JP2024042401A - Image processing device, control method and program for the image processing device - Google Patents

Abstract

An object of the present invention is to provide an image processing device, a control method for the image processing device, and a program that can maintain important colors even when the number of colors is reduced when compressing a color image.
An MFP 101 includes an important color designation unit 301 that designates important colors of a color image and generates designation information 302, and a color reduction image 304 that reduces the number of colors in the color image while leaving important colors in the designation information 302. A color reduction processing unit 303 generates a color reduction image 304, a color information integration unit 307 converts colors close to important colors into important colors and generates integrated color information 308, and a color reduction processing unit 307 performs color reduction for each color of the integrated color information 308. a binary image generation unit 313 that generates a binary image 314 of an image; a binary image compression unit 315 that generates binary image compressed data 316 for each color of the integrated color information 308 by compressing the binary image 314; The data integrating unit 317 generates compressed data 318 by integrating the value image compressed data 316 and the integrated color information 308.
[Selection diagram] Figure 3

Description

The present invention relates to an image processing apparatus, a method of controlling the image processing apparatus, and a program.

In recent years, with the spread of color printers and color scanners, the number of colored paper documents has increased, so it is now possible to scan colored paper documents, save them as electronic files, and send them via the Internet, etc. There are increasing opportunities to do so. However, since full-color data is large in size, it takes up a large amount of storage space in a storage device and places a heavy load on communication lines. Therefore, it is necessary to reduce the data size of full color data by some method. Methods to reduce the data size include, for example, compressing it into a binary image with pseudo gradation using error diffusion, compressing it in JPEG format, converting it to a palette color such as 8 bits and compressing it using ZIP. There are methods such as LZW compression. Furthermore, the method described in Patent Document 1 performs color reduction processing on a color image, outputs color information and an index color image, generates a binary image and background color information for each color, and uses methods such as MMR. Perform compression processing. As a result, the method described in Patent Document 1 achieves compression with better compression efficiency and reproducibility than the various compression methods described above.

Patent No. 3890250

By the way, when a paper document is scanned in color, the scan data contains variations in color due to scanning irregularities and the like, even if it is a single color, resulting in poor compression efficiency. For such an image, if the method described in Patent Document 1 is used, the binary image generated for each color is compressed using a method such as MMR while reducing the colors, so the compression efficiency when compressed is improved. be able to. However, in the method described in Patent Document 1, by performing color reduction and integration, for example, colors of logos, formats, etc., that is, colors that do not want to be changed (hereinafter referred to as "important colors"), are changed to similar colors. There was a problem that the colors were grouped together. Specifically, for example, when colors are reduced or merged to a small number of colors, such as 5 colors, if the paper document has 6 or more colors, the colors will be consolidated, so important colors will be changed to similar colors. There are cases where this happens.

The present invention has been made in view of the above problems. SUMMARY OF THE INVENTION An object of the present invention is to provide an image processing apparatus, a control method for the image processing apparatus, and a program that can maintain important colors even when the number of colors is reduced when compressing a color image.

In order to achieve the above object, an image processing device of the present invention includes an important color specifying means that generates specifying information by specifying an important color from among the colors used in a color image, and color reduction processing means for generating a color reduction image by reducing the number of colors in the color image while leaving the important colors based on the color reduction image; and a color determined to be close to the important color among the colors used in the color reduction image. a color information integrating means for generating color information by converting the color information into the important color; a binary image generating means for generating a binary image of the reduced color image for each color included in the color information; Binary image compression means for generating compressed binary image data for each color included in the color information by compressing an image; and generating compressed data by integrating the compressed binary image data and the color information. The method is characterized by comprising a data integration means.

According to the present invention, important colors can be maintained even if the number of colors is reduced when compressing a color image.

FIG. 1 is a diagram showing the configuration of a system including a multifunction device according to a first embodiment. FIG. 2 is a block diagram showing the hardware configuration of a multifunction peripheral. FIG. 2 is a diagram showing each functional component of the data processing section of the multifunction device and data processed or processed in each functional component. FIG. 3 is a diagram showing an example of a color image. FIG. 3 is a diagram illustrating an example of a screen for specifying important colors displayed on the operation unit of the multifunction device. It is a figure which shows an example of a color reduction image. FIG. 3 is a diagram showing an example of color information. FIG. 3 is a diagram showing the relationship between a color-reduced image and coordinates. FIG. 3 is a diagram for explaining a binary image for each representative color, which is generated based on a color reduction image and sorted integrated color information. 11 is a flowchart of a small number of colors compression process performed in the multifunction peripheral. It is a flowchart of color reduction processing. FIG. 2 is a diagram illustrating an example of a configuration of compressed data. FIG. 7 is a diagram illustrating an example of a screen for specifying important colors displayed on the operation unit of the multifunction device in the second embodiment.

Hereinafter, each embodiment of the present invention will be described in detail with reference to the drawings. However, the configurations described in each embodiment below are merely examples, and the scope of the present invention is not limited by the configurations described in each embodiment. For example, each part constituting the present invention can be replaced with any part that can perform the same function. Moreover, arbitrary components may be added. Further, any two or more configurations (features) of each embodiment can be combined.

(First embodiment)
The first embodiment will be described below with reference to FIGS. 1 to 12.

<System configuration>
FIG. 1 is a diagram showing the configuration of a system including a multifunction peripheral (hereinafter referred to as "MFP") 101 according to the first embodiment. In the system shown in FIG. 1, an MFP 101 and a personal computer (hereinafter referred to as "PC") 102 are connected via a network 103. In the MFP 101, the user can specify the destination (for example, the PC 102) to which the scanned image is to be sent and various other specifications related to scanning and transmission by using an operation unit (see 203 in FIG. 2) to be described later. As the various specifications, the user can specify resolution, compression rate, data format (for example, JPEG, TIFF, PDF, minority color compression, minority color compression (with OCR results)), and the like. In the following, a case will be described in which fewer color compression is specified as the data format. Note that details of minority color compression will be described later. Based on various specifications, the MFP 101 uses software or hardware functions to generate scan data of a paper document and sends it to a specified destination. Here, if the specified destination is the PC 102, the image sent to the PC 102 will be sent in a file format such as PDF, so it can be viewed with a general-purpose viewer included in the PC 102.

<MFP configuration>
FIG. 2 is a block diagram showing the hardware configuration of the MFP 101. As shown in FIG. 2, the MFP 101 includes a scanner unit 201 that is an image input device, a printer unit 202 that is an image output device, an operation unit 203 that is a user interface (UI), a control unit 204 that includes a memory, etc. has. The control unit 204 is a controller that is connected to the scanner section 201, printer section 202, and operation section 203, and also inputs and outputs image information and device information by connecting to the network 103. In the control unit 204, a CPU 205, a RAM 206, an operation unit I/F 207, a network I/F 208, a ROM 210, and a storage unit 211 are arranged on a system bus 216.

CPU 205 is a processor that controls the entire MFP 101 . The RAM 206 is a work memory for the CPU 205 to operate, and is also an image memory for temporarily storing image data. The operation unit I/F 207 is an interface unit with the operation unit 203 and outputs image data to be displayed on the operation unit 203 to the operation unit 203. Further, the operation unit I/F 207 plays a role of transmitting information input by the user of the MFP 101 using the operation unit 203 to the CPU 205. A network I/F 208 connects the MFP 101 to the network 103 and inputs and outputs information in packet format. The ROM 210 is a boot ROM and stores programs such as a boot program for the MFP 101. The storage unit 211 is a hard disk drive and stores control software for the MFP 101, image data, and the like.

The image bus interface 212 is a bus bridge that connects the system bus 216 and an image bus 217 that transfers image data at high speed, and converts the data structure. The image bus 217 is composed of a PCI bus, IEEE1394, or the like. A RIP (Ruster Image Processor) section 213, a device I/F section 214, and a data processing section 215 are arranged on the image bus 217. The RIP unit 213 analyzes a PDL (Page Description Language) code and develops it into a bitmap image of a specified resolution, which is a so-called rendering process. The device I/F section 214 is connected to the scanner section 201, which is an image input device, via a signal line 218, and to the printer section 202, which is an image output device, via a signal line 219.

The data processing unit 215 performs image processing of scan data input from the scanner unit 201 and data processing of a print image output to the printer unit 202, as well as processes such as minority color compression and OCR. As a result, compressed data (see 318 in FIG. 3), which will be described later, is generated. The generated compressed data is transmitted to a specified destination (for example, PC 102) via network I/F 208 and network 103. The data processing unit 215 also decompresses compressed data received via the network 103 and network I/F 208. The decompressed image is sent to the printer unit 202 via the device I/F 214 to be printed.

<Description of Data Processing Unit>
The data processing unit 215 will be described in detail below with reference to FIGS. 3 to 9. FIG. 3 is a diagram showing each functional component of the data processing unit 215 of the MFP 101 and data that is processed or has been processed in each functional component. FIG. 4 is a diagram showing an example of a color image. The color image is scan data obtained by reading a paper document with the scanner unit 201. As shown in FIG. 4, the color image of the first embodiment is composed of 401 (logo: red), 402 (title: orange), 403 (text1: black), 404 (text2: green), 405 (text3: light blue), 406 (page: blue), and the like. 401 (logo: red) shows an example of a logo displayed in red, which is one of the important colors. 402 (title: orange) shows an example of a title displayed in orange. 403 (text1: black) shows an example of text displayed in black. 404 (text2: green) shows an example of text displayed in green. 405 (text3: light blue) shows an example of text displayed in light blue. 406 (page: blue) shows an example of a format (page number) displayed in blue, which is one of the important colors. The format includes, for example, the page number, date, text, pattern, decoration, shading, fill, etc., which are commonly displayed in the header area or footer area of each page of a paper document. An important color is a color that should not be changed to another color even if the number of colors in a color image is reduced. Therefore, the color of a logo or the color of a format is likely to be an important color, as described above. Note that since a color image is scan data, even if it is a single color, it includes color variations.

Return to Figure 3. The important color designation unit 301 (important color designation means) sends information regarding the area including the important color in the color image to the color reduction processing unit 303 as designation information 302. The area including the important color is specified in advance by the user on the operation unit 203 using a preview image of the scan data displayed on the screen.

FIG. 5 is a diagram showing an example of a screen (first operation section) for specifying important colors displayed on the operation section 203. Reference numeral 501 indicates a checkbox in the header area, and if the header area has an important color, the user checks this checkbox. Reference numeral 502 denotes a footer area checkbox, which is checked by the user if the footer area has an important color. Reference numeral 503 indicates a check box for an arbitrary area, and when an important color is present in an arbitrary area, the user checks the check box, and further, the user specifies an arbitrary area by operating a touch panel using a touch pen or the like. . Note that in FIG. 5, an area surrounding "text3" is shown as an example of an arbitrary area. Reference numeral 504 is an area for displaying a preview image of scan data, and in FIG. 5, the color image of FIG. 4 is displayed as an example of the display. Further, in the first embodiment, as described above, red and blue are important colors. Therefore, in FIG. 5, checkbox 501 in the header area and checkbox 502 in the footer area are checked. In this way, the user can manually specify regions of important color within the color image. Further, as described above, a logo or format is often displayed in an important color in the header area or footer area. In such a case, the user can easily specify important colors manually by using the check box 501 in the header area or the check box 502 in the footer area on the screen of the operation unit 203 shown in FIG.

Return to Figure 3. The color reduction processing unit 303 (color reduction processing means) performs color reduction processing on the color image based on the preset number of colors and the designation information 302 of the important color designation unit 301, and generates a color reduction image 304. In the color reduction method in the color reduction processing unit 303, a plurality of representative colors are determined by selecting colors up to a preset number of colors in order of frequency in the histogram of RGB values. Thereafter, the colors of all pixels in the color image are assigned to the closest color among the plurality of representative colors, thereby reducing the color of the color image. As a result, a color-reduced image 304 is generated. Note that such a color reduction method is one method for explanation in the first embodiment, and is not limited thereto.

In the first embodiment, the preset number of colors includes the "number of colors within a page" and the "number of colors within an area." “Number of colors in page” and “Number of colors in area” are stored in the ROM 210. The "number of colors in a page" (third predetermined number) is the maximum number of output colors in a decoded color image (hereinafter referred to as "decoded image"). As a result, the number of colors in the decoded image is reduced to at least the "number of colors within a page." In the first embodiment, the "number of colors within a page" is set to 5. In this case, for example, in the case of a paper document containing five colors or less, it is possible to reduce the number of colors to a more appropriate number, improving compression efficiency. On the other hand, if the paper document contains more than five colors, the colors are reduced to fit within the five colors. The “number of colors in area” includes the maximum number of output colors in the decoded image of the area specified by the important color specification unit 301 (hereinafter referred to as “specified area”), and the area not specified by the important color specification unit 301. (hereinafter referred to as "non-designated area") is the maximum number of output colors in the decoded image. Therefore, the non-designated area is an area excluding the designated area from the color image. Note that in the first embodiment, as described above, the header area and footer area are designated areas (see FIG. 5). In addition, in the same manner as the "number of colors in a page", "number of colors in an area (specified area)" (first predetermined number) = 5, "number of colors in an area (non-specified area)" (second predetermined number) )=5. The total number of "number of colors in area (designated area)" and "number of colors in area (non-specified area)" needs to fall within the "number of colors in page." Therefore, for example, if there are two colors in the designated area and five colors in the non-designated area, they are integrated so that the total number of colors falls within five colors. Details of color integration will be described later.

FIG. 6 is a diagram showing an example of the reduced color image 304. FIG. 6 shows representative colors in the designated area (inside the dotted line frame) and representative colors in the non-designated area (outside the dotted line frame). In the designated area (within the dotted line frame), it is shown that the colors have been reduced to three colors: red representative color 601, blue representative color 606, and white representative color 607, which is the background color. On the other hand, in the non-specified area (outside the dotted line frame), there are five representative colors: orange representative color 602, black representative color 603, green representative color 604, light blue representative color 605, and white representative color 608, which is the background color. It is shown that the color is reduced.

Return to Figure 3. The color information generation unit 305 generates color information 306 based on the specification information 302 of the important color specification unit 301 and the color reduction image 304 of the color reduction processing unit 303. FIGS. 7A to 7E are diagrams showing examples of color information 306. FIG. 7A shows color information 306 of the specified area. The color information 306 of the specified area is composed of a representative color in the specified area, distribution range data (starting coordinates and ending coordinates), and the number of pixels having the representative color. FIG. 7B shows color information 306 of the non-designated area. Similarly, the color information 306 of the non-designated area is composed of a representative color in the non-designated area, distribution range data (starting coordinates and ending coordinates), and the number of pixels having the representative color. Therefore, color information 306 is generated for the colors used in reduced color image 304. FIG. 7E shows an example of the color values (L*a*b*) of the representative colors. Each representative color in FIG. 7(e) corresponds to the representative colors in FIGS. 7(a) and (b). Note that, for convenience, the color values (L*a*b*) in FIG. 7(e) have higher brightness and saturation than the actual scan data.

Furthermore, the distribution range data of the color information 306 is data of the coordinates of a pixel in the upper left corner (start coordinates) and the coordinates of a pixel in the lower right corner (end coordinates) for each representative color in the reduced color image 304. FIG. 8 is a diagram showing the relationship between the reduced color image 304 and coordinates. In FIG. 8(a), (X1, Y1) to (X'1, Y'1) are coordinates indicating the "logo" area. (X2, Y2) to (X'2, Y'2) are coordinates indicating the area of "title". (X3, Y3) to (X'3, Y'3) are coordinates indicating the area of "text1". (X4, Y4) to (X'4, Y'4) are coordinates indicating the area of "text2". (X5, Y5) to (X'5, Y'5) are coordinates indicating the area of "text3". (X6, Y6) to (X'6, Y'6) are coordinates indicating the "page" area. In FIG. 8(b), (X7, Y7) to (X'7, Y'7) are coordinates indicating the designated area (header area). (X8, Y8) to (X'8, Y'8) are coordinates indicating the designated area (footer area). (X9, Y9) to (X'9, Y'9) are coordinates indicating the non-designated area.

Return to Figure 3. The color information integration unit 307 integrates the color information 306 of the specified area and the color information 306 of the non-specified area so that the number of colors falls within the preset number of colors (number of colors in a page = 5), and generates integrated color information. 308 is generated. As described above, in the first embodiment, the color information 306 for the specified area consists of three colors, and the color information 306 for the non-specified area consists of five colors. ”=5, color integration is performed.

FIG. 7(f) shows a plot of the representative colors of FIG. 7(e) in the a*b* space. As shown in FIG. 7F, the color information integration unit 307 uses the color difference to determine that the representative colors of red and orange are close colors, and the representative colors of blue and light blue are close colors. It can be determined that there is. Here, if we simply integrate colors based on the side with a larger number of pixels, then according to the color information 306 of the specified area and the color information 306 of the non-specified area, red (100 pixels) < orange (500 pixels), which is important. The color red is replaced with orange. Furthermore, since blue (300 pixels)<light blue (530 pixels), the important color blue is replaced with light blue. Therefore, the color information integrating unit 307 (color information integrating means) integrates the color information 306 of the specified area and the color information 306 of the non-specified area based on the specified information 302, and creates integrated color information 308 (color information). generate. In other words, since red and blue, which are the representative colors of the color information 306 of the specified area, are important colors, they are held with priority by the color information integration unit 307 regardless of the number of pixels. Therefore, red and orange are combined into red, and the number of red pixels is 600 in total. Blue and light blue are combined into blue, and the number of blue pixels is 830 in total. Furthermore, the total number of pixels of the background color white is 1,000,000 pixels. This makes it possible to integrate the images so that the number of colors within the page is 5, which is the preset number of colors, while maintaining the important colors specified by the user. FIG. 7(c) shows integrated color information 308 in which the color information 306 of FIGS. 7(a) and 7(b) is integrated. The distribution range data is updated to include each representative color (see FIG. 9, which will be described later). Although the color difference is used in the determination by the color information integration unit 307 as an index representing the difference in color, it is not limited to this, and for example, brightness may be added.

Return to Figure 3. The color information sorting unit 309 generates sorted integrated color information 310 by sorting the integrated color information 308 in descending order of the number of pixels for each representative color. As a result, the color information of the representative color with the largest number of pixels appears at the top of the sorted integrated color information 310. FIG. 7(d) shows the sorted integrated color information 310. As shown in FIG. 7D, in the sorted integrated color information 310, the representative color of the color information with the largest number of pixels is white, which is the background color.

Return to Figure 3. The background color data generation unit 311 generates, as background color data 312, the color value of the representative color included in the highest color information among the sorted integrated color information 310. Note that in the first embodiment, RGB values of 8 bits each are assumed as the background color data 312, but the present invention is not limited to this. The binary image generation unit 313 (binary image generation means) generates a binary image 314 for each representative color based on the reduced color image 304 and the sorted integrated color information 310 (color information). At this time, the binary image generation unit 313 creates a binary image for each representative color of the sorted integrated color information 310, excluding the topmost representative color (white background color) of the sorted integrated color information 310. generate.

FIG. 9 is a diagram for explaining a binary image for each representative color, which is generated based on the color reduction image 304 of FIG. 6 described above and the sorted integrated color information 310. 901 indicates a binary image to which a red representative color is added. 902 indicates a binary image to which a representative color of black is added. 903 indicates a binary image to which the representative color of green is added. 904 indicates a binary image to which the representative color of blue is added. However, a binary image is not generated for the representative color of white, which is the background color. In FIG. 9, (X10, Y10) to (X'10, Y'10) are coordinates indicating the area of the representative red color after integration. (X11, Y11) to (X'11, Y'11) are coordinates indicating the area of the representative color of blue after integration. (X12, Y12) to (X'12, Y'12) are coordinates indicating the area of the white representative color after integration.

Return to Figure 3. The binary image compression unit 315 (binary image compression means) generates binary image compressed data 316 by compressing the binary image 314 generated for each representative color by the binary image generation unit 313. do. In the first embodiment, MMR compression is used as the compression method performed by the binary image compression unit 315, but the method is not limited to this. The data integration unit 317 (data integration means) integrates the binary image compressed data 316, the background color data 312, and the sorted integrated color information 310 (color information) to create compressed data 318 (see FIG. 12 described later). generate.

<Explanation of flowchart>
FIG. 10 is a flowchart of the minority color compression process performed by the MFP 101. Steps S1001 to S1009 (control method of the image processing apparatus) in the flowchart of FIG. 10 are realized in the MFP 101 by the CPU 205 of the control unit 204 (computer) loading the program stored in the storage unit 211 into the RAM 206 and executing it. be done. In the explanation of steps S1001 to S1009 of the flowchart in FIG. 10, the contents processed by each processing unit based on instructions from the CPU 205 will be explained. These points also apply to steps S1101 to S1108 in the flowchart of FIG. 11, which will be described later. In the MFP 101, when the user specifies minority color compression as a data format using the operation unit 203, the operation unit I/F 207 notifies the CPU 205 of the data format (minority color compression) specified by the user. This starts the flowchart of FIG.

As shown in FIG. 10, in step S1001, when the CPU 205 receives notification information from the operation unit I/F 207, the CPU 205 reads a paper document using the scanner unit 201 and generates scan data. The scan data in the first embodiment corresponds to the color image shown in FIG. 3, and an example of the color image is as described in FIG. 4 above. Furthermore, in addition to generating scan data, the CPU 205 generates a preview image of the scan data, and displays the preview image on the screen of the operation unit 203. Thereby, the user can use the preview image displayed on the operation unit 203 to specify in advance an area including an important color. In step S1002, the important color designation unit 301 sends information regarding the area including the important color designated in advance by the user to the color reduction processing unit 303 as designation information 302 (important color designation step).

In step S1003, the color reduction processing unit 303 performs color reduction processing on the color image based on the preset number of colors and the specification information 302 of the important color specification unit 301, and generates a color reduction image 304 (color reduction processing process). The generation uses the method described above. FIG. 11 is a flowchart of the color reduction process in step S1003.

As shown in FIG. 11, in step S1101, the color reduction processing unit 303 performs representative color determination processing (first determining means, second determining means). In this process, the color reduction processing unit 303 selects a plurality of representative colors (hereinafter referred to as "representative color group") by selecting colors in descending order of frequency in each of the designated area and non-designated area based on the designation information 302. ). In the first embodiment, the representative color group (first representative color group) of the designated area is determined so that the "number of colors in the area (designated area)" = 5, and the representative color group (first representative color group) of the non-designated area is 2 representative color group) is determined so that the "number of colors in area (non-designated area)" = 5. As a result, even if the scan data, which is a color image, contains color variations, the important color is basically one of the colors that constitute the representative color group of the specified area, so the first step in step S1104, which will be described later, Important colors can be retained during color reduction processing.

In step S1102, the color reduction processing unit 303 selects a pixel of interest in the color image. In the first embodiment, the selection of the pixel of interest is performed in the order of raster scanning of the entire color image. In step S1103, the color reduction processing unit 303 determines whether the pixel of interest selected in step S1102 is within a region including an important color designated in advance by the user, that is, within a designated region. If the color reduction processing unit 303 determines that the pixel of interest selected in step S1102 is a pixel within the designated area, the process advances to step S1104. On the other hand, if the color reduction processing unit 303 determines that the pixel of interest selected in step S1102 is not a pixel within the designated area, the process advances to step S1106.

In step S1104, the color reduction processing unit 303 performs first color reduction processing (first color reduction processing means). In this process, the color reduction processing unit 303 reduces the color by assigning, to the color of the pixel of interest selected in step S1102, a color determined to have the closest color difference among the colors of the representative color group of the designated area determined in step S1101. The process is performed to generate a color-reduced image 304. Note that in the first color reduction process, the color difference is used as an index representing the difference in color in the judgment of the color reduction processing unit 303; however, it is not limited to this; for example, by adding luminance Good too. In step S1105, the color information generation unit 305 generates color information 306 for the designated area based on the reduced color image 304 and the designation information 302 of the important color designation unit 301. Note that the color information 306 of the designated area is as described in FIG. 7(a) above.

In step S1106, the color reduction processing unit 303 performs second color reduction processing (second color reduction processing means). In this process, the color reduction processing unit 303 assigns, to the color of the pixel of interest selected in step S1102, a color determined to have the closest color difference among the colors of the representative color group of the non-specified area determined in step S1101. Color reduction processing is performed to generate a color reduction image 304. Note that in the second color reduction process, the color difference is used as an index representing the difference in color in the judgment of the color reduction processing unit 303; however, it is not limited to this; for example, the color difference may be Good too. In step S1107, the color information generation unit 305 generates color information 306 for the non-designated area based on the reduced color image 304 and the designation information 302 of the important color designation unit 301. Note that the color information 306 of the non-designated area is as explained in FIG. 7(b) above.

In step S1108, the color reduction processing unit 303 determines whether all pixels have been selected for the pixel of interest in the color image. If the color reduction processing unit 303 determines that all pixels have not been selected for the pixel of interest in the color image, the process returns to step S1102. On the other hand, if the color reduction processing unit 303 determines that all pixels have been selected for the pixel of interest in the color image, the process advances to step S1004 in FIG. 10. As described above, the color reduction process in step S1003 is divided into the first color reduction process in step S1104, which targets the specified area, and the second color reduction process, in step S1106, which targets the non-designated area. This enables appropriate color reduction processing for each of the designated and non-designated regions.

Return to FIG. 10. In step S1004, the color information integration unit 307 uses the color information 306 of the specified area and the color of the non-specified area based on the specified information 302 so that the preset number of colors falls within the "number of colors in a page" = 5. information 306. As a result, integrated color information 308 including the important color as a representative color is generated (color information integration step). The integration uses the method described above.

In step S1005, the color information sorting unit 309 generates sorted integrated color information 310 by sorting the integrated color information 308 in descending order of the number of pixels for each representative color. As a result, in the sorted integrated color information 310, the color information of the representative color with the largest number of pixels is placed at the top. In step S1006, the background color data generation unit 311 outputs the color value of the representative color at the top of the sorted integrated color information 310 as background color data 312.

In step S1007, the binary image generation unit 313 uses the reduced color image 304 and the sorted integrated color information 310 (excluding the topmost representative color) to A binary image 314 is generated (binary image generation step). The generation uses the method described above. Note that the binary image generation unit 313 may use integrated color information 308 (excluding the representative color with the largest number of pixels) instead of the sorted integrated color information 310 (excluding the highest representative color). . In step S1008, the binary image compression unit 315 generates compressed binary image data 316 by compressing the binary image 314 for each representative color described above using the MMR method (binary image compression step). Note that the binary image compressed data 316 is a data group composed of color information and MMR compressed data (see FIG. 12 described later). In step S1009, the data integration unit 317 collects the background color data 312, the binary image compression data 316, and the sorted integrated color information 310, generates compressed data 318, and outputs the compressed data 318 (data integration step). Thereafter, the flowchart of FIG. 10 ends. Note that the data integration unit 317 may use the integrated color information 308 instead of the sorted integrated color information 310.

Figure 12 is a diagram showing an example of the configuration of compressed data 318. As shown in Figure 12, the header of compressed data 318 contains information such as the size of the color image (number of pixels vertically and horizontally), the color value of the background color, and the resolution. The background color is basically the color with the largest number of pixels. Therefore, for example, if a paper document is printed on colored paper such as red, the color value of the background color will be a reddish value. However, it is considered that the background color is often white. Therefore, the data integration unit 317 judges the background color to be white, and if it is judged to be white, the color value of the background color may be omitted. In the white judgment, for example, if each of the RGB values is equal to or greater than a certain value and the difference between the respective values is within a certain value, it is considered to be white.

Following the header portion of the compressed data 318, compressed color data for each representative color is entered. The color compressed data corresponds to the binary image compressed data 316. As described above, the binary image compressed data 316 is composed of color information and MMR compressed data. The color information of the binary image compressed data 316 includes the coordinates of the pixel in the upper left corner of the representative color (start coordinates), the coordinates of the pixel in the lower right corner (end coordinates), the number of pixels of the representative color, and the coordinates of the pixel in the lower right corner of the representative color. It has color values (for example, RGB values). In the compressed data 318, if the number of colors remaining after excluding the background color is N, there are color compressed data with the same structure as many as the number N of colors. Of course, if the paper document is a monochrome original such as a blank sheet, color compressed data, that is, binary image compressed data 316 is not created. If the paper document is a black and white original, the number of color compressed data is 1, which is almost equivalent to a binary image. However, if the black pixels are only in a part of the black-and-white original, the MMR compressed data will have a smaller data size than when the entire black-and-white original is MMR-compressed because only that part is compressed.

Note that the method for decoding the compressed data 318 into a color image is performed as follows. The data processing unit 215 draws the entire area of the paper document using the background color stored in the header portion of the compressed data 318, and decompresses the MMR compressed data stored in the compressed data 318 in the order in which they are stored. Further, the data processing unit 215 overwrites the entire region drawn in the background color using the expanded image as a mask according to the position and color of the color information stored in the compressed data 318.

In this way, by having a binary image for each color, the MFP 101 can efficiently compress most color images.

(Second embodiment)
The second embodiment will be described below with reference to FIG. 13. The second embodiment is similar to the first embodiment except for the configuration of the screen for specifying important colors displayed on the operation unit 203 (see FIG. 5 described above). FIG. 13 is a diagram showing an example of a screen (second operation section) for specifying important colors displayed on the operation section 203 in the second embodiment. The screen shown in FIG. 13 is the same as the screen shown in FIG. 5 except that a box 1301 for specifying the number of important colors is provided. If the number of important colors is known, a number indicating the number of important colors is entered in box 1301 by the user. This allows the user to manually specify the number of important colors. Note that FIG. 13 shows that the number of important colors=2 is specified in box 1301.

(summary)
As described above, in the first embodiment and the second embodiment (hereinafter referred to as "the present embodiment"), the MFP 101 uses the specification information 302, which is information regarding the area including important colors, when compressing a color image. Important colors can be maintained even if the number of colors is reduced. Furthermore, the MFP 101 compresses the color image with a small number of colors by performing color reduction and integration using the specification information 302, which is information about the area including important colors, and reduces the data size of the compressed data 318. Efficiency can be improved. Furthermore, since color images are scanned data, they contain variations in color even if they are a single color, so noise may appear on a logo displayed in the important color red. However, the MFP 101 can turn the noise-laden logo into a single color of red, which is an important color, by performing color reduction or integration using the designation information 302, which is information about an area that includes an important color. The same holds true for the format (number of pages) displayed in the important color blue in a color image. Furthermore, as described above, the colors of logos and colors of formats are likely to be important colors, i.e., colors that do not want to be changed even if the number of colors in a color image is reduced. Therefore, as in this embodiment, when the color of the logo or the color of the format is an important color, the MFP 101 is very useful.

In this embodiment, the "number of colors in area (designated area)" and "number of colors in area (non-designated area)" used by the color reduction processing unit 303 are the same "5". Therefore, although the first color reduction process in step S1104 and the second color reduction process in step S1106 have been described as similar color reduction processes, they are not limited to this.

In this embodiment, the color information generating unit 305 outputs color information 306 of the designated area shown in FIG. 7(a), and outputs color information 306 (non-designated area) of the non-designated area shown in FIG. 7(b). In this regard, the color information 306 of the designated area shown in FIG. 7(a) includes two important colors, red and blue, as shown by 401 logo (logo: red) and 406 (page: blue) in FIG. 4. Furthermore, a color that the user wants to set as an important color is, for example, a monochrome logo (including a mark) or the color of the format of a paper document, and in such a case, the number of important colors is expected to be small, for example, "1" or "2".

On the other hand, if "number of colors in area (designated area)" = 5 as in this embodiment, actual scan data includes color variations, so in addition to the important colors red and blue, colors close to red The color information 306 (designated area) of the designated area may include a color close to blue or blue as a representative color. In such a case, the number of colors in the color information 306 of the specified area increases, so there is a risk that the compression efficiency will deteriorate. Therefore, it is desirable that the "number of colors in a region (designated region)" is smaller than the "number of colors in a region (non-designated region)." Therefore, by making the "number of colors in the area (designated area)" smaller than the "number of colors in the area (non-designated area)", the number of colors in the non-designated area where the second color reduction process of step S1106 was performed is Also, the number of colors in the designated area where the first color reduction process was performed in step S1104 is reduced. Thereby, the MFP 101 can maintain important colors even if the number of colors is reduced when compressing a color image, while improving compression efficiency with a more appropriate number of colors.

The disclosure of each embodiment includes the following configuration, method, and program.
(Configuration 1) Important color designation means for generating designation information by designating important colors from among the colors used in a color image;
color reduction processing means for generating a color reduction image by reducing the number of colors in the color image while leaving the important colors based on the specified information;
Color information integrating means for generating color information by converting a color determined to be close to the important color among the colors used in the color reduction image into the important color;
Binary image generation means for generating a binary image of the reduced color image for each color included in the color information;
Binary image compression means for generating compressed binary image data for each color included in the color information by compressing the binary image;
An image processing apparatus comprising: data integration means for generating compressed data by integrating the binary image compression data and the color information.
(Configuration 2) A first operation unit for a user to designate any region within the color image as a designated region;
The image processing apparatus according to configuration 1, wherein the important color designation means designates the important color from among the colors used in the designated area.
(Structure 3) The image processing apparatus according to Structure 2, wherein the specified area is a header area or a footer area.
(Structure 4) The color reduction processing means includes:
a first color reduction processing means that reduces the number of colors in the designated area to a first predetermined number while leaving the important colors based on the designated information;
Configuration 2 or 3 characterized in that it comprises a second color reduction processing means for reducing the number of colors in a non-designated area, which is an area excluding the designated area from the color image, to a second predetermined number set in advance. The image processing device described in .
(Structure 5) The image processing apparatus according to Structure 4, wherein the first predetermined number is smaller than the second predetermined number.
(Structure 6) The color reduction processing means includes:
a first determining means for determining a first representative color group having the first predetermined number of colors by selecting colors from the specified area in order of increasing number of pixels;
a second determining means for determining a second representative color group having the second predetermined number of colors by selecting colors from the non-designated area in order of increasing number of pixels;
The first color reduction processing means assigns the color used in the designated area to a color that is determined to be the closest among the colors in the first representative color group using an index representing a difference in color. , generate the reduced color image;
The second color reduction processing means assigns the color used in the non-designated area to a color that is determined to be closest among the colors in the second representative color group using an index representing a difference in color. The image processing apparatus according to configuration 4 or 5, wherein the image processing apparatus generates the color-reduced image.
(Structure 7) The color information integrating means generates the color information by converting a color of the second representative color group to a color determined to be close to a color of the first representative color group. The image processing device according to configuration 6, characterized in that:
(Configuration 8) The color information integrating means is configured to integrate the color information so that the number of colors in the color information is a third predetermined number preset as the maximum number of colors used in the decoded image of the color image. The image processing device according to configuration 7, wherein the image processing device generates the following.
(Configuration 9) The image processing device according to any one of configurations 1 to 8, further comprising a second operation unit for a user to input the number of important colors.
(Structure 10) The image processing apparatus according to any one of Structures 1 to 9, wherein the important color is a color of a logo or a color of a format in the color image.
(Structure 11) The image processing apparatus according to any one of Structures 1 to 10, wherein the color image is scan data.
(Method 1) An important color designation step of generating designation information by designating important colors from among the colors used in the color image;
a color reduction processing step of generating a color reduction image by reducing the number of colors in the color image while leaving the important colors based on the specified information;
a color information integration step of generating color information by converting a color determined to be close to the important color among the colors used in the color reduction image to the important color;
a binary image generation step of generating a binary image of the reduced color image for each color included in the color information;
a binary image compression step of generating compressed binary image data for each color included in the color information by compressing the binary image;
A method for controlling an image processing apparatus, comprising: a data integration step of generating compressed data by integrating the binary image compression data and the color information.
(Program 1) A program for causing a computer to execute each means of the image processing apparatus according to any one of Configurations 1 to 11.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and various modifications and changes can be made within the scope of the gist thereof. The present invention provides a program that implements one or more functions of each embodiment described above to a system or device via a network or a storage medium, and one or more processors of a computer in the system or device reads the program. It is also possible to implement the process by executing the process. The present invention can also be implemented by a circuit (eg, an ASIC) that implements one or more functions.

Furthermore, although the color image in this embodiment is scan data obtained by reading a paper document with the scanner unit 201, it is not limited to this, and may be created using a personal computer, smartphone, tablet terminal, imaging device, etc. It may also be a color image.

Further, in this embodiment, the MPF 101 has been described as a specific example of the image processing device of the present invention, but the present invention is not limited to this. There may be. Further, a personal computer, a smartphone, a tablet terminal, an imaging device, etc. may or may not have a scanner unit 201. However, when the scanner unit 201 is not provided and the color image is scan data, the scan data is sent to a personal computer, smartphone, tablet terminal, imaging device, etc.

101 MFP (image processing device)
301 Important color designation section (important color designation means)
302 Specification information 303 Color reduction processing section (color reduction processing means)
304 Color reduction image 307 Color information integration unit (color information integration means)
308 Integrated color information (color information)
313 Binary image generation unit (binary image generation means)
314 Binary image 315 Binary image compression unit (binary image compression means)
316 Binary image compressed data 317 Data integration section (data integration means)
318 Compressed data

Claims (13)

important color designation means for generating designation information by designating important colors from among the colors used in the color image;
color reduction processing means for generating a color reduction image by reducing the number of colors in the color image while leaving the important colors based on the specified information;
Color information integrating means for generating color information by converting a color determined to be close to the important color among the colors used in the color reduction image into the important color;
Binary image generation means for generating a binary image of the reduced color image for each color included in the color information;
Binary image compression means for generating compressed binary image data for each color included in the color information by compressing the binary image;
An image processing apparatus comprising: data integration means for generating compressed data by integrating the binary image compression data and the color information. comprising a first operation unit for a user to specify any area within the color image as a designated area;
The image processing apparatus according to claim 1, wherein the important color designation means designates the important color from among the colors used in the designated area. The image processing apparatus according to claim 2, wherein the specified area is a header area or a footer area. The color reduction processing means
a first color reduction processing means that reduces the number of colors in the designated area to a first predetermined number while leaving the important colors based on the designated information;
3. A second color reduction processing means for reducing the number of colors in a non-designated area, which is an area excluding the designated area from the color image, to a second predetermined number set in advance. 3. The image processing device according to 3. The image processing apparatus according to claim 4, wherein the first predetermined number is smaller than the second predetermined number. The color reduction processing means
a first determining means for determining a first representative color group having the first predetermined number of colors by selecting colors from the specified area in order of increasing number of pixels;
a second determining means for determining a second representative color group having the second predetermined number of colors by selecting colors from the non-designated area in order of increasing number of pixels;
The first color reduction processing means assigns the color used in the designated area to a color that is determined to be the closest among the colors in the first representative color group using an index representing a difference in color. , generate the reduced color image;
The second color reduction processing means assigns the color used in the non-designated area to a color that is determined to be closest among the colors in the second representative color group using an index representing a difference in color. 5. The image processing apparatus according to claim 4, wherein the reduced color image is generated by: The image processing device according to claim 6, characterized in that the color information integration means generates the color information by converting the colors of the second representative color group into colors that are determined to be close to the colors of the first representative color group. The color information integrating means generates the color information so that the number of colors in the color information is a third predetermined number preset as a maximum number of colors used in a decoded image of the color image. The image processing device according to claim 7, characterized by: The image processing apparatus according to claim 1, further comprising a second operation section for a user to input the number of important colors. The image processing apparatus according to claim 1, wherein the important color is a color of a logo or a color of a format in the color image. The image processing apparatus according to claim 1, wherein the color image is scan data. an important color designation step of generating designation information by designating important colors from among the colors used in the color image;
a color reduction processing step of generating a color reduction image by reducing the number of colors in the color image while leaving the important colors based on the specified information;
a color information integration step of generating color information by converting a color determined to be close to the important color among the colors used in the color reduction image to the important color;
a binary image generation step of generating a binary image of the reduced color image for each color included in the color information;
a binary image compression step of generating compressed binary image data for each color included in the color information by compressing the binary image;
A method for controlling an image processing apparatus, comprising: a data integration step of generating compressed data by integrating the binary image compression data and the color information. A program for causing a computer to execute each means of the image processing apparatus according to claim 1.

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