JP4742632B2 - Image processing apparatus, image processing method, and program - Google Patents

Description

  The present invention relates to an image processing apparatus, an image processing method, and a program for compressing image data.

  In recent years, with the widespread use of color printers, for example, business documents include color characters and color photographs. A document including such color information is digitized by a scanner or a copying machine and captured as a digital color image, and is used for processing such as editing, copying, and FAX transmission.

  However, in general, the amount of data of a digital color image is large, and when processing such as storage / communication is performed, the processing load on the hardware and network increases. Accordingly, there is a technique for compressing image data by a technique such as JPEG compression to reduce the amount of data related to storage or communication of digital color images.

  At this time, in order to further improve the compression rate, it is determined whether the image read from the scanner or the like is a digital color image or a monotone image, and if it is a monotone image, the color information is discarded and processed. The technology to do is also considered. As a specific example, it is determined whether or not a chromatic color is included in the read image, and when the chromatic color is included, the read image is subjected to compression processing as a digital color image, When a chromatic color is not included, some monotone images are subjected to compression processing by a method such as run length compression.

  Further, such a conventional image processing apparatus separates and divides the read image into a character area and a photographic area, determines whether the photographic area contains a chromatic color, and determines whether the photographic area includes a chromatic color. Is included, the read image is compressed as a digital color image, and if a chromatic color is not included, the image is compressed as a monotone image.

Patent Document 1 discloses a digital color copier equipped with such an image processing apparatus and outputting image data generated by the image processing apparatus.
JP-A-6-225167

  However, in the above-described conventional image processing apparatus, it is determined in common that all the separated and divided areas (character and photo areas) are handled as color or monotone. Therefore, even when a chromatic color is included only in a part of the photographic area, the entire image is treated as color image data and compressed. For this reason, compression efficiency may deteriorate.

  On the other hand, in the example of Patent Document 1, when a chromatic color is included in a character area, that is, even when a color character is included, if the photographic part is monotone, both the character area and the photographic area are monotone. The compression processing is performed as the image data. Therefore, even if the manuscript creator changes the color of a part of the text in order to emphasize a part of the character string in the sentence, the color is lost. There is a problem that the image is changed to an image that is not reflected.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an image processing apparatus capable of improving compression efficiency while retaining color information included in an original image. To do.

  The present invention for solving the problems of the above conventional example is an image processing apparatus, which separates image information to be processed and generates a plurality of image element information, and each of the image element information And a means for determining whether or not to perform compression as a color image, and a means for performing compression processing of each of the image element information based on the result of the determination.

  As described above, after the image to be processed is separated into image elements, either color or monotone compression processing is performed for each image element. That is, when a part of the image elements is a color image and the other image elements are monotone, the compression processing method is changed depending on whether or not each image element is a color. Thereby, it is possible to improve the compression efficiency while retaining the color information included in the original image.

  Here, the determination unit may determine that image element information satisfying a predetermined condition among the plurality of image element information is to be compressed as a monotone image.

  Further, a means for counting the number of chromatic pixels included in the image information to be processed as the total number of chromatic pixels, and the number of chromatic pixels included in the target image element information among the image element information. And a means for counting as the number of attention partial chromatic pixels, wherein the determination means is an image other than the attention image element information based on the counted total number of chromatic pixels and the number of attention partial chromatic pixels. It may be determined whether or not the element information is compressed as a color image.

  As a result, it is possible to determine whether or not image elements other than the image element of interest are compressed as color images without temporarily storing the below-described hole filling process results in the page memory, thereby saving memory resources and processing. The burden can be reduced.

  Here, the determination unit may determine whether or not to perform compression as a color image for each of the pixels forming the character shape and the background image serving as the background of the character shape.

  Also, an image processing method according to an aspect of the present invention separates image information to be processed, generates a plurality of pieces of image element information, and determines whether or not each of the image element information is compressed as a color image. And compressing each of the image element information based on the result of the determination.

  Furthermore, a program according to another aspect of the present invention includes a computer that separates image information to be processed and generates a plurality of pieces of image element information, and compresses each of the image element information as a color image. It is characterized in that a procedure for determining whether or not to perform and a procedure for performing compression processing of each of the image element information based on the result of the determination are characterized.

  Next, an image processing apparatus according to a first embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 1, the image processing apparatus 1 according to the present embodiment includes a processing control unit 11, a storage unit 12, an image input unit 13, an output unit 14, and an operation unit 15. ing.

  The processing control unit 11 is a program control device such as a CPU, and operates according to a program stored in the storage unit 12. In the present embodiment, the processing control unit 11 sets the image information input from the image input unit 13 as a processing target, performs predetermined image processing on the image information, and outputs the processed image data to the output unit 14. is doing.

  The storage unit 12 can be realized by a memory element such as a RAM or a disk device such as a hard disk. The storage unit 12 stores a program executed by the processing control unit 11. Further, the storage unit 12 stores image information and the like to be processed by the processing control unit 11, and also operates as a work memory of the processing control unit 11.

  The image input unit 13 is a scanner device, for example, and optically reads an image fixed on a paper medium or the like and outputs image information to be processed. In general, in the image information output by the image input unit 13, the value of each pixel is expressed in an RGB (red, blue, green) color space and output.

  The output unit 14 is, for example, a terminal or a printer connected to the network, stores the image data input from the processing control unit 11 as a file, and transfers it to a PC or the like connected to the network as necessary. It is formed on a medium and output.

  The operation unit 15 is a key input device, for example, and outputs the contents of the instruction operation to the processing control unit 11 in response to an input of a user instruction operation.

  Next, a specific example of processing in the processing control unit 11 will be described. In the present embodiment, the processing control unit 11 separates image information to be processed into a plurality of pieces of image element information, and performs compression processing as either a monotone image or a color image for each piece of image element information.

  In the following description, it is assumed that the processing control unit 11 processes a character area including characters as image element information and a background area including a pattern separately from input image information. Then, after separating the character region and the background region, the processing control unit 11 groups the character regions according to the color of the characters, binarizes them, and uses them for compression processing. For the background area, the presence / absence of a chromatic pixel is determined. If it is determined that the background area does not include a chromatic pixel, the background area is compressed as a monotone image (grayscale image). On the other hand, when it is determined that the background area includes chromatic pixels, the background area is compressed as a color image. In this way, one piece of compressed image information is generated including the image element information of the character area and the image element information of the background area, each compressed as an image having a property selected from either color or monotone.

  That is, highly efficient compression processing is selectively applied to each piece of image element information, and information about colors is retained. Thereby, it is possible to improve the compression efficiency while retaining the color information included in the original image.

  Next, the process of this process control part 11 is demonstrated in detail, referring FIG. FIG. 2 is a functional block diagram relating to image processing executed by the processing control unit 11.

  As shown in FIG. 2, the image processing executed by the processing control unit 11 functionally includes a color conversion unit 21, a preprocessing unit 22, a connected pixel extraction unit 23, a character region separation unit 24, and a character. The same color separation unit 25, binarization compression processing unit 26, background image filling processing unit 27, background image color determination unit 28, background image compression processing unit 29, and file composition unit 30 are included. It is configured.

  The processing control unit 11 according to the present embodiment first stores the read image information input from the image input unit 13 in the storage unit 12. Then, the image processing of FIG. 2 is started.

  Here, the color conversion unit 21 reads out the image information held in the storage unit 12 and converts the color space of the value of each pixel of the image information. Here, since the read image information is expressed in the RGB color space, for later image processing, for example, YCbCr (consisting of a luminance component and a color difference component) is used as a color space in which the luminance component is separated as an independent component. Color space) and output. Note that the processing of the color conversion unit 21 is not necessarily required when the image information to be processed uses a color space in which the luminance component is included as an independent component in advance.

  The preprocessing unit 22 detects noise in the image information output from the color conversion unit 21 and removes the detected noise from the document image data (noise removal processing). Filter processing such as processing for clarifying the contour (edge enhancement processing) is performed. The preprocessing unit 22 stores the filtered image information in a page memory secured in the storage unit 12.

  The connected pixel extracting unit 23 extracts a connected pixel group (a portion in which significant pixels are continuous) from the image information held in the storage unit 12. The connected pixel extraction unit 23 associates different label identifiers with each extracted connected pixel group. This process is a process called a so-called labeling process, and is a widely known process, and a detailed description thereof will be omitted here. In the present embodiment, the connected pixel extraction unit 23 associates information for specifying a connected pixel group (for example, coordinate values of each pixel included in the connected pixel group) and a label identifier, and stores the connected pixel data as the storage unit 12. To store.

  The character region separation unit 24 sequentially reads out the connected pixel groups included in the connected pixel data while referring to the connected pixel data stored in the storage unit 12, and among the connected pixel groups, the connected pixels related to the character image. Identify the group. Here, the determination of whether or not the connected pixel group is related to a character image is performed based on, for example, the circumscribed rectangle of the connected pixel group and the size (height, width, area, etc.). In other words, this method selects a circumscribed rectangle having a size corresponding to the size of the character on the assumption that the size of the character included in the image information is about 6 to 50 points. . The determination in the present embodiment is not limited to this, and based on the ratio between the area of the circumscribed rectangle and the area of the connected pixel group portion, the perimeter of the connected pixel group, etc., whether or not the character is a character is determined. You may judge.

  The character region separation unit 24 identifies the circumscribed rectangles of the connected pixel group that relate to the character region, and coordinates information (processing) that identifies the position of the character region, such as the position coordinates of the upper left corner and the lower right corner of the circumscribed rectangle. Coordinate information on target image information) is generated as character area coordinate data. Further, the character region separation unit 24 extracts bitmap data in the region specified by the character region coordinate data from the image information to be processed as character shape data for specifying the character shape. Then, the character region separation unit 24 stores an entry in which the character shape data is associated with the corresponding character region coordinate data in the storage unit 12 as an entry in the character region database.

  The character area identical color separation unit 25 sequentially reads character area coordinate data from the character area database stored in the storage unit 12. Then, on the image information to be processed, the data portion of the area corresponding to the read character coordinate data is referred to, and a representative value is determined for the pixel value included in the data portion. That is, the character area identical color separation unit 25 determines a representative color for each pixel group constituting each character.

  Here, the representative color (representative value) is determined as follows. For example, the character region identical color separation unit 25 may calculate an average value of gradation values of pixels constituting a character and use the average value as a representative value. Here, the average value is calculated by adding all the gradation values of significant pixels (pixels constituting the character) included in the character area and dividing the total value by the number of pixels constituting the character. Although the example using the average value has been described here, the representative value may be calculated by another method such as a method using another statistical value (for example, the mode value).

  In this way, the character region same color separation unit 25 determines a representative color for the character in the region corresponding to the read character coordinate data, and adds information on the representative color to the entry including the read character coordinate data, Add to the character space database.

  Further, the character area identical color separation unit 25 determines the representative color of the character in the area defined by all the character area coordinate data included in the character area database, and then performs the following process. That is, the character area identical color separation unit 25 refers to the character area database and groups the entries according to the difference between the representative values included in each entry within a predetermined range. For example, the character region identical color separation unit 25 selects one entry included in the character region database as a target entry, and associates a group identifier unique to the target entry and stores it in the storage unit 12. Further, the representative value (remarked representative value) included in this attention entry is acquired in advance. Then, entries other than the target entry are sequentially selected as comparison target entries, and while calculating the representative value (target representative value) included in the comparison target entry, the difference between the target representative value and the target representative value is calculated, When the difference is less than the predetermined range, the same group identifier as that associated with the target entry is stored in the storage unit 12 in association with the comparison target entry. Hereinafter, the above process is repeated until there is no entry associated with the group identifier while selecting one entry with no group identifier associated as the target entry.

  By this processing, even if the gradation value of each pixel varies during reading by the image input unit 13, the variation can be suppressed.

  The binarization compression processing unit 26 sequentially reads each entry from the character area database. Then, the character shape data (bitmap data) included in the read entry is binarized. As a result, the pixels (significant pixels) included in the character shape data and constituting the character are black pixels, and the other pixels are white pixels.

  Further, the binarization compression processing unit 26 scans the binarized character shape data in a raster scan order (from the upper left corner of the bitmap one line at a time from left to right, and moves to the lower line). While scanning, the character shape data binarized is run-length compressed by a technique such as MMR (Modified Modified Read) while scanning. The binarized compression processing unit 26 stores the compressed character shape data after the run length compression by overwriting the original character shape data.

  Thus, the storage unit 12 stores an entry that associates the compressed character shape data, the character region coordinate data, and the representative value information for each character information included in the image information to be processed. Will be.

  The background image embedding processing unit 27 sets the pixel value corresponding to the significant pixel in each character region generated by the character region separation unit 24 in the image information to be processed, in the vicinity of the pixel, It sets based on pixel values other than the pixel corresponding to the significant pixel in an area | region. For example, the background image filling processor 27 sequentially selects each pixel included in the image information to be processed as a target pixel while scanning each pixel in the scan line order. Then, it is checked whether or not the selected target pixel is a pixel corresponding to a significant pixel in each character region generated by the character region separation unit 24. If not, the pixel value of the target pixel is It is stored in the storage unit 12 as the immediately preceding value. If the target pixel is a pixel corresponding to a significant pixel in each character region generated by the character region separation unit 24, the value of the target pixel is replaced with the immediately preceding value held in the storage unit 12. .

  Thereby, the pixel which comprises a character shape is replaced with the pixel value of the background image of the vicinity among the image information used as the process target. Then, the background image embedding processing unit 27 secures the image information after the replacement in the page memory secured in the storage unit 12 as the image element information of the background area (separately from the page memory storing the pre-processed image). Page memory, hereinafter referred to as second page memory for distinction).

  When this process is performed, for example, when a chromatic color is included in the character portion and the background image includes only monotone pixels, the chromatic color constituting the character is overwritten with the monotone pixel values in the vicinity thereof, The background area is an image composed of only monotone pixels.

  The background image color determination unit 28 checks whether or not there is a chromatic pixel in the background area image held in the second page memory. If there is a chromatic pixel, the background image color determination unit 28 determines that the background region is a color image, and outputs the determination result to the background image compression processing unit 29. If there is no chromatic color pixel, the background area is determined to be a monotone image, and the determination result is output to the background image compression processing unit 29.

  The background image color determination unit 28 also counts the number of chromatic pixels included in the background region image input from the background image filling processing unit 27, and the number of chromatic pixels is set to a predetermined threshold value. If it is smaller, it may be determined that the image in the background area is a monotone image.

  In the description so far, the determination of whether or not the color is a chromatic color is performed as follows, for example. That is, the color difference component (Cb, Cr) of the pixel is detected, and the gradation value of both the color difference components is an intermediate value within the possible range (for example, if the color difference component is 8 bits, the intermediate value is 128). If it is an intermediate value, it is determined that the pixel is a monotone, and if not, it is determined that the pixel is a chromatic color. In this case, in consideration of the case where there is noise or an error in the color difference component, when the gradation value of both color difference components is in a predetermined range including an intermediate value (for example, from 125 to 131), the pixel is monotone. You may make it determine with it being a pixel of this.

  The background image compression processing unit 29 refers to the determination result input from the background image color determination unit 28, and uses the method determined in advance according to the determination result to store the image of the background area held in the second page memory. Is compressed to generate compressed background image data. For example, when a determination result that the background area image is a monotone image is input, multivalue compression processing is performed on the luminance component (Y) for each pixel of the background area image. When a determination result that the background area image is a color image is input, for each pixel of the background area image, both the luminance component (Y) and the color difference components (Cb, Cr) are input. Perform compression processing. As a compression method in this case, for example, a method such as JPEG compression is used.

  The file composition unit 30 generates one compressed image data including the compressed background image data and the compressed character area data, and outputs it to the output unit 14. The file compositing unit 30 expands the compressed background image data and generates an image of the background area as a bitmap in response to an external data read instruction, and the compressed character area data. May be included to reproduce the character area data, expand the character shape data, color the representative color, and draw the character. Thereby, printing to a printer is also possible.

  Next, the operation of the image processing apparatus 1 of this embodiment will be described. In the following description, as shown in FIG. 3, the image to be processed is composed of a color character string L1 (red here), a black character string L2, and a monotone pattern portion P. To do.

  The image processing apparatus 1 of the present embodiment extracts a circumscribed rectangle of the character area from the image information of the image shown in FIG. 3, and assigns a common group identifier to each character having a common representative color. 4A and 4B illustrate a circumscribed rectangle (indicated by a broken line in FIGS. 4A and 4B) that includes the entire character area to which a common group identifier is assigned.

  Further, significant pixels included in the character area are removed from the image information (FIG. 3) to be processed (FIG. 4 (c)), and a hole filling process is performed to generate an image of the background area (FIG. 4). 4 (d)).

  Here, the image processing apparatus 1 checks whether each of the character area and the background area is a color image or a monotone image. In the example of FIG. 3, since the character string L1 shown in FIG. 4A is red, it is determined to be a color image. Since the character string L2 shown in FIG. 4B is black, it is determined to be a monotone image. Furthermore, since the background area shown in FIG. 4D is monotone in this example, it is determined to be a monotone image.

  Therefore, the image processing apparatus 1 performs multi-value compression processing on the background area as a monotone image. Further, regarding the character region, the region including the black character string L2 is binarized and subjected to compression processing, and the representative color (black) of the target region database is associated with the compressed data. Further, the region including the red character string L1 is similarly binarized and subjected to compression processing, and the representative color (red) of the target region database is associated with the compressed data.

  In the above description, after the character region separation unit 24 generates the character region coordinate data and the character shape data, the character region identical color separation unit 25 groups each character region according to the representative color. However, it is not limited to this. For example, after generating the character area coordinate data and the character shape data, the color of the character area is determined with reference to the original image information to be processed, and it is determined that the character area includes a plurality of character colors. In this case, the image of each character area may be grouped by the representative color.

  Although an example in which the character region and the background region are separated has been described here, the character region, the design region, and the background region may be separated into three layers. Here, the picture area is defined by a rectangle circumscribing a relatively large size (for example, a size exceeding 50 points of a character) of a connected pixel group of significant pixels.

  Further, in place of the image processing shown in FIG. 2, whether or not the background area is handled as a color image is determined without generating the background area image, and a page memory for holding the background area image. The amount may be adjusted flexibly. That is, in the example shown in FIG. 2, since it is not known until the background area image is actually generated whether or not the background area is a color image, the page memory for holding the background area image is set as a color image. It was necessary to secure the image in a size that can hold one page, complete the generation of the background image for one page, determine whether the image is a color image, and then perform compression processing. By determining whether the background area is a color image or a monotone image before generation, compression processing while generating the background area image is possible, so the memory size that holds the background image is compressed. It is also possible to ensure that only the necessary band is required.

  Next, a second embodiment of the present invention according to this example will be described. The image processing apparatus 1 of the present embodiment has the same configuration as that of the first embodiment, but the contents of processing in the processing control unit 11 are different.

  That is, the processing control unit 11 according to the present embodiment performs color determination of the background area by determining the number of chromatic pixels included in the entire image information to be processed and the number of chromatic pixels included in the character area. The number of chromatic pixels to be included in the background region is estimated by counting (counting) and calculating the difference, and it is determined whether or not the background region is handled as a color image.

  That is, when the difference is smaller than a certain threshold value, it is determined that the background area should be treated as a monotone image, assuming that the background area does not include a chromatic color. Thereby, the capacity of the second page memory described in the first embodiment can be flexibly adjusted.

  As a specific example, image processing executed by the processing control unit 11 in the present embodiment will be described with reference to FIG.

  The image processing executed by the processing control unit 11 of the present embodiment is functionally the same as the color conversion unit 21, the preprocessing unit 22, the connected pixel extraction unit 23, the character region separation unit 24, and the character region. Color separation unit 25, binarization compression processing unit 26, background image filling processing unit 27, background image color determination unit 28 ′, overall image chromatic color pixel count unit 41, and character region chromatic color pixel number The count unit 42, the background image compression processing unit 29, and the file composition unit 30 are configured. In addition, about the thing which performs the process similar to what concerns on 1st Embodiment, the same code | symbol is attached | subjected and detailed description is abbreviate | omitted.

  The total image chromatic color pixel count counting unit 41 counts the number of chromatic pixels included in the image information after color conversion output from the color conversion unit 21. As a specific example, the whole image chromatic color pixel number counting unit 41 scans each pixel of the image information after color conversion stored in the storage unit 12 in the raster scan order, and the color difference components (Cb, Cr) The number of pixels (the number of chromatic pixels) that are outside the predetermined range from the intermediate value of the range that both of the gradation values can take (the intermediate value is 128 if the color difference component is 8 bits) Count. Then, the counted value is output as the total number of chromatic color pixels.

  In addition, the character area chromatic color pixel number counting unit 42 reads information on the image of the character area generated by the character area same color separation unit 25 from the storage unit 12 and selects an entry whose representative color is a chromatic color. The number of significant pixels in the character area corresponding to the entry (the number of chromatic pixels for each character area) is counted and summed up. Thus, the number of chromatic pixels in the entire character area is obtained. Then, the obtained value is output as character chromatic color pixel number data.

  The background image color determination unit 28 'calculates a difference obtained by subtracting the character area chromatic color pixel number data from the entire image chromatic color pixel number data. If the difference is equal to or smaller than a predetermined threshold, it is determined that the background area image is a monotone image. On the other hand, when the difference is larger than the threshold value, it is determined that the image in the background area is a color image. The result of this determination is output to the background image hole filling processing unit 27, and the background image hole filling processing unit 27 performs hole filling processing using only necessary color components based on the result of the determination. The background image compression processing unit 29 also determines whether the image of the background area is compressed as a color image or a monotone image based on the result of this determination, and the background image is output to the background image output from the hole filling processing unit. On the other hand, sequential compression processing is performed by the determined method.

  Furthermore, in the first and second embodiments described above, a photograph or the like may be converted into a monotone even if it is a color photograph. In such a case, regarding the pattern area, regardless of whether or not a chromatic color pixel value is included therein, it may be determined that the image area is a monotone image, and color information may be discarded and compression processing may be performed. . Thereby, compression efficiency can be improved. In this case, this processing may be performed when the user performs an instruction operation for discarding the color information about the pattern area from the operation unit 15.

1 is a configuration block diagram of an image processing apparatus according to a first embodiment of the present invention. 1 is a functional block diagram of an image processing apparatus according to a first embodiment of the present invention. It is explanatory drawing showing the example of the image information used as a process target. It is explanatory drawing showing the image processing example of the image processing apparatus which concerns on the 1st Embodiment of this invention. It is a functional block diagram of the image processing apparatus which concerns on the 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image processing apparatus, 11 Processing control part, 12 Storage part, 13 Image input part, 14 Output part, 15 Operation part, 21 Color conversion part, 22 Pre-processing part, 23 Concatenated pixel extraction part, 24 Character area separation part, 25 Character area same color separation unit, 26 binarization compression processing unit, 27 background image filling processing unit, 28, 28 'background image color determination unit, 29 background image compression processing unit, 30 file composition unit, 41 overall image chromatic color Pixel number counting unit, 42 Character area chromatic color pixel number counting unit.

Claims (4)

It means for separating the image information of one document to be processed in the image information of the image information and the background area of the character region,
Determination means for determining the presence or absence of a chromatic color in the background region based on the image information of the background region;
Means for selectively executing compression processing as a monotone image and compression processing as a color image on the image information of the background area according to the determination result of the determination means;
Means for determining a representative color of each character based on image information of the character region;
Means for grouping the image information of the character area for each of the representative colors within a predetermined range;
Means for performing binarization processing on the image information of the character region and compressing the image information;
Means for associating the representative color with the compressed image information of the character area;
An image processing apparatus comprising: The image processing apparatus according to claim 1.
Means for counting the number of chromatic pixels included in the image information to be processed as the total number of chromatic pixels;
Means for counting the number of chromatic pixels included in the character area as the number of chromatic pixels in the character area ;
Said determining means, said had counted the whole chromatic pixel number and the character region chromatic group Dzu to the number of pixels, it is determined whether to compress the image information of the background region as a color image,
An image processing apparatus. Separating image information of one document to be processed into image information of a character area and image information of a background area ,
Based on the image information of the background area, determine the presence or absence of chromatic color in the background area,
In accordance with the determination result, a compression process as a monotone image and a compression process as a color image are selectively executed on the image information of the background area,
Determining the representative color of each character based on the image information of the character region;
Grouping the image information of the character region for each of the representative colors within a predetermined range,
After performing binarization processing on the image information of the character area, the image information is compressed,
Associating the representative color with the compressed image information of the character area;
An image processing method. On the computer,
A procedure for separating image information of one original to be processed into image information of a character area and image information of a background area ;
A procedure for determining the presence or absence of a chromatic color in the background region based on the image information of the background region;
A procedure for selectively executing a compression process as a monotone image and a compression process as a color image for the image information of the background region according to the determination result;
A procedure for determining a representative color of each character based on image information of the character region;
A procedure for grouping the image information of the character region for each of the representative colors within a predetermined range;
A procedure of performing binarization processing on the image information of the character region and compressing the image information;
Associating the representative color with the compressed image information of the character region;
A program characterized by having executed.

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