JP2006333175A - Image processor, image processing method and image processing program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To attain character quality uniform with a high compression rate by using a simple image processing mode. <P>SOLUTION: Image data is separated into a character region and a non-character region, that is, a foreground region and a background region on the basis of a characteristic amount such as a distribution state of histogram and is separately stored in a separated data storing part 232. A representative color discriminating part 233 represents one plane by a monochromatic image on the basis of the image data stored in the foreground image storing part of the separated data storing part 232 and discriminates the number of colors of the foreground region on the basis of this representation result. Compression processing corresponding to the discriminated number of colors of the foreground region is applied to the foreground region, and the foreground region is stored in a data by colors storing part 234. However, when the discriminated number of colors of the foreground is within the range between one and five colors, a foreground color rechecking/region reextracting part 235 discriminates the number of colors of the foreground region again. When the number of colors is discriminated to be large, the region is switched from the foreground region to a background region and compressed as a background region. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image processing apparatus, an image processing method, and an image processing program that compress and store document image data input using an image input device such as a scanner device or a digital camera at a high compression rate.

In recent years, scanner devices and digital camera devices have become widespread, and various techniques for facilitating the handling of image information in image information processing have been developed. One of them is a compression coding technique for image information used for shortening the communication time when transmitting / receiving a file by personal computer communication or the like, and storing a large amount of data in a storage device.
This compression encoding technology for image information is a technology for reducing the amount of image information, and there are a variety of methods depending on the characteristics and application of the image data.
Conventionally, various compression processing techniques for reducing image data have been proposed including the following patent documents.
JP 2004-248271 A

Patent Document 1 proposes a technique for improving the efficiency of compression encoding, improving the convenience of image data, and improving the efficiency of image processing by compressing and encoding as different components for each region of an image. .
Specifically, first, the read image data is divided into a plurality of regions by performing image region separation. Then, a different component is created for each divided image region, and the image is compression-encoded with different settings (compression encoding method, quantization level, data format, etc.) for each component as necessary.
In particular, by dividing an image into a specific area and other areas, or a character area, a line drawing area, a photographic area, and a background area, compression coding according to the characteristics of the area can be executed.

In addition to the technique proposed in Patent Document 1 described above, a high compression technique in which the compression rate of image data is further increased is also proposed.
In this high compression technique, a technique of subtracting the foreground (character) image is used to ensure a high compression rate.
In particular, when the foreground color is one color and the image data can be expressed in 1 bit / pixel, it is possible to cope with a method capable of high compression in general, such as MMR (Modified Modified READ: G4 facsimile encoding method) compression.

When the foreground is expressed by one color, it is an essential condition that the document is a monotone image or that the character portion serving as the foreground is expressed by one color.
For this reason, it is usually set so that the foreground state of the document is determined by performing gray scale discrimination processing and the like, and the foreground is processed with one color only when it is in gray scale.

In order to automatically switch the method of high compression processing according to the original image appropriately, determination processing such as gray scale determination processing for automatically acquiring information of the original image (original) such as the foreground state is required.
However, it is possible to identify malfunctions (error processing) such as determining a yellowish original image such as newspaper as a color image, or determining an original image with a small amount of line marker or handwritten red pen as a monochrome image. There is a risk that this will occur at the stage.

When such a malfunction occurs, an erroneous determination result different from the actual document information is obtained at the stage of the determination process, so that the expected image processing result cannot be obtained in many cases.
In view of this, the present invention provides a first image processing apparatus, an image processing method, and an image processing program that enable image compression that achieves a high compression rate and uniform character quality using a simple image processing method. Objective.
In addition, the present invention is an image processing that can suppress the influence of the influence on the data after the compression encoding process even when erroneous processing is performed in the foreground (character) information determination process. A second object is to provide an apparatus, an image processing method, and an image processing program.

  In the first aspect of the present invention, a separation unit that separates image data into a foreground region that is a character part and a background region that is a non-character part, and a plane in the foreground region separated by the separation unit is a monochromatic image. A color number determination unit that expresses and determines the number of colors in the foreground region based on the result, and a compression unit that compresses data using a predetermined compression method according to the number of colors determined by the color number determination unit And the storage means for storing the image data compressed by the compression means in a predetermined storage area for each compression method, to achieve the first object.

  In the invention according to claim 2, in the invention according to claim 1, when the number of representative colors determined by the number-of-colors determination unit is less than a predetermined number, before performing compression processing by the compression unit, Re-discriminating means for discriminating the number of colors in the foreground area again, and when the number of colors discriminated by the redetermining means is larger than the number of colors discriminated by the color number discriminating means, And switching means for switching to the second object.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, at least one of the number-of-colors discriminating means and the redetermining means has one representative color of the foreground image for each plane. The number of colors in the foreground region is determined based on the determined representative color information.

  According to a fourth aspect of the present invention, in the first, second, or third aspect of the present invention, a plurality of planes in the foreground area are set.

  According to a fifth aspect of the present invention, in the first, third, fourth, or fifth aspect of the present invention, at least one of the color number determining means and the re-discriminating means is an edge portion in the foreground region. The number of colors in the foreground region is discriminated based on the color feature information excluding.

  The invention according to claim 6 is an image processing method used when performing compression processing of image data using a computer, wherein the image data includes a foreground area that is a character part, a background area that is a non-character part, and And a second step of expressing the plane in the foreground region separated in the first step as a single color image and determining the number of colors in the foreground region based on the result, A third step of compressing data using a predetermined compression method according to the number of colors determined in the second step, and a method of compressing the image data compressed in the third step into a predetermined storage area And the fourth step of storing separately to achieve the first object.

  According to the seventh aspect of the present invention, there is provided an image processing program used when image data compression processing is performed using a computer, wherein the image data includes a foreground region that is a character portion, a background region that is a non-character portion, and A separation function for separating the image into a plurality of colors, a plane in the foreground area separated by the separation function stage is expressed by a single color image, and a color number determination function for determining the number of colors in the foreground area based on the result, and the number of colors A compression function for compressing data using a predetermined compression method according to the number of colors determined by the determination function; a storage function for storing image data compressed by the compression function in a predetermined storage area for each compression method; The first object is achieved by realizing the above in a computer.

  According to the first, sixth, or seventh aspect of the invention, the number of colors in the foreground area is determined based on the result of expressing the plane in the foreground area with a single color image, and a predetermined number corresponding to the determined number of colors is determined. By compressing data using this compression method, it is possible to perform image compression that achieves a high compression rate and uniform character quality using an image processing method that is simple in the compression means.

  According to the second aspect of the present invention, the number of colors in the foreground area is determined again before performing the compression process, and the number of colors determined again is larger than the number of colors determined by the color number determination means. By switching the corresponding foreground area to the background area, even if it is erroneously processed in the foreground (character) information discrimination process stage, the effect is reflected in the data after the compression encoding process. Can be suppressed.

According to the invention described in claim 3, by appropriately determining the number of colors in the foreground area based on the representative color information for determining one representative color of the foreground image for each plane, The number can be determined.
According to the invention described in claim 4, by setting a plurality of planes in the foreground area, it is possible to cope with compression of image data having a plurality of character colors.
According to the fifth aspect of the present invention, it is possible to appropriately determine the number of colors in the foreground area by determining the number of colors in the foreground area based on the color feature information excluding the edge portion in the foreground area.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to FIGS.
In the present embodiment, a digital copying machine will be used as an example of an image forming apparatus equipped with an image processing apparatus that performs image data encoding processing.
FIG. 1 is a block diagram showing a schematic configuration of a digital copying machine 1 according to the present embodiment.
The digital copying machine 1 includes a printer engine 2 that forms an image on a sheet or the like by an electrophotographic process, and a scanner 3 that reads an image of a document.

The digital copying machine 1 includes a controller 5 having a microcomputer. The controller 5 includes a main controller that controls the entire digital copying machine 1 and a plurality of sub-controllers that control each part of the controller 5.
The printer engine 2 includes a photoreceptor, a developing device, a cleaning device, and a charging device, and processes for forming dry toner images of K, M, C, and Y (black, magenta, cyan, and yellow) colors. Electrostatic latent images of K, M, C, and Y color images are optically written on the photosensitive members of the cartridges 11K, 11M, 11C, and 11Y, the transfer belt 12, the fixing device 13, and the process cartridges 11K, 11M, 11C, and 11Y. Color writing devices 14K, 14M, 14C, and 14Y are provided.

The digital copying machine 1 also includes paper feed trays 15a to 15c that store transfer materials (recording paper, OHP, etc.) for recording color images.
The process cartridges 11K, 11M, 11C, and 11Y are formed by superimposing toner images of K, M, C, and Y colors on the transfer belt 12.
The superimposed toner images are transferred to a transfer material supplied from the paper feed trays 15 a to 15 c and fixed by the fixing device 13.
The digital copying machine 1 also includes an image processing device 26 having a band buffer 22, an encoding unit 23, a decoding unit 24, and a page memory 25.

The band buffer 22 is a buffer for storing pixel data included in one band among a plurality of bands constituting image data for one page. A band indicates a region of image data composed of a predetermined number of pixel lines.
The digital copying machine 1 is configured to receive image data from a predetermined network 4 such as a LAN via a communication interface (not shown).
When the image data input via the network 4 is data in the PDL (page description language) format, the RIP unit 21 performs drawing processing on a band basis and converts it into a bitmap format, and the image processing device 26 Output to.

The encoding unit 23 is an encoding device for encoding the image data stored in the band buffer 22.
The decoding unit 24 is a decoding device for decoding the compression code.
The page memory 25 is a memory for storing (storing) image data for a predetermined page as a compression code. The page memory 25 according to the present embodiment can store a compression code string for one page of A4 size image data.

The hard disk 27 is a memory (storage device) provided to acquire and store the compression code string stored in the page memory 25 and to re-store the compression code string in the page memory 25 as necessary.
The RGB → CMYK conversion unit 28 receives image data represented by RGB (red, green, blue) color signals in band units from the band buffer 22 and converts them into CMYK signals.
The K, M, C, and Y color gradation processing units 29K, 29M, 29C, and 29Y each perform a function of reducing the K, M, C, and Y color multivalued data and converting it into write data.

In the present embodiment, the band buffer 22 stores 600 dpi image data of 8 bits per pixel, which is converted to 1200 dpi of 1 bit per pixel by the K, M, C, and Y color gradation processing units 29K, 29M, 29C, and 29Y. Convert to image data.
The K, M, and C color write data are stored in the line memories 16K, 16M, and 16C in order to adjust the image formation start timing, and the K, M, and C color data are overlapped on the transfer material. M, C, and Y color writing devices 14K, 14M, 14C, and 14Y, that is, the printer engine 2 that performs image formation.

FIG. 2 is a diagram illustrating functional blocks of the encoding unit 23 according to the present embodiment.
The encoding unit 23 includes an input image storage unit 230, a binarization / region recognition unit 231, a separated data storage unit 232, a representative color determination unit 233, a color-specific data storage unit 234, a foreground color recheck / region reextraction unit 235. , A gray / color discrimination unit 236 and an output image data storage unit 237 are provided.
The input image storage unit 230 is an area for storing image data read (input) from the band buffer 22.

The binarization / region recognition unit 231 performs binarization processing and region recognition (identification) processing on the image data stored in the input image storage unit 230, and converts the image data into foreground (character) data and background data. And to separate.
The binarization process is a process for obtaining a binary image from a grayscale image. Here, threshold processing is used. Note that the threshold setting method used in this process is a method based on a density histogram, a method that utilizes the local properties of an image, a method that uses this property, a method that divides an image into several, and sets each region, There are adaptive processing methods.

The area recognition (identification) process is a process for recognizing (identifying) a character area and a non-character area. Here, the analysis is performed by analyzing the feature amount of the image data, for example, the distribution state of the histogram.
The separated data storage unit 232 is a region for storing foreground (character) data and background data separated by the binarization / region recognition unit 231 according to data, and includes a foreground image storage unit and a background image storage unit. Yes.

The representative color determination unit 233 determines the number of colors of the foreground (character) data based on the image data stored in the foreground image storage unit of the separation data storage unit 232.
Specifically, one representative color of the foreground image is determined for each plane, that is, the number of colors of foreground (character) data when the foreground image is expressed as a single color image for each plane is determined.
Here, the number of representative colors of the foreground image data is determined (determined) based on the histogram distribution and the color continuity of color information excluding the feature amount of the foreground image data, for example, the edge portion of the foreground image data.

For each color type of the foreground (character) data discriminated by the representative color discriminating unit 233, the color-specific data storage unit 234, specifically, foreground for each of the full color, 6 to 256 colors, 2 to 5 colors, and one color. (Character) This is an area for storing data.
The foreground color re-check / area re-extraction unit 235 checks the foreground color again for the data stored in the 2-5 color data storage unit and the 1 color data storage unit in the color-specific data storage unit 234, and displays the representative color If there is a color that is not included, the dot is switched from foreground to background.

The gray / color determining unit 236 determines whether the image data stored in the background image storage unit of the separated data storage unit 232 is gray image data or color image data.
The output image data storage unit 237 is a region for storing processed image data in a different compression format for each region, and includes a foreground JPEG format storage unit, a foreground mask MMR format storage unit, and a foreground (character) PNG format. A storage unit, a foreground (character) MMR format storage unit, and a background 8/24 bit JPEG format storage unit are provided.
The background 8 / 24-bit JPEG format storage unit is configured to store 8-bit data and 24-bit data separately.

  JPEG (Joint Photographic Experts Group) indicates an international standard method for still image compression standardized by a joint working group of ISO and ITU-T. MMR (Modified Modified READ) is an ITU-T recommendation T.264. 6 indicates an image encoding method of G4 facsimile, and PNG (Portable Network Graphics) indicates an image file format developed in consideration of handling graphics data in a network environment.

  The encoding unit 23 hierarchically compresses and encodes the data finally stored in the output image data storage unit 237 for each tile to generate code data. Then, the encoding unit 23 combines the generated code data into one code string.

Next, image processing in the encoding unit 23 according to the present embodiment will be described.
FIG. 3 is a flowchart showing a procedure of image processing in the encoding unit 23 according to the present embodiment.
First, the encoding unit 23 inputs the image data (image data) read from the band buffer 22 to the input image storage unit 230 (step 11). This image data is full-color image data.

Then, the binarization / region recognition unit 231 executes an optimal binarization process on the image data stored in the input image storage unit 230 (step 12). Note that these processes are performed by analyzing the distribution state of the histogram indicating the characteristics of the image data.
After performing the binarization processing, the binarization / region recognition unit 231 executes region recognition (identification) processing (step 13). Here, ruled line image identification, line data extraction, and the like are performed.

The binarization / region recognition unit 231 separates the binarized and region recognition (identification) image data into foreground (character) data and background data (step 14).
When separated as foreground (character) data (step 14; foreground), the separated foreground (character) image data is stored in the foreground image storage unit of the separated data storage unit 232 (step 15).
If the background data is separated (step 14; background), the separated background image data is stored in the background image storage unit of the separated data storage unit 232 (step 22).

Next, the representative color determining unit 233 executes a representative color determining process for determining the number of colors of the foreground (character) data based on the image data stored in the foreground image storage unit of the separated data storage unit 232 (step 16). ).
Here, the type of the number of colors of the foreground (character) data, that is, four types of patterns including full color, 6 to 256 colors, 2 to 5 colors, and 1 color are discriminated.
The foreground (character) data color number discrimination processing is performed by histogram distribution state analysis processing, color set clustering, or the like.

  When the data of the target image is determined to be full color or 6 to 256 colors (step 16; full color, 6 to 256 colors), the representative color determination unit 233 outputs the image data to the foreground color JPEG in the output image data storage unit 237. Output to corresponding areas of the format storage unit, foreground mask MMR format storage unit, foreground (character) PNG format storage unit, foreground (character) MMR format storage unit, and background 8 / 24-bit JPEG format storage unit (step 17), and the process is terminated. To do. Note that when outputting to the output image data storage unit 237, compression processing of a predetermined format is performed and stored as compressed foreground image data.

On the other hand, when the data of the target image is determined to be 1 to 5 colors (step 16; 1 to 5 colors), the foreground color re-check / area re-extraction unit 235 performs the 2 to 5 color data in the color-specific data storage unit 234. The foreground color is checked again for the data stored in the storage unit and the one-color data storage unit, and a color extraction process not included in the representative color is performed (step 18).
Then, as a result of checking the foreground color again, it is determined whether or not a color extraction process not included in the representative color has been performed, that is, whether or not only the foreground color is present (step 19). Specifically, it is determined whether or not the image data includes (exists) a color (other color) different from the color extracted in the previous determination process.

If the image data does not include a color (other color) different from the color extracted in the previous determination process (step 19; Y), the process proceeds to step 17, and the image data of that area is stored.
On the other hand, when the image data contains a color (other color) different from the color extracted in the previous discrimination process (step; N), the color is extracted in the different color / non-different color area separation process, that is, the previous discrimination process. A region of a color different from the selected color (different color) and a region of a color that is not that color (non-different color) are separated (step 20).

If it is separated as a non-different color area (step 20; non-different color area), the process proceeds to step 17 to store the image data of that area.
On the other hand, when separated as a different color area (step 20; different color area), the foreground color re-check / area re-extraction unit 235 performs a process of switching the foreground image data of the area to background image data (step 21). Proceed to step 22.
As a result, if the foreground image data has a color number far from the representative color number obtained in the processing of step 16, that portion can be deleted from the foreground and compressed as background image data.

For the data stored in the background image storage unit of the separated data storage unit 232, the encoding unit 23 determines whether there is data with a history of switching from the foreground image data to the background image data ( Step 23).
When there is data with a history of switching from the foreground image data to the background image data (step 23; Y), the data of that area is stored in the output 8 / 24bit JPEG format storage unit of 24bit data in the output image data storage unit 237. The background image data is output to the area (step 24), and the process is terminated.
On the other hand, when there is no data with a history of switching from the foreground image data to the background image data (step 23; N), the gray / color discrimination unit 236 is stored in the background image storage unit of the separated data storage unit 232. It is determined whether the image data is gray image data or color image data (step 25).

As a result, when the background image data is color image data (step 25; color), the process proceeds to step 24.
If the background image data is gray image data (step 25; gray), the data in that area is output as background image data to the 8-bit data storage area of the background 8 / 24-bit JPEG format storage section in the output image data storage section 237. (Step 26), the process is terminated.

  In the present embodiment, it is possible to cope with compression of image data having a plurality of character colors by setting a plurality of planes of foreground image data. For example, two planes can be set to correspond to black + red character image data.

In the representative color discrimination process for discriminating the number of colors of the foreground (character) data in step 16, there is a case where an erroneous judgment (erroneous recognition) is made depending on the threshold level (tuning accuracy) set at the time of discrimination. The misrecognition of the foreground color becomes a problem when the foreground color is about one to several colors, which may cause the following problems.
-The text color is not the same as the original (red text is not red).
-The character color does not have a uniform density.
・ If a part of a photo is mistakenly recognized as a character, it will stand out as noise.

Therefore, in the present embodiment, when the foreground color is about 1 to 5 colors, the foreground color is rechecked and the region is re-extracted in step 18 when the foreground data is stored, and the foreground color is again displayed. If there is a color that is not included in the representative color after checking, a process of switching the dot (pixel) from the foreground to the background is performed.
As a result, the above-described problems caused by abnormal colors can be appropriately avoided.
That is, since it is possible to recover data that does not produce an abnormal result even if the representative color determination process for determining the number of colors of the foreground (character) data in step 16 fails, the threshold value setting in the representative color determination process ( Since the range of color discrimination tuning) can be expanded, the threshold tuning process can be easily performed. Further, it is possible to finally correct an error in automatic determination.

In the present embodiment, when the foreground color re-check / area re-extraction unit 235 performs the process of switching from the foreground image data to the background image data, the background image gray / color discrimination process in step 25 is not performed. Are stored in 24-bit color.
This is in consideration of the possibility of malfunction of the gray / color discrimination process in step 25. That is, even if the gray / color discrimination process determines that the document is a gray document, the foreground image data is switched to the background image data. This is because dots (pixels) are not limited to gray images.

In addition, by performing the process of switching from the foreground image data to the background image data, it is possible to reproduce a color faithful to the document even when the character color of the image data (document data) is not one color.
Note that when gray image data is stored separately in 8-bit and 24-bit JPEG format, the data size is three times different, but the image data (file) size does not change much. Therefore, there is no inconvenience even if gray image data is stored in the 24-bit JPEG format by mistake.

  According to the present embodiment, the size of the file (image data) can be reduced by storing the foreground color as one to several colors of MMR plane data using a simple image processing method. It is possible to obtain an effect that a character color is obtained and finally a uniform and easy-to-read character color is obtained.

  Also, the foreground (character) is usually processed as having an arbitrary color. However, since the foreground (character) is set to one color, the foreground (character) is originally used only for one color. In addition, it is possible to suppress malfunctions (incorrect processing) such as the density is not constant and the red character should be mixed with another color.

According to the present embodiment, it is possible to reduce the amount of character information by making the character color a single color, improve the ease of compression, and suppress (reduce) the size of image data. Even if a malfunction (erroneous processing) occurs in the single color check of the document, it is possible to suppress the erroneous single color of the character and finally obtain a correct color result.
As described above, according to the present embodiment, it is possible to suppress abnormal results (defective output images) by simple and high-speed processing.

  According to the present embodiment, according to the characteristics (characteristics) of the image data, for example, when the character color is one color, the background JPEG + 1 plane MMR, and when the character color is 2-5 colors, the background JPEG + 2-5 planes If the character color is 6 to 256 colors, the background JPEG + 4/8 bit PNG, if the character color is full color, the background JPEG + foreground JPEG + mask MMR, if the character color is grayscale, the background 24 bit JPEG + foreground color 8 bit JPEG + By switching the high compression method such as the mask MMR, the optimum image quality and compression rate can be achieved according to the input image data (original data).

1 is a block diagram showing a schematic configuration of a digital copying machine according to an embodiment. It is the figure which showed the functional block of the encoding part which concerns on this Embodiment. It is the flowchart which showed the procedure of the image process in the encoding part which concerns on this Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Digital copier 2 Printer engine 3 Scanner 4 Network 5 Controller 11 Process cartridge 12 Transfer belt 13 Fixing device 14 Color writing device 15 Paper feed tray 16 Line memory 21 RIP part 22 Band buffer 23 Encoding part 24 Decoding part 25 Page Memory 26 Image processing device 27 Hard disk 28 Conversion unit 29 Color gradation processing unit 230 Input image storage unit 231 Binary / area recognition unit 232 Separated data storage unit 233 Representative color discrimination unit 234 Color-specific data storage unit 235 Foreground color re-check Area re-extraction unit 236 Gray / color discrimination unit 237 Output image data storage unit

Claims (7)

Separating means for separating the image data into a foreground region which is a character portion and a background region which is a non-character portion;
Expressing the plane in the foreground area separated by the separating means by a single color image, and determining the number of colors in the foreground area based on the result,
Compression means for compressing data using a predetermined compression method according to the number of colors determined by the number of colors determination means;
Storage means for storing the image data compressed by the compression means in a predetermined storage area for each compression method;
An image processing apparatus comprising: When the number of representative colors determined by the color number determination unit is less than a predetermined number, a re-determination unit that determines the number of colors in the foreground area again before performing compression processing by the compression unit;
Switching means for switching the corresponding foreground area to the background area when the number of colors determined by the redetermination means is greater than the number of colors determined by the color number determination means;
The image processing apparatus according to claim 1, further comprising:   At least one of the number-of-colors determining unit and the re-determining unit determines the number of colors in the foreground region based on representative color information in which one representative color of the foreground image is determined for each plane. The image processing apparatus according to claim 1, wherein:   4. The image processing apparatus according to claim 1, wherein a plurality of planes in the foreground area are set.   The at least one of the color number determination unit and the re-discrimination unit determines the number of colors in the foreground region based on color feature information excluding an edge portion in the foreground region. The image processing apparatus according to claim 3, 4 or 5. An image processing method used when compressing image data using a computer,
A first step of separating the image data into a foreground region that is a character portion and a background region that is a non-character portion;
A second step of expressing the plane in the foreground region separated in the first step as a single color image and determining the number of colors in the foreground region based on the result;
A third step of compressing the data using a predetermined compression method according to the number of colors determined in the second step;
A fourth step of storing the image data compressed in the third step in a predetermined storage area for each compression method;
An image processing method comprising: An image processing program used when image data is compressed using a computer,
A separation function that separates image data into a foreground area that is a character part and a background area that is a non-character part;
Representing the plane in the foreground area separated by the separation function stage as a single color image, and determining the number of colors in the foreground area based on the result,
A compression function for compressing data using a predetermined compression method according to the number of colors determined by the color number determination function;
A storage function for storing the image data compressed by the compression function in a predetermined storage area for each compression method;
An image processing program for causing a computer to realize the above.

Images