JP2010278650A - Image compression processor, image forming apparatus, computer program, recording medium, and image compression method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image compression processor, an image forming apparatus, a computer program, a recording medium, and an image compression method for increasing a compression rate of an image, reducing a memory capacity at performing compression/expanding processing, and simplifying the management of encoding data. <P>SOLUTION: In an image compression part 22 of a compression processing part of a printer, image data are separated into character/line drawing data and image data by an image separation part 221 and respective data are stored to a first band buffer 222 and a second band buffer 223. A luster scan output part 224 and a block scan output part 225 read respective data separately, and output them to a first compression part 226 and a second compression part 227, and reversible compression and irreversible compression of the respective data are performed. Respective code data are stored to a first code buffer 228 and a second code buffer 229. A code combining part 260 reads the respective code data from the respective code buffers and combines them into one code data. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to image compression that separates and encodes character image and / or line image and image image data into character image and / or line image area data and image area data. The present invention relates to a processing apparatus, an image forming apparatus, a computer program, a recording medium, and an image compression method.

In printing apparatuses (image forming apparatuses) such as digital multifunction peripherals and laser printers, usually, print data is temporarily stored in a storage medium such as a hard disk, and the print data is read out from the storage medium for printing, reprinting, and filing. Various print jobs are performed.
Since the amount of print data is A4 size, it is approximately 96 MB in 600 dpi and RGB format, it is common to compress and store data on the hard disk from the viewpoint of the storage capacity and transfer bandwidth of the hard disk.

There are reversible and irreversible compression methods for color image data. As lossless compression methods, JPEG-LS (Lossless Joint Photographic Experts Group) and JBIG (Joint Bi-Level Image Experts Group), lossy compression There is JPEG. Conventionally, compression has been performed using any one of the methods, but each has advantages and disadvantages.
For example, when compression is performed only with the lossless compression method, there is a problem that the compression rate is low although there is no deterioration in image quality at the time of decompression. (In particular, deterioration is easily perceived in high-frequency components such as characters).

Therefore, in order to satisfy both the compression rate and the image quality, the image data is separated into a character area and an image area, a reversible compression is performed on the character area, and an irreversible compression is performed on the image area. The compression is performed using
However, in this method, it is necessary to manage the code data output from a plurality of compressors as separate files at the time of compression, and to restore one image based on the image data output from the plurality of decompressors at the time of restoration. There is a problem that it is necessary to prepare one page of buffer memory because it is necessary to synthesize.

  In the image encoding device of Patent Document 1 that solves this problem, image data is divided into rectangular blocks, and the image data in the block is separated into a plurality of signals (TAG, character line drawing, natural image). Yes. Next, the separated TAG is subjected to binary image lossless encoding, the character / line image is subjected to multivalued image lossless encoding, and the natural image is subjected to multivalued image lossy encoding, and encoded so that the code data is cut off at the block boundary. Then, the code data in the same block is synthesized (the natural image code data, the character / line image code data, and the TAG code data in the same block are arranged continuously), and the code data output from a plurality of compressors is combined. The code data management is simplified by consolidating the blocks into one block. In this image encoding apparatus, the memory capacity necessary for image composition is reduced by compressing and expanding in block units. That is, the compression / decompression process can be performed with the memory capacity of one block.

Japanese Patent Laid-Open No. 10-13688

  However, in the image encoding apparatus of Patent Document 1, when compressing data, the data is always read from the memory by the block scan method and output to the compressor, so that the JPEG compression optimal for the input by the block scan method is performed. However, in the case of a compression method that employs predictive coding such as JPEG-LS and JBIG, there is a problem that the compression rate decreases when data is read from the memory by the block scan method and compressed.

  FIG. 14 is an explanatory diagram illustrating a pixel to be referred to when a predicted value of the target pixel x is calculated in JPEG-LS. JPEG-LS is a compression method that performs prediction using a sample value adjacent to the target pixel x, and refers to the values of the pixels c, b, and d above the target pixel x and the value of the pixel a adjacent to the left. To do. In many cases, using the fact that the difference between a certain sample value and the next sample value is close to 0, the difference value from the predicted sample value is encoded instead of encoding each sample individually. That is, a difference value between pixels is obtained, the difference values are classified, and a prediction error is encoded. When processing with the block scan method, the number of pixels at the top, left, and right ends is larger than when processing with the raster scan method, so the number of effective peripheral pixels decreases (prediction accuracy deteriorates). ) The compression rate decreases.

  The present invention has been made in view of such circumstances. The image data is divided into a plurality of areas after being divided into arbitrary band sizes, and a raster scan method and a block scan corresponding to each compression means. By inputting each data to each compression means using one of the input methods, the compression rate can be improved, the capacity of the storage means used during compression and decompression processing can be reduced, and multiple compression An image compression processing apparatus, an image forming apparatus, and a computer that realizes simplification of the management of code data by combining the code data output from the means into one code data and outputs the synthesized image, and having a good image quality It is an object to provide a program, a recording medium, and an image compression method.

  An image compression processing apparatus according to the present invention divides an image configured by arranging a plurality of pixels in a matrix in a column direction, and sets data corresponding to the divided image to a plurality of regions based on pixel attributes. Separating means for separating data, and a plurality of storage means for storing each separated data separately. After each data is encoded and compressed by a reversible compression means or a lossy compression means, each encoded data is 1 An image compression processing apparatus combined with one data, the first data reading means for sequentially reading data corresponding to the pixels in the same row for the data stored in one storage means and giving the data to the lossless compression means With respect to the data stored in the other storage means, the data corresponding to the pixels in the same row are sequentially read out for each block obtained by dividing the image into a plurality of rows in the row direction. Characterized in that it comprises a second data reading means for providing the compression means.

The lossless compression means is suitable for data input by the raster scan method, and the lossy compression means is suitable for data input by the block scan method. In the present invention, the data is read from the storage means by the first data reading means (output by the raster scan method) to the lossless compression means, and the second data reading means (output by the block scan method) is output to the lossy compression means. ), The data is read out from the storage means and output, so that the compression rate is improved as compared with the case where the data is output to all the compression means by the block scan method and compressed.
In addition, since processing is performed in units of multiple rows (bands), the capacity of the storage means used during compression / decompression processing (the amount of data to be stored) can be reduced compared to processing in units of pages. The code data output from the compression means is packed into one code data and output to the storage means, so that the management of the code data can be simplified.

  The image compression processing apparatus according to the present invention is characterized in that the separation means separates image data into data of a plurality of regions every 8 rows.

  In the present invention, for example, when the JPEG method is used as the irreversible compression method, JPEG is processed in units of 8 × 8 pixels called MCU (Minimum Coded Unit), so the optimum number of lines (number of rows) for compression with JPEG. ) Can be processed. Thereby, the capacity of the buffer and the circuit scale can be efficiently reduced.

  The image compression processing device according to the present invention is characterized in that the separation means separates image data into data of a region corresponding to a character image and / or line image and data of a region corresponding to an image image. To do.

  In the present invention, the character image and / or line image data containing a lot of high frequency components and the image image data containing little high frequency components are separated, so that the character image and / or line image data is reversible. By compressing, it is possible to further improve the image quality when the compressed data is expanded and the image is synthesized. Further, the image rate can be further improved by irreversibly compressing the image data.

  In the image compression processing apparatus according to the present invention, the first data reading unit reads the data from a storage unit that stores data of an area corresponding to a character image and / or a line image, and the second data reading unit includes: The data is read out from a storage unit that stores data of an area corresponding to an image.

  In the present invention, since the character image and / or line image data is output to a reversible compression means suitable for input by the raster scan method, the compression rate can be improved as compared with the case of outputting by the block scan method. Degradation of image quality during expansion can be suppressed.

  The image compression processing apparatus according to the present invention includes means for receiving selection of a reading means for reading data from each storage means.

  In the present invention, various compression methods can be specified by the user, such as when irreversibly compressing a character image and / or line image to further improve the compression rate, or when reversibly compressing an image image to suppress image quality degradation, etc. Can be combined.

  An image forming apparatus according to the present invention includes any one of the above-described image compression processing apparatuses.

  In the present invention, image quality deterioration can be suppressed while improving the compression rate.

  A computer program according to the present invention causes a computer to divide an image configured by arranging a plurality of pixels in a matrix shape into a plurality of regions in a column direction, and to convert data corresponding to the divided images into a plurality of regions based on pixel attributes This is a computer program that separates each separated data, stores each separated data separately, encodes each data by lossless compression or lossy compression, and then compresses each data into one data. Then, with respect to the data of one area stored in the computer, the step of sequentially reading out the data corresponding to the pixels in the same row and performing lossless compression, and the image of the data of the other area stored in the computer For each block that is divided into multiple rows in the row direction, the data corresponding to the pixels in the same row is read out sequentially and lossy compression is performed. Characterized by a step for.

  In the present invention, the above-described image compression processing apparatus can be realized by realizing each unit of the above-described image compression processing apparatus with a computer.

  A computer-readable recording medium according to the present invention records the above-described computer program.

  In the present invention, the above-described image compression processing apparatus can be realized on a computer by an image compression processing program read from a recording medium.

  In the image compression method according to the present invention, an image configured by arranging a plurality of pixels in a matrix is divided into a plurality of columns, and data corresponding to the divided images is data of a plurality of regions based on pixel attributes. An image compression method in which each separated data is stored separately, each data is encoded and compressed by lossless or irreversible compression, and then each encoded data is combined into one data, A step of sequentially reading out the data corresponding to the pixels in the same row and reversibly compressing the data of one area stored, and for each block obtained by dividing the image in the row direction for the data of the other area stored And sequentially reading data corresponding to pixels in the same row and irreversibly compressing the data.

  In the present invention, the compression method is selected in accordance with the data of each area, and the read / output method that is suitable for the selected compression method of the raster scan method and the block scan method is used to store the data from the storage means. By reading the data and outputting it to the compression means, the compression rate is improved as compared with the case where the data is read / output only by the block scan method.

According to the present invention, the data is read from the storage means by the first data reading means (output by the raster scan method) to the lossless compression means, and the second data reading means (by the block scan method) is output to the lossy compression means. Output), the data is read from the storage means and output, so that the compression rate can be improved.
Since the image data is divided by an arbitrary band size and subjected to compression and decompression processing, the capacity of the storage means (the amount of data to be stored) used during processing can be reduced.
Further, since the code data output from the plurality of compression means is combined and output as one code data, the management of the code data is simplified.

1 is a block diagram illustrating a configuration of a printer according to a first embodiment of the present invention. It is a figure which shows the structure and data flow of an image processing part which concern on Embodiment 1 of this invention. It is a block diagram which shows the structure of the image compression part which concerns on Embodiment 1 of this invention. It is a flowchart which shows the procedure of the compression process by CPU of SoC which concerns on Embodiment 1 of this invention. It is explanatory drawing which shows the case where it outputs to a compression part by a raster scan system. It is explanatory drawing which shows the case where it outputs to a compression part by a block scan system. It is explanatory drawing which shows the format of the code data output to HDD. It is explanatory drawing which shows an example of a code identifier. It is a graph which shows the result of having measured the code size at the time of outputting to the 1st compression part the image data of a plurality of samples which consist of 640x480 pixels to the 1st compression part by each method of a block scan system and a raster scan system. . The horizontal axis represents a block scan code size, and the vertical axis represents a graph size ratio obtained by dividing the raster scan code size by the block scan code size. It is a figure which shows the structure and data flow of the image processing part of the printer which concern on Embodiment 2 of this invention. It is a block diagram which shows the structure of the image compression part which concerns on Embodiment 2 of this invention. It is a flowchart which shows the procedure of the compression process by CPU of SoC which concerns on Embodiment 2 of this invention. In JPEG-LS, it is explanatory drawing which shows the pixel referred when calculating the predicted value of the attention pixel x.

Hereinafter, the present invention will be specifically described with reference to the drawings showing embodiments thereof.
Embodiment 1 FIG.
FIG. 1 is a block diagram illustrating a configuration of a printer (image forming apparatus) 10 including an image compression unit (image compression processing apparatus) according to Embodiment 1 of the present invention.
The printer 10 includes a SoC (System on Chip) 1 that includes a CPU that controls the printer 10 and processes image data, an image processing unit 2 that performs compression, expansion, and color correction of image data, and development, transfer, An image forming unit that forms an image by performing processing such as fixing is provided. The print engine unit 3 records an image on a recording medium such as paper based on the input image data, and stores the image data. And a hard disk (HDD) 4 to be placed. The SoC 1, the image processing unit 2, and the HDD 4 are connected via a bus.
A system memory 5 used as a work memory by the CPU is connected to the SoC 1, and a local memory 6 for temporarily storing image data is connected to the image processing unit 2. The system memory 5 also stores an image compression processing program (computer program) according to the present invention.

  A personal computer (PC) 20 is connected to the printer 10 via a network or the like. The PC 20 is equipped with application software such as a word processor and a spreadsheet, and manuscript data created by the user using the application software is given to the printer driver installed on the PC 20, and the printer driver converts the manuscript data into print data. And the print data is given to the printer 10.

  The print data is converted into image data (bitmap data) that can be printed by the image processing unit 2 by the CPU built in the SoC 1 of the printer 10. The image data is subjected to various processes and then the print engine unit 3. And the print engine unit 3 prints the image.

FIG. 2 is a diagram illustrating a configuration and a data flow of the image processing unit 2.
When printing is instructed on the application software installed on the PC 20, print data described in page description language data is generated by the printer driver.
This print data is transferred to the printer 10 via the network, and is supplied from the SoC 1 of the printer 10 to the image processing unit 2. The image processing unit 2 includes a raster data generation unit 21, an image compression unit 22, an image expansion unit 23, a color correction unit 24, and a halftone processing unit 25.
The raster data generation unit 21 generates RGB raster data (image data: bitmap data) and attribute data indicating the target of each pixel. Examples of this attribute include images that are natural images such as photographs and paintings, vector graphics that include line segments, and characters. As an example, the raster data generation unit 21 includes, for each pixel, first attribute data indicating that the pixel includes many high-frequency components such as characters or lines, or pixels that do not include many high-frequency components such as images. It is assumed that second attribute data indicating this is generated and output to the image compression unit 23.

  The raster data generation unit 21 performs an operation based on the luminance of each pixel and generates attribute data. For example, by performing a first-order differentiation on the luminance of the pixel and specifying a pixel having the maximum differential value, a pixel having an abrupt luminance change with respect to an adjacent pixel is specified. When the difference in luminance between the pixel having this sudden change in brightness and the adjacent pixel is calculated and the calculated difference is equal to or greater than a preset threshold value, the character for the pixel having the sudden change in brightness is calculated. Or the 1st attribute data which shows that it is a pixel containing many high frequency components like a line is produced | generated. On the other hand, when the calculated difference is less than a preset threshold value, second attribute data indicating that the pixel does not contain a high frequency component such as a natural image or a photograph is generated. To do. In addition, when the differential value of the first derivative is equal to or greater than a predetermined threshold, for the pixel corresponding to the differential value, first attribute data indicating a pixel including a lot of high frequency components such as characters or lines is generated, Second attribute data indicating that when the differential value of the primary differential is less than a predetermined threshold, the pixel corresponding to the differential value is a pixel that does not contain much high frequency components, such as a natural image or a photograph. May be generated. In addition, second order differentiation is performed on the luminance of the pixels constituting the image data, and a pixel having a differential value of 0 (a pixel having a sudden luminance change with respect to the adjacent pixel) is specified. The difference in luminance may be calculated.

Since the image data is about 96 MB (600 dpi: RGB format) for one page of A4 paper, the image data is compressed and obtained by the image compression unit 22 from the viewpoint of the storage capacity of the HDD 4 and the data transfer bandwidth. The encoded data is stored in the HDD 4.
The compressed (code) data stored in the HDD 4 is read and decompressed by the image decompression unit 23. Thereafter, the color correction unit 24 converts the RGB signals into CMYK (C: cyan, M: magenta, Y: yellow, K: black) digital color signals that can be printed, and matches the color reproduction characteristics of the print engine unit 3. Color correction is performed.
Then, after the output tone correction processing corresponding to the characteristics of the print engine unit 3 is performed in the halftone processing unit 25 on the image portion of the image data, the image is finally separated into pixels, and each level is divided. Tone reproduction processing (halftone generation) is performed so that the tone can be reproduced, and engine output data is generated and output to the print engine unit 3.

FIG. 3 is a block diagram showing a configuration of the image compression unit 22 in FIG. 2 and also shows a data flow.
The image compression unit 22 includes an image separation unit (separation unit) 221, a first band buffer 222, a second band buffer 223, a raster scan output unit (first data reading unit) 224, and a block scan output unit (second data reading unit). ) 225, a first compression unit 226, a second compression unit 227, a first code buffer 228, a second code buffer 229, and a code combination unit 260.

The image data and attribute data generated by the raster data generation unit 21 are input to the image separation unit 221.
In the image separation unit 221, based on the attribute data, the image data includes characters and / or line drawing data (hereinafter referred to as “character / line drawing data”) that contains a lot of high frequency components, and images such as natural images that do not contain much high frequency components. Separated from data.
The separated character / line drawing data and image data are stored in the first band buffer 222 and the second band buffer 223, respectively.
In this embodiment, since compression processing is performed for each band including a plurality of pixel lines (rows), the sizes of the first band buffer 222 and the second band buffer 223 are set to [main scanning (pixel line: row). Of pixels] × (number of lines per band). Here, it is assumed that one band is 8 lines (rows).
The character / line drawing data stored in the first band buffer 222 is read out by the raster scan output unit 224 by the raster scan method and output to the first compression unit 226.
The image data stored in the second band buffer 223 is read by the block scan output unit 225 by the block scan method and output to the second compression unit 227.

The character / line drawing data output by the raster scan output unit 224 is reversibly compressed by the first compression unit 226. As an example of the compression method of the first compression unit 226, the above-described JPEG-LS method, which is one of the reversible compressions most suitable for compression of character / line image data, can be cited. The first compression unit 226 is suitable for data input by a raster scan method.
The image data output by the block scan output unit 225 is irreversibly compressed by the second compression unit 227. As an example of the compression method of the second compression unit 227, there is a JPEG method that is one of irreversible compressions that is optimal for image data compression. Data input by the block scan method is suitable for the second compression unit 227.
In the JPEG method, discrete cosine transform (DCT) is applied to each pixel value in units of block images of 8 × 8 pixels, and converted to frequency coefficients that are coefficients for each frequency component of each basis function of frequency conversion. To do. Then, the converted frequency coefficient is approximated by quantization. The quantization is performed by dividing each element of the frequency coefficient of 8 rows and 8 columns after the DCT is performed by each corresponding element of a quantization table composed of a total of 64 quantization coefficients of 8 rows and 8 columns. . Then, compressed data is generated by entropy encoding the integer part (quantization index) of the numerical value obtained by quantization using Huffman code or the like. In the case of a general image, the absolute value of the frequency coefficient tends to be smaller as the frequency component of a higher order (high frequency component), and the human visual characteristics have a lower resolution with respect to high frequencies. Among them, the amount of data is reduced by finely quantizing the low frequency component and coarsely quantizing the high frequency component.

  The code data compressed by the first compression unit 226 and the second compression unit 227 is temporarily stored in the first code buffer 228 and the second code buffer 229. After the compression processing of data for one band is completed, the code combining unit 260 reads each code data from each code buffer, combines it with one code data, and outputs it to the HDD 4.

Hereinafter, an image compression method using the printer 10 according to the first embodiment will be described.
The CPU of the SoC 1 reads the image compression processing program stored in the system memory 5 and executes the image compression processing according to the program.
FIG. 4 is a flowchart showing a procedure of compression processing by the CPU of SoC1. Hereinafter, a case where image data for one page is compressed will be described.
The CPU inputs image data and attribute data from the raster data generation unit 21 to the image separation unit 221 (S1).
Then, the image separation unit 221 separates the image data into character / line drawing data and image data pixel by pixel based on the attribute data (S2), and the separated character / line drawing data and image data are respectively sent to the first band buffer 222, It is stored in the second band buffer 223 (S3).
Next, the CPU determines whether or not character / line drawing data and image data for one band are stored in the first band buffer 222 and the second band buffer 223 (S4). When it is determined that character / line drawing data and image data for one band are not stored in the first band buffer 222 and the second band buffer 223 (S4: NO), the process returns to step S1.

  When the CPU determines that character / line drawing data and image data for one band have been stored in the first band buffer 222 and the second band buffer 223 (S4: YES), the raster scan output unit 224 receives the first band buffer. Character / line drawing data is read from the image data 222 by the raster scan method and output to the first compression unit 226. Further, the CPU causes the block scan output unit 225 to read the image data from the second band buffer 223 by the block scan method, and outputs the image data to the second compression unit 227. Then, the first compression unit 226 performs lossless compression on the character / line drawing data by the above-described JPEG-LS method or the like, and the second compression unit 227 performs lossy compression on the image data by the above-described JPEG method or the like (S5). ).

FIG. 5 is an explanatory diagram showing a case where data is output to the compression unit by the raster scan method. As shown in FIG. 5, the raster scan method is a method in which image data is read pixel by pixel from the left to the right (in the same row) in the main scanning direction, and each row is read and output continuously from top to bottom. .
FIG. 6 is an explanatory diagram illustrating a case where data is output to the compression unit using the block scan method. As shown in FIG. 6, the block scan method is a method in which an image is divided into 8 × 8 pixel rectangular blocks, and the inside of the block is raster-scanned pixel by pixel from left to right and from top to bottom. is there.

Then, the CPU outputs the code data from the first compression unit 226 and the second compression unit 227 to the first code buffer 228 and the second code buffer 229 and stores them. Further, the code combining unit 260 reads each code data from the first code buffer 228 and the second code buffer 229, combines each code data into one code data (combines into one packet), and HDD4. (S6).
The CPU determines whether code data for one page has been output to the HDD 4 (S7). If the CPU determines that the code data for one page has not been output to the HDD 4 (S7: NO), the process returns to step S1. If it is determined that one page of code data has been output to the HDD 4 (S7: YES), the image data compression process is terminated.

FIG. 7 is an explanatory diagram showing the format of the code data output to the HDD 4.
Information related to image data such as a job management number and an image size is stored in the header at the top of the code. Subsequent to this header, a first band code, a second band code,... Nth band code and each band code are output. Each band code includes a code identifier, a lossless compression code obtained by lossless compression of character / line image data, a code identifier, and an irreversible compression code obtained by lossy compression of image data.

  FIG. 8 is an explanatory diagram showing an example of the above-described code identifier. Information for identifying code data such as the type of compression method (method) and code size is defined as a code identifier, the type of compression method is defined in the 7th bit, and code size data in the 0th to 6th bits. Is stored.

FIG. 9 shows the result of measuring the code size when the image data of a plurality of samples composed of 640 × 480 pixels is output to the first compression unit 226 by the block scan method and the raster scan method, respectively, and compressed by JPEG-LS. It is a graph which shows. The horizontal axis indicates the code size by the raster scan method, and the vertical axis indicates the code size by the block scan method. An auxiliary line indicated by a dotted line indicates that the code size is the same in both systems.
It can be seen from the graph of FIG. 9 that the code size obtained by the block scan method is larger than the code size obtained by the raster scan method.
FIG. 10 is a modification of the graph of FIG. The horizontal axis represents the code size of the block scan method, and the vertical axis represents the code size ratio obtained by dividing the code size of the raster scan method by the code size of the block scan method. From this graph, the code size ratio is in the range of 0.1 to 0.4, and is always 1 or less. As a result, it was confirmed that the accuracy of prediction of the pixel of interest by the peripheral pixels is improved and the compression rate is higher when the output is compressed by the raster scan method than when the output is compressed by the block scan method.

  As described above, the compressed (code) data compressed in the image compression unit 22 and stored in the HDD 4 is expanded in the image expansion unit 23 as described above, and the expanded data is subjected to color correction, tone reproduction processing, and the like. After being processed, it is output to the print engine unit 3 and an image is printed on paper or the like.

  As described above, in this embodiment, since the character / line drawing data is input by the raster scan method to the first compression unit 226 that performs the lossless compression by the JPEG-LS method, the deterioration of the image quality at the time of printing is suppressed. However, at the time of compression, the compression rate can be improved as compared with the case where the character / line drawing data is input to the first compression unit 226 by the block scan method.

In addition, since compression processing is performed in units of a plurality of rows (bands) of an image, it is possible to reduce the capacity of the memory (first code buffer 228, second code buffer 229) that stores each code before combining the code data. it can. Since the code data output from the first code buffer 228 and the second code buffer 229 are packed into one code data and output to the HDD 4, the management of the code data is simplified.
Since the band is composed of 8 pixel rows, processing can be performed with the optimum number of lines for compression by the JPEG method in which processing is performed in units of 8 × 8 pixels. Thereby, the capacity and circuit scale of the second code buffer 229 can be efficiently reduced.
In the present embodiment, the case of encoding based on RGB signals has been described, but the present invention is not limited to this, and encoding may be performed based on YCbCr signals.

Embodiment 2. FIG.
The printer 30 according to the second embodiment of the present invention has the same configuration as the printer 10 according to the first embodiment, and the configuration of the image compression unit 82 of the image processing unit 8 is the image compression unit according to the first embodiment. 22 is different. The printer 30 includes a register I / F 7.
FIG. 11 is a diagram illustrating the configuration and data flow of the image processing unit 8 of the printer 30. In the figure, the same parts as those in FIG. The image processing unit 8 includes a raster data generation unit 81, an image compression unit 82, an image expansion unit 83, a color correction unit 84, and a halftone processing unit 85. The raster data generation unit 81, the image expansion unit 83, the color correction unit 84, and the halftone processing unit 85 are the raster data generation unit 21, the image expansion unit 23, the color correction unit 24, and the intermediate of the printer 10 according to the first embodiment. The tone processing unit 25 has the same configuration.
The CPU of the SoC 1 is configured to receive various instructions and selections that are made by a user pressing an operation button of a display unit (not shown) such as a touch panel of the printer 30. When the display unit displays a selection screen for selecting one of the lossless compression method and the lossy compression method for each of the character / line drawing data and the image data, and receives a selection from the user, the CPU Stores the compression method setting in the compression mode register 865 of the image compression unit 82 via the register I / F 7.

FIG. 12 is a block diagram illustrating a configuration of the image compression unit 82.
The image compression unit 82 includes an image separation unit 821, a first band buffer 822, a second band buffer 823, raster scan output units 824 and 826, block scan output units 825 and 827, first compression units 828 and 860, and second compression. Sections 829 and 861, a first code buffer 862, a second code buffer 863, and a code combining section 864. The first compression units 828 and 860 perform lossless compression, and the second compression units 829 and 861 perform lossy compression.

As described above, the compression mode register 865 stores the compression method setting. The set information is transmitted to the raster scan output units 824 and 826, the block scan output units 825 and 827, the first compression units 828 and 860, the second compression units 829 and 861, and the code combination unit 864.
Image data and attribute data are input from the raster data generation unit 81 to the image separation unit 821.
In the image separation unit 821, the image data is separated into character / line drawing data and image data based on the attribute data.
The separated character / line drawing data and image data are stored in the first band buffer 828 and the second band buffer 829, respectively.
In the present embodiment, since compression processing is performed for each band of 8 pixel rows, the size of the first band buffer 828 and the second band buffer 829 is the number of pixels in main scanning (pixel line: row) × 8. It becomes.

  When the user selects to compress the character / line image data by the lossy compression method and the image data to be compressed by the lossless compression method, that is, the character / line image data is compressed by the second compression unit 829 and the image data is compressed. When the data is selected to be compressed by the first compression unit 860, the character / line drawing data stored in the first band buffer 822 is read by the block scan output unit 825 by the block scan method, and the second compression unit 829. The image data stored in the second band buffer 823 is read out by the raster scan output unit 826 by the raster scan method and output to the first compression unit 860.

The image data output by the block scan output unit 825 is irreversibly compressed by the second compression unit 829. An example of the compression method of the second compression unit 829 is the JPEG method.
The image data output by the raster scan output unit 826 is reversibly compressed by the first compression unit 860. An example of the compression method of the first compression unit 860 is a JPEG-LS method.

  The code data compressed by the second compression unit 829 and the first compression unit 860 is temporarily stored in the first code buffer 862 and the second code buffer 863. After the compression processing for one band is completed, the code combining unit 864 reads each code data from the first code buffer 862 and the second code buffer 863 and combines them into one code data and outputs it to the HDD 4.

  When the user selects to compress the character / line image data by the lossless compression method and the image data to be compressed by the lossy compression method, that is, the character / line image data is compressed by the first compression unit 828, and the image data is compressed. When the data is selected to be compressed by the second compression unit 861, the character / line drawing data stored in the first band buffer 822 is read out by the raster scan output unit 824 by the raster scan method, and the first compression unit To 828. The image data stored in the second band buffer 823 is read by the block scan output unit 827 by the block scan method and output to the second compression unit 861.

The image data output by the raster scan output unit 824 is reversibly compressed by the first compression unit 828 by the JPEG-LS method or the like.
The image data output from the block scan output unit 827 is irreversibly compressed by the second compression unit 861 using the JPEG method or the like.

  The code data compressed by the first compression unit 828 and the second compression unit 861 is temporarily stored in the first code buffer 862 and the second code buffer 863. After the compression processing for one band is completed, the code combining unit 864 reads each code data from the first code buffer 862 and the second code buffer 863 and combines them into one code data and outputs it to the HDD 4.

The image compression method using the printer 30 according to the second embodiment will be described below.
The CPU of the SoC 1 reads the image compression processing program stored in the system memory 5 and executes the image compression processing according to the program.
FIG. 13 is a flowchart showing a procedure of compression processing by the CPU of SoC1.
The CPU determines whether print data has been input from the PC 20 (S11).
When it is determined that the print data has been input (S11: YES), the display unit selects one of the lossless compression method and the lossy compression method for each of the character / line drawing data and the image data. A selection screen is displayed, and it is determined whether selection of a compression method for each data has been received from the user (S12). Here, which one of the first compression unit 828 and the second compression unit 829 compresses the character / line image data, and which of the first compression unit 860 and the second compression unit 861 is performed on the image data. The selection of whether or not to perform compression may be accepted. The CPU functions as “means for accepting selection of reading means for reading data from the storage means”.

When determining that the selection of the compression method or the compression unit is not accepted (S12: NO), the CPU repeats this determination.
When the CPU determines that the selection of the compression method or the compression unit has been received (S12: YES), the raster data generation unit 21 generates image data (raster data) and attribute data, and the image separation unit 821 generates the image data and attribute. Data is input (S13).
Then, the image separation unit 821 separates the image data into character / line drawing data and image data attribute data pixel by pixel based on the attribute data (S14), and the separated character / line drawing data and image data are respectively sent to the first band buffer. The data is stored in the second band buffer 823 (S15).

Next, the CPU determines whether image data for one band has been stored in the first band buffer 822 and the second band buffer 823 (S16). When it is determined that the image data for one band is not stored in the first band buffer 822 and the second band buffer 823 (S16: NO), the process returns to step S13.
When the CPU determines that the image data for one band has been stored in the first band buffer 822 and the second band buffer 823 (S16: YES), the compression method in which the character / line image data and the image data are respectively selected. The character / line drawing data and image data are read out to the corresponding output unit and output to the corresponding compression unit so that the data is compressed (S17).

  For example, if the user selects to compress character / line image data by the lossy compression method and the image data to be compressed by the lossless compression method, and this selection is set, the CPU stores the data in the first band buffer 822. The stored character / line drawing data is read by the block scan output unit 825 by the block scan method, and is output to the second compression unit 829, and is irreversibly compressed by the second compression unit 829. Then, the image data stored in the second band buffer 823 is read out by the raster scan output unit 826 by the raster scan method, output to the first compression unit 860, and reversibly compressed by the first compression unit 860.

When the compression ends in each compression unit, the CPU outputs code data from each compression unit to the first code buffer 862 and the second code buffer 863 and stores the code data in the first code buffer 862 and the second code buffer 862. Code data is read from the code buffer 863, packed into one code data (combined into one packet), and output to the HDD 4 (S18).
The CPU determines whether or not the code data related to all image data for which printing has been instructed has been output to the HDD 4 (S19). If the CPU determines that the code data related to all the image data has not been output to the HDD 4 (S19: NO), the process returns to step S13. If it is determined that the code data related to all the image data has been output to the HDD 4 (S19: YES), the compression process is terminated.

In the present embodiment, when the character image and / or line image data is irreversibly compressed to further improve the compression rate, the image image data is reversibly compressed to suppress image quality degradation, etc. Various compression methods can be combined depending on the specification. Therefore, it is possible to flexibly cope with the compression method (reversible or irreversible) designated by the user, and the data is supplied to the corresponding compression unit by the data input method optimal for the compression method, so that the compression rate is improved. It becomes possible.
In the present embodiment, each time a print instruction is received from a user, the selection of a compression method or compression unit is described. However, the present invention is not limited to this. The selection may be accepted and stored in the compression mode register 865. However, each time a print instruction is received, when selecting a compression method or a compression unit, various compression methods can be combined corresponding to each area of the print image.

  In the first and second embodiments, the case where the printers 10 and 30 are applied as the image forming apparatus has been described. However, the present invention is not limited to this. A digital multi-function peripheral having a copy function and a fax function may be used.

Further, the case where the image separation units 221 and 821 of the image compression units 22 and 82 separate the text / line drawing data and the image data has been described, but the data separation method is not limited to this.
Although the case where the data compression process is performed for each band of 8 rows has been described, the number of rows is not limited to 8 rows. However, when compression processing is performed for each band of 8 rows, when the JPEG method is used as the lossy compression method, processing can be performed with the optimum number of rows for compression by the JPEG method in which processing is performed in units of 8 × 8 pixels. Since this is possible, the number of rows is preferably eight.

Further, the image compression method is not limited to the case where the CPU is realized by executing it according to the image data compression processing program stored in the system memory 5. The program may be stored in a ROM (not shown). The system memory 5 and the ROM correspond to the recording medium of the present invention.
The recording medium of the present invention may be a portable recording medium that records program codes (execution format program, intermediate code program, source program) for performing image data compression processing. In this case, the printers 10 and 30 include a program reading device, or a program reading device is connected to the printers 10 and 30, and the program is read by inserting the recording medium into the program reading device.
Recording media include tape-based recording media such as magnetic tape and cassette tape, magnetic disks such as flexible disks and hard disks, and disk-based recording media such as optical disks such as CD-ROM / MO / MD / DVD, IC cards (memory Card-type recording media such as optical cards, etc., or fixed memory such as mask ROM, EPROM (Erasable Programmable Read Only Memory), EEPROM (Electrically Erasable Programmable Read Only Memory), flash ROM, etc. And a recording medium carrying a program code.

  The program stored in the recording medium may be configured to be accessed and executed by the CPU. The CPU reads the program code, the read program code is downloaded to the program storage area, and the program is executed. It may be configured. It is assumed that this download program is stored in the system memory 5 in advance.

  Further, the image forming apparatus according to the present embodiment may be a medium that can be connected to a communication network including the Internet and that carries the program code in a fluid manner so as to download the program code from the communication network. When the program is downloaded from the communication network as described above, the download program is stored in the system memory 5 in advance or installed from another recording medium. Furthermore, the program code may be in the form of a computer data signal embedded in a carrier wave, embodied by electronic transmission.

1 SoC
2, 8 Image processing unit 21, 81 Raster data generation unit 22, 82 Image compression unit 221, 821 Image separation unit 222, 822 First band buffer 223, 823 Second band buffer 224, 824, 826 Raster scan output unit 225, 825, 827 Block scan output unit 226, 828, 860 First compression unit 227, 829, 861 Second compression unit 228, 862 First code buffer 229, 863 Second code buffer 260, 864 Code combination unit 865 Compression mode register 23 , 83 Image decompression unit 24, 84 Color correction unit 25, 85 Halftone processing unit 3 Print engine unit 4 HDD
5 System memory 6 Local memory 7 Register I / F
10, 30 Printer 20 PC

Claims (9)

Separation means for dividing an image configured by arranging a plurality of pixels in a matrix in a column direction, and separating data corresponding to the divided image into data of a plurality of regions based on pixel attributes, and separation An image compression processing apparatus that includes a plurality of storage means for storing each data separately, encodes each data by a lossless compression means or an irreversible compression means, and then compresses each data into one data. There,
First data reading means for sequentially reading data corresponding to pixels in the same row for data stored in one storage means and giving the data to the lossless compression means;
For data stored in other storage means, second data that sequentially reads out data corresponding to the pixels in the same row for each block obtained by dividing the image into a plurality of rows in the row direction and gives the data to the irreversible compression means And an image compression processing apparatus.   The image compression processing apparatus according to claim 1, wherein the separation unit separates the image data into data of a plurality of regions every 8 rows.   3. The image according to claim 1, wherein the separation unit separates the image data into data of a region corresponding to a character image and / or a line image and data of a region corresponding to the image image. Compression processing device. The first data reading means reads the data from a storage means storing data of a region corresponding to a character image and / or a line image;
4. The image compression processing apparatus according to claim 3, wherein the second data reading unit reads the data from a storage unit that stores data of an area corresponding to an image.   4. The image compression processing apparatus according to claim 3, further comprising means for receiving selection of a reading means for reading data from each storage means.   An image forming apparatus comprising the image compression processing apparatus according to claim 1. The computer divides the image formed by arranging a plurality of pixels in a matrix in the column direction, and the data corresponding to the divided image is separated into data of a plurality of regions based on the attribute of the pixel. A computer program for storing each data separately, encoding each data by reversible compression or irreversible compression, and then combining each encoded data into one data,
A step of causing a computer to sequentially read out data corresponding to pixels in the same row and reversibly compress the stored data in one area;
A step of causing the computer to sequentially read out the data corresponding to the pixels in the same row for each block formed by dividing the image into a plurality of rows in the row direction, and to perform irreversible compression on the stored data of other regions. A computer program comprising:   A computer-readable recording medium on which the computer program according to claim 7 is recorded. An image configured by arranging a plurality of pixels in a matrix is divided into a plurality of columns, and data corresponding to the divided image is separated into data of a plurality of regions based on the attributes of the pixels. An image compression method for storing each separately, encoding each data by reversible compression or irreversible compression, and then combining each encoded data into one data,
For the stored data of one region, the step of sequentially reading out the data corresponding to the pixels in the same row and performing lossless compression;
A step of sequentially reading data corresponding to pixels in the same row and irreversibly compressing each block obtained by dividing the image in the row direction with respect to the stored data of other regions. Image compression method.

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