JPH10243241A - Method and device for compressing image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and a device for compression with which the compressibility of image data to be transferred is improved and a compression processing program can be reduced. SOLUTION: A data scan processing process P4-1 laterally scans one line of image data in each plane for each reference color expressing a color. A differential extraction processing process P4-2 exclusively ORs the scanned line and a preceding scan line and stores the result in a work area 4-5. A compression processing process P4-3 extracts the result and encode and compresses it into a setting pattern 1 composed of a color-setting bit group and a bit group for pattern discrimination which is discriminable from setting patterns 1 and 2, setting pattern 2 composed of a bit group for color setting and a bit group for run length setting, and setting pattern 3 composed of a bit group for pattern discrimination which is discriminable from the setting patterns 1 and 2 and a bit group for a run length setting longer than the setting pattern for each run length.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image compression method and apparatus for an image display service for transferring image data over a network and displaying the image data on a terminal or the like.

[0002]

2. Description of the Related Art Conventionally, techniques for compressing still image data include techniques such as a run-length encoding method, an MH encoding method, and a JPEG method. Hereinafter, a run-length encoding method will be described as an example.

FIG. 6 shows the relationship between rows and pixels, FIG. 7 shows a flowchart of image compression processing according to the prior art, and FIG. 8 shows an example of image compression processing.

[0004] The run-length encoding method is a method of recording a pixel and the number of consecutive times when there is a continuous pixel in one row.

[0005] Image data consists of rows and pixels as shown in FIG. In the compression, a process of reading one line at a time on a line-by-line basis and compressing pixels is performed.

First, in the scanning process P2-1,
One line of the image data 2-3 is scanned and the work area 2-
4 is stored.

Next, in the compression process P2-2, one line of image data is read from the work area 2-4, the pixels and the number of consecutive appearances are counted from the head, and the compressed data 2-
Output as 5. In the case of the image compression processing example shown in FIG. 8, since the scanned original data 3-1 continues from the beginning with one pixel of white, two pixels of black, and three pixels of white, the compressed data 3-2 (2 in FIG. 7) “Corresponding to −5) is output as“ white 1, black 2, white 3 ”.

[0008]

Since image data has a large data amount, it takes time to transfer the data through a network or the like. When transferring image data from an image data server using a low-speed line (e.g., 9600 bps) and displaying the image on a terminal in a system that provides various image providing services on the terminal, it takes a long time to transfer the image data and the service on the terminal is realized. Hateful. Even when image data is compressed, about 50% is used in the run-length encoding method, and 50% is used in the lossless compression in JPEG.
%, And the reduction of the image transfer time is about し て も even if it is compressed. In JPEG, when irreversible compression is performed, the compression ratio is higher, but on the other hand, the compression program is large, and it is difficult to adopt it in a low resource terminal such as a portable terminal. In particular, in the case of image data having a sharp outline such as map data, the JPEG method is unsuitable because of its low compression ratio. Since the conventional still image compression technology has the above-described problems, the image providing service is provided only through a LAN or the like having a high transfer rate, or the CD-RO is used.
Measures based on environmental constraints such as storing image data in M and storing it in a terminal in advance have been taken. Therefore, there has been a demand for a compression method and apparatus that can increase the compression ratio of image data to be sent and can use a small compression processing program.

SUMMARY OF THE INVENTION An object of the present invention is to provide a compression method and apparatus which can increase the compression ratio of image data to be transferred and can reduce the size of a compression processing program.

[0010]

In order to solve the above-mentioned problems, an image compression method according to the present invention has a plane for each reference color representing a color, and converts image data displayed by synthesizing each plane into a bit pattern. In the image compression method to be set, a data scanning process for scanning image data line by line in a horizontal direction, a setting pattern 1 including a bit group for setting a color and a bit group for distinguishing a bit pattern, and a color are set. And a compression processing step of compressing the scanned data with a bit setting pattern of a setting pattern 2 comprising a bit group and a bit group for setting a run length.

Alternatively, in an image compression method in which a plane is provided for each reference color representing a color and image data displayed by combining the planes is set as a bit pattern, a data scan for scanning the image data line by line in a horizontal direction. A processing step, a difference extraction processing step of taking an exclusive OR between the data of the scanned row and the data of the previous scan row to extract a difference, and a distinction between a bit group and a bit pattern for setting a color. The data of the first row scanned and the data of the difference are compressed by a bit setting pattern of a setting pattern 1 composed of a bit group to be represented and a setting pattern 2 composed of a bit group for setting a color and a bit group for setting a run length. Compression processing step.

Alternatively, in an image compression method having a plane for each reference color representing a color, and setting image data displayed by combining the planes into a bit pattern, data for scanning image data line by line in a horizontal direction. A scan processing step, a setting pattern 1 including a bit group for setting a color and a bit group indicating the distinction between bit patterns;
A setting pattern 2 consisting of a bit group for setting a color and a bit group for setting a run length, and a bit group for setting a color and a bit pattern for which the setting pattern can be distinguished from the run length setting portion of the setting pattern 2 A compression processing step of compressing the scanned data by a bit setting pattern of a setting pattern 3 including a bit group representing a distinction and a run length setting bit group capable of setting a run length longer than the setting pattern 2 by adding a bit from the setting pattern 2 And the following.

Alternatively, in an image compression method having a plane for each reference color representing a color and setting image data displayed by combining the planes into a bit pattern, data for scanning the image data line by line in a horizontal direction. A scan processing step, a difference extraction processing step of taking an exclusive OR between the data of the scanned row and the data of the previous scan row to extract a difference, and distinguishing a bit group and a bit pattern for setting a color Is compared with a setting pattern 1 consisting of a bit group representing a color, a setting pattern 2 consisting of a bit group for setting a color and a bit group for setting a run length, and a bit group for setting a color and a run length setting portion of the setting pattern 2. A bit group representing the distinction of the bit pattern that can be distinguished from the setting pattern and a bit is added from the setting pattern 2 and longer than the setting pattern 2 Characterized in that it has a setting pattern 3 consisting of the run-length setting bit group can be set down length, a compression process for compressing the data of the first line and the difference between the data the scan by the bit setting pattern.

In order to solve the above-mentioned problems, an image compression apparatus according to the present invention has a plane for each reference color representing a color, and sets image data displayed by combining the planes into a bit pattern. In the apparatus, a data scan processing unit that scans image data row by row in a horizontal direction, a setting pattern 1 including a bit group for setting a color and a bit group for distinguishing a bit pattern, a bit group and a run for setting a color And a compression processing section for compressing the scanned data with a bit setting pattern of a setting pattern 2 including a bit group for setting a length.

Alternatively, in an image compression apparatus having a plane for each reference color representing a color and setting image data to be displayed by synthesizing each plane into a bit pattern, data for scanning the image data line by line in a horizontal direction. A scan processing unit, a difference extraction processing unit that performs an exclusive OR operation on the data of the scanned row and the data of the previous scan row to extract a difference, and distinguishes a bit group and a bit pattern for setting a color. The data of the first row scanned and the data of the difference are compressed by a bit setting pattern of a setting pattern 1 consisting of a bit group representing a color and a setting pattern 2 consisting of a bit group for setting a color and a bit group for setting a run length. And a compression processing unit.

Alternatively, in an image compression apparatus which has a plane for each reference color representing a color and sets image data to be displayed by synthesizing each plane into a bit pattern, data for scanning image data line by line in a horizontal direction. A scan processing unit, a setting pattern 1 including a bit group for setting a color and a bit group indicating distinction of a bit pattern, a setting pattern 2 including a bit group for setting a color and a bit group for setting a run length, and A bit group to be set, a bit group representing a bit pattern distinction that can be distinguished from the set pattern by comparing with the run length setting portion of the setting pattern 2, and a bit longer than the setting pattern 2 and a run length longer than the setting pattern 2 can be set. According to the bit setting pattern of the setting pattern 3 including the run length setting bit group, Characterized by comprising a compression unit for compressing the data of data and the difference, the.

Alternatively, in an image compression apparatus which has a plane for each reference color representing a color and sets image data to be displayed by synthesizing each plane into a bit pattern, data for scanning image data line by line in a horizontal direction. A scan processing unit, a difference extraction processing unit that performs an exclusive OR operation on the data of the scanned row and the data of the previous scan row to extract a difference, and distinguishes a bit group and a bit pattern for setting a color. Is compared with a setting pattern 1 consisting of a bit group representing a color, a setting pattern 2 consisting of a bit group for setting a color and a bit group for setting a run length, and a bit group for setting a color and a run length setting portion of the setting pattern 2. A bit group representing the distinction of the bit pattern that can be distinguished by the setting pattern, and a bit longer than the setting pattern 2 by adding a bit from the setting pattern 2. The setting pattern 3 consisting of bit group run-length setting that can be set, characterized by comprising: a compression unit for compressing the data of the data and the difference of the first line which is the scan by the bit setting pattern.

According to the present invention, the compression rate of image data is increased as compared with the conventional method by efficiently storing compressed data by encoding for each run length using the above set pattern. Further, a higher compression ratio is realized by reducing the amount of data by extracting the exclusive OR of the data of the scanned row and the data of the previous row and extracting and compressing the difference. These solve the problem of the present invention that the image data transfer time is shortened. Further, in the present invention, by adopting the image compression method based on the run length, the size of the compression program is reduced as compared with JPEG or the like, and an image compression method effective for small resource terminals such as portable terminals is provided. In particular, in the case of image data having a strong correlation between rows, such as map data, if the difference is calculated by exclusive OR, the number of short runs and long runs increases. A compression ratio can be realized.

[0019]

Embodiments of the present invention will be described below with reference to the drawings.

As a first embodiment of the present invention, a case will be described in which the number of bits is 2 and the setting patterns 1 to 3 are used to represent a color displayed on a plane.

FIG. 1 is a flowchart of an image compression process in this embodiment, FIG. 2 shows an example of a difference extraction process, and FIG. 3 shows a bit pattern for storing compressed data (bits for representing colors displayed on a plane). Number = 2). The relationship between rows and pixels is as shown in FIG. The actual compression processing flow will be described below with reference to the drawings.

First, the data scanning process P4-1
Then, one line of the image data 4-4 is scanned and stored in the work area 4-5. In the case of scanning the first row, the process proceeds to the compression process P4-3. Otherwise, the process proceeds to the compression process P4-3 via the difference extraction process P4-2.

Next, in the difference extracting step P4-2, the previous line and the line just scanned are taken out from the work area 4-5,
The exclusive OR is calculated for the two rows, and the result is stored in the work area 4-5. FIG. 2 shows an example of a method of calculating an exclusive OR. (A) is the original data 5-1 and (b)
Is post-difference extraction data 5-2. When exclusive OR of quaternary image data is taken, white is used for the same color, and color of the pixel of the row just scanned is different (black in the example in the figure) if different.
Set.

In the compression process P4-3, the data obtained as a result of the exclusive OR operation from the work area 4-5 is taken out, encoded for each run length, and output as compressed data 4-6. FIG. 3 shows a bit pattern for storing compressed data (the number of bits for representing a color displayed on a plane = 2). The bit pattern to be stored is changed for each run length so that the data is efficiently stored.

It should be noted that the difference extraction step P4-2 is not performed, and the data scan processing step P4-1 and the compression processing step P4-1 are not performed.
Image compression with a sufficient compression effect can be realized by performing only the two processes of step 3.

The bit pattern generation method is as follows.

First, a bit pattern is set on a byte-by-byte basis for easy processing.

In order to provide three bit patterns, two bits are required for discrimination, so the number of bits for discriminating the bit pattern is two.

In the setting pattern 1 shown in FIG. 3A, first, a bit for discriminating a bit pattern is required. There are two bits (b4, b5 = 1, 1), and the remaining bits are six bits. Therefore, when the number of bits for representing the color displayed on the plane is 2, up to the run length 3, the pixel colors P0, P1, P2 at the respective run lengths 1, 2, 3
Can be set at a predetermined 2-bit position as it is. The setting pattern 1 is a bit pattern used up to the run length 3.

Next, the setting pattern 2 has two bits for representing the color displayed on the plane, so that two bits are used for the color setting (P0) and for the run length setting (r5 to r0). The remaining 6 bits are used. Set the color at the beginning and the run length at the rest. At this time, since the setting pattern 2 corresponds to a run length longer than the setting pattern 1, it is used from the run length 4. In order to use the setting pattern 2 for the widest range of run lengths, in the setting pattern 1, color is set to the first 2 bits, 2 bits to distinguish the bit pattern from the next 2 bits, and color to the remaining 4 bits. Set 1 for the bit pattern distinction.

Further, in order to correspond to the setting pattern 3 having a longer run length than the setting pattern 2, bit coding is performed with 2 bytes in consideration of ease of processing. A color is set at the beginning with 2 bits. In order to distinguish between the setting pattern 2 and the setting pattern 3 and to make the setting pattern 2 correspond to the longest run length, the setting pattern 2 corresponds to the run length 47, and 0 is set to the bits b5 to b2 of the setting pattern 3. . Run lengths r9 to r0 are set in the remaining 10 bits of the setting pattern 3.

According to the above bit pattern, when the run is 1 to 3, the setting pattern is 1, when the run is 4 to 47, the setting pattern is 2, and when the run is 48 to 1023.
In the case of, the setting pattern 3 is used. Setting pattern 1
In the case of run 3 or less, the color P0 of the first pixel is set in the first two bits in one byte, 1 is set in the next two bits,
The color P1 of the second pixel is set in the next two bits, and the color P2 of the third pixel is set in the last two bits. Setting pattern 2
Then, the color P0 is set in the first two bits in one byte,
The run lengths r5 to r0 are set in the remaining 6 bits. In the setting pattern 3, the data is stored using two bytes. The color P0 is set in the first 2 bits, 0 is set in the next 4 bits, and the run lengths r9 to r0 are set in the remaining 10 bits.

The method of distinguishing the set patterns in the compression process P4-3 is as follows.

When bit b5 = 1 and bit b4 = 1, the setting pattern is 1.

When bit b5 = 0, bit b4 = 0, bit b3 = 0, and bit b2 = 0, the setting pattern is 3. Other than the above, the setting pattern 2 is used. Setting pattern 2
Is used when the run length is 4 or more and 47 or less. In this case, since the bits b5 to b2 are set from "0001" to "1011", the bits b5 and b4 do not become 1 and the bits b5 to b2 do not become all 0s. This makes it possible to distinguish between 1 and 3, and efficient bit coding can be realized.

The above-described data scanning process P4-1
To the compression process P4-3 are repeated from the first line to the last line of the image data.

When setting patterns 1 and 2 are used, setting patterns 1 and 2 may be used as the bit patterns in FIG.

Next, as a second embodiment of the present invention, a case will be described in which the number of bits for representing a color displayed on a plane is 3 and the setting patterns 1 to 3 are used.

FIG. 4 shows a bit pattern for storing compressed data (the number of bits for representing a color displayed on a plane =
3) is shown.

The flow of the compression process is the same as in the case of two planes.

In the compression process P4-3, the bit pattern shown in FIG. 4 is used. In the bit pattern generation procedure, the number of bits for representing the color displayed on the plane is two.
Is the same as The setting pattern 1 is used when the run is 1 to 2, the setting pattern 2 is used when the run is 3 to 23, and the setting pattern 3 is used when the run is 24 or more. In the setting pattern 1, in the case of the run 2 or less, the color P0 of the first pixel is set in the first three bits within one byte,
1 is set in the next two bits, and the color P1 of the second pixel is set in the next three bits. In setting pattern 2, within one byte,
The color P0 is set in the first three bits, and the run lengths r4 to r0 are set in the remaining five bits. In the setting pattern 3, the setting pattern 2 is extended by bytes and stored using 2 bytes. The color P0 is set in the first three bits, 0 is set in the next four bits, and the run lengths r8 to r0 are set in the remaining nine bits.

The method of distinguishing the set patterns in the compression process P4-3 is as follows.

When bit b4 = 1 and bit b3 = 1, the setting pattern is 1.

When bit b4 = 0, bit b3 = 0, bit b1 = 0, and bit b1 = 0, the setting pattern is 3. Other than the above, the setting pattern 2 is used. Setting pattern 2
Is used when the run length is 2 or more and 23 or less. In this case, since the bits b4 to b1 are set from "0001" to "1011", the bits b4 and b3 do not become 1 and the bits b4 to b1 do not become all 0s. 1, 3 can be distinguished.

In the case where the number of planes is four or more, a bit pattern can be set by extending the above. When the number of planes is 4, a bit pattern may be set with two bytes instead of a bit pattern with one byte. Also, it is naturally possible to perform image compression using only the fixed length setting patterns of the setting pattern 1 and the setting pattern 2, and even in this case, image compression with a sufficiently high compression effect can be realized.

Next, the configuration of an image compression apparatus will be described as a third embodiment of the present invention.

FIG. 5 is a functional block diagram showing the configuration of this embodiment.

Reference numeral 8-1 denotes an input section for inputting an image to be compressed.

Reference numeral 8-2 denotes a control unit for executing the image compression processing of the present invention on the image input from the input unit 8-1, and includes a data scan processing unit 8-5 and a difference extraction processing unit 8-
6 and a compression processing unit 8-7.

An output unit 8-3 outputs an image compressed by the control unit 8-2.

8-4 is a data scan processing unit 8-5,
This work memory is used as a work area for temporarily storing scan data, data after difference extraction, data compressed according to a set pattern, and the like in the difference extraction processing unit 8-6 and the compression processing unit 8-7.

The data scan processing section 8-5 scans one line of image data and stores it in a work area in the work memory 8-4. The same processing as the above-described data scanning process P4-1 is performed.

The difference extraction processing section 8-6 calculates the exclusive OR of the previous row and the currently scanned row, and stores the result in the work area in the work memory 8-4.
The same process as the above-described difference extraction process P4-2 is performed.

The compression processing unit 8-7 takes out the data resulting from the exclusive OR operation in the work area in the work memory 8-4, encodes it for each run length, and outputs it as compressed data as the output unit 8-3. Output to The same process as the above-described compression process P4-3 is performed.

The image compression processing of the present invention can be realized by the above blocks.

[0056]

According to the present invention, it is possible to realize a higher image data compression ratio than in the prior art, so that the image data transfer time can be reduced. Therefore, when using a line as in the past, LA
N or other high-speed lines, or
The image providing service at the terminal can be realized even by using a low-speed line (9600 bps or the like) without the restriction condition that the image is stored in the terminal in the ROM. Further, since the compression program is small, the present invention can be applied to a portable terminal that is a small resource terminal. According to the present invention,
Mobile computing using very effective image data as provided information becomes possible, and desired image information can be obtained anytime and anywhere. According to the present invention, high compression can be realized by performing three processes of a data scan process, a difference extraction process, and a compression process.
Even if only the two steps of the data scan processing step and the compression processing step are performed without performing the difference extraction processing step, a sufficiently high compression effect can be obtained as compared with the related art.

[Brief description of the drawings]

FIG. 1 is a flowchart of an image compression process according to a first embodiment of the present invention.

FIGS. 2A and 2B are diagrams illustrating an example of a difference extraction process in the first embodiment.

FIGS. 3A, 3B, and 3C show compressed data storage bit patterns (the number of bits for representing a color displayed on a plane = 2) in the first embodiment. FIG.

FIGS. 4A, 4B, and 4C are bit patterns for storing compressed data (the number of pits representing a color displayed on a plane = 3) according to the second embodiment of the present invention;
FIG.

FIG. 5 is a functional block diagram showing a third embodiment of the present invention.

FIG. 6 is a diagram showing the relationship between rows and pixels.

FIG. 7 is a flowchart of a conventional image compression process.

FIG. 8 is a diagram illustrating an example of image compression processing according to the related art.

[Explanation of symbols]

 P4-1 Data scanning process P4-2 Difference extraction process P4-3 Compression process 4-4 Image data 4-5 Work area 4-6 Compressed data 5-1 Original data 5-2 ... Data after difference extraction 8-1 ... Input unit 8-2 ... Control unit 8-3 ... Output unit 8-4 ... Work memory 8-5 ... Data scan processing unit 8-6 ... Difference extraction processing unit 8-7 ... Compression Processing unit

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Kazuo Morimura 3-19-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo Inside Nippon Telegraph and Telephone Corporation

Claims (8)

[Claims] A plane for each reference color representing a color;
In an image compression method for setting image data displayed by synthesizing each plane into a bit pattern, a data scanning process in which image data is scanned one line at a time in a horizontal direction and a bit group and a bit pattern for setting a color are distinguished. A compression processing step of compressing the scanned data with a bit setting pattern of a setting pattern 1 composed of a group of bits to be represented and a setting pattern 2 composed of a bit group for setting a color and a bit group for setting a run length. An image compression method comprising: 2. An image compression method comprising a plane for each reference color representing a color and setting image data to be displayed by synthesizing each plane into a bit pattern. A processing step; a difference extraction processing step of extracting a difference by taking an exclusive OR between the data of the scanned row and the data of the previous scan row; and distinguishing a bit group and a bit pattern for setting a color. The data of the first row scanned and the data of the difference are compressed by a bit setting pattern of a setting pattern 1 composed of a bit group to be represented and a setting pattern 2 composed of a bit group for setting a color and a bit group for setting a run length. An image compression method, comprising: a compression processing step. 3. A plane is provided for each reference color representing a color.
In an image compression method for setting image data displayed by synthesizing each plane into a bit pattern, a data scanning process in which image data is scanned one line at a time in a horizontal direction and a bit group and a bit pattern for setting a color are distinguished. A comparison is made between a setting pattern 1 consisting of a group of bits to be represented, a setting pattern 2 consisting of a bit group for setting a color and a bit group for setting a run length, and a bit group for setting a color and a run length setting portion of the setting pattern 2. A setting pattern 3 including a bit group representing a bit pattern capable of distinguishing a setting pattern and a run length setting bit group capable of setting a run length longer than the setting pattern 2 by adding a bit from the setting pattern 2
A compression process of compressing the scanned data according to a bit setting pattern. 4. A plane is provided for each reference color representing a color.
In an image compression method for setting image data displayed by synthesizing each plane into a bit pattern, a data scanning process of scanning image data one row at a time in a horizontal direction; A difference extraction process of extracting a difference by taking an exclusive OR with data, a setting pattern 1 including a bit group for setting a color and a bit group for distinguishing a bit pattern, and a bit group for setting a color A setting pattern 2 including a bit group for setting a run length, a bit group for setting a color, a bit group representing a distinction of a bit pattern capable of distinguishing a setting pattern from a run length setting portion of the setting pattern 2, and A setting pattern consisting of a run length setting bit group that can add a bit to the setting pattern 2 and set a run length longer than the setting pattern 2 3
A compression process of compressing the first row of the scanned data and the difference data according to a bit setting pattern. 5. It has a plane for each reference color representing a color,
In an image compression apparatus for setting image data displayed by synthesizing each plane into a bit pattern, a data scan processing unit that scans the image data one row at a time in a horizontal direction, and distinguishes a bit group and a bit pattern for setting a color. And a compression processing unit that compresses the scanned data with a bit setting pattern of a setting pattern 1 including a group of bits to be represented and a setting pattern 2 including a bit group for setting a color and a bit group for setting a run length. An image compression apparatus characterized by the above-mentioned. 6. It has a plane for each reference color representing a color,
An image compression apparatus for setting image data displayed by combining each plane into a bit pattern, comprising: a data scan processing unit that scans image data one row at a time in a horizontal direction; A difference extraction processing unit for extracting a difference by taking an exclusive OR with data; a setting pattern 1 comprising a bit group for setting a color and a bit group for distinguishing a bit pattern; and a bit group for setting a color And a compression processing unit that compresses the data of the first row scanned and the difference data according to the bit setting pattern of the setting pattern 2 including a bit group for setting a run length. . 7. It has a plane for each reference color representing a color,
In an image compression apparatus for setting image data displayed by synthesizing each plane into a bit pattern, a data scan processing unit that scans the image data one row at a time in a horizontal direction, and distinguishes a bit group and a bit pattern for setting a color. A comparison is made between a setting pattern 1 consisting of a group of bits to be represented, a setting pattern 2 consisting of a bit group for setting a color and a bit group for setting a run length, and a bit group for setting a color and a run length setting portion of the setting pattern 2. A setting pattern 3 including a bit group representing a bit pattern capable of distinguishing a setting pattern and a run length setting bit group capable of setting a run length longer than the setting pattern 2 by adding a bit from the setting pattern 2
A compression processing unit for compressing the data of the first row scanned and the data of the difference according to a bit setting pattern. 8. It has a plane for each reference color representing a color,
An image compression apparatus for setting image data displayed by combining each plane into a bit pattern, comprising: a data scan processing unit that scans image data one row at a time in a horizontal direction; A difference extraction processing unit for extracting a difference by taking an exclusive OR with data; a setting pattern 1 comprising a bit group for setting a color and a bit group for distinguishing a bit pattern; and a bit group for setting a color A setting pattern 2 including a bit group for setting a run length, a bit group for setting a color, a bit group representing a distinction of a bit pattern capable of distinguishing a setting pattern from a run length setting portion of the setting pattern 2, and Setting pattern 3 consisting of a run length setting bit group that can add a bit to setting pattern 2 and set a run length longer than setting pattern 2
A compression processing unit for compressing the data of the first row scanned and the data of the difference according to a bit setting pattern.