JPH08186721A - Picture data compression device and picture data expansion device - Google Patents

Abstract

PURPOSE: To efficiently compress picture data in spite of the characteristics of pictures. CONSTITUTION: A CPU 103 counts the number of picture elements for which the same display state is continued from the picture data before compression stored in a RAM 102, divides the counted value into the blocks of the bit number of each prescribed number, combines only required blocks with color code data corresponding to the counted value and thus, compresses the picture data. At this time, an identification flag for identifying the group is added to the respective blocks. The data are expanded by judging the kind of the data by the value of the identification flag.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for compressing / decompressing image data.

[0002]

2. Description of the Related Art Currently, various methods have been developed for compressing image data. A palette method is one of the compression methods.
In this palette method, the minimum number of bits that can represent the number of colors represented by image data is used as the data length of the color code, and the represented colors are associated with the numbers represented by this data length, respectively. It is intended for compression. With this palette method, for example, if there are 15 types of colors to be expressed, it is possible to associate the colors respectively expressed by the values of 0D to 14D (D is a decimal number) with one-to-one correspondence. Since the data length of the color code is 4 bits, the image data can be compressed.

However, this palette method is effective for image data of an image having the characteristic that the color of each pixel changes sequentially, but the same color such as an animation image may continue continuously. For image data of an image having many characteristics, it is necessary to have the color data for each pixel, so that there is a problem that the data compression rate is low.

An object of the present invention is, regardless of the characteristics of an image,
Efficiently compressing image data.

[0005]

An image data compression apparatus according to the present invention comprises a counting means for counting the number of pixels in the same state from image data, and a count value counted by the counting means for each preset number of digits. An encoding unit that divides the block into blocks and encodes the blocks encoded by the encoding unit according to a count value, and extracts only necessary blocks, and an identification code for identifying the blocks in the extracted blocks. After adding each, the image data compression means for generating compressed image data by combining the block to which the identification code is added with the display data representing the state of the pixel.

On the other hand, the image data decompressing device of the present invention, the image data compressed by the image data compressing device,
The image data decompressing unit is provided for decoding the count value from the block to which the identification code is added by discriminating the type of data by the value of the identification code, and expanding the display data according to the decoded count value. ing.

Further, in the image data compression apparatus of the present invention, the counting means counts a value obtained by subtracting a predetermined number from the value of the number of pixels, and the image data compression means allocates a predetermined number of values to the display data, An identification code for identifying whether or not the blocks to which the identification code is added are combined is added to the display data.

On the other hand, the image data decompressing device of the present invention, the image data compressed by the image data compressing device,
By determining the type of data by the identification code added to each of the display data and the block, the count value is decoded from the block to which the identification code is added, and the decoded count value and a predetermined number assigned to the display data. The image data decompressing means for decompressing the display data according to the above is provided.

It is desirable that the display data is data coded according to the number of states represented by the compressed image data.

[0010]

According to the present invention, when the number of pixels in the same state is counted from the image data, the counted value is divided into blocks each having a predetermined number of digits and encoded, and the encoded block is converted according to the count value. Necessary blocks are extracted, and the identification codes for identifying the groups are added to the extracted blocks, respectively, and then the blocks to which the identification codes are added are combined with the display data indicating the state of the pixel (color or brightness). By doing so, compressed image data is generated.

As a result, the number of pixels in the same state is represented by only the required number of bits, and the amount of data is efficiently compressed. Further, the decompression of the compressed data can be easily decompressed because the data type can be discriminated by the value of the identification code added to each block.

Further, by assigning a predetermined number of values to the display data, it becomes possible to represent the image data without combining the blocks, and it is possible to efficiently compress the image data in which adjacent pixels often have different states. It is possible to do so. Data can be easily decompressed by adding an identification code for identifying the presence or absence of a block to the display data.

[0013]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a block diagram showing the system configuration of an image forming apparatus (image data compression apparatus / image data expansion apparatus) 100 according to the first embodiment.

This image forming apparatus compresses image data /
As shown in FIG. 1, the input operation unit 101 has various switches (not shown) and a RAM (Random Access Mem) for storing compressed image data.
mory) 102 and this RAM 102, which will be described in detail later.
The image data compressed by the
CP for decompressing the compressed image data stored in 02
U (Central Processing Unit) 103 and CPU 10
Input the image data transferred from No.3, V (video) R
VDP (video display processor) 104 which converts it into a predetermined format and writes it on the AM 105
A display 106 for displaying an image on its screen according to the image data written in the VRAM 105 by the VDP 104; and an interface (I / F) 107 connected to an external device for outputting image data such as a scanner or a magnetic disk device. It consists of

Here, although not particularly shown, the CPU
A ROM (Read Only Memory) storing various control programs and control data is connected to 103.
Various processes performed by the CPU 103 are performed according to the program read from the ROM.

An outline of the operation of the above configuration will be described. The CPU 103 executes control of contents according to user's operations on various switches of the input operation unit 101. When the user specifies the input of image data by operating the input operation unit 101, the CPU 103
Outputs an instruction for transferring the image data via the I / F 107 to the external device, thereby inputting the image data transferred from the external device via the I / F 107. Here, in the present embodiment, the external device connected to the I / F 107 will be described below as a scanner (not shown).

The scanner reads an image formed on the recording paper 201 by raster-scanning the recording paper 201, as shown in FIG. 2, for example. As a result, the data of each pixel is sequentially output from the scanner to the CPU 103 in the order of the scan.

When the CPU 103 inputs the image data transferred from the scanner via the I / F 107, it temporarily stores it in the RAM 102. When the storage of this image data is completed, the number of colors represented by this image data is counted from each pixel data of the image data stored in the RAM 102, and the data of the minimum number of bits capable of expressing this number of represented colors. Create a palette data group having a length.
When the creation of the palette data group is completed, the image data stored in the RAM 102 is compressed.

FIG. 3 is an explanatory diagram showing an example of the structure of compressed image data. The image data stored as a set of pixel data (color code) in the RAM 102 is shown in FIG.
As shown in, color code data (pallet number) 30
It is compressed into image data in which 1 and a continuous code data group 302 representing the number of pixels of the color code data 301 that are continuous are included in one data group. The continuous code data group 302 is composed of continuous code data 303 to 305. Each of the continuous code data 303 to 305 has an identification code 303a, 304a for indicating that they constitute one data group.
305a is added to each. Each identification code 303a,
The values set in 304a and 305a are "0",
“0” and “1”, but “0” indicates that there is continuous code data following this continuous code data,
"1" indicates that the continuous code data ends here. Note that "x" and "y" in the figure indicate the respective data lengths.

FIG. 4 shows the compression of the above-mentioned image data.
~ It will be specifically described with reference to FIG. 4 is shown in FIG.
6 is an explanatory diagram showing an example of a state of an image formed on the recording paper 201 of FIG. “A”, “B”, and “C” in the figure each indicate one pixel and also the color code of that pixel. Therefore, the contents of the image data shown in FIG.
First, 5 pixels with color code "A" are arranged in a row, then 4 pixels with color code "B", 7 pixels with color code "A", and color Pixels having a code “C” are arranged in a row in the order of 16 pixels. The compression of image data will be described by taking the case of compressing the image data shown in FIG. 4 as an example.

When the image data shown in FIG. 4 is compressed, for example, assuming that the continuous code data length x is 2 bits, the compressed image data is as shown in FIG. In FIG. 6, 6
02 is color data of “A”, 603 and 604 are continuous code codes indicating the number of consecutive pixels of the color code of “A”, 603a and 604a are identification codes added to each continuous code data, The color code 602 and the continuous code data 603 and 604 form one data group 601.

The high-order 2 bits indicating the number of consecutive pixels are assigned to the continuous code data 603, and the low-order 2 bits indicating the number of consecutive pixels are assigned to the continuous code data 604. Therefore, when the continuous code data 603 and 604 are to be returned to the data representing the actual continuous number, the continuous code data 603 is shifted to the upper side by 2 bits, and the continuous code data 603 shifted by 2 bits is converted to the continuous code 60.
Add to 4.

The image data compressed as described above is R
It is stored in the allocated area in the AM 102. Specifically, as shown in FIG. 7, a region 701 has a bitmap width (dots in the main scanning direction), a region 702 has a bitmap height (dots in the sub scanning direction), and a region 703.
Is the maximum value of the members of the palette data group (the maximum value of the color code data), the area 704 is the bit length of the continuous code length (the value of the continuous code data length x), the area 705 is the palette data group, and the area 706 is Each of the compressed data groups (see FIG. 6) described above is stored. Thus the area 706
Decompression of the compressed data stored in will be described later.

The palette data group stored in the area 705 is stored in the form of a table in which palette numbers and color codes are uniquely associated with each other, as shown in FIG. Also, the data length of the color code becomes the value of "y" in the figure depending on the number of the palette numbers.

Next, a CP for compressing the above-mentioned image data
The operation of U103 will be described in detail with reference to the flowcharts of the data compression processing shown in FIGS. 9 and 10.
First, in step 901, 0 is set in each of the P1 register and the P2 register. The P1 register indicates the relative address within the area where the image data before compression is stored, and the other P2 register indicates the relative address within the area where the image data after compression is stored.

In step 902, the color code (pixel data) is read using the value of the P1 register as an address and stored in the A register. Then, step 903
The P1 register is incremented by, and 1 is set in the T register in step 904. This T register is for counting the number of consecutive pixels of the same color.

In step 905, P1 whose value is updated in step 903 or step 908 described later is set.
The color code is read using the value of the register as an address and stored in the B register. As a result, color data (pixels) adjacent to the color data (pixels) stored in the A register are stored in the B register, and then step 9
At 06, it is determined whether the value of the A register is equal to the value of the B register.

If it is determined that the value of the A register is not equal to the value of the B register, the process proceeds to step 910 described later, and conversely, if these values are determined to be equal, that is, pixels of the same color are adjacent to each other. If so, step 90
The process shifts to 7.

In step 907, the T register is incremented to count the number of consecutive pixels of the same color, and in step 908, the P1 register is incremented. After that, in step 909, it is determined from the value of the P1 register whether or not all the color code readings are completed. If it is determined that the color code readings are not all completed, the process returns to step 905, and vice versa. If it is determined that the reading has been completed, the process proceeds to step 910.

The above-described processing of steps 905 to 909 is repeated until it is determined in step 906 that the value of the A register is not equal to the value of the B register or it is determined in step 909 that the reading of the color data is completed.
As a result, the number of pixels in which the same color is continuous is stored in the T register.

In step 910, the content (color code) stored in the A register is stored in the RAM 102 using the value of the P2 register as an address. When this store is completed, the P2 register is incremented in step 911, and the process proceeds to step 912 in FIG.

In step 912 of FIG. 10, the number of bits constituting the T register is a predetermined constant N from the upper side for each predetermined number of bits (two bits in this embodiment, see FIG. 6).
Divide into blocks. When the T register is divided into N blocks, 1 is set in the n register designating the divided block in step 913. Then, the process proceeds to step 914.

In step 914, it is determined whether or not there is "1" in the bits of the block designated by the value of the n register from the upper side. If it is determined that there is no bit of "1" in the block, it is next determined in step 915 whether or not there is a bit of "1" in the upper block. If it is determined that there is "1" in the upper block, the process proceeds to step 917 described later, and conversely, if it is determined that there is no bit that is "1" in the upper block, n in step 916. After incrementing the register, the process returns to step 914.

By repeating the above-mentioned steps 914 to 916 until the bit "1" is detected in the block designated by the n register in step 914,
Unnecessary upper-side blocks are removed as continuous code data in the T register.

In step 917, it is determined whether or not the value of the n register is equal to the constant N, that is, whether or not it is the lowest block of the T register. The value of the n register is a constant N
If it is not equal to, each bit of the block designated by the value of the n register is shifted to the left (upper side) by 1 bit in step 918, and "0" is put in the least significant bit. As a result, the identification code indicating the continuation of the continuous code data of the color code stored in the RAM 102 in step 910 of FIG. 9 is added.

Then, in step 919, the contents of the block shifted by 1 bit are stored in the address within the area indicated by the value of the P2 register. When this store is completed, the P2 register is incremented in step 920, the n register is incremented in step 921, and the process returns to step 914.

In step 917, the value of the n register is the constant N.
Until it is determined that the value is equal to the value of
By repeatedly performing the processing of 921, only the block required as the continuous code data has “0” in the least significant bit.
Is added and stored in the RAM 102.

On the other hand, if it is determined in step 917 that the value of the n register is equal to the value of the constant N, the following step 922
In the block designated by the value of the n register, that is, each bit of the block at the lowermost side is shifted to the left by 1 bit (upper side), and "1" is put in the least significant bit. As a result, the identification code indicating the end of the continuous code data of the color code stored in the RAM 102 in step 910 of FIG. 9 is added.

Then, in step 923, the contents of the block shifted by 1 bit are stored in the address within the area indicated by the value of the P2 register. When this store is completed, the P2 register is incremented in step 924, the P1 register is incremented in step 925,
That is, after updating the address in which the color code read from the RAM 102 is updated next, the process proceeds to step 926.

In step 926, it is determined from the value of the P1 register whether or not all the color data has been read. When it is determined that all color data has been read,
If it is determined that the series of processing has been completed and the reading of the data has not been completed, the value of the B register is set in the A register in step 927, the process returns to step 904, and the subsequent processing is performed. Do the same.

The processes of steps 904 to 927 described above are repeatedly executed until it is determined in step 926 that the reading of the color data is completed. As a result, the uncompressed color code (image data) is a data group composed of a color code and at least one continuous code data representing the number of consecutive pixels of the color code, as shown in FIG. It is stored in the RAM 102 as one unit.

As described above, the content of the image data is represented by the color code and the continuous code data indicating the length in which the pixels of the color code are continuous, so that it is compared with the conventional case where the color code is provided for each pixel. Then, the compression rate of the image data of an image in which each area is painted in the same color as in an animation image can be significantly increased. Further, since the continuous code data is divided into blocks of a predetermined number of bits and the identification code is added to this block, the continuous code data of the required number of bits can be added to the color code, so that pixels of the same color are connected. The change in the number can be dealt with, and the compression rate can be further improved.

Here, although not particularly shown, the compressed image data once stored in the address of the designated area is then packed in a state in which each color code and continuous code data are connected in bit units. , Area 70 shown in FIG.
6 is stored. As a result, the compressed image data is
It is stored in the RAM 102 in a compressed state regardless of the bit lengths of the color code and the continuous code data. At this time, the color code is the palette number (color code data).
Is replaced by

Next, the decompression (decompression) process according to this embodiment will be described with reference to the flowchart of the decompression process shown in FIG. This processing is executed when an instruction is given to display the image data stored in the compressed RAM 102. First, in step 1101, the pointer is moved to the beginning of the area 706 in which the compressed data group is stored. Set to a value that indicates a bit. This pointer is
A variable whose value is stored in a register (not shown) in the RAM 102. Although not shown, an initial value is set in a register indicating an address for writing the expanded image data, and a value indicating the total number of pixels of the image data is d.
It is set in the register.

In step 1102, the palette number (color code data) is read from the area 706 while incrementing the pointer, and the subsequent step 1103
Now, referring to the area 705 in which the palette data group is stored, the color code corresponding to the palette number is extracted. After that, in step 1104, 0 is set in the b register for counting the number of writing this color code.

At step 1105, the continuous code data y is extracted while incrementing the pointer, and at step 1106, the extracted continuous code data y is b.
Add to register.

At step 1107, the pointer is incremented to take out the identification flag of the continuous code data y, and at step 1108, the value of the identification flag is set to 1.
Whether or not, that is, whether or not the data to be extracted next is color code data is determined. If the value of this identification flag is 0, then in step 1109, the content of the b register is shifted to the upper side by the continuous code length x bits (2 bits in this embodiment), and then the processing of step 1105 is performed. Return. If the value of the identification flag is 1, the data to be extracted next becomes color code data, and the process proceeds to step 1110. By shifting to the processing of step 1110, the value of the b register, that is, the number of pixels in which the same color is continuous is determined.

In step 1110, the address to be written in the RAM 102 is incremented while the step 11
RA of the color code fetched in 03 by the value of b register
Write to M102.

At step 1111, the value of the b register is subtracted from the d register (d = d−b). This gives d
A value indicating the total number of remaining pixels will be set in the register. Then, in step 1012, it is determined whether or not the value of the d register is larger than 0, that is, whether or not all the decompression of the compressed data (= width of the bitmap × height) is completed. It If it is determined that all decompression has not been completed, the process returns to step 1102. Conversely, if it is determined that all decompression has been completed,
Here, a series of processing ends.

As described above, since the type of the data to be read next can be known from the value of the identification flag added to the continuous code data, it is possible to easily decompress the compressed image data.

Next, the second embodiment will be described. The configuration of the second embodiment is basically the same as that of the first configuration, but the method of compressing / decompressing image data is different. Therefore, only the different parts will be described using the same reference numerals as in the first embodiment.

The first embodiment is effective for improving the compression rate of image data in the case of an image in which pixels of the same color are often continuous, such as an animation image. But,
Since at least one piece of continuous code data corresponds to one color code, it is conceivable that the compression rate is lowered in an image in which pixels of the same color are rarely continuous, such as a natural image.

For example, when the image shown in FIG. 12 is formed on the recording paper, the data can be efficiently compressed for the upper two lines by the first embodiment, but the pixel for the lower one line. Color code is "A",
Since it changes in the order of “B” and “C”, the compression rate decreases for this line. The second embodiment is designed to prevent the compression rate from decreasing even in such a case.

In the second embodiment, in order to suppress the decrease in the compression rate, the color code data (palette number) is used after compression.
It is assumed that the pixel itself means one pixel, and when two or more pixels of the same color are continuous, a value obtained by subtracting 1 from the number of actual pixels in the continuous color is represented by continuous code data. Therefore,
The contents when the image of FIG. 12 is compressed are as shown in FIG.

When the color code data itself shows a value, it is impossible to judge whether or not the color code data is combined with the continuous code data to form a data group. Therefore, in the second embodiment, the identification flag is added to the color code data.

FIG. 14 is an explanatory diagram showing a configuration example of image data when the image shown in FIG. 12 is compressed by the second embodiment. As shown in FIG. 14, one data group 1401 which is a unit of image data in compression includes color code data 1402 corresponding to the color code “A”, continuous code data 1403, and 1404. Are identification flags 1402a, 1403a and 1404, respectively.
a.

When the value of each identification flag is "0", it indicates that there is subsequent data, and when it is "1", it indicates that one data group ends. Therefore, the value of the identification flag identification flag 1402a is "0", the value of the identification flag 1403a is 0, and the value of the identification flag 1404a is "1".

Thus, by assigning a preset value to the color code data itself, each pixel can be represented by only one color code data even if the third line portion of FIG. 12 is compressed. Data can be compressed more efficiently than in the first embodiment. As a result, it is possible to efficiently perform compression of data while suppressing fluctuations in the compression rate, regardless of the type of image such as an animation image or a natural image.

Next, the CPU 10 for compressing the above data
The operation of No. 3 will be described in detail with reference to the flowcharts of the data compression processing shown in FIGS. First, in step 1501, 0 is set in each of the P1 register and the P2 register. The value of the relative address in the area where the image data before compression is stored is set in this P1 register, and the value of the relative address in the area where the image data after compression is stored is set in the other P2 register. Set.

In step 1502, the color code (pixel data) is read using the value of the P1 register as an address and stored in the A register. Then step 15
The P1 register is incremented by 03, and step 15
At 04, 0 is set in the T register. This T register is for counting the number of consecutive pixels of the same color, and is set to 0 because the color code data itself represents 1.

In step 1505, step 150
3 or the color code is read using the value of the P1 register whose value has been updated in step 1508 described later as an address, and this is stored in the B register. This gives A
The color code (pixel) adjacent to the color code (pixel) stored in the register is stored in the B register, and then in step 1506, it is determined whether the value of the A register is equal to the value of the B register.

If it is determined that the value of the A register is not equal to the value of the B register, the process proceeds to step 1510 described later, and conversely, if it is determined that these values are equal, that is, pixels of the same color are connected. Judgment, Step 1
The processing moves to 507.

In step 1507, the T register is incremented to count the number of consecutive pixels of the same color. In step 1508, the P1 register is incremented. Then, step 1509
In the above, it is judged from the value of the P1 register whether or not the reading of the color code is completed. If it is judged that the reading of the color code is not completed, the process returns to the step 1505, and conversely the reading is completed. If it is determined, the process proceeds to step 1510.

In step 1506, it is judged that the value of the A register is not equal to the value of the B register, or step 150
The processes of steps 1505 to 1509 described above are repeatedly performed until it is determined in 9 that the reading of the color data is completed. As a result, the T register is incremented each time the processing is repeated, and the number of pixels in which the same color is continuous is stored.

In step 1510, it is determined whether or not the value of the T register is 0, that is, whether or not pixels of the same color are connected. If it is determined that the value of the T register is 0, then in step 1511 the contents (color code) of the A register are shifted to the left by 1 bit (upper side), and the least significant bit is "1", that is, the color code data is continued. A value indicating that there is no continuous code data is put in the identification flag and stored in the C register. Next, in step 1512, the value of the P2 register is used as an address to store the contents of the C register in the RAM 102, and in step 1513 the P2 register is incremented. After that, step 153 in FIG. 16 described later.
The processing shifts to 1.

On the other hand, if it is determined in step 1510 that the value of the T register is not 0, that is, it is determined that pixels of the same color are connected, then in step 1514, the content (color code) of the A register is shifted by 1 bit to the left ( Shift to the upper side)
"0" is placed in the least significant bit, that is, a value indicating that there is continuous code data following the color code data is put in the identification flag and stored in the C register. Next, in step 1515, the value of the P2 register is used as an address to store the contents of the C register in the RAM 102, and in step 1516, the P2 register is incremented. Then, the process proceeds to step 1517 of FIG.

As described above, "0" or "1" is set in the identification flag added to the color code data according to the value of the T register. In step 1517 of FIG. 16, a plurality of bits forming the T register are divided into blocks of a predetermined number N from the upper side for each predetermined number of bits (2 bits in the second embodiment, see FIG. 14). To do.
When the T register is divided into N pieces, 1 is set in the n register indicating the divided block in step 1518. Then, the process proceeds to step 1519.

In step 1519, it is determined whether or not there is "1" in the bits of the block designated by the value of the n register from the upper side. If it is determined that there is no "1" bit in the block, then it is determined in step 1520 whether or not there is a "1" bit in the block higher than the block. "1" in the upper block
If it is determined that there is a bit, the process proceeds to step 1522 described later, and conversely, if it is determined that there is no bit that is “1” in the upper block, step 152.
After incrementing the n register by 1, step 15
Returning to the processing of 19.

By repeating the above-mentioned steps 1519 to 1521 until the bit "1" is detected in the block designated by the n register in step 1519, the high-order data unnecessary as continuous code data in the T register is obtained. Side blocks are removed.

In step 1522, it is determined whether or not the value of the n register is equal to the constant N, that is, whether or not the value of the n register indicates the lowermost block of the T register. If it is determined that the value of the n register is not equal to the constant N, then in step 1523, each bit of the block specified by the value of the n register is shifted to the left by 1 bit (upper side), and "0" is placed in the least significant bit. "Enter. As a result, the identification code indicating the continuation of the continuous code data of the color code stored in the RAM 102 in step 1514 of FIG. 15 is added.

Thereafter, in step 1524, the contents of the block shifted by 1 bit are stored in the address within the area indicated by the value of the P2 register. When this store is completed, the P2 register is incremented in step 1525, the n register is incremented in step 1526, and the process returns to step 1519.

Until it is determined in step 1522 that the value of the n register is equal to the value of the constant N, the above-mentioned step 151
By repeating the processing of 9 to 1526, only the blocks required as the continuous code data are stored in the RAM 102 with "0" added to the least significant bit.

On the other hand, if it is determined in step 1522 that the value of the n register is equal to the value of the constant N, the following step 15
At 27, each bit of the block designated by the value of the n register, that is, the least significant block is shifted to the left by one bit (upper side), and "1" is put in the least significant bit. As a result, the identification code indicating the end of the continuous code data of the color code stored in the RAM 102 in step 1514 of FIG. 15 is added.

Thereafter, in step 1528, the contents of the block shifted by 1 bit are stored in the address within the area indicated by the value of the P2 register. When this storage is completed, the P2 register is incremented in step 1529, the P1 register is incremented in step 1530, that is, the address where the color code to be read next from the RAM 102 is stored is updated, and then the process proceeds to step 1531.

At step 1531, it is judged from the value of the P1 register whether or not the reading of all the color codes has been completed. If it is determined that the reading of all the color codes has been completed, a series of processes ends here, and conversely, if it is determined that the reading of the color codes has not ended, B is determined in step 1532.
After setting the register value to the A register, step 1
Returning to the processing of 504, the subsequent processing is similarly executed.

Until it is judged in step 1531 that the reading of the color code is completed, the above-mentioned steps 1504 to 15
The process of 32 is repeatedly executed. As a result, in the uncompressed color data (image data), as shown in FIG. 14, continuous code data is added to the color code data in accordance with the number of pixels continuous in the same color to form one data group.

As described above, since the color code data itself has a value, a high compression rate can be achieved when compressing image data in which the color code is different for each pixel, as compared with the first embodiment. Can have

Here, although not particularly shown, the compressed image data once stored in the address of the designated area is then packed into a state in which each color code and continuous code data are connected in bit units. , Area 70 shown in FIG.
6 is stored. As a result, the compressed image data is
It is stored in the RAM 102 in a compressed state regardless of the bit lengths of the color code and the continuous code data. At this time, the color code is the palette number (color code data).
Is replaced by

Next, decompression (expansion) according to the second embodiment.
The processing will be described with reference to the flowchart of the decompression processing shown in FIG. This process is performed by the compressed RAM1
This is executed when the display of the image data stored in 02 is instructed. First, in step 1701, the pointer is moved to the area 7 where the compressed data group is stored.
Set to the value indicating the first bit of 06. This pointer is a variable whose value is stored in a register (not shown) in the RAM 102. Although not shown, an initial value is set in a register indicating an address for writing the expanded image data, and a value indicating the total number of pixels of the image data is set in the d register.

In step 1702, the color code data (palette number) is read from the area 706 while incrementing the pointer, and the subsequent step 1703.
Now, referring to the area 705 in which the palette data group is stored, the color code corresponding to the palette number is extracted.

In step 1704, the fetched color code is written in the current write address of the RAM 102, and this address is incremented. In the following step 1705, 1 is subtracted from the d register (d = d-
1) In step 1706, it is determined whether or not the value of the d register is greater than 0, that is, whether or not the expansion of the image data is completed.

If it is determined in step 1706 that the value of the d register is 0 or less, a series of processing is terminated here,
On the contrary, if it is determined that the value is larger than 0, then in step 1707, the pointer is looked at and the identification flag of this color code data is taken out. When this identification flag is taken out, it is determined in step 1708 from the value of the identification flag whether the next data is color code data or continuous code data. If it is determined to be color code data, the process returns to step 1702. On the contrary, if it is determined to be continuous code data, 0 is set in the b register for counting the number of color codes to be written in step 1709.

At step 1710, the continuous code data y is extracted while the pointer is incremented, and at step 1711 the continuous code data y extracted is b.
Add to the register (b = b + y).

In step 1712, the pointer is incremented to extract the identification flag of the continuous code data y, and in step 1713, it is determined whether the data to be extracted next is color code data or continuous code data depending on the value of the identification flag. judge. If it is determined in step 1713 that the data is continuous code data, then in step 1714 the b register is shifted up by the bit length x of the continuous code data, and then the process returns to step 1710. By performing the processing of steps 1710 to 1914, a value obtained by subtracting 1 from the number of pixels actually connected is set in the b register.

On the other hand, if it is determined in step 1713 that the data to be extracted next is color code data, then step 1
In 715, the color code extracted in step 1703 is written by incrementing the write address by the value of the b register. In the following step 1711, the value of the b register is subtracted from the d register (d = d−b), and then, in step 1717, whether or not the value of the d register is greater than 0, that is, all of the compressed data It is determined whether or not the expansion has been completed. If it is determined that all decompression has not been completed, step 1702
If it is determined that all the decompression has ended, the series of processes ends here.

As described above, the compressed image data can be expanded by determining the type of the next data based on the value of the identification flag added to each of the color code data and the continuous code data. The decompressed image data stored in the RAM 102 is read by the CPU 103 and transferred from the CPU 103 to the VDP 104, so that the image is displayed on the display 106.

In the first and second embodiments, the continuous code data of one color code data has the same bit length even if there are a plurality of them. However, as the number of bits increases exponentially with each increment of the number of digits, for example, blocking the T register from 4 bits to 3 bits from the lower side. To
The number of bits, that is, the continuous code data length may be changed.

[0088]

As described above, according to the present invention,
When the number of pixels in the same state is counted from the image data, the counted count value is divided into blocks each having a predetermined number of digits and encoded, and only the necessary blocks are extracted from the encoded blocks according to the count value. In order to generate compressed image data by adding an identification code for identifying the block to each of the extracted blocks, and combining display data representing a pixel state in the block to which the identification code is added, The number of pixels in the same state can be expressed only by the required number of bits, and the amount of data can be efficiently compressed.

Further, by assigning a predetermined number of values to the display data, it becomes possible to represent the image data without combining the blocks, and it is possible to efficiently compress the image data in which adjacent pixels often have different states. Can be done on a regular basis.

Decompression of compressed data is performed by displaying the display data,
Since the type of data can be discriminated from the value of the identification code added to each block, it can be easily expanded.

[Brief description of drawings]

FIG. 1 is a block diagram showing a system configuration of a first embodiment.

FIG. 2 is an explanatory diagram showing a method of reading an image on a recording sheet.

FIG. 3 is an explanatory diagram showing a configuration example of image data compressed by this embodiment.

FIG. 4 is an explanatory diagram showing an example of a state of an image on a recording sheet.

FIG. 5 is an explanatory diagram showing an example of contents of image data.

FIG. 6 is an explanatory diagram showing a configuration example of compressed image data.

FIG. 7 is an explanatory diagram showing an example of a state of image data.

FIG. 8 is an explanatory diagram showing a configuration of data stored in a palette data storage area.

FIG. 9 is a flowchart showing a data compression process according to the first embodiment (No. 1).

FIG. 10 is a flowchart showing a data compression process according to the first embodiment (No. 1).

FIG. 11 is a flowchart showing a decompression process according to the first embodiment.

FIG. 12 is an explanatory diagram showing an example of a state of an image on a recording sheet.

FIG. 13 is an explanatory diagram illustrating a content example of image data.

FIG. 14 is an explanatory diagram showing a configuration example of compressed image data.

FIG. 15 is a flowchart showing a data compression process according to the second embodiment (No. 1).

FIG. 16 is a flowchart showing a data compression process according to the second embodiment (No. 1).

FIG. 17 is a flowchart showing a decompression process according to the second embodiment.

[Explanation of symbols]

 100 image forming apparatus 101 input operation unit 102 RAM 103 CPU

Claims (5)

[Claims] 1. A counting means for counting the number of pixels in the same state from image data, and an encoding means for dividing the count value counted by the counting means into blocks each having a predetermined number of digits for encoding. , The blocks encoded by the encoding means are extracted according to the count value, and only the necessary blocks are extracted, and the identification codes for identifying the blocks are added to the extracted blocks, and then the identification codes are added. And an image data compression unit that generates compressed image data by combining the block with the display data indicating the state of the pixel. 2. An apparatus for decompressing image data compressed by the image data compression apparatus according to claim 1, wherein the identification code is added by determining the type of data by the value of the identification code. An image data decompression device comprising: an image data decompression means for decompressing the compressed image data by decoding the count value from a block and expanding the display data according to the decoded count value. 3. The counting means counts a value obtained by subtracting a predetermined number from the value of the number of pixels, and the image data compressing means allocates the predetermined number of values to the display data and the identification code. The image data compression apparatus according to claim 1, wherein an identification code for identifying whether or not the blocks added with are combined is added to the display data. 4. A device for decompressing image data compressed by the image data compression device according to claim 3, wherein the type of data is discriminated by an identification code added to each of the display data and the block. The compressed image data is expanded by decoding the count value from the block to which the identification code is added and expanding the display data according to the decoded count value and a predetermined number assigned to the display data. An image data decompression device comprising image data decompression means. 5. The image data compression apparatus according to claim 1, wherein the color data is data coded according to the number of states represented by the image data to be compressed. .