image with a large dynamic range. Can be obtained.

  A bright image as a whole originally has a small amount of color material consumption, and the color material saving effect is small even when the color material saving process is performed. Further, when the strong color material saving process is performed, unacceptable image quality degradation is likely to occur. On the other hand, a dark image as a whole has a large amount of color material consumption, has a large color material saving effect due to the color material saving process, and even if a strong color material saving process is performed, the image quality is unlikely to be a problem. The invention according to claims 3 and 9 obtains an average value or a median value in addition to a dynamic range for luminance or brightness as histogram information, and the average value or median value is less than a predetermined value (when the image is dark as a whole). The color material saving process is controlled according to the dynamic range. If the average or median is greater than or equal to the specified value (when the image is bright as a whole), the color material saving process is the weakest. While suppressing deterioration of the image quality of a bright image, a sufficient color material saving effect can be obtained for a dark image as a whole.

  If the image is divided into objects such as images, characters, graphics, etc., the image object is bitmap data, so histogram information can be easily obtained. However, since the objects of characters and graphics are described by codes or commands, they are simple. Cannot acquire histogram information. In addition, as described above, the influence of the color material saving process on the image quality of the image object varies considerably depending on the distribution state of luminance or brightness. According to the fourth and tenth aspects of the present invention, in the case of an image divided into such objects, histogram information of density or lightness for the image object is acquired, and the intensity of the color material saving process for the image object is used as the histogram information. By controlling accordingly, it is possible to save the color material with the image quality degradation suppressed for the image object. It should be noted that a character or graphic object may be subjected to a color material saving process having a predetermined strength, and such a mode is naturally included in the present invention.

  According to the fifth and eleventh aspects of the present invention, image area separation is performed, and the intensity of the color material saving process for the image area is controlled according to the histogram information of the brightness or brightness of the image area. It is possible to save color material with reduced image quality degradation in the image area. Note that a region other than the image region in the image (such as a character region) may be subjected to a color material saving process having a predetermined strength, and such a mode is naturally included in the present invention.

  According to the sixth and twelfth aspects of the present invention, since the intensity of the color material saving process is controlled in accordance with the histogram information about luminance or lightness, color difference or chromaticity, more accurate color material saving is performed on the color image. be able to. For example, even if the dynamic range of the brightness is small, if the dynamic range of the color difference in the blue direction is large, it is considered that the image represents meaningful information by a change in the color in the blue direction. It is preferable to control the strength of the color material saving process according to the dynamic range of the color difference. According to the inventions according to claims 6 and 12, such control is also possible. Further, if the intensity of the color material saving process is controlled according to the average value or minimum value of the dynamic range of luminance or lightness, color difference or chromaticity, etc., it becomes easier to preserve the details of the image. According to the present invention (Claims 6 and 12), such control is also possible.

  The present invention can be widely applied to an image processing apparatus having an image output function such as a printer, a copier, and a fax machine. Here, an embodiment of the present invention will be described using a printer as shown in FIG. 1 as an example.

  1 includes a CPU 201, an NVRAM 202, a program ROM 203, a RAM 204, an engine interface 205, an engine 206, a panel interface 207, a panel device 208, a host interface 209, a disk interface 210, a disk device 211, an image processing unit 250, and the like. It is configured.

  The CPU 201 controls the entire printer by a control program stored in the program ROM 204, a mode instruction from the panel device 208, and a command from the host device 100. The NVRAM 202 is a nonvolatile RAM that stores data such as the contents of mode instructions from the panel device 208.

  The RAM 204 is used as a work memory for the CPU 201, a buffer for input data, a page buffer for print data, a memory for download fonts, and the like.

  The engine interface 205 is an interface for communicating commands and statuses and print data with the engine 206. The engine 206 is a mechanism for printing an image on a sheet or the like using a color material.

  The panel interface 207 is an interface that communicates commands and status with the panel device 208. The panel device 208 is an input / output device such as a touch panel, and is used for displaying a printer status and the like and inputting a mode instruction from an operator.

  The host interface 209 is an interface (for example, Centronics, RS232C) that communicates with the host computer 100.

  The disk interface 210 is an interface for communicating with the disk device 211. The disk device 211 is a disk device (for example, a hard disk device) that stores font data, programs, print data, and the like.

  The image processing unit 250 performs color conversion processing, color material saving processing, and the like, and is the portion most relevant to the present invention. Details thereof will be described later.

  Here, the operation of the printer 200 will be briefly described. Input RGB image data sent from the host computer 100 through the host interface 209 is divided into three types of objects, characters, graphics, and images, and has a data format that can be interpreted by the printer. Each of these object data has its data format interpreted, and is collectively developed into a one-page RGB bitmap image. The RGB bitmap image is stored in a RAM (page buffer) 204. These processes are executed by the CPU 201.

  The RGB bitmap image is subjected to color conversion processing and color material saving processing by the image processing unit 250 to become a CMYK bitmap image which is a color material signal, and is stored again in the RAM (page buffer) 204. Here, the engine 206 uses color materials of C (cyan), M (magenta), Y (yellow), and K (black).

  Alternatively, input RGB image data sent from the host computer 100 is subjected to color conversion processing and color material saving processing by the image processing unit 250 for each object, and becomes a CMYK image object. Next, the CMYK image object is developed into a CMYK bitmap image by the CPU 201 and stored in a RAM (page buffer) 204.

  The CMYK bitmap image stored in the RAM (page buffer) 204 as described above is subjected to halftone processing corresponding to the engine 206 by the CPU 201 and then sent to the engine 206 via the engine interface 205 for printing. Is done.

[Example 1]
In Embodiment 1 of the present invention, an RGB bitmap image developed in a RAM (page buffer) 204 is input to the image processing unit 250 by the CPU 201, and the CMYK signal that is a color material signal is converted from the RGB signal in the image processing unit 250. Conversion to color material and color material saving processing are performed. The processed CMYK bitmap image is stored in the RAM (page buffer) 204 again.

  An example of the processing flow in the image processing unit 250 is shown in FIG. Hereinafter, the processing content in the image processing unit 250 will be described with reference to this processing flow.

  The input RGB bitmap image is converted from an RGB signal to a CMYK signal for each pixel to obtain a CMYK bitmap image (step 300). For this conversion processing, for example, a memory map interpolation method using a three-dimensional lookup table (LUT) can be used. These color signals are multilevel signals, and are assumed to be 8-bit signals here.

Further, a process of acquiring histogram information of a component corresponding to the luminance or brightness of the RGB bitmap image is performed (step 301). Specifically, for example, an RGB bitmap image is converted from an RGB signal to a luminance / chrominance signal, for example, a YCbCr signal. The conversion from RGB signal to YCbCr signal is as follows: Y = 0.299 × R + 0.587 × G + 0.114 × B
Cb = BY
Cr = R−Y
Can be performed. In the above equation, Y is a luminance signal, Cb is a color difference signal in the blue direction, and Cr is a color difference signal in the red direction. Here, since only the luminance signal is used, it is not necessary to obtain the Cb and Cr signals. Then, a histogram of luminance signals of all pixels is calculated to obtain histogram information. Here, the dynamic range is obtained as the histogram information.

  FIG. 3 shows an example of a histogram and a dynamic range. A predetermined threshold value may be set in consideration of the influence of noise and the like, and the difference between the maximum luminance and the minimum luminance whose frequency exceeds the threshold value may be obtained as a dynamic range (in FIG. 3, the threshold value is 0). ) Is shown for convenience, but is not limited to this).

  Next, a color material saving LUT corresponding to the luminance dynamic range is created (step 302), and color material saving processing is performed on the CMYK bitmap image using the created LUT (step 303). The color material saving process is a process for reducing the amount of color material by causing the value of the CMYK signal, which is a color material signal, to occur. Here, table conversion using a one-dimensional LUT is performed on each CMYK signal. To do.

  An example of the color material saving LUT is schematically shown in FIG. Here, an LUT is created such that the color material saving rate increases (the amount of decrease in the CMYK signal value increases) as the dynamic range increases, and is used for the color material saving process. Of course, the larger the color material saving rate, the stronger the color material saving process.

Specifically, such an LUT is created by the following procedure, for example. First, the save rate parameter α corresponding to the obtained dynamic range ΔY
α = 1− (1/2) (ΔY / 255)
Is calculated.

  Next, for the LUT having the same input / output data value as shown in FIG. 5, the output data value is multiplied by the save rate parameter α to obtain a color material saving LUT. For example, when ΔY = 255, that is, the dynamic range is maximum, α = 1/2, and the color material saving rate is also maximum. FIG. 6 shows the LUT when α = 1/2. By such a method, it is possible to create an LUT in which the color material save rate is increased as the dynamic range is increased.

  Although the save rate parameter α is continuously controlled here, it can also be controlled step by step. For example, it is possible to control in two steps, such as α = ½ when the dynamic range is 128 or more and α = 1 when the dynamic range is less than 128. In this case, when the dynamic range is less than 128, the color material is not substantially saved.

  In FIG. 2, the conversion process from RGB signals to CMYK signals (step 300) is shown to start from the beginning, but the present invention is not limited to this. For example, it may be executed immediately before step 303.

  FIG. 7 shows a functional block diagram of the image processing unit 250 according to the first embodiment. In FIG. 7, color conversion means 350 is means for converting RGB signals into CMYK signals, and this corresponds to step 300 in FIG. The histogram information acquisition unit 351 is a unit that calculates a luminance histogram from the RGB bitmap image and acquires a dynamic range as the histogram information, and this corresponds to step 301 in FIG. The color material saving processing unit 352 creates an LUT corresponding to the luminance dynamic range acquired by the histogram information acquisition 351, and the table conversion using the LUT saves the larger the dynamic range for the CMYK bitmap image. This is a means for performing a color material saving process with a large rate, and this corresponds to steps 302 and 303 in FIG.

  Note that the CPU 201 can also execute the processing of the image processing unit 250 described above. In this case, a program for executing the processing procedure shown in FIG. 7, in other words, a program for realizing the function of each means shown in FIG. Such embodiments are also encompassed by the present invention.

[Example 2]
In the first embodiment, an RGB bitmap image of one page is input to the image processing unit 250 and processed, but it can be processed not for the entire page but for each object.

  A second embodiment for performing such processing for each object will be described below. In the second embodiment, input RGB image data sent from the host computer 100 through the host interface 209 is first subjected to color conversion processing and color material saving processing for each object by the image processing unit 250 to obtain a CMYK image. Become an object. The CMYK image object is developed into a CMYK bitmap image by the CPU 201 and stored in a RAM (page buffer) 204.

  Of the character, graphics, and image objects, the image object is in the bitmap image format, but the character and graphics objects are in a format expressed by a character code or a command that can be interpreted by the printer. Then, it is difficult to extract histogram information. Therefore, in the second embodiment, the image processing unit 250 performs color material saving processing corresponding to the dynamic range only for the image object, and for the characters and graphics, the color material saving is performed at a fixed save rate. Processing will be performed.

  An example of the processing flow of the image processing unit 250 is shown in FIG. Hereinafter, the processing content in the image processing unit 250 will be described with reference to this processing flow.

  When one RGB image object is input, conversion processing from an RGB object to a CMYK object is performed (step 400). Further, it is determined whether or not the object is an image object (step 401).

  If it is determined that the object is an image object (Yes in step 401), since the object is an RGB bitmap image, a luminance histogram is created by converting the RGB signal into a YCbCr signal, and the dynamic range is used as the histogram information. (Step 402), an LUT corresponding to the dynamic range is created (step 402), and color material saving processing by table conversion using this LUT is applied to the converted CMYK bitmap image in step 400 ( Step 405), the processing for the object is terminated. The processing contents of steps 402 and 404 are the same as those of steps 301 and 302 of the first embodiment.

  When the input RGB image object is not an image object, that is, a character or graphics object (No in step 401), a default color material saving LUT not related to the dynamic range is created (step 403). The color material saving process at a constant saving rate using the above is applied to the CMYK image object (step 405). In creating the default color material saving LUT, the save rate parameter α is set to 1/2, for example.

  It is also possible to determine the character object and the graphic object, and to make the save rate different between the character object and the graphics object. For example, it is possible to prioritize readability only for character objects, and set the save rate parameter α to 1 so as not to save the color material. Such an embodiment is also encompassed by the present invention.

  In the processing flow shown in FIG. 8, the step 400 is represented as starting from the beginning, but the present invention is not limited to this. For example, it may be executed immediately before step 405.

  FIG. 9 shows a functional block diagram of the image processing unit 250 according to the second embodiment. In FIG. 9, an object discriminating unit 450 is a unit that discriminates whether or not an input RGB image object is an image object, and corresponds to step 401 in FIG. The object type discrimination information is input to the color conversion unit 451 together with the input RGB image object. The color conversion means 451 is a means for converting an RGB image object into a CMYK image object, and this corresponds to step 400 in FIG. The converted CMYK image object is input to the color material save processing means 452 together with the object type discrimination information. The histogram information acquisition unit 453 is a unit that calculates a luminance histogram from an image object (RGB bitmap image) and acquires a dynamic range as histogram information, which corresponds to step 402 in FIG. The color material saving processing unit 452 creates an LUT corresponding to the dynamic range of luminance acquired by the histogram information acquisition unit 453 in the case of an image object (step 402), and in the case of an object other than the image object, a default LUT. This is means for creating an LUT (step 403) and generating a CMYK image object subjected to color material saving processing by table conversion using the created LUT.

  Note that the CPU 201 can also execute the processing of the image processing unit 250 described above. In this case, a program for executing the processing procedure shown in FIG. 8, in other words, a program for realizing the function of each means shown in FIG. 9 is stored in the program ROM 203 or the like. Such embodiments are also encompassed by the present invention.

[Example 3]
The second embodiment is applied when the image data is divided for each object, but the same color is applied to an RGB bitmap image that is not divided for each object, for example, an RGB bitmap image read by a scanner. There are times when you want to perform a material save process. The third embodiment which will be described below corresponds to such a case.

  FIG. 10 is a functional block diagram of the image processing unit 250 according to the third embodiment. An RGB bitmap image as read by a scanner is input to the image processing unit 250.

  In FIG. 10, an image area separating unit 501 is an apparatus that separates an RGB bitmap image into either a character area or an image area, and adds area information for each pixel of the RGB bitmap image. Here, the region information is 1 bit, and is set to “1” for a character region and “0” for an image region. There are various conventional image area separation processing methods, and any method may be used. The simplest method is to detect an edge value for each pixel such as a primary differential value, determine a pixel having an edge value equal to or greater than a predetermined threshold as a character area, and use an area that is not a character area as an image area. is there. The RGB bitmap image to which the region information is added is sent to the color conversion means 502 and the histogram information acquisition means 504.

  The color conversion unit 502 is a unit that performs processing for converting an RGB bitmap image into a CMYK bitmap image while maintaining the region information for the input RGB bitmap image with region information. It should be noted that different conversion may be performed between the character area and the image area with reference to the area information. The CMYK bitmap image with area information is input to the color material save processing means 503.

  The histogram information acquisition unit 504 is a unit that calculates a luminance (or brightness) histogram of the image area of the RGB bitmap image and acquires a dynamic range as the histogram information. Specifically, the RGB signal is converted from the RGB signal to the YCbCr signal, which is a luminance color difference signal, for only the pixel whose region information added to the RGB bitmap image is “0”, and the histogram of the luminance signal Y is calculated. To do. Then, the dynamic range as the histogram information is sent to the color material saving processing means 503.

  The color material save processing unit 503 creates a color material save rate LUT (for image processing) according to the dynamic range by the same method as in the first embodiment, and α = 1, that is, an LUT that does not perform color material save ( Create for character area. Then, the color material saving process using the LUT is performed on the input CMYK bitmap image. For the pixel having the area information “0” (image area pixel), the image area LUT is used and the area information is “1”. A character area LUT is used for the pixel "" (character area pixel). In this way, by properly using the two LUTs according to the area information, it is possible to save the color material according to the dynamic range for the image area without saving the color material for the character area.

  In the third embodiment, control is performed so that the color material is not substantially saved for the character area. However, it is also possible to perform the color material save by setting α to a value other than 1. Embodiments are also encompassed by the present invention.

  Note that the CPU 201 can also execute the processing of the image processing unit 250 described above. In this case, a program for realizing the function of each unit shown in FIG. 10 is stored in the program ROM 203 or the like. Such embodiments are also encompassed by the present invention.

[Other embodiments]
In the first, second, and third embodiments, the luminance histogram is calculated, the dynamic range is obtained as the histogram information, and this is used to control the strength of the color material save. However, the present invention is not limited to this. Without. For example, as the histogram information, in addition to the histogram dynamic range, one or more of the average value or median value of luminance, the maximum luminance value or the minimum luminance value whose frequency exceeds a predetermined threshold value, and the color material saving It is also possible to use it for strength control, and such a mode is naturally included in the present invention.

  FIG. 11 shows an example of a luminance histogram calculated for two images. The histogram in FIG. 11A and the histogram in FIG. 11B are greatly different in average value but have the same dynamic range. According to the first embodiment, the color material saving process with the same color material saving rate is performed on such two images.

  However, since an image having a luminance histogram as shown in FIG. 11A is distributed in a bright area, the color material consumption at the time of output is an image having a luminance histogram as shown in FIG. It is expected to be less than the color material consumption. That is, even if the color material saving process is performed on the image as shown in FIG. 11A, the color material saving effect is small as compared with the image as shown in FIG.

  Therefore, in a modification of the first embodiment, an average value (or median value) of luminance is obtained as luminance histogram information in addition to the dynamic range, and the color material saving rate parameter based on the dynamic range similar to that of the first embodiment is obtained. In addition to the control of α, for example, when the average value is 128 or more, the color material saving rate parameter α is forcibly set to 1. As a result, when the average value is 128 or more, the color material saving process is substantially not performed, and when the average value is less than 128, the color material saving rate is larger as the dynamic range is larger. Processing is performed. Thus, it is possible to save color material consumption while suppressing image quality degradation of bright images. Similar control can be performed on the image object or the image area in the second and third embodiments, and such an aspect is also included in the present invention.

  In the first, second, and third embodiments, luminance histograms are calculated, and the strength of the color material saving process is controlled using the dynamic range. However, it is also possible to calculate histograms of the color difference signals Cb and Cr and use the histogram information.

  For example, it is also effective to control the intensity of the color material saving process according to the maximum value in the dynamic range of the luminance signal Y and the color difference signals Cb and Cr. For example, even if the dynamic range of luminance is small, when the dynamic range of the color difference signal Cb in the blue direction is large, it is considered that the image expresses meaningful image information by a change in the color in the blue direction. Therefore, it is preferable to control the strength of the color material saving process according to the dynamic range of the color difference signal Cb. Such embodiments are also encompassed by the present invention. Of course, the intensity of the color material saving process can be controlled according to the average value or the minimum value of the dynamic range of Y, Cb, and Cr. In this way, it is easier to preserve the detailed representation of the image. Such an embodiment is also included in the present invention.

  In each of the above embodiments, the histogram is calculated by converting the RGB signal into the YCbCr signal that is the luminance color difference signal. For example, the histogram is converted into the Lab uniform color space signal, and the lightness signal L (and the chromaticity signal a *, It is also possible to calculate a histogram of b *). Such embodiments are also encompassed by the present invention. It is also possible to calculate a histogram based on the CMYK signal which is a color material signal, and such an aspect is also included in the present invention. In short, a histogram of luminance components and the like of an image to be subjected to the color material saving process is calculated, and histogram information such as the dynamic range is used for controlling the strength of the color material saving process.

  In addition, the computer program described in connection with the first, second, and third embodiments, the same computer program corresponding to the above-described modification, a magnetic disk, an optical disk, a magneto-optical disk, a nonvolatile memory card, and the like on which these programs are recorded Computer-readable storage media such as these semiconductor storage elements are also included in the present invention.

FIG. 2 is a block diagram for explaining an internal configuration of the printer according to the embodiment of the invention. 3 is a flowchart illustrating an example of a processing flow in Embodiment 1. It is a figure which shows the example of a brightness | luminance histogram and a dynamic range. It is explanatory drawing of the color material saving LUT according to a dynamic range. It is a figure which shows LUT with the same input-output data value. FIG. 6 is a diagram illustrating an example of a color material saving LUT in which an output data value is changed according to a dynamic range. FIG. 3 is a block diagram illustrating a functional configuration of an image processing unit according to the first embodiment. 10 is a flowchart illustrating an example of a processing flow in the second embodiment. FIG. 6 is a block diagram illustrating a functional configuration of an image processing unit according to a second embodiment. FIG. 10 is a block diagram illustrating a functional configuration of an image processing unit according to a third embodiment. It is a figure which shows the example of the brightness | luminance histogram from which a dynamic range is the same, but an average value differs.

Explanation of symbols

100 Host computer 200 Printer 201 CPU
250 Image processing unit 350 Color conversion unit 351 Histogram information acquisition unit 352 Color material save processing unit 450 Object determination unit 451 Color conversion unit 452 Color material save processing unit 453 Histogram information acquisition unit 501 Image area separation unit 502 Color conversion unit 503 Color material Save processing means 504 Histogram information acquisition means

Claims (14)

Color conversion means for converting input image data into image data of a color material signal;
Color material save processing means for performing color material save processing on the image data converted by the color conversion means;
Histogram information acquisition means for acquiring histogram information about the brightness or brightness of the input image data,
The color material saving processing means controls the intensity of the color material saving processing according to the histogram information. The histogram information is a dynamic range,
The image processing apparatus according to claim 1, wherein the color material saving processing unit increases the strength of the color material saving processing as the dynamic range increases. The histogram information is a dynamic range and an average value or a median value,
The color material saving processing means increases the strength of the color material saving processing as the dynamic range is larger when the average value or median value is less than a predetermined value, and the average value or median value is equal to or greater than the predetermined value. 2. The image processing apparatus according to claim 1, wherein the intensity of the color material saving process is minimized in a case. The input image data is divided for each object,
The histogram information acquisition means acquires histogram information for an image object,
The image processing apparatus according to claim 2, wherein the color material saving processing unit controls the intensity of the color material saving processing for the image object according to the histogram information. An image area separating means for separating the input image data into an image area and an area other than the image area;
The histogram information acquisition means acquires histogram information for the image region,
The image processing apparatus according to claim 2, wherein the color material saving processing unit controls the intensity of the color material saving processing for the image area according to the histogram information. The histogram information acquisition means acquires histogram information about color difference or chromaticity in addition to histogram information about luminance or brightness,
6. The color material save processing unit controls the intensity of the color material save process according to the histogram information acquired by the histogram information acquisition unit. Image processing device. A color conversion step of converting input image data into image data of a color material signal;
A color material saving process for applying a color material saving process to the image data converted by the color conversion process;
A histogram information acquisition step of acquiring histogram information about luminance or brightness of the input image data,
In the color material saving process, the intensity of the color material saving process is controlled according to the histogram information. The histogram information is a dynamic range,
The image processing method according to claim 7, wherein the color material saving processing step increases the strength of the color material saving processing as the dynamic range increases. The histogram information is a dynamic range and an average value or a median value,
In the color material saving process step, when the average value or the median value is less than a predetermined value, the strength of the color material saving process is increased as the dynamic range is increased, and the average value or the median value is greater than or equal to the predetermined value. 8. The image processing method according to claim 7, wherein the intensity of the color material saving process is made weakest in some cases. The input image data is divided for each object,
The histogram information acquisition step acquires histogram information about the image object,
10. The image processing method according to claim 8, wherein the color material saving process step controls the intensity of the color material saving process for the image object according to the histogram information. An image area separation step for separating the input image data into an image area and an area other than the image area;
The histogram information acquisition step acquires histogram information for the image region,
10. The image processing method according to claim 8, wherein the color material saving process step controls the intensity of the color material saving process for the image area according to the histogram information. The histogram information acquisition step acquires histogram information about color difference or chromaticity in addition to histogram information about luminance or brightness,
The image according to any one of claims 8 to 11, wherein the color material saving process step controls the intensity of the color material saving process in accordance with the histogram information acquired by the histogram information acquisition step. Processing method.   A program for causing a computer to execute each step of the image processing method according to any one of claims 8 to 12.   A computer-readable storage medium storing a program for causing a computer to execute each step of the image processing method according to any one of claims 7 to 12.

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