JP2012054842A - Image processing device and processing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a compression ratio in image compression.SOLUTION: For a tile image composed of a predetermined number of pixels that is determined to have three or less colors in the tile image and to have two or less colors in all blocks of 2×2 pixel size composing the tile image, an image processing device generates first packet data including color data information of a first color indicating color data of a pixel at a predetermined position in each block, color data information of the three or less colors existing in the tile image, first pattern information for specifying the arrangement pattern of color data in the each block, and selection information for selecting color data information of a second color different from the color data information of the first color in each of the blocks from among the color data information of the three or less colors.

Description

  The present invention relates to a technique for compressing an image into predetermined block units.

  Conventionally, there is a high demand for high-resolution color images, and digital multifunction peripherals are increasingly handling images with a resolution of 1200 dpi or higher in order to meet the demand for higher image quality. As the resolution of an image increases, there is a problem that the number of pixels that require image processing increases dramatically and the processing load increases. For example, when the resolution is doubled from 600 dpi to 1200 dpi, the number of pixels to be processed is quadrupled. In addition to this digital multi-function peripheral, image processing apparatuses such as digital cameras and facsimile machines compress color image data in order to save memory and hard disk capacity and reduce the time required for writing them. High speed is realized.

  As a color still image compression method, a JPEG method using discrete cosine transform and a method using wavelet transform are often used. In this type of encoding method, generally, an image is encoded into a predetermined block (for example, 8 × 8 or 16 × 16 pixel unit), and high compression efficiency is achieved by performing discrete cosine transform, quantization, and entropy encoding. Have achieved. Since this type of encoding method is a variable-length encoding method, the code amount changes for each image to be encoded.

  When the above-described image compression is used, in order to refer to the pixel data and convert the pixel data, it is necessary to decode the compressed data. In other words, image processing cannot be performed with the compressed data as it is, and decoding processing is necessarily required, and it is necessary to perform processing on every pixel of all pixels of the high resolution data, resulting in an increase in processing time. .

  As a technique for performing compression processing without encoding pixel data, a known run-length compression method for storing pixel data and its continuous number or an edge is detected for each block, and two colors of the edge are stored. Thus, a technique for compressing is disclosed (for example, Patent Document 1).

JP 2008-271046 A

  In the above-mentioned Patent Document 1, the inside of a block is made into two colors, and shape information relating to the arrangement of the two colors and color information of the two colors are stored.

  On the other hand, in order to further improve image quality and processing speed, the present applicant has made the following proposal in Japanese Patent Application No. 2009-212444. In this proposed technique, image data is first divided into blocks each having a size of 2 × 2 pixels, and the color data of each pixel in the block is compared, so that the arrangement pattern information of the color data included in the block of interest and the block of interest And color data information for the number of colors included in the. The color data information is converted into first color data information corresponding to a pixel at a predetermined position in the block and other color data information (second to fourth color data information (interpolation data information)). The information is divided and stored together with the arrangement pattern information in different memory areas.

  As a result, high image quality is achieved without degrading the image quality of blocks having more than two colors. In addition, by placing the thinned image data at a specific position in the continuous memory area as the first color data information, it is possible to handle the low resolution image without decoding the high resolution image, thereby increasing the processing speed. Trying to realize.

  On the other hand, in the case of the technique proposed by the present applicant in Japanese Patent Application No. 2009-221444, it is assumed that an encoding process is performed on an image composed of a large number of colors. The pixel) holds the interpolation data information.

  Therefore, in the case of an image having a relatively small number of colors, a large number of blocks having similar interpolation data information are generated, which is not efficient. In particular, in an office environment where a digital multi-function peripheral is used, printing of document images is the main use, and most of the images are handled with a small number of colors.

  When a slightly larger block (tile) unit (for example, 64 × 64 pixels) is used as a transfer unit used between bus interfaces, the pixels in each tile may be configured with two or three colors. The majority.

  Therefore, in the present invention, when an image composed of a small number of two to three colors is encoded, the memory capacity necessary for the interpolation data can be saved.

  An object of the present invention is to improve the compression rate during image compression.

  An image processing apparatus according to the present invention is an image processing apparatus that processes a tile image having a predetermined number of pixels, and the tile image has 3 colors or less and 2 × 2 pixels that constitute the tile image Determining means for determining whether or not all of the blocks of size are 2 colors or less, and all of the blocks of 2 × 2 pixels in which the tile image is within three colors and which constitutes the tile image by the determining means For a tile image determined to be 2 colors or less, color data information of a first color indicating color data of a pixel at a predetermined position in each block, and the 3 existing in the tile image Color data information within two colors, first pattern information for specifying an arrangement pattern of color data in each block of two or less colors, and each of two or less colors among the color data information within three colors Bro Generating means for generating first packet data including selection information for selecting color data information of a second color different from the color data information of the first color in the first color data.

  According to the present invention, it is possible to improve the compression ratio at the time of image compression, and it is possible to suppress a decrease in system efficiency by suppressing an increase in data amount. Furthermore, it is possible to suppress an increase in cost due to an increase in the capacity of a memory or the like and a decrease in processing speed of the image processing system due to an increase in resolution.

1 is a diagram illustrating an example of a configuration of a digital multifunction peripheral (MFP). The figure which shows the structural example of the controller shown in FIG. The figure which shows the number in the case of the combination which the pattern of 4 colors can take in the block of 2x2 pixels. The figure which shows the relationship between the pattern shown in FIG. 3, and a pattern flag. (A) is an example of a color pattern that can be taken by a 2 × 2 pixel block, (B) is a relationship between a representative color and an interpolation color, (C) is an example of a color pattern expressed using an interpolation color selection bit, FIG. The flowchart which shows the detail of the compression method performed in a compression part. The figure which shows the relationship between a page, a tile, and a block. The figure which shows the data structure of the packed data. The figure which shows an example of a structure of a packet management table. The figure which shows the address of each packet written in the memory space. 10 is a flowchart showing color number determination processing in compression processing. The block diagram which shows the structure of a compression part. The flowchart which shows a packet data correction process. Replacement interpolation color buffer empty flag table. FIG. 6 is a diagram showing the relationship between colors stored in a replacement interpolation color buffer and generated interpolation color selection bits. An example of data structure and header information of packet data before and after modification. The figure which shows the storage position of the three interpolation colors in the 2nd, 3rd, 4th color storage part after an interpolation color replacement process. The block diagram which shows the internal structure of an expansion | deployment part. The flowchart of the expansion | deployment process of packet data.

  Hereinafter, embodiments for carrying out the invention will be described in detail with reference to the drawings. In this embodiment, a digital multi-function peripheral (MFP) having a plurality of functions such as scanning, printing, and copying will be described as an example of the image processing apparatus.

[Configuration of digital multifunction peripheral (MFP)]
As shown in FIG. 1, the controller 101 is connected to a scanner 102 as an image input device and a printer 103 as an image output device. Further, the controller 101 is connected to a network 104 such as a LAN or a public line (WAN) to input / output image information and device information and develop an image of PDL data.

  A CPU 105 is a processor that controls the entire MFP in accordance with a program stored in an HDD storage unit 107 described later. The memory 106 is a system work memory for operating the CPU 105, and is also an image memory for temporarily storing image data. The HDD storage unit 107 is a hard disk drive, and stores system software, programs, image data, and the like.

  Next, detailed processing of each unit of the controller 101 will be described with reference to a configuration example of the controller 101 shown in FIG. First, a case where image data scanned by the scanner 102 is read will be described. The scanner image processing unit 201 receives RGB (red, green, blue) three-color image data read by the scanner 102, performs image processing such as shading processing and filter processing on the image data, and compresses the data. Performs image compression processing. Then, the compressed data (compressed data) is stored in the memory 106 by the DMAC (direct memory access controller) 203 via the image memory bus.

  Next, when printing scanned image data, the DMAC 211 transfers the compressed data stored in the memory 106 to the color processing unit 212 via the image memory bus. Then, the color processing unit 212 converts into a CMYK (cyan, magenta, yellow, black) color space. Thereafter, the color processing unit 212 further performs color processing such as density adjustment and printer gamma correction on each value of CMYK, and then the data after the color processing is stored again in the memory 106 by the DMAC 211 via the image memory bus. To do. Thereafter, in order to perform image processing for printing, the DMAC 221 reads the compressed data stored in the memory 106 via the image memory bus, and the expansion unit 222 expands the raster image data. The raster CMYK image data is input to the print image processing unit 223, performs area gradation processing by a dither method or an error diffusion method, and outputs the result to the printer 103.

  When the scanned image data is transmitted to the network, the DMAC 211 transfers the compressed data stored in the memory 106 to the color processing unit 212 via the image memory bus. After the color processing unit 212 performs display gamma adjustment, paper background color adjustment, and the like, the color processing unit 212 performs conversion to a YCbCr (luminance, BLUE color difference, RED color difference) color space. Then, the DMAC 211 stores the data processed by the color processing unit 212 in the memory 106 again via the image memory bus. Thereafter, in order to perform image processing for transmission, the DMAC 231 transfers the compressed data stored in the memory 106 to the expansion unit 232 via the image memory bus. Then, the expansion unit 232 expands the compressed data into raster image data. After that, if the transmission processing unit 233 performs color image transmission on the raster YCbCr image data, JPEG compression processing is performed. If the monochrome binary image transmission is performed, binarization is performed on the Y data, and JBIG compression or the like is performed. And output to the network 104.

  When saving scanned image data, the DMAC 241 transfers the compressed data stored in the memory 106 to the disk spool high compression / decompression unit 242 via the image memory bus. In the disk spool high compression / decompression unit 242, the writing speed of the HDD is slower than that of the memory. Thereafter, the compressed data is stored in the HDD storage unit 107 via the disk access controller 243. In addition, when the compressed data stored in the HDD storage unit 107 is transferred again to the memory 106, the above-described processing may be performed in reverse.

  Here, a case where PDL data sent from another device connected via the network 104 shown in FIG. Although the PDL interpretation unit is not shown in FIG. 2, the CPU 105 functioning as the PDL interpretation unit interprets the PDL data and outputs the display list as a result to the memory 106. Thereafter, the rendering unit 251 renders the display list stored in the memory 106 into raster RGB image data, and the compression unit 252 performs image compression processing. Then, the DMAC 253 stores the compressed data in the memory 106 via the image memory bus.

  It should be noted that the process of printing, transmitting to a network, and storing the PDL data can be realized by performing the same process as in the case of scanned image data.

  Next, raster image data compression processing, which is a feature of the present invention, will be described in detail. In this embodiment, the compression unit 252 compresses a raster image generated from PDL data, and the compression unit 202 compresses a raster image obtained by scanning. However, the present invention is not limited to this configuration. . For example, instead of separately providing the compression units 202 and 252 as shown in FIG. 2, a common compression unit may be provided.

  In this embodiment, first, raster image data in units of pages is divided into blocks of 2 × 2 pixels, and data compression processing is performed in units of blocks extracted by division. Here, before explaining the compression processing, the number of combinations is considered according to the number of colors occupied in 2 × 2 4-pixel data. In this case, since the number of pixels is four, the number of colors occupied therein is a maximum of four colors, and there are at most combinations of one to four colors in the block. FIG. 3 shows the number of combinations of the four color patterns.

  First, in the case of one color in the block, four pixels are configured in the same color, so there are only one combination. Next, consider the case where the block has two colors. As shown in FIG. 3, the number of combinations when two colors are laid out in four pixels is that the color of a pixel at a predetermined position (in this embodiment, the upper left pixel) is the first color (representative color). A color different from the first color is considered as the second color. Then, since the first color or the second color enters the remaining three pixels other than the upper left pixel, a total of seven combinations can be considered except for the case where the four pixels have the same color.

  Next, consider the case where the block has three colors. The number of three colors laid out in four pixels can be rephrased as the number of only one of the three colors used twice. Of the four pixel coordinates, two pixels have the same color. What is necessary is just to obtain | require the number of cases. That is, the number in the case of three colors is a combination of taking two coordinates from four seats, and there are six ways in total. Finally, when the block is composed of four colors, there is only one.

  When the numbers in all cases of 1 to 4 colors are summed, a total of 15 patterns can be considered. Further, considering that a flag (identifier) is added to identify all these patterns, 4 bits are required as the data amount of the flag. The relationship between these 15 patterns and flags is defined as shown in FIG. 4, and this flag is hereinafter referred to as a “pattern flag”.

  As described above, in the technique proposed in Japanese Patent Application No. 2009-212444, the image data is divided into blocks of 2 × 2 pixel size, and the arrangement pattern information of the color data included in each of the divided blocks is the 15 Output using a street pattern flag (4 bits). Further, the color data information for the number of colors included in each block includes color information (first color data information) corresponding to a pixel at a predetermined position in the block (for example, the upper left pixel), and other colors. The data information (second to fourth color data information (interpolation data information)) is output separately. Then, the arrangement pattern information output from each block in the image data, the first color data information, and the second to fourth color data information are stored together in different memory areas.

  On the other hand, in the case of a document image or the like that is often handled by the MFP, most blocks are often composed of two colors or less in a 2 × 2 pixel block unit. Therefore, in the present embodiment, a compression method suitable for tiles in which tiles (64 × 64 pixels) are within 3 colors and all 2 × 2 pixel blocks in the tiles are within 2 colors will be described. Note that the image data is divided into 64 × 64 pixel size tiles, and for each of the divided tiles, the tile is composed of 3 colors or less and all 2 × 2 pixel blocks in the tile are composed of 2 colors or less. Determine if it is. It is desirable that the compression process is switched for each tile according to the determination result. That is, if the tile has 3 colors or less and all 2 × 2 pixel blocks in the tile are composed of 2 colors or less, the tile is compressed by the compression method described later. Otherwise, the above-mentioned Japanese Patent Application No. 2009-212444 is described. It is desirable to perform the compression using the compression method proposed in the above.

  Next, a description will be given of a compression method according to the present embodiment, which is suitable when a tile has three colors or less and all 2 × 2 pixel blocks in the tile are configured by two colors or less. In the 2 × 2 pixel block, there are eight possible combinations of patterns of up to two colors, one for all pixels of the same color shown in FIG. 3 and seven for two colors. Since there are only 8 types of pattern flags representing 0 to 7 as shown in FIG. 4, the 8-bit pattern patterns can be identified as 3-bit flags.

  Here, FIG. 5A shows a part of an arrangement pattern of colors that can be taken by a 2 × 2 pixel block composed of up to two colors. FIG. 5A shows the relationship among the pattern flag, representative color (first color), and interpolation color (second color) for each image. In FIG. 5A, the color of the black circle position (the upper left pixel) indicates the representative color (first color).

  In the present embodiment, when transferring to the image memory bus, a block having a predetermined number of pixels (64 × 64 pixels) is used as a unit (hereinafter referred to as “tile unit”), and the number of colors configured in the tile unit. Is limited to 3 colors. The relationship between the representative color and the interpolation color in this example is shown in FIG. That is, it is assumed that the number of colors existing in the 64 × 64 tile is within 3 colors and the number of colors existing in the 2 × 2 block is within 2 colors. At this time, as shown in FIG. 5B, since the representative color is one of the three colors in the tile, interpolation colors other than the representative color can be any one of the remaining two colors. is there. Therefore, if a representative color in a block of 2 × 2 pixels can be specified, an interpolation color selection bit (1 bit) for identifying which of the remaining two interpolation colors is provided, so that the 2 × 2 pixel can be identified. It is possible to select the interpolation color within the block.

  A 3-bit pattern flag (first pattern information for specifying an arrangement pattern within two colors), a 1-bit interpolation color selection bit (selection information), a representative color of each block, and the three colors in the tile A part of the color pattern expressed by using and is shown in FIG. As described above, when the number of colors in the tile is 3 colors and the number of colors in the 2 × 2 pixel block is within 2 colors, the 3-bit pattern flag, the interpolation color selection bit, the color data of the representative color of each block, If the color data of the three colors in the tile is held, the color arrangement of each block can be specified. That is, even if the color data of the interpolation color (second color) is not held for each block, the interpolation color is specified from the color data of the three colors in the tile by referring to the interpolation color selection bit. Will be able to. Details of the interpolation color selection bit will be described later with reference to FIG.

[Packet generation]
The image processing apparatus according to the present embodiment cuts raster image data in units of 64 × 64 pixel size tiles, compresses them, and transfers them to the image memory bus in order to enhance random access in raster image data compression processing.

  Details of the packet generation method executed by the compression units 202 and 252 will be described with reference to FIG. First, raster image data is input for each page shown in FIG. 7 (S601). Then, one page background pixel is set for each page of image data (S602). This is pixel data to be used as an initial storage block at the time of compression processing, and normally white (255 for 8-bit RGB color images and 0 for CMYK images) is normally used. Next, the image data to be input to the compression units 202 and 252 is divided into tile units of a predetermined size (64 × 64 pixels), and one unprocessed tile is set as a processing target (S603). In this example, there are 32 × 32 2 × 2 pixel blocks in one tile. FIG. 7 is a diagram illustrating the relationship between one page, a 64 × 64 pixel tile, and a 2 × 2 pixel block.

  Next, predetermined fixed-length header information is added to the tile to be processed (S604). This header information is information such as page ID, tile coordinates, color space, number of bits of pixel data, tile data size, presence / absence of attribute information, and compression flag. Here, the page ID is a unique ID number assigned to each page. The tile coordinate is coordinate information indicating where the tile is located on the raster image in page units. As shown in FIG. 7, the tile coordinates are described using X coordinates and Y coordinates. The color space is information indicating an identifier for identifying whether the tile is an RGB image, a CMYK image, or a GRAY-SCALE image. The number of bits of pixel data is information indicating the bit length per pixel in the tile. The data size is information in byte units indicating the data size of the first color of the tile and the data size of the second, third, and fourth color data. The presence / absence of attribute information is information indicating whether or not attribute information such as characters and photographs is added to the image data in units of pixels. The compression flag is flag information indicating whether the tile is compressed data or non-compressed data, and is set in S607 and S609 described later.

  Next, the compression process is applied to each tile described above (S605). Details of this compression processing will be described later.

  Next, the data size of the compressed tile data is calculated. This is the sum of the pattern flag size, the first color data size, the second, third, and fourth color data sizes. Since the pattern flag is always given, there is no guarantee that the data size is compressed compared to the original image data. For this reason, if the data size of the tile data after the compression processing exceeds the data size of the original tile data, it is better to output the original image data in terms of overall memory efficiency. Therefore, the data size after the compression process is compared with the original data size (S606), and if the original data size is exceeded, the header compression flag is set to “0” (S607). The compression flag is set to “1” (S609).

  Then, the tile data compressed in response to the result of the comparison or the original tile data is packed into one data together with the header information of the tile (S608, S610). The data structure of the packed data is shown in FIG. Hereinafter, a unit of data including the above-described header is referred to as a “packet”. In order to make such a packet, after the compression process is completed for each tile and the data size is determined, the data is packed with the space between the first color storage unit and the second, third, and fourth color storage units packed. To do. Thereafter, the data is output to the memory via the DMAC (S611). Next, the coordinates and sizes of the packets are listed as a list and created as a packet management table (S612). An example of this packet management table is shown in FIG. By repeating the above-described processing up to the last tile (YES in S613), the compression processing of the raster image for each page is completed.

  When packet data is written to the memory in units of tiles as described above, as shown in FIG. 10, the size differs for each packet, and the leading address of each packet is skipped. Therefore, the start address of a packet at an arbitrary coordinate is searched using the packet management table shown in FIG. Therefore, if the write address of the head packet is known, the head address of an arbitrary packet can be obtained using the data size up to the coordinates described in the packet management table as an offset. For example, when the third packet shown in FIG. 10 is read, the total size of the first and second packets is obtained from the packet management table, and the third packet address is calculated by applying an offset to the address of the head packet. And it becomes possible to acquire the data of a 3rd packet by reading data from there.

  As described above, since arbitrary data can be accessed in tile units, partial processing of an image becomes possible. For example, when it is desired to extract and process a partial area of an image, it is only necessary to acquire and process packet data corresponding to the area.

  In contrast to the compression processing described above, the decompression processing executed by the decompression units 222 and 232 is processed using information described in each header because a header is assigned to each packet. First, when the compression flag indicates non-compression, the data from which the header has been removed is output, and when the compression flag indicates compression, decompression processing is performed. In the expansion process, the pattern flag storage position, the first color data storage position, and the second, third, and fourth color storage positions are obtained from the header, and the subsequent processing is sequentially expanded into tile image data as in the above-described embodiment. .

  For example, since the position of the pattern flag is a fixed-length header, it can be obtained by offsetting. If the tile size is 64 × 64 pixels, the size of the pattern flag is fixed at 64 × 64 bits, and the first color data is obtained by applying an offset from the pattern flag position. The second, third, and fourth color data are obtained by referring to the first color size described in the header and applying an offset from the data position of the first color.

[Compression processing]
Next, details of the compression processing in step S605 described above will be described with reference to FIGS. FIG. 12 is a block diagram illustrating a configuration in the compression unit 202 (or 252) that executes the compression processing in step S605.

  The compression units 202 and 252 first store the input tile image of 64 × 64 pixel size in the tile buffer 1201. The piece extracting unit 1202 cuts out a 2 × 2 pixel unit block image (hereinafter, a 2 × 2 pixel block is referred to as a piece) from the tile image stored in the tile buffer 1201. Then, the index generation unit 1203 compares the color data of each pixel in each cut out piece, and as described with reference to FIG. 4, the pattern indicating the arrangement pattern of the color data included in each piece Specify the flag (4 bits). Here, the pattern flag (4 bits) is also referred to as second pattern information.

  The pattern flag (4 bits) has a total of 15 patterns shown in FIG. 4, and is specified by comparing with each pattern. Then, color data corresponding to a pixel at a predetermined position (for example, upper left) of the piece is extracted as color data information of the first color. Further, when it is determined that the number of colors included in the piece is any one of 2 to 4, the second color data information to the fourth color corresponding to the arrangement pattern defined by the specified pattern flag. Extract color data information of the color.

  The color data information corresponding to the number of colors included in each piece extracted in this way is used as color data information of the first color corresponding to the pixel at a predetermined position (for example, upper left) in the block, and the other color data information. The data is output separately for the color data information of the second color to the fourth color. The color data information of the first color is called a representative color, and the color data information of the second color to the color data of the fourth color is called an interpolation color.

  In this embodiment, information for specifying the arrangement of color data in each piece is called an index, and the index generation unit 1203 outputs a 4-bit pattern flag as an index at this point as described above. Shall.

  The index, representative color, and interpolation color data generated by the index generation unit 1203 is read by the packet generation unit 1208 and the constituent color number determination unit 1204. The packet generation unit 1208 collectively stores the index, representative color, and interpolation color information output from each piece by the index generation unit 1203 in different memory areas in the packet buffer 1209. Furthermore, packet data is generated by adding header information including information such as page ID, tile coordinates, tile / packet data size, and compression flag. On the other hand, the constituent color number determination unit 1204 has a tile (2 × 2 pixel block) within three tiles within the tile image to be processed based on the information on the index, representative color, and interpolation color information, and constituting the tile image. ) It is determined whether or not everything is composed of two colors or less. If the configuration color number determination unit 1204 determines that such a configuration is made, the header correction unit 1210, the interpolation color replacement unit 1211, and the index rewrite unit 1212 correct the packet data generated by the packet generation unit 1208. To do. Details will be described later.

  Next, the configuration color number determination process executed in the configuration color number determination unit 1204 will be described with reference to FIG. In the component color number determination process, it is determined whether the tile image has the above-described number of component colors (three colors or less in the tile and all the blocks are within two colors) and the color corresponding to three or less colors constituting the tile image. Performs processing to store data in the buffer. In this determination, if the tile does not correspond, the component color over detection signal “1” is generated.

  First, as described above, the constituent color number determination unit 1204 reads the index, representative color, and interpolation color data generated by the index generation unit 1203 (S1101). Next, the constituent color number determination unit 1204 uses one of the 2 × 2 pixel blocks (pieces) as a target piece, refers to the read index, analyzes the arrangement information of the colors constituting the target piece, The number is checked (S1102). Since the index is represented by the pattern flag (4 bits) value shown in FIG. 4, when the pattern flag value is “0”, the number of constituent colors is one and the pattern flag value is any of “1-7”. In the case of "", the number of constituent colors is two. When the pattern flag value is “any of 8 to D”, the number of constituent colors is three, and when the pattern flag value is “E”, the number of constituent colors is four. .

  First, it is determined whether or not the number of constituent colors is one (S1103). As a result of the determination, in the case of one color (the pattern flag value is “0”), the 2 × 2 pixel block is represented by only one representative color and there is no interpolation data, so writing to the replacement interpolation color buffers 1205 to 1207 is performed. If not, the process proceeds to S1116. Otherwise, the process proceeds to S1104.

  Next, it is determined whether the number of constituent colors is 2 or 3 to 4 (S1104). Here, in the case of two colors (when the pattern flag value is “1” to “7”), the process proceeds to S1105, and when the number of colors constituting the 2 × 2 pixel block is three or four (the pattern flag value is In the case of 8 to E), the process proceeds to S1117. If it is determined that there are two colors, it is determined whether or not there are two or more empty spaces in the replacement interpolation color buffers 1205 to 1207 in order to store the color data of the two colors (S1105). The empty information of the replacement interpolation color buffers 1205 to 1207 is managed by a replacement interpolation color buffer 1 to 3 empty flag table as shown in FIG. Since the replacement interpolation color buffers 1205 to 1207 are all empty at the time of default, “1” indicating the empty state is set in the replacement interpolation color buffers 1 to 3 empty flags. In S1105, the number of replacement interpolation color buffer 1 to 3 empty flags being “1” is counted. If the total is 2 or more, it is determined that the buffer empty number is 2 or more, and the process proceeds to S1106. In the case, the process proceeds to S1107. If there are two empty spaces, the representative color and the interpolation color are written in the empty buffers of the replacement interpolation color buffers 1205 to 1207, respectively. Then, “0” is set in the empty flag corresponding to the written buffer. (S1106).

  If two or more vacancies do not exist, it is determined whether there is one vacancy (S1107). If the total obtained by counting the number of replacement interpolation color buffers 1 to 3 in the S1105 empty flag being “1” is 1, it is determined that there is one empty space, and the process proceeds to S1108. Otherwise, S1113 is performed. Proceed to If there is one free space, two buffered interpolation color data are read from the replacement interpolation color buffers 1205 to 1207 (S1108). Next, the pixel values of the read two interpolation color data are compared with the pixel values of the two color data (representative color and interpolation color) of the block of interest (S1109). Then, it is determined whether or not the two colors match the read interpolation color data (S1110). If they match, since both colors have already been written to the buffer, it is determined that writing to the empty buffer is unnecessary, and the process proceeds to S1116. If they do not match, the process proceeds to S1111.

  If the two colors do not match, it is determined whether only one of the colors matches (S1111). If only one color matches, the color data that does not match is written to an empty buffer (S1112). Then, “0” is set in the empty flag corresponding to the written buffer. On the other hand, if none of the colors match, there are two colors other than the data for the two colors stored in the replacement interpolation color buffers 1205 to 1207 in the 2 × 2 pixel block of interest. It shows that. That is, since the number of constituent colors of the tile is four or more and indicates that the tile is not subject to interpolation color replacement processing, the process advances to step S1117.

  If there is no free space for the replacement interpolation color buffer in S1107, the buffered three pieces of interpolation color data are read from the replacement interpolation color buffers 1205-1207 (S1113). Then, the read pixel values of the three interpolation color data are compared with the pixel values of the two color data (representative color and interpolation color) of the block of interest (S1114). It is determined whether or not the two colors of the block match any of the read interpolation color data (S1115). As a result of the determination, if they match, since both colors have already been written to the buffer, it is determined that writing to the buffer is unnecessary, and the process proceeds to S1116. On the other hand, if they do not match, it indicates that colors other than the data for the three colors stored in the replacement interpolation color buffers 1205 to 1207 exist in the focused 2 × 2 pixel block. ing. That is, since the number of constituent colors of the tile is four or more and indicates that the tile is not subject to interpolation color replacement processing, the process advances to step S1117. In S1117, the number of constituent colors of the 2 × 2 pixel block of interest is 3 or 4 (“NO” in S1304), or the number of constituent colors of the tile of interest is 4 or more (“NO” in S1111 or S1115). Determined in the previous step. That is, it is determined that the tile is not subject to interpolation color replacement processing. In this case, the configuration color number determination unit 1204 determines that the configuration color number is over and notifies the header correction unit 1210, the interpolation color replacement unit 1211, and the index conversion unit 1212 (S1117).

  It is determined whether the above-described processing has been repeated up to the last piece in the tile (S1116), and if there is a piece that has not been focused on yet, the processing returns to S1102 with the piece as a processing target. On the other hand, when it is determined that the determination for all pieces has been completed, it is determined that the tile is the interpolation color replacement target tile. That is, if the tile image is within 3 colors and all of the pieces (2 × 2 pixel blocks) are within 2 colors, YES is determined in S1116. The process shown in FIG. 11 is performed for each tile constituting the page image.

  Note that if all pieces in the tile image are configured with two or less colors and the color types of all the two color pieces are within three colors in the tile, YES is determined in S1116. This means that the representative color of a piece composed of one color may be different from the color of a piece composed of two colors. The present invention can also be applied to an image that satisfies such conditions. However, since the position of the pixel of the different color needs to match the position of the piece of one color, an image satisfying such a condition rarely appears. Therefore, most tile images determined as YES in S1116 are those in which the tile image is composed of three colors or less and all the pieces in the tile image are composed of two colors or less.

  Next, when the configuration color number determination unit 1204 determines that the tile has 3 colors or less and all 2 × 2 pixel blocks in the tile are configured with 2 colors or less, the process is executed on the tile image. Interpolation color data replacement processing and index rewriting processing will be described with reference to FIG.

  That is, when it is determined in the above-described constituent color number determination process that the tile is the interpolation color replacement process target, the following process is executed. The interpolation color replacement unit 1211 executes processing for replacing the interpolation color data (second to fourth color data) stored in the packet buffer with the color data held in the replacement interpolation color buffers 1205 to 1207. Then, the index rewriting unit 1212 generates an interpolation color selection bit for each 2 × 2 pixel block and rewrites the index (pattern flag of each piece (4 bits) → pattern flag (3 bits) + interpolation color selection bit ( 1 bit)).

  First, it is determined whether a notification that the number of configuration colors has been exceeded is received from the configuration color number determination unit 1204 (S1301). If it is determined in S1117 of the above-described constituent color number determination process that the constituent color number is exceeded, the process for the target tile is terminated, and the process proceeds to the next tile process. If not, the index generation unit 1203 reads the index, representative color, and interpolation color of the image data in piece units (S1302). Then, based on the read index value, it is determined whether or not the number of constituent colors of the read piece is two colors (S1303). If it is determined in step S1303 that there are not two colors, there is no interpolation color data, so it is determined that the piece is not a target of interpolation color data replacement processing, and the flow advances to step S1312. In this case, if there are three or more colors, it is determined as YES in S1301, and here, it is determined that one color (the pattern flag value is “0”). In addition, since the index (4-bit pattern flag) value is “0”, the expansion can be performed by assuming that the 3-bit pattern flag is “0” and the interpolation color selection bit is “0”, so it is necessary to rewrite the index value. Absent.

  On the other hand, when it is determined in S1303 that the number of constituent colors is two (the pattern flag value is any one of 1 to 7), it is determined as a piece to be subjected to replacement processing of interpolation color data, and the process proceeds to S1304, where the interpolation color data is converted. In order to replace it, the process proceeds to a process of generating an interpolation color selection bit.

  In step S1304, the pixel values of the colors stored in the replacement interpolation color buffers 1205, 1206, and 1207 are compared with the representative color and the interpolation color (S1304). FIG. 15 shows the relationship between the colors stored in the replacement interpolation color buffers 1205, 1206, and 1207 and the interpolation color selection bits to be generated. Depending on which buffer stored in the replacement interpolation color buffer 1205, 1206, 1207 (hereinafter referred to as buffers 1, 2, 3) matches the representative color and interpolation color of the current piece of interest being referred to The interpolation color selection bit is switched. In order to express the interpolation color selection bit by only 1 bit, “0”, “1” is selected depending on which buffer among the remaining two buffers other than the buffer in which the interpolation color is stored. "To work. As shown in FIG. 15, when interpolation color data is stored in a smaller numbered buffer among the remaining two buffers storing colors different from the representative color, “0” is generated as the interpolation color selection bit. To do. When interpolation color data is stored in a larger numbered buffer, “1” is generated as the interpolation color selection bit. Details will be described below.

  First, it is determined whether or not the color stored in the replacement interpolation color buffer 1205 (buffer 1) matches the representative color of the focused piece (S1305). If they match, the process proceeds to S1306, and if they do not match, the process proceeds to S1309.

  In step S1306, it is determined whether the color stored in the replacement interpolation color buffer 1206 (buffer 2) matches the interpolation color of the focused piece. If they match, the process proceeds to S1307. If they do not match, it is determined that the interpolation color is stored in the replacement interpolation color buffer 1207 (buffer 3), and the process proceeds to S1308.

  In S1309, it is determined whether or not the color stored in the replacement interpolation color buffer 1206 (buffer 2) matches the representative color of the focused piece (S1309). If they match, the process proceeds to S1310. If they do not match, it is determined that the representative color is stored in the replacement interpolation color buffer 1207 (buffer 3), and the process proceeds to S1311.

  In step S1310, it is determined whether the color stored in the replacement interpolation color buffer 1205 (buffer 1) matches the interpolation color of the focused piece. If they match, the process proceeds to S1307. If they do not match, it is determined that the interpolation color is stored in the replacement interpolation color buffer 1207 (buffer 3), and the process proceeds to S1308.

  In step S1311, it is determined whether the color stored in the replacement interpolation color buffer 1205 (buffer 1) matches the interpolation color of the focused piece. If they match, the process proceeds to S1307. If they do not match, it is determined that the interpolation color is stored in the replacement interpolation color buffer 1206 (buffer 2), and the process proceeds to S1308.

  In S1307, since the interpolation color of the current piece of interest is stored in the smaller numbered buffer of the remaining two buffers other than the buffer storing the representative color, “0” is generated as the interpolation color selection bit. To do. On the other hand, in S1308, since the interpolation color of the current piece of interest is stored in the larger numbered buffer of the remaining two buffers other than the buffer storing the representative color, “1” is set as the interpolation color selection bit. Generate.

  In S1312, it is determined whether or not generation of the interpolation color selection bit has been completed up to the last piece in the tile. If it is not the last piece yet, the process returns to S1302, and the above-described processing is repeated with the next piece as the target piece to be processed. On the other hand, if it is the last piece, the process proceeds to S1313.

  In step S1313, the packet generation unit 1208 corrects the packet data stored in the packet buffer 1209 (packet data correction process). In the packet data correction process, the interpolation color replacement unit 1211 replaces the interpolation color data, the index rewriting unit 1212 rewrites the index, and the header correction unit 1210 corrects the header information.

  When packet data is stored in the packet buffer 1209, the packet generation unit 1208 notifies the header correction unit 1210, the interpolation color replacement unit 1211, and the index rewriting unit 1212 of the storage address of the generated packet data. To do. The header correcting unit 1210, the interpolation color replacing unit 1211, and the index rewriting unit 1212 correct the stored packet data based on the notified storage address.

  The interpolation color replacement unit 1211 stores the interpolation colors stored in the second, third, and fourth color storage units of the packet data related to the tile image in the replacement interpolation color buffers 1205, 1206, and 1207 (buffers 1, 2, and 3). Replace with the stored data for three colors.

  The index rewriting unit 1212 rewrites the 4-bit pattern flag value (0 to 7) generated by the index generation unit 1203 for each piece to a 3-bit pattern flag value (0 to 7). Along with this rewriting, the interpolation color selection bit (1 bit) set in S1307 and S1308 is set. That is, the 4-bit pattern flag value for each piece is rewritten with a 1-bit interpolation color selection bit and a 3-bit pattern flag value.

  The header correction unit 1210 corrects the data size information of the second, third, and fourth color storage units held in the header information to 9 bytes, and “1” indicating that the replacement has been performed in the interpolation color data replacement flag. ”Is set.

  FIG. 16 shows an example of the data structure and header information of the first packet data (FIG. 16 (a)) before modification of the packet data and the second packet data after modification (FIG. 16 (b)) according to the present invention. is there. FIG. 16 shows an example where the color space is RGB and the number of bits of pixel data is 8 bits. As shown in FIG. 16 (a), the area required for the second, third, and fourth color storage parts before the packet data correction is all pieces (1024 pieces) in the 64 × 64 pixel tile. Assuming that all pixels are composed of different colors (four colors), a maximum of 9216 bytes are required. In addition, for all pieces, if all four pixels in each piece have the same color, the second to fourth colors do not exist in each piece, so the second, third, and fourth color storage units are minimum. 0 bytes. That is, the second, third, and fourth color storage units before the packet data correction are 0 to 9216 bytes in size.

  On the other hand, as shown in FIG. 16B, after performing the packet data correction processing on the tile image to be replaced with the interpolation color data (the tile image is 3 colors or less and each piece is 2 colors or less), Then: Since the interpolation color data for three colors are stored in the second, third, and fourth color storage units, data for 9 bytes is stored. The header information is corrected by converting the data size information of the second, third, and fourth color storage units into 9 bytes and setting indicating that the interpolation color data replacement flag has been replaced. .

  FIG. 17 shows the relationship of allocation of the three interpolation colors in the second, third, and fourth color storage units of the packet data after the interpolation color replacement process is performed in S1313. As shown in FIG. 17, the interpolation color replacement unit 1211 sequentially reads out the interpolation color data stored in the replacement interpolation color buffers 1205 to 1207, and the address position of the second, third, and fourth color storage unit base addresses of the packet data. Are stored in the second, third, and fourth color storage units starting from.

  In the index rewriting process, a 4-bit pattern flag as shown in FIG. 5A is represented by a 3-bit pattern flag and a 1-bit interpolation color selection bit as shown in FIG. Rewrite with index. The interpolation color selection bits generated in S1307 and S1308 are stored at addresses corresponding to the piece coordinates of the internal buffer (not shown) together with the lower 3 bits of information of the 4-bit pattern flag. Here, the information of the upper 1 bit is not used when the constituent colors are two colors or less. That is, the index rewriting unit 1212 reads the rewritten index value (pattern flag (3 bits) + interpolation color selection bit (1 bit)) corresponding to each piece from the internal buffer, and stores it in the pattern flag storage unit of the packet buffer 1209. Perform the writing process.

  When the modification of the packet data is completed, the packet data stored in the packet buffer 1209 is stored in the memory 106 via the image memory bus. Thereafter, packet data generation and interpolation data replacement processing are similarly performed for the remaining tile images, and the above-described processing is repeated for all tiles.

[Deployment processing]
Finally, a method for developing packet data into tile images will be described with reference to FIGS. FIG. 18 is a block diagram illustrating an internal configuration of the expansion units 222 and 232.

  The packet data to be expanded is stored in the packet buffer 1901, and the header analysis unit 1902 analyzes the interpolation color data replacement flag in the header information of the stored packet data to determine whether the packet data has undergone interpolation color replacement. judge. In the case of packet data in which interpolation color replacement has been performed, the replaced packet data expansion unit 1903 specifies the second color for each piece based on the index, the representative color, and the three colors of interpolation color data, and each piece. Reproduce the color scheme. Here, the index is a 3-bit pattern flag and an interpolation color selection bit.

  Further, in the case of packet data in which interpolation color replacement has not been performed, the non-replacement packet data expansion unit 1904, for each piece, an index, a representative color (first color color data information), and an interpolation color (second to fourth). Color data information), and reproduce the color arrangement of each piece. The index is a 4-bit pattern flag. Each reproduced piece is sequentially written into the tile buffer 1906 by the piece writing unit 1905. When all pieces included in the packet data are reproduced, the image data stored in the tile buffer is output as a tile image. When reproducing the page image, the tile image development process may be performed in order for all the packet data.

  FIG. 19 is a flowchart showing details of the packet data expansion processing.

  In step S2001, the expansion unit 222 (or 232) reads the expansion target packet data from the packet data stored in the memory 106 into the packet buffer 1901.

  The header analysis unit 1902 analyzes the header information of the read packet data (S2002), and determines whether the interpolation color data replacement flag is 1 (S2003).

  If it is determined that the interpolation color data replacement flag is 1 (that is, replaced packet data), the process advances to step S2004, and the replaced packet data expansion unit 1903 reads index data for the first piece. Further, the replaced packet data expansion unit 1903 reads the representative color of the piece from the first color storage unit of the packet data (S2005), and reads out the interpolated color data of the three colors from the second, third, and fourth color storage units ( S2006). Then, the read three color interpolation color data and the representative color of the piece are compared, and the interpolation color data matching the representative color and the two color interpolation color data not matching the representative color are specified (S2007). Next, it is determined whether the interpolation color selection bit of the piece included in the read index data is 0 or 1 (S2008). If it is determined that the interpolation color selection bit of the piece is 0, the interpolation color data closer to the base address among the two interpolation color data that does not match the representative color of the piece is the second color in the piece. The color data is specified as color data (S2009).

  On the other hand, when it is determined that the interpolation color selection bit of the piece is 1, the interpolation color data that is far from the base address among the interpolation color data of two colors that do not match the representative color of the piece is displayed in the piece. The second color data is specified (S2010). As a result, the replaced packet data expansion unit 1903 obtains the 3-bit pattern flag, the representative color (first color data information), and the interpolation color (second color data) included in the index data for the processing target piece. Information) can be specified and the color scheme of the piece is reproduced. The piece writing unit 1905 writes the reproduced color scheme of the piece in the tile buffer 1906 (S2011). It is determined whether all pieces included in the packet data have been processed (S2012). If it is determined that there is an unprocessed piece, the process returns to S2004 with the next piece as a processing target. On the other hand, if it is determined that all pieces have been processed, the process proceeds to S2013, and the tile image written in the tile buffer 1906 is output.

  As shown in FIGS. 16B and 17, the interpolation color replaced packet data is stored in the second, third, and fourth color storage units as replacement interpolation color buffers 1205 to 1207 (buffers 1 to 1 in FIG. 15). (Corresponding to 3) is stored in order. Therefore, as can be seen from FIG. 15, in S2009, the interpolated color data closer to the base address of the second, third, and fourth color storage units is selected as the second color, and in S2010, the farther from the base address. The interpolated color data is selected as the second color.

  On the other hand, if it is determined in S2003 that the interpolation color data replacement flag is 0 (that is, non-replacement packet data), the process proceeds to S2014, and the non-replacement packet data expansion unit 1903 reads the index data regarding the first processing target piece. . Further, the non-replacement packet data expansion unit 1904 reads the representative color of the processing target piece from the first color storage unit of the packet data (S2015). Further, when the number of colors indicated by the index (4-bit pattern flag) of the processing target piece is 2 to 4 colors, the non-replacement packet data expansion unit 1904 interpolates the piece from the second, third, and fourth color storage units. Color data (color data of the second to fourth colors) is read (S2016). As a result, the non-replacement packet data expansion unit 1904, with respect to the processing target piece, includes a 4-bit pattern flag, representative color (first color data information), and interpolation color (second to fourth colors) included in the index data. Color data information) can be specified, and the color arrangement of the piece is reproduced. The piece writing unit 1905 writes the reproduced color scheme of the piece in the tile buffer 1906 (S2017). It is determined whether all pieces included in the packet data have been processed (S2018). If it is determined that there is an unprocessed piece, the process returns to S2014 with the next piece as a processing target. On the other hand, if it is determined that all pieces have been processed, the process proceeds to S2013, and the tile image written in the tile buffer 1906 is output.

  The development process described above is a process for obtaining an image with the original resolution. However, if it is desired to obtain image data with half the resolution, it is only necessary to extract the color data stored in the first color storage unit. . This is because the representative colors of each piece are stored in the first color storage unit in raster order.

  According to the present embodiment, it is noted that document images used in the office are mostly composed of two to three colors even when viewed in tile units, and the interpolation data of each tile is compressed. Thus, the compression rate can be improved.

  In addition, by increasing the compression rate, the increase in data volume is suppressed to reduce the decrease in system efficiency, and the processing speed of the image processing system is decreased due to the increase in cost due to the increase in memory capacity and the increase in resolution. Can be suppressed.

[Other Embodiments]
The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, or the like) of the system or apparatus reads the program. It is a process to be executed.

Claims (8)

An image processing apparatus that processes a tile image composed of a predetermined number of pixels,
Determining means for determining whether or not the tile image has 3 colors or less and all of the 2 × 2 pixel size blocks constituting the tile image have 2 colors or less;
With respect to the tile image in which the inside of the tile image is determined by the determination means to be within 3 colors and all of the 2 × 2 pixel size blocks constituting the tile image are 2 colors or less, Color data information of the first color indicating the color data of the pixel at the determined position, color data information within the three colors existing in the tile image, and an arrangement pattern of color data in each block of the two colors or less Color data information of a second color different from the color data information of the first color in each block of the two or less colors is selected from the first pattern information for specifying the color and the color data information of the three colors or less Generating means for generating first packet data including selection information for
An image processing apparatus comprising:   For the tile image in which the determination unit determines that the tile image has three colors or less and all the 2 × 2 pixel size blocks constituting the tile image are not two colors or less, Color data information of the first color indicating color data of pixels at a predetermined position in each block; color data information of second to fourth colors different from the color data information of the first color in each block; 2. The image processing apparatus according to claim 1, wherein second image data including second pattern information for specifying an arrangement pattern of color data in each block is generated. The generating means includes
The tile image is divided into blocks each having a size of 2 × 2 pixels,
By comparing the color data of each pixel in each of the divided blocks, the second pattern information indicating the arrangement pattern of the color data included in each block is specified,
Extracting color data information of the first color indicating color data of a pixel at a predetermined position in each block;
From the blocks determined that the number of color data included in each block is any one of 2 to 4, the second to second corresponding to the arrangement pattern defined by the specified second pattern information. Extract color data information of 4 colors,
Generating the second packet data including the second pattern information, color data information of the first color in each block, and color data information of the second to fourth colors in each block;
For the tile image in which the determination means determines that the tile image has three colors or less and all the 2 × 2 pixel size blocks constituting the tile image have two colors or less, the second image The second pattern information included in the packet data is rewritten with the first pattern information and the selection information, and the color data of the second to fourth colors in each block included in the second packet data The image processing apparatus according to claim 2, wherein the first packet data is generated by replacing information with color data information within the three colors existing in the tile image.   4. The image processing according to claim 3, wherein the header information of the first packet data includes a flag indicating replacement with the color data information within the three colors existing in the tile image. 5. apparatus.   The second pattern information is represented by 4-bit data, the first pattern information is represented by 3-bit data, and the selection information is represented by 1-bit data. The image processing apparatus according to item.   The image processing apparatus according to claim 1, wherein the tile image is an image generated by dividing a page image into sizes of 64 × 64 pixels. A processing method of an image processing apparatus for processing a tile image composed of a predetermined number of pixels,
A determining step for determining whether or not the inside of the tile image is within 3 colors and all of the 2 × 2 pixel size blocks constituting the tile image are 2 colors or less;
For the tile image in which the generation unit determines that the inside of the tile image is within three colors and all of the 2 × 2 pixel size blocks constituting the tile image are two colors or less in the determination step, Color data information of a first color indicating color data of a pixel at a predetermined position in each block, color data information within the three colors existing in the tile image, and color in each block of the two colors or less Color of a second color different from the color data information of the first color in each block of the two or less colors among the first pattern information for specifying the arrangement pattern of data and the color data information within the three colors Generating a first packet data including selection information for selecting data information;
A processing method characterized by comprising:   The program for functioning a computer as an image processing apparatus of any one of Claims 1 thru | or 6.

Images