JP2000333017A - Image processor for compression and expansion and electronic printer utilizing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the overall compression rate while suppressing deterioration in image quality by selecting an optimum compression system and compressing image data for each dot. SOLUTION: This image processing unit selects a compression system in response to number of colors of a dot group included in a prescribed area (block) and compresses/expands image data. When number of colors of the dot group is small, compression/expansion is conducted by a reversible compression processing and in the case that number of colors of the dot group is large, compression/expansion is conducted by an irreversible compression processing. Since number of colors in a prescribed area of image data such as characters and graphics is comparatively small and image data such as an image have comparatively larger color number within the prescribed area, the optimum compression system is selected by utilizing the tendency.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus for performing compression and decompression and an electronic printing apparatus using the same, and more particularly, to an optimal compression method for dot (pixel) image data. The present invention relates to an image processing apparatus capable of preventing image quality deterioration and an electronic printing apparatus using the same.

[0002]

2. Description of the Related Art When printing image data including color data for each dot (pixel) generated by a host computer, print data having the dot image data is supplied to an electronic printing apparatus. An electronic printing apparatus such as a page printer performs image processing such as image processing of dot image data or synthesis of a plurality of images in accordance with a print mode of a built-in print engine, a color space of toner or ink, and the like. Then, in the electrophotographic apparatus, the dot image data for one page is once compressed and stored in the image memory,
The compressed image data is decompressed (decompressed) in accordance with the operation of the print engine and supplied to the print engine as image data for printing. Alternatively, the decompressed image data is supplied to a color conversion circuit, color-converted into a color space for a print engine, subjected to necessary color correction, and supplied to a print engine.

[0003] Print data includes image data of characters and graphics (images and graphs generated by a computer) and image data of an image composed of natural images such as photographs. Image data of characters and graphics is color-coded for each relatively large area, and therefore, the number of colors included in a relatively small area is small. On the other hand, in image data of an image, the color of each dot tends to change at random, and even within a relatively small area, the same color is less frequently repeated and the number of colors tends to increase.

On the other hand, data compression methods include a loss-less compression method (Lossless compression method) such as a run-length method for compressing the same data repetition with the head data and the number of repetitions, a method using a color palette, and the like. There is an irreversible compression method (Lossy compression method) in which a part of the data is changed to a value that can be easily compressed and compression is performed.

[0005] Since the lossless compression method is an algorithm for compressing the original data without changing it, the original data can be completely restored from the compressed data. Therefore, there is no deterioration in image quality due to the expanded image data. However, in the case of image data such as characters and graphics, the compression ratio of the data is relatively good because the same color is frequently repeated. Gets worse.

On the other hand, the irreversible compression method is an algorithm for increasing the compression ratio by changing the original data. Therefore, if the compressed data is decompressed, the original data cannot be completely restored and the image quality deteriorates. . Therefore, image data of an image has a relatively high compression ratio and is slightly affected by image quality degradation, but image data such as characters and graphics is greatly affected by image quality degradation.

[0007]

In a conventional image processing apparatus that involves compression and decompression in an electronic printing apparatus, the compression algorithm is fixed at a uniform level. There is a problem that the compression ratio is deteriorated, and when the lossy compression method is adopted, there is a problem that the image quality of character or graphics image data is deteriorated.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image processing apparatus capable of compressing / expanding image data for each dot by an optimum compression method and an electronic printing apparatus using the same.

It is a further object of the present invention to provide an image processing apparatus capable of compressing / expanding image data for each dot by a compression method having a high compression ratio and an electronic printing apparatus using the same.

Another object of the present invention is to provide an image processing apparatus capable of compressing / expanding image data for each dot by a compression method having a high compression rate without deteriorating the image quality, and an electronic printing apparatus using the same. To provide.

[0011]

In order to achieve the above object, an image processing apparatus according to the present invention selects a compression method in accordance with the number of colors of a dot group included in a predetermined area and performs compression / compression.
Perform extension. When the number of colors of the dot group is small, compression / expansion is performed by the reversible compression method, and when the number of colors of the dot group is large, compression / expansion is performed by the irreversible compression method. Image data such as characters and graphics has a relatively small number of colors in a given area, and image data such as images has a relatively large number of colors in a given area. Select a method.

The image processing apparatus of the present invention may perform only the above-described compression, or may perform only decompression on the image data thus compressed. For example, the above-described compression may be performed by software by a host computer, and the above-described decompression may be performed in an electrophotographic apparatus supplied with the compressed data.

[0013] To achieve the above object, the present invention provides:
In an image processing apparatus for compressing and expanding image data having color data for each dot, a color number of a dot group in a predetermined area is detected from the image data, and the detected color number is set to a first value. At the time of the number of colors, the image data of the dot group in the predetermined area is compressed and decompressed by the reversible compression method, and when the detected number of colors is the second number of colors larger than the first number of colors, the predetermined The image data of the dot group in the area is compressed and decompressed by a lossy compression method.

According to another aspect of the present invention, there is provided an image processing apparatus for compressing and expanding image data having color data for each dot. Detecting the number of colors of the group, and when the detected number of colors is equal to or less than the reference number of colors, the image data of the dot group in the predetermined area is compressed and decompressed by a reversible compression method, and the number of detected colors is determined. When the number is larger than or equal to the reference color number, the image data of the dot group in the predetermined area is compressed and decompressed by a lossy compression method.

In the above invention, the number of reference colors is appropriately changed.

According to the above-described invention, it is possible to provide an image processing apparatus capable of increasing the overall compression ratio while minimizing deterioration of image quality from image data having color data for each dot.

Further, according to the present invention, the above-described image processing apparatus is applied to an electronic printing apparatus.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. However, such embodiments do not limit the technical scope of the present invention.

FIG. 1 is an overall configuration diagram of an electrophotographic apparatus according to the present embodiment. The electrophotographic apparatus 10 is connected to the host computer 1 via the interface circuit 30, and includes the print engine 28 and the other image processing apparatuses 1
It is composed of 1. The image processing device 11 includes a CPU 12,
A ROM 34 storing an interpretation program for interpreting print data described in a predetermined print language supplied from the host computer 1, and a first image memory 14 used when performing a raster operation such as synthesizing a plurality of images. And a second image memory 16 for temporarily storing compressed image data for each page, a compression circuit 18 for performing compression, and the like. These are connected via a common bus 32. First and second image memories 14,
Reference numeral 16 is a semiconductor device such as a dynamic RAM.

The number-of-colors designation register 20 is a register for designating the number of reference colors used for selecting a compression method, and the number of reference colors is set by the CPU 12.
It is referenced by the compression circuit 18. Further, the image processing apparatus 1
1 is a DMA (direct memory access) 22 for directly reading compressed image data for printing recorded in the second image memory 16, a decompression circuit 24 for decompressing the compressed image data read therefrom, A color conversion circuit 26 that converts the decompressed image data into data for a print engine 28. The color conversion circuit 26 is a circuit that converts, for example, decompressed RGB image data into YMCK image data of the toner used in the print engine 28, and also performs a color correction process as necessary.

The operation from image processing to printing is as follows. First, print data written with a predetermined description generated by application software of the host computer 1 is supplied to the image processing device 11 of the electronic printing device 10. The CPU 12 executes the interpretation program 34, interprets the print data, generates image data including color data for each dot, and records the image data in the image memory 14. This image data may be, for example, color data in the RGB color space or color data in the CMYK color space corresponding to the toner of the print engine 28.

The CPU 12 performs processing such as synthesis of a plurality of images using the image memory 14 as necessary. Then, image data including color data for each dot to be finally printed is compressed by the compression circuit 18 and recorded in the second image memory 16. For example, in the second image memory 16, compressed image data for a plurality of pages is recorded. The compression circuit 18
An optimal compression method is selected from image data for each dot to generate compressed image data.

Next, the DMA 22 reads out the compressed image data recorded in the second image memory 16,
It is supplied to the expansion circuit 24. The decompression circuit 24 includes the compression circuit 1
8 decompresses the compressed image data according to the selected compression method. If the image data is RGB color data, the expanded image data is converted into CMYK color data by a color conversion circuit 26 and supplied to a print engine 28. If the image data is CMYK color data, the expanded image data is supplied to the print engine 28 without color conversion.

FIG. 2 is a diagram for explaining an example of image data for each dot. FIG. 2 shows dots D1, D
2. . . The image data stream of Dn is shown, and the image data of dot D1 is shown. The image data of the dot D1 is, for example, color data of a total of 24 bits composed of gradation data of 8 bits each for RGB. Therefore, RG
Each of B has 256 gradations, and can express about 16 million colors in total. Alternatively, the image data of the dot D1 is composed of 8-bit gradation data of each of CMYK corresponding to the color of the toner of the print engine 28, and is 32-bit color data in total. Also in this case, the color can represent about 16 million colors from the 24-bit color data, and the black and white can represent 256 gradations.

FIG. 3 is a diagram for explaining a block corresponding to a predetermined area in the present embodiment. The image data is color data for each dot, and the image data is a data stream along a raster (row). In the present embodiment, a block (predetermined area) composed of a 4 × 4 dot group is defined. That is, one block is 4
Each of the four rasters is composed of four dots. As shown in FIG. 3, a plurality of blocks B1, B2. . . . Bk. . . Bn
Are arranged on a matrix.

In the present embodiment, in order to detect an optimal compression method, the number of colors is detected for each block of 4 × 4 and a total of 16 dots. As shown in FIG. 2, when the color data of each dot matches, they are treated as the same color, and when they do not match, they are treated as different colors. The maximum number of colors in a block of 16 dots is 16. If the color data of all 16 dots is the same, the number of colors is one. Then, a block having a relatively small number of detected colors is compressed and decompressed by a reversible compression method. In addition, a block having a relatively large number of detected colors is compressed and decompressed by a lossy compression method.

Comparing the two blocks, a block having a large number of colors employs the irreversible compression system, and a block having a small number of colors employs the lossless system. As described later, in the present embodiment, a reference color number is set for a plurality of blocks, and when the number of blocks exceeds the reference number of colors, an irreversible compression method is adopted. When the number of colors is equal to or less than the number of colors, a lossless compression method is adopted.

When the number of colors in a block composed of 4 × 4 dot groups is large, the image tends to be an image such as a photograph. In such a narrow area, color data varies from dot to dot. In such a case, the compression rate can be increased by performing compression using a lossy compression method. In the irreversible compression method, since original data is partially changed and compressed, the image quality of decompressed image data deteriorates. However, in the case of an image such as a photograph, a slight deterioration in image quality does not have a great effect. On the other hand, in a block, when the number of colors is small, the image tends to be an image such as a character or graphics, and when the color data does not vary for each dot and the frequency of repeating the same color data is relatively high,
Even if compression is performed by the reversible compression method, a high compression ratio is obtained. The image quality of the decompressed image data does not deteriorate.

FIG. 4 is a diagram for explaining compression / decompression in this embodiment. The compression method by the compression circuit 18 and the decompression method by the decompression circuit 24 in the image processing apparatus 11 according to the present embodiment will be described with reference to FIG. The original image data recorded in the first image memory 14 corresponds to FIG.
As shown in (a), it is handled as stream data of a block composed of 4 × 4 dots. In the figure, the number of colors of each block is shown in parentheses. That is, blocks B1, B
The number of colors of 2, B3, B4, B5, Bn is, for example, 3,
12, 4, 4, 13, and 10. It is also assumed that the reference color number set in the color number register 20 by the CPU 12 is set to 9 colors.

Next, the number of colors of each block is detected.
As shown in (b), a block whose color number is 9 or less as the reference color number is a block group to which the lossless compression method is applied, and a block whose color number is more than 9 as the reference color number is an irreversible block. It is separated into blocks to which the compression method is applied. That is, as shown in FIG. 4B, the blocks B1, B3,
B4 to Bm are separated into blocks to which the lossless compression method is applied, and blocks B2 to Bn are separated into blocks to which the lossy compression method is applied. At this time, separation information data is generated as shown in FIG. That is, in the separation information data, a flag of “0” is associated with the lossless compression method, and a flag of “1” is associated with the lossy compression method.

As shown in FIG. 4C, the image data of the classified block sequence is compressed as a continuous image data by a lossless compression method or a lossy compression method. That is, FIG. 4C shows the final compressed image data, which is recorded in the second image memory 16 of FIG. 1 for each page (or for each band). By compressing as continuous block image data, the compression ratio can be further increased, especially in the case of the reversible compression run-length method.

Next, when decompressing, as shown in FIG. 4D, losslessly compressed data among the compressed image data is decompressed together. The decompression algorithm at this time follows the lossless compression method. Also, the irreversibly compressed data is expanded together. This decompression algorithm follows a lossy compression method. As described above, since the compressed image data of each system is expanded together, the expansion circuit described later can be simplified. As a result of this elongation, FIG.
The decompressed image data is divided into continuous data of a plurality of blocks B1, B3, B4 to Bm by a reversible compression method and continuous data of a plurality of blocks B2 to Bn by an irreversible method.

Therefore, finally, the original image data is generated as shown in FIG. 4E by referring to the separation information data created first. That is, if the value of the separation information is 0, the reversible block is output, and if the value of the separation information is 1, the irreversible block is output in order. )).

FIG. 5 is a configuration diagram of the compression circuit 18 in the present embodiment. FIG. 6 is a configuration diagram of the expansion circuit 24 in the present embodiment. FIG. 7 is an operation flowchart of the compression circuit of FIG. 5, and FIG. 8 is an operation flowchart of the decompression circuit of FIG.

The compression circuit 18 shown in FIG. 5 includes a block data memory 52 for temporarily storing one block of uncompressed data 50 read from the image memory 14, and a color number counting circuit 54 for counting the number of colors in the block. When,
A reversible compression circuit 58 activated by an activation signal S1 from a color number counting circuit 54, a reversible compressed data memory 60 storing the compressed data, a lossy compression circuit 62 activated by an activation signal S2, and a non-reversible compression circuit 62 storing the compressed data And a lossless compressed data memory 64. Further, there is provided a separation information memory 66 for recording separation information when a plurality of blocks are classified into a lossless compression method and a lossy compression method. And
The compressed data recorded in the respective compressed data memories 60 and 64 and the separation information data recorded in the separation information memory 66 are stored as compressed data 68 in the second image memory 16. Color number counting circuit 5
4 has a color memory 56 for storing different color data detected in the block, and a color number counter 58 for counting the detected different colors. The start signals S1 and S2 are supplied to the respective compression circuits 58 and 62 as appropriate by comparing the reference colors.

The operation of the compression circuit 18 will be described with reference to FIG. One block of data is read from the bit-wise image data of one page stored in the first image memory 14 and recorded in the block data memory 52 (S10). Therefore, the block data memory 52 stores color data of 16 dots corresponding to one block in the present embodiment. Next, the color number counting circuit 54 executes the step S11 indicated by the broken line in FIG. The color count circuit 54 first clears the color memory 56 and the color counter 58 (S12).

Next, the color number counting circuit 54 reads the color data of the first dot from the block data memory 52 (S14). Then, it is checked whether or not the color data of the dot is registered in the color memory 56 (S1).
6). In the case of the color data of the first dot, the color memory 56
Nothing is registered in the color number counting circuit 5
No. 4 judges that the color is a new color and counts up the number of colors of the color number counter 58 (S18). Note that the color number designation register 20
For example, 9 is set as the reference color number. Then, the number of colors becomes 1 for the first color, and it is determined that the number is smaller than the reference number of colors 9 (S20), and the color data is registered in the color memory 56 (S22). Since all dot processing has not been completed (S24), the color data of the next dot is read from the block data memory 52 (S2).
6).

The number-of-colors counting circuit 54 performs the process S1.
The processing from 6 to S26 is repeated for the color data of all the dots. However, when the value of the color number counter 58 exceeds the reference color number 9 (S20), the color number counting circuit ends the processing. When the number of detected colors exceeds the reference color number 9 (S20), the block is classified as a lossy compression method. Then, the color number counting circuit 54 activates the activation signal S2 to cause the irreversible compression circuit 62 to compress the image data in the block data memory 52 (S3).
0). On the other hand, if the number of colors of 16 dots is counted and the number of colors of reference is 9 or less, the block is classified as a lossless compression method. Then, the color number counting circuit 54 starts the activation signal S1.
Is activated, and the image data in the block data memory 52 is compressed by the reversible compression circuit 58 (S2).
8).

The respective compressed image data are recorded in the compressed image memories 60 and 64, respectively. Further, the color number counting circuit 54 outputs separation information indicating whether the block is classified into a lossless compression method or a lossy compression method.
It is stored in the separation information memory 66 (S32). That is, the flag data of "0" or "1" is recorded in the memory 66 in the order of blocks (S36).

The above processes S10 to S32 are performed for all the blocks in one page or one band (S34). Finally, the compressed image data 68 together with the separation information data are stored in the respective memories 66. , 60, 64, and are recorded in the second image memory 16 for recording the compressed image data.

In the above embodiment, the reference color number is set to 9 which is larger than half the maximum color number 16. This is because a lossless compression method is applied to a block having a small number of colors as much as possible to prevent deterioration in image quality. Conversely, if it is desired to increase the compression ratio even if the image quality deteriorates to some extent, the number of reference colors is set to half of the maximum number of colors 16 or lower. Alternatively, when it is desired to increase the image quality, the number of reference colors is set to a value larger than 9, and most blocks are compressed by the lossless compression method, so that the image quality of the image data is prevented from deteriorating.

Next, the decompression circuit 24 shown in FIG. 6 is a reversible decompression circuit 70 for decompressing the compressed image data 68 read from the second image memory 16 by the DMA circuit 22 (not shown). A lossy expansion circuit 74; a lossless expansion data expansion memory 72 for recording expanded image data;
6 and a selector circuit 80 for rearranging the blocks in accordance with the separation information in the separation information memory 78.

The operation of the decompression circuit 24 will be described with reference to the flowchart of FIG. As shown in FIG. 4C, in the second image memory 16, lossless compressed data and lossy compressed data are separately recorded. Then, the DMA circuit 22 (not shown) reads the reversible compressed data in the second image memory 16, and the reversible decompression circuit 70 decompresses the data by the reversible compression method (S40). As a result, the original data of a continuous block classified according to the lossless compression method is stored in the decompression memory 72. Next, the DMA circuit 22 (not shown) reads the irreversible compressed data in the second image memory 16, and the irreversible decompression circuit 74 decompresses the data by the irreversible compression method (S42). As a result, the original data of a continuous block classified according to the lossy compression method is stored in the decompression memory 76.

Then, the DMA circuit 22 reads the separation information data from the second image memory 16 and stores it in the separation information memory 78 (S44). Then, the expansion circuit 24
Selector 80 selects expanded image data for each block in the expansion memory 72 or 76 in accordance with the separation information in the separation information memory 78, rearranges the data in the original data block order, and outputs it as uncompressed data 82. I do. That is,
The image data is returned to the image data of the block sequence as shown in FIG. The uncompressed data 82 is supplied to the print engine 28 via the color conversion circuit 26 or directly.

The decompression circuit 24 separates the compressed data of a plurality of blocks of the reversible compression system from the compressed data of a plurality of blocks of the irreversible compression system. To perform the decompression process, thereby simplifying the circuit configuration.

Next, a modification of the compression circuit 18 will be described. In the above embodiment, the color number designation register 20
, The reference color number 9 is fixedly set. On the other hand, in the modified example, if the image data for one page is compressed and the compression ratio is not sufficiently high, the CPU 12 sets a lower reference color number in the color number designation register 20. Alternatively, if the compression ratio is sufficiently high, the CPU 12
Thus, a higher reference color number is set in the color number designation register 20. This reference color number can be reset for each page, or can be dynamically changed while monitoring the compression ratio for several pages.

In another modification of the compression circuit 18, two types of reversible compression circuits 58, a run-length compression circuit and a compression circuit using a pallet, are provided, and compression is performed using one of the compression circuits. As a result, if the compression ratio does not increase, the compression is changed to the other compression circuit. If the compression ratio does not increase in any of the compression circuits, the setting of the number of reference colors is changed to be lower as in the above-described modification.
Thereby, the number of blocks to which the lossy compression method is applied is increased, and the overall compression ratio is increased.

FIG. 9 is an overall configuration diagram of an electrophotographic system which is a modification of the present embodiment. In this variation,
The host computer 1 has image processing means for performing the above-described compression, and the electrophotographic apparatus 10 to which compressed image data is supplied therefrom has an image processing means for performing the above-mentioned decompression. In FIG. 9, parts corresponding to those in FIG. 1 are given the same reference numerals.

The host computer 1 is connected via a bus 4 to a CPU 2, a compression circuit 18, a color designation register 20, an interface 3 and an image memory 5.
Then, according to the above algorithm, the image data generated by the predetermined application program is compressed by the compression circuit 18 and stored in the image memory 5. The compressed image data is supplied to the electrophotographic apparatus 10 as print job data. The compression circuit 18 also generates separation information data as described above, and this data is also supplied to the electrophotographic apparatus 10.

The host computer 1 can also compress the image data by using compression software having a similar compression algorithm instead of the dedicated compression circuit 18. For example, the above-described compression processing can be performed by a printer driver installed in the host computer 1.

In the electrophotographic apparatus 10, the compressed image data included in the received print job data is temporarily stored in the image memory 16. Then, by the expansion circuit 24,
The compressed image data is expanded in the same manner as described above, and a print drive signal corresponding to the expanded image data is supplied to the print engine 28. Also in the electrophotographic apparatus 10, the above-described decompression processing can be performed by software.

[0052]

As described above, according to the present invention, the optimum compression method can be selected from the image data for each dot, so that the compression ratio can be increased and the deterioration of the image quality can be minimized.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of an electrophotographic apparatus according to an embodiment.

FIG. 2 is a diagram for describing an example of image data for each dot.

FIG. 3 is a diagram for explaining a block corresponding to a predetermined area in the embodiment.

FIG. 4 is a diagram for explaining compression / decompression in the embodiment.

FIG. 5 is a configuration diagram of a compression circuit 18 according to the present embodiment.

FIG. 6 is a configuration diagram of a decompression circuit 24 in the present embodiment.

FIG. 7 is an operation flowchart of the compression circuit of FIG. 5;

FIG. 8 is an operation flowchart of the decompression circuit of FIG. 6;

FIG. 9 is an overall configuration diagram of an electrophotographic system which is a modification of the present embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Electronic printing apparatus 11 Image processing apparatus 16 Image memory 18 Compression circuit 24 Decompression circuit 28 Printing engine

Continued on the front page F-term (reference) 2C087 AA15 AB05 BC02 BC05 BD01 BD35 BD36 BD40 5B021 AA01 AA02 CC08 LL05 5C059 KK01 MA00 MA45 PP14 PP15 PP20 SS28 TA17 TB08 TC01 TD12 UA02 UA05 UA29 UA38 5C078 AA09 CA02 DA02H JJ35 KK42

Claims (13)

[Claims] 1. An image processing apparatus for compressing and decompressing image data having color data for each dot, wherein the number of colors of a dot group in a predetermined area is detected from the image data. When the number is the first number of colors, the image data of the dot group in the predetermined area is compressed by a reversible compression method,
Decompressing and compressing and decompressing the image data of the dot group in the predetermined area by an irreversible compression method when the detected color number is a second color number larger than the first color number. Image processing device. 2. The apparatus according to claim 1, wherein the predetermined area has a plurality of dots in a plurality of rows and a plurality of columns. 3. The area according to claim 2, wherein the image data is compressed and decompressed as a plurality of the predetermined areas according to the lossless compression method as a continuous area, and the plurality of the predetermined areas according to the lossy compression method are continuous. An image processing apparatus for compressing and expanding such image data. 4. An image processing apparatus for compressing and expanding image data having color data for each dot, wherein the number of colors of a group of dots in a predetermined area is detected from the image data, When the number is less than or less than the reference color number, the image data of the dot group in the predetermined area is compressed and expanded by the lossless compression method, and when the detected number of colors is greater than or equal to the reference number of colors, An image processing apparatus for compressing and expanding image data of a dot group in a predetermined area by a lossy compression method. 5. The image processing apparatus according to claim 4, wherein the predetermined area has a plurality of dots in a plurality of rows and a plurality of columns. 6. The image processing apparatus according to claim 5, wherein the reference color number is changed and set as appropriate. 7. The image processing apparatus according to claim 5, wherein the reference color number is set to a number larger than half of the number of dots in the predetermined area. 8. The image processing apparatus according to claim 5, wherein the plurality of predetermined areas according to the lossless compression method are compressed and decompressed as continuous areas, and the plurality of predetermined areas according to the irreversible compression method are defined as continuous areas. An image processing apparatus for compressing and decompressing the image data. 9. An electronic printing apparatus having the image processing device according to claim 1, further comprising: an image memory storing image data compressed by the image processing device; and an image memory storing the image data stored in the image memory. According to the image data decompressed by the image processing device,
An electronic printing apparatus, comprising: a print engine that performs printing. 10. An image processing apparatus for compressing image data having color data for each dot, wherein the number of colors of a dot group in a predetermined area is detected from the image data, and the detected number of colors is At the time of the first number of colors, the image data of the dot group in the predetermined area is compressed by a lossless compression method, and when the detected number of colors is the second number of colors larger than the first number of colors, Image processing for compressing image data of a group of dots in a predetermined area by a lossy compression method, and generating data indicating the lossless compression method or the lossy compression method for the compressed image data; apparatus. 11. An image data having color data for each dot, wherein when the number of colors of a dot group in a predetermined area is the first number of colors, the image data of the dot group in the predetermined area is reversibly compressed. When the compressed image data is the second color number larger than the first color number, the image data of the dot group in the predetermined area is decompressed with respect to the compressed image data compressed by the lossy compression method. In the image processing apparatus, the image data of the predetermined area compressed by the lossless compression method is decompressed by the lossless compression method, and the image data of the predetermined area compressed by the lossy compression method is An image processing apparatus for decompressing the image using the irreversible compression method. 12. An image processing apparatus for compressing image data having color data for each dot, wherein the number of colors of a group of dots in a predetermined area is detected from the image data, and the detected number of colors is determined. When the number of colors is equal to or less than the reference color number, the image data of the dot group in the predetermined area is compressed by a reversible compression method, and when the detected number of colors is greater than or equal to the reference number of colors, An image processing apparatus, wherein image data of a dot group is compressed by a lossy compression method, and data indicating whether the lossless compression method or the lossy compression method is generated for the compressed image data. 13. An image data having color data for each dot, wherein the image data of the dot group in the predetermined area is reversibly compressed when the number of colors of the dot group in the predetermined area is equal to or less than the reference color number. Image processing in which the image data of the dot group in the predetermined area is decompressed by the irreversible compression method when the number of colors is larger than or equal to the reference number of colors. In the apparatus, image data of a predetermined area compressed by the lossless compression method is decompressed by the lossless compression method, and image data of a predetermined area compressed by the lossy compression method is decompressed by the non-reversible compression method. An image processing apparatus characterized in that the image is expanded by a reversible compression method.