JP2009212789A - Image compressor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image compressor with which compression per block over a plurality of lines is attained by reducing capacity of a memory for temporary storage used in compression. <P>SOLUTION: The image compressor is provided with: a first compression part 11 which compresses image data of one line per area with the predetermined number of pixels (for example, four pixels) to generate primary compression data; first to fourth line memories 21-24 which store the primary compression data generated by the first compression part 11 by every line; and a second compression part which performs compression per large area (block) of four pixels×four pixels constituted of four areas distributed to four lines based on the primary compression data stored in the line memories. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image compression apparatus that compresses an image, and more particularly, to an image compression apparatus that compresses an image by dividing the image into a plurality of blocks.

  In an apparatus such as a digital multi-function peripheral, image data is compressed and stored in order to reduce the storage capacity required when image data in bitmap format is stored in a memory or a hard disk device.

  One of the compression methods is a BTC (Block Truncation Coding) compression method. In BTC compression, an image to be compressed is divided into blocks each having a predetermined number of pixels (for example, 4 pixels × 4 pixels), and each block is information indicating the distribution range of gradation values of pixels belonging to the block (for example, , The maximum value and the minimum value), and the compressed data represented by the code data obtained by normalizing the gradation value of each pixel in the block within the distribution range with the gradation number smaller than the gradation number of the original image data. Generate.

  At the time of decompression, a representative value for each value of the code data is determined from the distribution range of gradation values indicated by the maximum value and the minimum value included in the compressed data, and each code data included in the compressed data is an image of the corresponding representative value. It is designed to restore the image by converting it to data.

  For example, FIG. 8 shows the original image data 80 for one block of 4 pixels × 4 pixels in which each pixel is represented by 8-bit 256 gradations (in the figure, the gradation value is expressed in hexadecimal). A case where BTC compression is performed on code data of 4 bits (four gradations) and further expanded is illustrated.

  At the time of compression, the maximum value B6h and the minimum value 32h of the gradation values in the block are detected, the distribution range having these as both ends is equally divided into four, and the gradation value D is the maximum value (B6h) ≧ D> threshold 3 ( 95h) pixel is 2-bit code data “11”, threshold 3 (95h) ≧ D> threshold 2 (74h) is code data “10”, threshold 2 (74h) ≧ D> threshold 1 (53h) ) Are encoded into code data “01”, and pixels with threshold 1 (53h) ≧ D ≧ minimum value (32h) are encoded into code data “00”. The compressed data 81 is composed of code data for these 16 pixels, data indicating a maximum value B6h and a minimum value 32h, and the amount of data is 6 bytes.

  At the time of decompression, the maximum value B6h indicated by the data in the compressed data 81 is set to the representative value 4 corresponding to the code data “11”, and the minimum value 32h is set to the representative value 1 corresponding to the code data “00”. Of the two boundary values that divide the range indicated by the value (B6h to 32h) into three equal parts, the larger 8Ah corresponds to the representative value 3 corresponding to the code data “10”, and the smaller 5Eh corresponds to the code data “01”. Set to a representative value of 2. Then, each code data included in the compressed data 81 is converted into a representative value corresponding to the value of the code data, so that the image data 82 for one block is expanded.

  In order to increase the compression ratio, BTC compression is performed on a block basis, and then the BTC compressed data is converted into a secondary block using JBIG (Joint Bi-level Image Experts Group) or MH method. There is an image processing apparatus for compression (see, for example, Patent Document 1).

JP 2007-43577 A

  In a multifunction machine or the like, image data output from the scanner unit is compressed in parallel with the document reading operation by the scanner unit. FIG. 9 shows a configuration example of a conventional compression circuit configured to compress image data sequentially input line by line from the scanner unit.

  The scanner unit 91 sequentially outputs image data to be compressed in line units. The line memory 1 is a memory that holds image data for the first line, the line memory 2 is a memory that holds image data for the second line, the line memory 3 is a memory that holds image data for the third line, and the line memory 4 is 4 This is a memory for holding the image data of the line. The BTC compression unit 95 is a circuit that performs BTC-compliant compression processing with 4 pixels × 4 pixels as one block, and the BTC decompression unit 96 is a circuit that performs BTC-compliant decompression processing. The counter 97 counts the number of lines, outputs an enable signal for starting processing to each unit, and the control unit 98 controls the whole.

  The control unit 98 operates the counter 97 and outputs each enable signal EN1 to EN3 from the counter 97, thereby operating each circuit unit. Specifically, the counter value and each enable signal are 0 in the initial state. When the counter value becomes 1, the enable signal EN1 becomes 1, and the image data for one line input from the scanner unit 91 is held in the line memory 1. Similarly, when the counter value becomes 2, the enable signal EN1 becomes 2, and the image data for one line from the scanner unit 91 is held in the line memory 2. When the counter value becomes 3, the enable signal EN1 becomes 3, and the image data for one line from the scanner unit 91 is held in the line memory 3. When the counter value becomes 4, the enable signal EN1 becomes 4, and the scanner unit 91 Is stored in the line memory 4.

  When the counter value becomes 5, the enable signal EN2 becomes 1, and in response to this, the BTC compression unit 95 performs BTC compression processing on the image data held in the line memories 1 to 4, and when the counter value becomes 6, the enable signal EN3. In response to this, the BTC decompression unit 96 decompresses the BTC compressed data, and the decompressed image data is output to the printer unit 99 and printed. FIG. 10 shows a timing chart of the above operation.

  As described above, in order to compress image data sequentially input for each line in units of blocks extending over a plurality of lines, a line memory for at least a plurality of lines included in the block is required. There has been a problem that the memory capacity for holding data increases.

  This problem occurs at the stage of the primary compression even when the compressed data subjected to the primary compression in units of blocks as in the technique disclosed in Patent Document 1 is combined into a plurality of blocks and subjected to secondary compression.

  The present invention is intended to solve the above problem, and provides an image compression apparatus capable of realizing block unit compression across a plurality of lines by reducing the capacity of a temporary holding memory used at the time of compression. The purpose is that.

  The gist of the present invention for achieving the object lies in the inventions of the following items.

[1] A first compression unit that generates primary compression data obtained by compressing image data of one line in an area unit of a predetermined number of pixels;
A second compression unit that compresses the primary compressed data generated by the first compression unit into a large area unit composed of a plurality of areas distributed over a plurality of lines;
An image compression apparatus comprising:

  In the above invention, the first compression unit compresses image data for one line in an area unit of a predetermined number of pixels (for example, 4 pixels) and outputs primary compression data, and the second compression unit outputs a plurality of primary compression data. Compressed into a large area unit composed of a plurality of areas distributed over the lines (for example, four areas distributed over adjacent four lines). As a result, it is possible to reduce the memory area for temporarily storing image data and the like during compression, compared to the case where large area unit compression is performed directly from the original image data.

[2] The second compression unit compresses image data obtained when decompressing primary compressed data for a plurality of areas constituting the large area in units of the large area. [1] The image compression apparatus described in 1.

  In the above invention, the primary compressed data for a plurality of areas constituting a large area is not compressed as it is, but the image data obtained when the primary compressed data is expanded is compressed in a large area unit. Thereby, secondary compressed data corresponding to the case where the original image data is directly compressed in units of blocks can be obtained. Therefore, when decompressing, it is not necessary to decompress in two stages, and image data can be obtained directly by decompressing secondary compressed data.

[3] A storage unit for storing the primary compressed data generated by the first compression unit is provided. The second compression unit is stored in the storage unit and is primary compressed data for a plurality of areas constituting the large area. The image compression apparatus according to [1] or [2], wherein the large area is compressed based on the above.

  In the said invention, primary compression data are once memorize | stored in a memory | storage part, and are read from this memory | storage part, and secondary compression is performed. Compared to the case where the original image data is held in the storage unit and compressed from the original image data directly in units of blocks, the primary compressed data is held in the storage unit, so that the memory capacity required for the storage unit is reduced.

[4] The first compression unit compresses the next line after compressing the image data for one line,
The image compression according to [3], wherein the second compression unit compresses the large area after primary compressed data for a plurality of areas constituting the large area is stored in the storage unit. apparatus.

  In the above invention, the image data for one line is primarily compressed, and then the next line is temporarily compressed. The storage unit stores primary compressed data for a plurality of lines included in the large area, and secondary compression is started when the image data for the plurality of lines included in the large area are arranged in the storage unit. Of the lines included in the large area, for the line in which primary compressed data is finally generated, the large area to be compressed is stored even before the primary compressed data of the entire line is stored in the storage unit. Secondary compression may be started at the stage when primary compressed data in the area included in is complete.

[5] The first compression unit performs BTC compression with the area as one block,
The image compression apparatus according to any one of [1] to [4], wherein the second compression unit performs BTC compression with the large area as one block.

  According to the image compression apparatus according to the present invention, it is possible to perform block unit compression across a plurality of lines while reducing the capacity of a temporary holding memory used at the time of compression.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows the configuration of an image compression / decompression apparatus 10 according to an embodiment of the present invention. The image compression / decompression apparatus 10 has a function of compressing input image data and a function of expanding compressed image data. The image compression / decompression apparatus 10 is connected to a scanner unit 5 serving as a supply source of image data to be compressed and a printer unit 7 that prints an image on a recording sheet based on the decompressed image data.

  The scanner unit 5 includes a line image sensor that reads an original image for one line in the main scanning direction, and a relative moving unit that relatively moves a reading position by the line image sensor in a sub-scanning direction orthogonal to the main scanning direction. ing. By repeating the reading operation in units of lines while relatively moving the reading position of the line image sensor with respect to the original in the sub-operation direction, an image of the original on a two-dimensional plane is read. The line image sensor sequentially outputs an analog signal corresponding to the read image for one line from one end of the line to the other end, and the analog signal is converted into digital image data in the output order from the scanner unit 5. The image is output to the image compression / decompression apparatus 10. Here, the scanner unit 5 outputs image data in which each pixel is represented by 8-bit 256 gradations.

  The image compression / decompression apparatus 10 holds first data for sequentially compressing image data sequentially input from the scanner unit 5 and first compression data for one line each of primary compression data output from the first compression unit 11. 4th line memory 21-24, the 2nd compression part 12 which compresses the primary compression data currently hold | maintained at the 1st-4th line memories 21-24, and outputs secondary compression data, The 2nd compression part 12 Are provided with a BTC decompression unit 13 for decompressing the secondary compressed data output to the image data, a counter 14, and a control unit 15.

  The first compression unit 11 compresses one line of image data into areas of a predetermined number of pixels. Here, as shown in FIG. 2, the image data LG for one line is BTC-compressed in units of areas of four pixels from the head, and primary compressed data E corresponding to each area is output.

  The first compression unit 11 outputs primary compressed data obtained by compressing the image data of the 4N-3 (N is an integer of 1 or more) line to the first line memory 21 to hold it. Also, the primary compressed data obtained by compressing the image data of the 4N-2 line is output to the second line memory 22 and held, and the primary compressed data obtained by compressing the image data of the 4N-1 line is stored in the third line memory 23. The first compressed data obtained by compressing the image data of the 4N-th line is output to the fourth line memory 24 and held.

  The 2nd compression part 12 compresses the primary compression data produced | generated by the 1st compression part 11 to the large area unit comprised by the several area disperse | distributed to several lines. Here, the second compression unit 12 is a block composed of four areas at the same offset position from the head of each line from the four consecutive lines stored in the first to fourth line memories 21 to 24. BTC compression is performed in units of large areas. That is, as shown in FIG. 3, the secondary compression is performed in units of blocks BL of 4 pixels (main scanning direction) × 4 pixels (sub-scanning direction) with the upper left corner of the document image G as a base point.

  The BTC decompression unit 13 decompresses the secondary compressed data into image data in units of blocks. The counter 14 counts the number of lines to be processed and outputs a processing start enable signal to each unit. The control unit 15 performs overall control of the operation of the image compression / decompression apparatus 10.

  The image compression / decompression apparatus 10 includes a hardware circuit such as a sequencer or a logic circuit incorporating a microprogram, and a memory. The image compression / decompression apparatus 10 may be realized by executing a predetermined program in a computer apparatus including a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like.

  The image compression / decompression apparatus 10 operates the counter 14 by the control unit 15 and outputs the enable signals EN1 to EN3 corresponding to the counter value from the counter 14, so that each circuit unit (the first compression unit 11, the second compression unit 11, and the second compression unit 11). The compression unit 12 and the BTC decompression unit 13) are operated.

  Specifically, in the initial state, the counter value of the counter 14 and the enable signals EN1 to EN3 are 0. When the control unit 15 instructs the scanner unit 5 to start reading a document, the scanner unit 5 starts a document reading operation.

  When the counter value of the counter 14 becomes 1, the enable signal EN1 becomes 1, and in response to this, the first compression unit 11 sequentially captures image data for one line ((4N-3) line) from the scanner unit 5, The image data is primarily compressed in units of areas of adjacent four pixels, and the generated primary compressed data of each area is sequentially held in the first line memory 21.

  Similarly, when the counter value of the counter 14 becomes 2, the enable signal EN1 becomes 2, and in response to this, the first compression unit 11 receives image data for the next one line ((4N-2) line) from the scanner unit. Are sequentially compressed, and the image data is primarily compressed in units of adjacent four pixels, and the generated primary compressed data of each area is sequentially held in the second line memory 22.

  When the counter value of the counter 14 becomes 3, the enable signal EN1 becomes 3, and in response to this, the first compression unit 11 sequentially outputs image data for the next one line ((4N-1) line) from the scanner unit 5. Then, the image data is subjected to primary compression in units of adjacent four pixels, and the generated primary compressed data of each area is sequentially held in the third line memory 23.

  When the counter value of the counter 14 becomes 4, the enable signal EN1 becomes 4, and in response to this, the first compression unit 11 sequentially takes in the image data for the next one line ((4N) line) from the scanner unit, Image data is primarily compressed in units of adjacent four pixels, and the generated primary compressed data of each area is sequentially held in the fourth line memory 24.

  When the counter value becomes 5, the enable signal EN1 returns to 0 and the enable signal EN2 becomes 1. In response to this, the second compression unit 12 secondarily compresses the primary compressed data held in the first to fourth line memories 21 to 24 in units of blocks (large areas). When the counter value becomes 6, the enable signal EN2 returns to 0, the enable signal EN3 becomes 1, the BTC decompression unit 13 BTC decompresses the secondary compressed data, and the decompressed image data is output to the printer unit 7. Printed. FIG. 4 shows a timing chart of the above operation.

  The secondary compressed data output from the second compression unit 12 is stored in a storage device such as an HDD (Hard Disk Drive), and is read out from the HDD and decompressed by the BTC decompression unit 13 when an output request is received later. The printer unit 7 may be configured to print out.

  Next, details of primary compression by the first compression unit 11 and secondary compression by the second compression unit 12 will be described.

The first compression unit 11 primarily compresses each line in units of adjacent four pixels. Here, BTC compression is performed so that one pixel is represented by 4-gradation 2-bit code data. Specifically, the maximum value Max and the minimum value Min of the gradation values of pixels belonging to one area composed of four pixels adjacent in the main scanning direction are obtained, and the maximum value Max and the minimum value Min are determined at both ends. Threshold value 1, threshold value 2, and threshold value 3 (threshold value 1 <threshold value 2 <threshold value 3) for dividing the gradation range to be divided into four regions (here, divided into four equal parts) are calculated. And when it is set as the gradation value D of the pixel,
If maximum value ≧ D> threshold 3, region 3 and code data “11”
If threshold 3 ≧ D> threshold 2, area 2, code data “10”
If threshold 2 ≧ D> threshold 1, area 1 and code data “01”
If threshold 1 ≧ D ≧ minimum value, area 0, code data “00”
Are given as 2-bit code data for the pixel. Then, primary compressed data including data indicating the maximum value Max, data indicating the minimum value Min, and code data (2 bits × 4 pixels) given to each pixel is generated.

  FIG. 5 shows the process from compression to decompression, focusing on one block (large area). This block includes an area A1 for the first line, an area A2 for the second line, an area A3 for the third line, and an area A4 for the fourth line.

  When the first compression unit 11 performs compression, for example, the area A1 of the first line has the maximum value 50h and the minimum value 32h, and is calculated as threshold 1 = 39h, threshold 2 = 41h, threshold 3 = 48h. A pixel with a gradation value D of 50h ≧ D> 48h is code data “11”, a pixel with 48h ≧ D> 41h is code data “10”, and a pixel with 41h ≧ D> 39h is code data “01”. , The pixels of 39h ≧ D ≧ 32h are converted into code data “00” to generate primary compressed data E1.

  After the primary compression for four lines is completed, the second compression unit 12 compresses the primary compressed data in units of blocks. That is, primary compressed data in four areas existing in four lines constituting a block to be compressed is read from the first to fourth line memories 21 to 24, and these primary compressed data are compressed and subjected to secondary compression. Generate data. The generated secondary compressed data is decompressed by the BTC decompression unit 13, and decompressed image data EX is generated.

  In the example of FIG. 5, primary compressed data E1 corresponding to the area A1 of the first line, primary compressed data E2 corresponding to the area A2 of the second line, and primary compressed data E3 corresponding to the area A3 of the third line, Based on the primary compression data E4 corresponding to the area A4 of the fourth line, secondary compression in block units constituted by these four areas A1 to A4 is performed.

  At this time, the second compression unit 12 compresses the image data obtained when the primary compressed data E1 to E4 for a plurality of areas (four areas) constituting the block are expanded in units of blocks. Specifically, as shown in FIG. 6, each primary compression data E1 to E4 is expanded to generate expanded image data (intermediate image data) ME for one block, and this intermediate image for one block is generated. The data ME is again BTC-compressed so that each pixel has 4 gradations and 2 bits to generate secondary compressed data EE.

  The decompression of the primary compressed data in each area is performed as follows. Among the boundary values that divide the gradation range having the maximum value Max indicated by the data in the primary compressed data into the representative value 4, the minimum value Min as the representative value 1, and the maximum value Max and the minimum value Min as both ends into three equal parts. The smaller value is set to representative value 2 and the larger value is set to representative value 3. Then, each code data included in the primary compressed data includes the code data “00” as the representative value 1, the code data “01” as the representative value 2, the code data “10” as the representative value 3, and the code data “11”. "Is converted into a representative value 4 and expanded into image data.

Compression of the intermediate image data ME obtained by expanding the primary compression data E1 to E4 is performed as follows. Among the 16 pixels included in the intermediate image data ME, the maximum value Max and the minimum value Min of the gradation value are obtained, and the gradation range having both ends of the maximum value Max and the minimum value Min is divided into four regions (here Then, threshold 1, threshold 2, and threshold 3 (threshold 1 <threshold 2 <threshold 3) are calculated, and the gradation value D of the pixel is
If maximum value ≧ D> threshold 3, region 3 and code data “11”
If threshold 3 ≧ D> threshold 2, area 2, code data “10”
If threshold 2 ≧ D> threshold 1, area 1 and code data “01”
If threshold 1 ≧ D ≧ minimum value, area 0, code data “00”
Is given as code data for the pixel. Then, secondary compressed data including data indicating the maximum value Max, data indicating the minimum value Min, and code data (2 bits × 16 pixels) given to each pixel is generated. In the example of FIG. 6, the maximum value Max in the intermediate image data is B6h, the minimum value Min is 32h, and the threshold value 1 = 53h, the threshold value 2 = 74h, and the threshold value 3 = 95h are calculated. Pixels with a gradation value D of B6h ≧ D> 95h are code data “11”, pixels with 95h ≧ D> 74h are code data “10”, and pixels with 74h ≧ D> 53h are code data “01”. In addition, pixels with 53h ≧ D ≧ 32h are converted into code data “00” to generate secondary compressed data EE.

  It is not necessary to actually generate the intermediate image data ME on the memory in the process of generating the secondary compressed data from the primary compressed data for a plurality of areas constituting one block, and representative values 1 to 4 for each area Further, it may be configured to perform processing for converting each code data of the primary compressed data into code data of the secondary compressed data from the maximum value Max and the minimum value Min in the block unit and the threshold value 1 to the threshold value 3. .

  In this way, the image data to be compressed is primarily compressed by the first compression unit 11 for each line, and the generated primary compressed data is compressed in units of blocks over four lines, so that the original image data is directly in units of blocks. Compared with the case of BTC compression, the memory capacity of the first to fourth line memories 21 to 24 holding image data can be reduced. That is, the original image data for one block composed of 4 pixels × 4 pixels is 8 bits × 16 pixels = 136 bits, but in the primary compressed data, one area has a maximum value of 8 bits + a minimum value of 8 bits + 2 Since 4 bits × 24 pixels = 24 bits, it is 96 bits for 4 areas. Therefore, the memory capacity required for the line memory can be reduced to 3/4 compared with the case where the original image data is directly compressed in units of blocks.

  Further, since the image data obtained when the primary compressed data for one block is expanded is BTC-compressed for each block, secondary compressed data corresponding to the case where the original image data is directly compressed for each block can be obtained. it can. Therefore, when decompressing, it is not necessary to decompress in two stages, and image data can be obtained directly by decompressing secondary compressed data. Also, almost the same compressed data can be obtained from the original image data as when BTC compression is performed in units of blocks. In the example of FIG. 6, the secondary compressed data is the same as the compressed data (compressed data 81 in FIG. 8) when BTC compression is performed directly from the original image data in units of blocks, and the decompressed image data also matches. ing.

  FIG. 7 shows the flow of the compression / decompression operation performed by the image compression / decompression apparatus 10. The counter value is initialized to 0 (step S101). Thereafter, when the counter value becomes 1, one line of image data (original image data) to be compressed is input from the scanner unit 5 (step S102), and this is subjected to primary compression sequentially (step S103), and the generated primary compressed data. Is held in the line memories 21 to 24 corresponding to the value of the enable signal EN1 (step S104).

  If the counter value of the counter 14 is not 5 (step S105; N), the process returns to step S102 to perform primary compression of the next line. If the counter value is 5 (step S105; Y), secondary compression in units of blocks is performed based on the primary compression data held in the first to fourth line memories 21 to 24 (step S106). Thereafter, the secondary compressed data is sequentially decompressed by the BTC decompression unit 13 (step S107) and output to the printer unit 7 (step S108). It is determined whether or not the processing of all image data for one page has been completed (step S109). If the processing has not been completed (step S109; N), the process returns to step S101 to process the next four lines. If completed (step S109; Y), this process ends (end).

  The embodiment of the present invention has been described with reference to the drawings. However, the specific configuration is not limited to that shown in the embodiment, and there are changes and additions within the scope of the present invention. Are also included in the present invention.

  For example, in the embodiment, the first compression unit 11 divides one line of image data into 4-pixel area units and performs primary compression. However, the primary compression is not necessarily performed on a line. It doesn't matter. For example, a rectangular area of 2 pixels × 2 pixels may be used as an area for primary compression, and secondary compression may be performed on a large area basis including a plurality of areas based on primary compression data for a plurality of areas. At this time, the primary compressed data is not compressed as it is, but the image data obtained when the primary compressed data is expanded is compressed in units of large areas. That is, the first compression unit generates primary compressed data obtained by compressing image data of an image to be compressed in units of predetermined areas, and the second compression unit performs primary for a plurality of areas generated by the first compression unit. Based on the compressed data, the image data obtained when the primary compressed data corresponding to the plurality of areas is expanded may be compressed into a large area unit composed of the plurality of areas.

  In addition, the number of bits per pixel in the original image data, the number of bits of code data per pixel at the time of compression, the size of one area, the size of one block, etc. are not limited to those exemplified in the embodiment. . However, (number of bits per pixel of original image data × 2 + number of bits of code data per pixel in primary compressed data × number of pixels in one area) <(number of bits per pixel of original image data × The size of the area and the number of bits of code data are set so that the relationship of the number of pixels in one area) is established. Thereby, the memory capacity of the line memory is reduced.

  The apparatus that supplies the image data to the image compression / decompression apparatus 10 is not limited to the scanner unit 5, and the supply source is not limited. For example, it may be image data received from outside via communication.

1 is a block diagram illustrating a schematic configuration of an image compression / decompression apparatus according to an embodiment of the present invention. It is explanatory drawing which illustrated by contrasting the image data of 1 line, and the primary compression data obtained by carrying out the primary compression of this. It is explanatory drawing which shows the relationship between a document, each line, and a block. 3 is a timing chart showing the operation of the image compression / decompression apparatus 10. It is explanatory drawing which illustrated the process from the compression to expansion | extension, paying attention to one block (large area). It is explanatory drawing which shows the process of carrying out the secondary compression from the primary compression data for 1 block. 3 is a flowchart showing an operation sequence of the image compression / decompression apparatus 10. It is explanatory drawing which shows each data at the time of BTC compression and expansion | extension by the block unit of 4 pixels x 4 pixels. It is a block diagram which shows the structural example of the image compression / decompression apparatus conventionally used. 10 is a timing chart showing the operation timing of the apparatus shown in FIG. 9.

Explanation of symbols

DESCRIPTION OF SYMBOLS 5 ... Scanner part 7 ... Printer part 10 ... Image compression / expansion apparatus 11 ... 1st compression part 12 ... 2nd compression part 13 ... BTC expansion | extension part 14 ... Counter 15 ... Control part 21 ... 1st line memory 22 ... 2nd line memory 23 ... 3rd line memory 24 ... 4th line memory A1-A4 ... Area BL ... Original image data E, E1-E4 ... Primary compression data LG ... Image data for 1 line ME ... Intermediate image data EE ... Secondary compressed data EX ... Image data after decompression

Claims (5)

A first compression unit that generates primary compression data obtained by compressing one line of image data in an area unit of a predetermined number of pixels;
A second compression unit that compresses the primary compressed data generated by the first compression unit into a large area unit composed of a plurality of areas distributed over a plurality of lines;
An image compression apparatus comprising: The said 2nd compression part compresses the image data obtained when the primary compression data for several areas which comprise the said large area are expand | extended in the said large area unit. Image compression device. A storage unit that stores primary compression data generated by the first compression unit is provided. The second compression unit is based on primary compression data for a plurality of areas constituting the large area, which is stored in the storage unit. The image compression apparatus according to claim 1, wherein the large area is compressed. The first compression unit compresses image data for one line and then compresses the next line,
The image compression according to claim 3, wherein the second compression unit compresses the large area after primary compressed data for a plurality of areas constituting the large area is stored in the storage unit. apparatus. The first compression unit performs BTC compression with the area as one block,
The image compression apparatus according to any one of claims 1 to 4, wherein the second compression unit performs BTC compression with the large area as one block.

Images