JP4795166B2 - Image compression apparatus, method and program, recording apparatus and method, image decompression apparatus, method and program, and recording medium - Google Patents

Description

  The present invention relates to image compression for compressing image data. The present invention relates to decompression of compressed image data.

  In an image forming apparatus such as a printer, a copier, a facsimile machine, or a multifunction machine having these functions, an electrophotographic system is adopted for image formation. In such an image forming apparatus, first, laser light is irradiated while being scanned on the photosensitive drum based on the image data of the original image read by the image forming apparatus itself or another image reading apparatus or the like. An electrostatic latent image is formed on the peripheral surface of the photosensitive drum. Next, the electrostatic latent image is developed by a developing device, whereby a toner image is formed on the peripheral surface of the photosensitive drum. Next, the toner image is transferred to a transfer material such as paper and fixed, thereby forming an image. In addition, toner images corresponding to the respective color components of cyan (C), magenta (M), yellow (Y), and black (K) are formed, and these toner images are transferred and fixed onto the transfer material while being superimposed. As a result, full-color image formation is possible.

  In recent years, there has been a demand for improvement in image quality when printing an image with an image forming apparatus. Screen processing is known as one technique for improving the image quality. In this screen processing, multi-value data is converted into binary data, and by reducing the screen frequency (reducing the number of screen lines), an image with a large number of gradations and a smooth gradation is formed. By increasing the frequency (increasing the number of screen lines), an image with high resolution is formed.

  When printing is performed by the image forming apparatus, image processing such as screen processing is performed. In this case, it is necessary to develop image data in a storage element, and a storage element having a relatively large capacity is required.

  In addition, image data generated by a scanner, a digital camera, or the like has been increased in capacity due to recent high resolution and colorization. For this reason, a large-capacity recording medium is required to store the image data.

  For these reasons, there is a demand for a compression technique for reducing the capacity of image data. The compression technique includes an uncompressed image obtained by decompressing compressed image data, such as Huffman coding, run length coding, LZ (Lempel-Ziv) coding, and the like. Lossless compression (reversible encoding) that completely returns to, and lossy compression (irreversible encoding), such as JPEG (Joint Photograph Experts Group), where the decompressed image does not return completely to the image before compression There is.

As such a compression technique, for example, there is a technique disclosed in Patent Document 1 and a technique disclosed in Patent Document 2. In the compression technique disclosed in Patent Document 1, when input image data is expanded as image data, the image data is expanded as binary image data at a first resolution (low resolution) and stored in storage means. The binary image data is converted into multi-valued image data, and the converted multi-valued image data has a second resolution higher than the first resolution in order to improve gradation. The image data converted into the resolution (high resolution) and further converted into the second resolution is converted into binary image data. For this reason, the storage capacity of the storage means (memory) for storing the image data is reduced. Further, in the compression technique disclosed in Patent Document 2, single image data is separated into a plurality of bit planes, and the bit data at the same position constituting the plurality of bit planes is arranged in the vicinity position to obtain a single image data. Bit planes are combined and the bit planes are compressed. For this reason, the compression capacity is reduced during multi-valued image compression.
JP 2000-255120 A JP 2001-0669505 A

  By the way, there are various types of images such as image images such as photographic images and images, and line images such as text characters, color characters, lines and figures. In an image, for example, a higher gradation is preferable, such as 8 bpp (bits per pixel), but the resolution does not necessarily have to be high, and for example, about 300 dpi (dots per inch) is sufficient. On the other hand, in a line drawing, it is preferable that the resolution is high, for example, 1200 dpi, but the gradation is not necessarily high, and may be 1 bpp, for example. Therefore, when the image image is compressed, it is preferable to compress the image so that the gradation is preserved in the uncompressed image and the uncompressed image. On the other hand, when the line image is compressed, the decompression is performed. It is preferable to perform compression so that the resolution is preserved in the later image and the image before compression.

  However, the technique disclosed in Patent Document 1 and the technique disclosed in Patent Document 2 preferentially store either the gradation or the resolution according to such characteristics in the image to be compressed, and There is a disadvantage that the image cannot be compressed.

  On the other hand, even if there is a compression technique that preferentially stores either the gradation or the resolution according to the characteristics of the image to be compressed and compresses the image to be compressed, the image to be compressed is an image. In the case of an image including a line drawing and a line drawing, if the gradation is preferentially stored, the area of the line drawing in such an image is not properly compressed, and if the resolution is preferentially saved, There is a disadvantage that the area of the image in the image is not properly compressed.

  The present invention has been made in view of the above circumstances, and can appropriately store the gradation and resolution in accordance with the above-described characteristics in the image to be compressed and compress the image data of the image to be compressed. An object of the present invention is to provide an image compression apparatus, an image compression method, an image compression program, and a recording medium on which the image compression program is recorded. An object of the present invention is to provide a recording apparatus and a recording method for recording compressed compressed image data on a recording medium. An object of this invention is to provide the recording medium which recorded the compressed image data compressed. An object of the present invention is to provide a compressed image format for recording compressed image data on a recording medium. An object of the present invention is to provide an image decompression apparatus, an image decompression method, an image decompression program, and a recording medium on which an image decompression program is recorded, which decompresses compressed compressed image data.

As a result of various studies, the present inventor has found that the above object is achieved by the present invention described below. That is, an image compression apparatus according to an aspect of the present invention includes a blocking unit that divides image data including a plurality of pixels to which multi-value data is allocated into a plurality of blocks including a plurality of pixels, and the data includes A plurality of representative values are selected from a range of possible values, and a tag information generation unit that assigns an index indicating the representative value to each of the plurality of representative values, and the data of each pixel in the block An encoding unit that converts the pixel data into the index based on the representative value of the pixel and the pixel data, and the tag information generation unit includes a value of the pixel data in the compression target block. equal with selecting a plurality of representative values number in descending order of the data, to grant each index that points to the representative value to the plurality of representative values Turkey The features. An image compression method according to another aspect of the present invention includes a step of dividing image data including a plurality of pixels to which multi-value data is allocated into a plurality of blocks including a plurality of pixels, and the data is Selecting a plurality of representative values from a range of possible values; assigning an index indicating the representative value to each of the plurality of representative values; and data for each pixel in the block. Converting the pixel data into the index based on the value and the pixel data, and selecting the plurality of representative values includes: the number of data equal to said that you select a plurality of representative values in descending order of the.

According to this configuration, first, the image data is divided into a plurality of blocks composed of a plurality of images, a plurality of representative values are selected from a range of values that the data can take, and an index indicating the representative value is selected. Are assigned to a plurality of representative values. This index is also an identifier for identifying and specifying the representative value. The index may be an arbitrary code, but a code expressed by a small number of bits is preferable from the viewpoint of reducing the data capacity. For each block, the data of each pixel of the block is converted into an index based on the plurality of representative values and the data of the pixel. For this reason, the image data of the block includes, in each pixel, encoded image data including a plurality of indexes generated by converting the pixel data into indexes, a plurality of representative values, and a plurality of representative values. It is compressed into tag information composed of a plurality of associated indexes. Then, by compressing each block in this way, the image data is compressed as a set of image data of the compressed block. Therefore, the image data of the image to be compressed can be compressed by appropriately storing the gradation and resolution according to the above characteristics. According to the above configuration, the plurality of representative values are selected in descending order of the number of data having the same value among the data of each pixel in the block to be compressed. For this reason, when the data of each pixel in the block is converted into an index, a representative value that is even closer to the value of the data of the pixel can be selected, and the index of the pixel is assigned to the index indicating the selected representative value. Data is converted. Therefore, according to this configuration, the reversibility is further improved .

An image compression program for causing a computer to execute according to another aspect of the present invention divides image data including a plurality of pixels to which multi-value data is allocated into a plurality of blocks each including a plurality of pixels. Selecting a plurality of representative values from a range of values that can be taken by the data, assigning an index indicating the representative value to each of the plurality of representative values, and each pixel in the block Converting the pixel data into the index based on the plurality of representative values and the pixel data, and selecting the plurality of representative values for each pixel in the block to be compressed of the data, characterized that you select a plurality of representative values in the order number of the data is greater equal value. Furthermore, in a computer-readable recording medium on which an image compression program to be executed by a computer according to another aspect of the present invention is recorded, the image compression program includes pixels assigned with multi-value data. Dividing the plurality of image data into a plurality of blocks made up of a plurality of pixels, selecting a plurality of representative values from a range of values that the data can take, and an index indicating the representative value a step of applying to a plurality of representative values, the data of each pixel in the block, and a step of converting the data of the pixels in the index based on the data of the pixel and the plurality of representative values, the The step of selecting a plurality of representative values includes the step of selecting data of each pixel in the block to be compressed. Characterized that you select a plurality of representative values in the order equal number of data is large values.

According to this configuration, the image compression program divides the image data into a plurality of blocks composed of a plurality of images, selects a plurality of representative values from a range of values that the data can take, and an index indicating the representative value. Each of the selected representative values is assigned to each block, and for each block, the data of each pixel of the block is converted into an index based on the plurality of representative values and the data of the pixel. By compressing each block in this way, the image data is compressed as a set of image data of the compressed block. Therefore, according to this configuration, an image compression program is provided that compresses image data of an image to be compressed by appropriately storing gradation and resolution in accordance with the characteristics described above, and recording the image compression program A recording medium is provided. According to the above configuration, the plurality of representative values are selected in descending order of the number of data having the same value among the data of each pixel in the block to be compressed. For this reason, when the data of each pixel in the block is converted into an index, a representative value that is even closer to the value of the data of the pixel can be selected, and the index of the pixel is assigned to the index indicating the selected representative value. Data is converted. Therefore, according to this configuration, an image compression program in which the reversibility is further improved is provided, and a recording medium on which the image compression program is recorded is provided .

  In the image compression described above, in the generation of tag information, among the data of each pixel in the block to be compressed, a plurality of representative values are selected in descending order of the number of data having the same value, and the representative value is indicated. It is preferable that an index is assigned to each of the plurality of representative values.

  According to this configuration, the plurality of representative values are selected in descending order of the number of data having the same value among the data of each pixel in the block to be compressed. For this reason, when the data of each pixel in the block is converted into an index, a representative value that is even closer to the value of the data of the pixel can be selected, and the index of the pixel is assigned to the index indicating the selected representative value. Data is converted. Therefore, according to this configuration, the reversibility is further improved.

  Furthermore, in the above-described image compression, when generating tag information, first, a plurality of representative values are selected in descending order of the number of data having the same value among the data of each pixel in the block to be compressed. Next, the pixel data not selected as the plurality of representative values is assigned to the closest representative value among the plurality of representative values. Next, the representative value is corrected by an average value of the representative value to which the pixel data is allocated and the pixel data. An index indicating the representative value is assigned to each of the plurality of representative values. It is preferable that the generation of tag information is processed in this way.

  According to this configuration, the plurality of representative values are first selected in descending order of the number of data having the same value among the data of each pixel in the block to be compressed. The representative value is corrected to the average value of the pixel data and the representative value by assigning the pixel data not selected as the representative value to the representative value closest to the representative value. For this reason, when the data of each pixel in the block is converted into an index, a representative value that is even closer to the value of the data of the pixel can be selected, and the index of the pixel is assigned to the index indicating the selected representative value. Data is converted. Therefore, according to this configuration, the reversibility is further improved.

  In the above image compression, in encoding, for each pixel data in the block, a representative value closest to the pixel data is selected from among a plurality of representative values, and an index of the selected representative value is used. The pixel data is preferably converted.

  According to this configuration, when the data of each pixel in the block is converted into an index, a representative value closest to the pixel data is selected from among a plurality of representative values, and the selected representative value is indicated. Pixel data is converted into an index. For this reason, according to this structure, reversibility improves more.

  Further, in the above-described image compression, it is preferable that the sizes in the plurality of blocks are equal and the number of the representative values in the plurality of blocks is equal.

  According to this configuration, since the sizes in the plurality of blocks are equal and the number of representative values in the plurality of blocks is equal, the data capacities of the compressed blocks are equal. For this reason, when each compressed block is stored in the storage element or the recording medium, it is stored at equal intervals, so that data of any compressed block can be easily read out. Therefore, the data of any compressed block can be decompressed.

In another aspect of the present invention, compression target image data including a plurality of pixels to which multi-value data is allocated is divided into a plurality of blocks each including a plurality of pixels, and each of the plurality of blocks is A plurality of representative values selected from a range of values that can be taken by the data, and a plurality of representative values selected in descending order of the number of data having the same value among the data of each pixel in the block to be compressed. A coded image composed of a plurality of indices each associated with a value, the plurality of representative values and indicating the representative value, and a plurality of indexes associated with the plurality of pixels and converted from the pixel data It is a recording device that records data on a recording medium. In another aspect of the present invention, image data to be compressed including a plurality of pixels to which multi-value data is allocated is divided into a plurality of blocks each including a plurality of pixels, and each of the plurality of blocks is A plurality of representative values selected from a range of values that can be taken by the data, and a plurality of representative values selected in descending order of the number of data having the same value among the data of each pixel in the block to be compressed. A coded image composed of a plurality of indices each associated with a value, the plurality of representative values and indicating the representative value, and a plurality of indexes associated with the plurality of pixels and converted from the pixel data This is a recording method for recording data on a recording medium.

According to this configuration, each block obtained by dividing the image data to be compressed is associated with a plurality of representative values selected from a range of values that the data can take, and a plurality of representative values, A plurality of indexes indicating the representative value and encoded image data composed of a plurality of indexes corresponding to the plurality of pixels and converted from the pixel data are recorded on the recording medium. For this reason, the image data to be compressed is appropriately stored in gradation and resolution in accordance with the characteristics, and is compressed and recorded on the recording medium. Since the capacity is smaller than the capacity of the image data to be compressed, the recording apparatus and the storage method having such a configuration can store the image data to be compressed on the recording medium with a smaller capacity than when the image data to be compressed is stored as it is. Can do. According to the above configuration, the plurality of representative values are selected in descending order of the number of data having the same value among the data of each pixel in the block to be compressed. For this reason, when the data of each pixel in the block is converted into an index, a representative value that is even closer to the value of the data of the pixel can be selected, and the index of the pixel is assigned to the index indicating the selected representative value. Data is converted. Therefore, according to this configuration, the reversibility is further improved .

Furthermore, in a computer-readable recording medium on which compressed image data is recorded according to another aspect of the present invention, the compressed image data is a compression target including a plurality of pixels to which multi-value data is allocated. The image data is divided into a plurality of blocks composed of a plurality of pixels, and for each of the plurality of blocks, a plurality of representative values selected from a range of values that the data can take , the block to be compressed A plurality of representative values selected in descending order of the number of pieces of data having the same value, a plurality of indexes respectively corresponding to the plurality of representative values, and indicating the representative value; And encoded image data composed of a plurality of indexes each associated with a pixel and converted from the pixel data. That.

According to this configuration, the compressed image data includes a plurality of representative values selected from a range of values that the data can take and a plurality of representative values for each of the blocks into which the image data to be compressed is divided. A plurality of indexes that are associated with each other and indicate representative values, and encoded image data that is associated with each of a plurality of pixels and includes a plurality of indexes obtained by converting pixel data. For this reason, in the compressed image data, the image data to be compressed is compressed with the gradation and resolution appropriately stored in accordance with the characteristics. Since the volume of the compressed image data is smaller than the volume of the image data to be compressed, the compressed image data can be stored in a storage element or recording medium having a smaller capacity than when the image data to be compressed is stored as it is. According to the above configuration, the plurality of representative values are selected in descending order of the number of data having the same value among the data of each pixel in the block to be compressed. For this reason, when the data of each pixel in the block is converted into an index, a representative value that is even closer to the value of the data of the pixel can be selected, and the index of the pixel is assigned to the index indicating the selected representative value. Data is converted. Therefore, according to this configuration, the reversibility is further improved .

In another aspect of the present invention, image data to be compressed including a plurality of pixels to which multi-value data is allocated is divided into a plurality of blocks each including a plurality of pixels, and each of the plurality of blocks is A plurality of representative values selected from a range of values that can be taken by the data, and a plurality of representative values selected in descending order of the number of data having the same value among the data of each pixel in the block to be compressed. A coded image composed of a plurality of indices each associated with a value, the plurality of representative values and indicating the representative value, and a plurality of indexes associated with the plurality of pixels and converted from the pixel data In the image decompression apparatus for decompressing compressed image data comprising data, the index for each index in the encoded image data Scan, characterized in that it comprises a decoding unit for converting the index representative value pointed to. Furthermore, in another aspect of the present invention, image data to be compressed including a plurality of pixels to which multi-value data is allocated is divided into a plurality of blocks each including a plurality of pixels, and each of the plurality of blocks is A plurality of representative values selected from a range of values that can be taken by the data, and a plurality of representative values selected in descending order of the number of data having the same value among the data of each pixel in the block to be compressed. A coded image composed of a plurality of indices each associated with a value, the plurality of representative values and indicating the representative value, and a plurality of indexes associated with the plurality of pixels and converted from the pixel data In the image decompression method for decompressing compressed image data comprising data, for each index in the encoded image data, the index Characterized in that it comprises the step of converting the index to a representative value box pointed.

  According to this configuration, for each index in the encoded image data, the index is converted into a representative value indicated by the index. For this reason, the compressed image data can be appropriately decompressed.

In another aspect of the present invention, compression target image data including a plurality of pixels to which multi-value data is allocated is divided into a plurality of blocks each including a plurality of pixels, and each of the plurality of blocks is A plurality of representative values selected from a range of values that can be taken by the data, and a plurality of representative values selected in descending order of the number of data having the same value among the data of each pixel in the block to be compressed. A coded image composed of a plurality of indices each associated with a value, the plurality of representative values and indicating the representative value, and a plurality of indexes associated with the plurality of pixels and converted from the pixel data In an image decompression program for causing a computer to execute an image decompression process for decompressing compressed image data comprising data, the encoded image For each index in the data, characterized in that it comprises the step of converting the index to a representative value the index points to. Furthermore, in another aspect of the present invention, image data to be compressed including a plurality of pixels to which multi-value data is allocated is divided into a plurality of blocks each including a plurality of pixels, and each of the plurality of blocks is A plurality of representative values selected from a range of values that can be taken by the data, and a plurality of representative values selected in descending order of the number of data having the same value among the data of each pixel in the block to be compressed. A coded image composed of a plurality of indices each associated with a value, the plurality of representative values and indicating the representative value, and a plurality of indexes associated with the plurality of pixels and converted from the pixel data And an image decompression program for causing the computer to execute an image decompression process for decompressing the compressed image data. A recording medium readable for each index in the encoded image data, characterized by comprising the step of converting the index to a representative value the index points to.

  According to this configuration, the image decompression program converts each index in the encoded image data into a representative value indicated by the index. Therefore, according to this configuration, an image decompression program for appropriately decompressing compressed image data is provided, and a recording medium on which the image decompression program is recorded is provided.

An image compression apparatus, an image compression method, an image compression program, and a recording medium on which the image compression program according to the present invention is recorded, appropriately store gradation and resolution according to the above characteristics in the image to be compressed, and it is possible to compress the image data of the image, is that to further improve than reversibility.

A recording apparatus and a recording method according to the present invention are compression in which image data of a compression target image is compressed by appropriately storing gradation and resolution according to the above characteristics in the compression target image and further improving reversibility. Image data can be recorded on a recording medium. In the present invention, a recording medium on which such compressed image data is recorded can be provided .

  The image decompression apparatus, the image decompression method, the image decompression program, and the recording medium recording the image decompression program according to the present invention can appropriately decompress the compressed image data.

  Embodiments according to the present invention will be described below with reference to the drawings. In addition, the structure which attached | subjected the same code | symbol in each figure shows that it is the same structure, The description is abbreviate | omitted.

  An image compression apparatus, an image compression method, an image decompression apparatus, an image decompression method, a recording apparatus, and a recording method according to the present invention include an image forming apparatus that forms an image by an electrophotographic method such as a printer, a copier, a facsimile machine, and a multifunction machine, It can be applied to an image reading apparatus that reads an image such as a scanner and generates image data, a digital camera that generates image data, a computer that performs image processing of image data, storage of image data, and the like. As an example, a case where the present invention is applied to a color printer will be described below. In this case, as will be understood from the following description, the recording medium on which the image compression program according to the present invention is recorded, the recording medium on which the image decompression program is recorded, and the recording medium on which the compressed image data is recorded are used as storage elements of a color printer. Realized. The image compression program and the image decompression program according to the present invention are held in a storage element of a color printer and executed by a CPU (Central Processing Unit). The compressed image format according to the present invention is realized on a storage element of a color printer. The same applies when the present invention is applied to other image forming apparatuses, image reading apparatuses, digital cameras, computers and the like.

  FIG. 1 is a schematic sectional view mainly showing a mechanical configuration of a color printer in the embodiment. FIG. 2 is a block diagram mainly showing an electrical configuration of the color printer in the embodiment.

  1 and 2, the color printer CP includes a paper storage unit 10, a transfer unit 20, a fixing unit 30, a paper discharge unit 40, a paper conveyance path 50, a control unit 60, and an interface unit (hereinafter, referred to as “printing unit”). The sheet storage unit 10, the transfer unit 20, the fixing unit 30, the sheet conveyance path 50, the control unit 60, and the IF unit 70 are provided in the substantially box-shaped apparatus main body 1. The paper discharge unit 40 is provided at the top of the apparatus main body 1.

  The paper storage unit 10 stores paper P as an example of a transfer material used for printing processing, and feeds out the paper P under the control of the control unit 60. A predetermined number (one in this embodiment) of paper cassettes 11 is provided in the paper storage unit 10 so as to be detachable from the apparatus main body 1. At the upstream end of the paper cassette 11 (upper left of the paper cassette 11 in the example shown in FIG. 1), a pickup roller 12 that feeds the paper P from the paper bundle one by one is provided. The paper P fed out of the paper cassette 11 by driving the pickup roller 12 is fed to the paper transport path 50.

  Under the control of the control unit 60, the transfer unit 20 controls the sheet P that is fed out from the sheet bundle stored in the sheet storage unit 10 based on the image signal received by the IF unit 70 from another computer or the like. The image is transferred. The transfer unit 20 includes an image forming unit 21 that forms a toner image, and a transfer device 27 that transfers the toner image formed by the image forming unit 21 to a sheet P.

  The image forming unit 21 includes a yellow unit 21Y, a magenta unit 21M, a cyan unit 21C, and a black unit that are sequentially arranged in a substantially horizontal direction from the upstream side (the right side of the paper surface in FIG. 1) to the downstream side. 21K and an exposure unit 24 disposed at the lower position of each unit. Each of these units 21Y, 21M, 21C, and 21K has the same configuration, and is positioned and attached to each device in the apparatus main body 1 with a predetermined relative positional relationship. In the present specification, when referring generically, it is indicated by a reference symbol without a suffix, and when referring to an individual configuration, it is indicated by a reference symbol with a suffix.

  Each of these units 21Y, 21M, 21C, and 21K includes a photosensitive drum (image carrier) 22, a charger 23, a developing device 25, and a cleaning device 26. The photosensitive drum 22 is arranged in the front-rear direction. 1 is provided so as to be rotatable around a drum shaft extending in a direction (perpendicular to the paper surface of FIG. 1), and from the position directly below the photoconductive drum 22 along the peripheral surface of the photoconductive drum 22, A charger 23, a developing device 25, and a cleaning device 26 are arranged in the counterclockwise direction that is the rotational direction.

  The photosensitive drum 22 is for forming an electrostatic latent image and a toner image (visible image) according to the electrostatic latent image on the peripheral surface. The charger 23 forms a uniform charge on the peripheral surface of the photosensitive drum 22 rotating counterclockwise around the drum axis. For example, the peripheral surface abuts on the peripheral surface of the photosensitive drum 22. However, it is configured to include a charging roller that applies electric charges to the photosensitive drum 22 while being driven to rotate. The developing device 25 supplies toner to the peripheral surface of the photosensitive drum 22 to attach the toner to the portion where the electrostatic latent image is formed on the peripheral surface, and thereby the toner image is formed on the peripheral surface of the photosensitive drum 22. To form. In the present embodiment, in order to cope with color, yellow (Y) toner is stored in the developing device 25Y of the yellow unit 21Y, and magenta (M) toner is stored in the developing device 25M of the magenta unit 21M. The cyan (C) toner is accommodated in the developing device 25C of the cyan unit 21C, and the black (K) toner is accommodated in the developing device 25K of the black unit 21K. The cleaning device 26 is for removing the toner remaining on the peripheral surface of the photosensitive drum 22 after the transfer process and cleaning it. The peripheral surface of the photosensitive drum 22 cleaned by the cleaning device 26 is again directed to the charger 23 for the next image forming process.

  The exposure unit 24 irradiates the peripheral surface of the rotating photosensitive drum 22 between the charger 23 and the developing device 25 with a laser beam to which intensity is applied based on the image data, thereby the photosensitive drum. An electrostatic latent image is formed on the peripheral surface 22. The exposure unit 24 applies the laser beams corresponding to the colors yellow, magenta, cyan, and black to the photosensitive drums 22Y, 22M, 22C, and 22K in the units 21Y, 21M, 21C, and 21K in order to correspond to the colors. It is configured to irradiate. When the peripheral surface of the charged photoconductor drum 22 is irradiated with laser light, the charged portion of the irradiated portion is erased in accordance with the intensity of the laser light. An image is formed. The image data includes yellow, magenta, developed colors generated by the control unit 60 by performing image processing such as known color correction processing and screen processing on an image signal from an external device such as a computer received by the IF unit 70. Each image data (raster data) of cyan and black. In each image data, gradation data is assigned to each pixel as multi-value data.

  The transfer device 27 is a device for transferring the toner image formed on the peripheral surface of the photosensitive drum 22 onto the paper P, and includes an intermediate transfer belt 271, a primary transfer roller 272, a driving roller 273, a driven roller 274, and a second roller. A next transfer roller 275 is provided. The intermediate transfer belt 271 is endless, and is stretched to a position immediately above the units 21Y, 21M, 21C, and 21K by the primary transfer roller 272, the drive roller 273, and the driven roller 274, and the rotational driving force of the drive roller 273 Can be rotated clockwise.

  The primary transfer roller 272 is provided so as to correspond to the photosensitive drums 22Y, 22M, 22C, and 22K of the units 21Y, 21M, 21C, and 21K, and holds the intermediate transfer belt 271 from the photosensitive drum 22 to the intermediate transfer belt 271. Is arranged to prevent the floating. The secondary transfer roller 275 is disposed at a position facing the drive roller 273 on the outer peripheral surface of the intermediate transfer belt 271. The drive roller 273 is grounded. The primary transfer roller 272 is configured to apply a voltage having a polarity opposite to that of the toner as a primary transfer bias while the toner image in the image area is primarily transferred from the photosensitive drum 22 to the intermediate transfer belt 271. . The secondary transfer roller 275 is configured to apply a voltage having a polarity opposite to that of the toner as a secondary transfer bias while the toner image on the intermediate transfer belt 271 is secondarily transferred to the paper P. Yes. As described above, the color printer CP according to the present embodiment employs the indirect transfer method.

  An intermediate transfer belt cleaning device 276 is provided on the right side of the driven roller 274 in the drawing, and the toner remaining on the surface of the intermediate transfer belt 271 after the toner image is transferred to the paper P is intermediate. The intermediate transfer belt 271 removed by the transfer belt cleaning device 276 and cleaned thereby is supplied to the photosensitive drum 22.

  The fixing unit 30 performs a fixing process by heating on the toner image of the paper P subjected to the transfer process by the transfer unit 20 under the control of the control unit 60, and a heat roller having an energized heating element mounted therein. 31 and a pressure roller 32 which is opposed to the heat roller 31 and whose peripheral surfaces are arranged to face each other. Then, the paper P after the transfer process is composed of a heat roller 31 that is driven to rotate clockwise around the roller axis, and a pressure roller 32 that is driven to rotate counterclockwise around the roller axis. By passing through the nip portion between them, heat from the heat roller 31 is obtained and fixing processing is performed. The paper P subjected to the fixing process is discharged to the paper discharge unit 40 through the paper conveyance path 50.

  The paper discharge unit 40 discharges the paper P that has been subjected to the fixing process by the fixing unit 30 and stores the discharged paper P. The paper discharge unit 40 is formed by recessing the top of the apparatus main body 1, and a paper discharge tray 41 for receiving the discharged paper P is formed at the bottom of the concave recess.

  The sheet conveyance path 50 conveys the sheet P fed from the sheet storage unit 10 to the sheet discharge unit 40 via the transfer unit 20 and the fixing unit 30 under the control of the control unit 60.

  The control unit 60 is connected to the paper storage unit 10, the transfer unit 20, the fixing unit 30, the paper conveyance path 50, and the IF unit 70, and controls these units according to the function, thereby controlling each unit of the color printer CP. For example, a CPU (Central Processing Unit) 61, various programs executed by the CPU 61, data necessary for the execution, and the like are stored in advance, and a storage element 62 that serves as a so-called working memory of the CPU 61 and its peripheral circuits, etc. It is composed of a microcomputer equipped.

  The storage element 62 of the control unit 60 includes, for example, a ROM (Read Only Memory) that is a nonvolatile storage element, an EEPROM (Electrically Erasable Programmable Read Only Memory) that is a rewritable nonvolatile storage element, and a volatile storage element. And a RAM (Random Access Memory). The storage element 62 functionally includes an image storage unit 621 that stores image data, and a compressed image storage unit 622 that stores compressed image data (compressed image data). The compressed image storage unit 622 is associated with a tag information storage unit 6221 that stores tag information including a plurality of representative values and indexes associated with the plurality of representative values, and a plurality of pixels in the block. And an encoded image storage unit 6222 for storing encoded image data composed of a plurality of indexes into which the data is converted. The representative value is a value selected from a range of values that the gradation data can take. The index is a code indicating the representative value, and is also an identifier for identifying and specifying the representative value. Any code can be used, but a code expressed by a small number of bits is preferable from the viewpoint of reducing the data capacity of the index. In this embodiment, numbers are used as will be described later. The block is a small area divided from the image data to be compressed including a plurality of pixels, and includes a plurality of pixels. Of course, the number of pixels of the block is smaller than the number of pixels of the image data to be compressed.

  The CPU 61 of the control unit 60 executes a color correction process functionally by executing an image processing program for performing image processing, an image compression program for compressing image data, an image decompression program for decompressing compressed image data, and the like. And an image processing unit 611 that performs image processing such as screen processing, a compression unit 612 that compresses image data, and a decompression unit 613 that decompresses compressed image data. The compression unit 612 reads out image data for each block from the image data to be compressed, thereby selecting a plurality of representative values and a plurality of indexes as well as a block reading unit 6121 that divides the image data to be compressed into a plurality of blocks. The tag information generation unit 6122 for generating tag information and the pixel data in each block are converted into an index based on a plurality of representative values and pixel data. Thus, an encoding unit 6123 that generates encoded image data and a compressed image writing unit 6124 that stores the compressed image data of the block in the compressed image storage unit 622 are provided. The block reading unit 6121 corresponds to an example of a blocking unit in the claims. The decompressing unit 613 includes a compressed image reading unit 6131 that reads the compressed image data of the block from the compressed image storage unit 622, a decoding unit 6132 that converts the index into the representative value indicated by each index in the encoded image data, A block writing unit 6133 that writes the image data of the block converted into the representative value into a predetermined storage area in the image storage unit 621 so that the image data before compression (image data to be compressed) is reconstructed. .

  The IF unit 70 is connected to an external device such as a computer via a LAN (Local Area Network) or a USB (Universal Serial Bus) cable, and transmits various signals between the control unit 60 and an external device such as a computer. For example, a network interface (10 / 100Base-TX) or a USB interface is used.

  An outline of the image forming operation in the color printer CP having such a configuration will be described. First, after charging the photosensitive drum 22 by the charger 23, exposure is performed by the exposure unit 24, and the electrostatic latent image is transferred to the photosensitive member. It is formed on the surface of the drum 22. The electrostatic latent image is converted into a toner image by the developing device 25, and the toner image formed on the surface of the photosensitive drum 22 is transferred onto the intermediate transfer belt 271 by the transfer bias applied to the primary transfer roller 272. The Then, the residual toner remaining on the photosensitive drum 22 without being transferred to the intermediate transfer belt 271 is cleaned by the cleaning device 26 and stored in a collection bottle (not shown). Such exposure, development, and transfer operations are sequentially performed on the development colors of yellow, magenta, cyan, and black, and the toner images of the respective colors are superimposed on the surface of the intermediate transfer belt 271 so that the intermediate transfer belt. A full-color toner image is formed on 271.

  When the full-color toner image is formed on the intermediate transfer belt 271, the secondary transfer roller 275 is brought into contact with the intermediate transfer belt 271, and is conveyed from the sheet storage unit 10 to the transfer position by the sheet conveyance path 50 in time. The full color toner image formed on the intermediate transfer belt 271 is transferred onto the paper P by the secondary transfer bias applied to the secondary transfer roller 275. The full color toner image transferred to the paper P is fixed to the paper P by heating and pressurization by the fixing unit 30, and the paper P is discharged to the paper discharge unit 40. The toner remaining on the intermediate transfer belt 271 is cleaned by bringing the intermediate transfer belt cleaning device 276 of the intermediate transfer belt 271 into contact with the intermediate transfer belt 271 after the secondary transfer, and is stored in a collection bottle (not shown). Is done.

  Here, when the electrostatic latent image is formed on the peripheral surface of the photosensitive drum 22, the image data used by the exposure unit 24 to impart intensity to the laser light is generated as follows.

  FIG. 3 is a flowchart showing the compression operation in the color printer of the embodiment. FIG. 4 is a flowchart showing the decompression operation in the color printer of the embodiment. FIG. 5 is a diagram for explaining an operation of dividing image data into a plurality of blocks. Each rectangle in FIG. 5 represents a block, and an arrow line indicates a division order. FIG. 6 is a diagram for explaining compression and decompression operations in the color printer of the embodiment. 6A shows the image data of the block before compression, FIG. 6B shows the image data (encoded image data) of the block after compression, and FIG. 6C shows the image data of the block after decompression. Each of the rectangles in FIGS. 6A, 6B, and 6C represents a pixel, and the right side of FIG. 6B represents tag information including a representative value and an index assigned to the representative value. The numerical values in the rectangles in FIGS. 6A and 6C represent the gradation data of the pixel, and the numerical values in the left rectangle in FIG. 6B represent the index of the pixel. FIG. 7 is a diagram for explaining a storage state (compressed image format) of a representative value, an index, and encoded image data in a storage element in each block.

  First, an image signal from an external device such as an image reading device, a digital camera, or a computer is received by the IF unit 70, and image data is generated based on the image signal by the CPU 61 of the control unit 60, and the image data is stored as original image data. Stored in the unit 621. The original image data is image data generated based on an image signal from an external device, and is image data before image processing such as color correction processing or screen processing is performed for print output.

  In FIG. 3, when the original image data for one block or more is stored in the image storage unit 621, the block reading unit 6121 of the compression unit 612 reads the original image data for one block from the image storage unit 621 (S11). The reading of the original image data for one block is executed based on a predetermined rule set in advance. For example, as shown in FIG. 5, this reading is sequentially performed from one end of the leading end of the original image toward the other end, and when it reaches the other end, it returns to one end of the next stage. Reading in this order is performed from the leading edge to the trailing edge of the original image. An original image is an image represented by original image data. As a result, the original image data of the original image is divided into a plurality of blocks B1, B2, B3,..., Bn−1, Bn.

  Next, the tag information generation unit 6122 of the compression unit 612 selects a predetermined number of representative values from a range of values that can be taken by the data allocated to the pixels (S12). In the present embodiment, the data assigned to the pixels is gradation data representing gradation. The number of representative values to be selected is set as appropriate according to specifications and the like, but the compression rate decreases when the number of representative values is large, and the compression rate increases when the number of representative values is small.

  The plurality of representative values are selected from, for example, gradation data of each pixel in the compression target block. As will be described later, the gradation data of each pixel is replaced with a representative value in step S14. When the representative value is selected in this way, the pixel having the gradation data selected as the representative value is displayed in the gradation. Since the data is replaced with the representative value as the gradation data, the reversibility is improved. Further, for example, as the plurality of representative values, a plurality of representative values may be selected in descending order of the number of data having the same value among the data of each pixel in the block to be compressed. When the representative value is selected in this way, the number of pixels that can be replaced with the representative value increases according to the gradation data of the pixel, so that the reversibility is further improved. In the present embodiment, in order to further improve the reversibility, first, the tag information generation unit 6122 includes a plurality of pieces of gradation data having the same value among the gradation data of each pixel in the compression target block. Temporarily selecting a representative number of representative values (S121). Next, the tag information generation unit 6122 displays the gradation data of the pixels that were not selected as the plurality of representative values in this process S121, from the plurality of representative values temporarily selected in this process S121. The assigned representative value is corrected by an average value of the gradation data of the assigned pixel and the assigned representative value (S122). In the present embodiment, the representative value is selected in this way. When the representative value is selected in this way, the gradation data that has not been selected as the representative value can be replaced with a representative value having a closer value, thereby further improving the reversibility.

  For example, as shown in FIG. 6A, one pixel whose gradation data is 3, one pixel whose gradation data is 6, two pixels whose gradation data is 8, More specifically, in the case of a 4 × 4 square block composed of 4 pixels with data 67, 5 pixels with gradation data 153, and 3 pixels with gradation data 255. Specifically, processing S12 (processing S121, processing 122) will be described as follows. It should be noted that 8bpp gradation data is assigned to each pixel. For this reason, the range of values that the gradation data can take is an integer value of 0 to 255.

  If the gradation data are arranged in the order of the number of gradation data having the same value, 153, 67, 255, 8, 6, 3 are obtained. If, for example, only four representative values are selected according to the specification or the like, 153, 67, 255, and 8 are temporarily selected as a plurality of representative values in step S121. In the process S122, first, the gradation data 6 and 3 which are not selected in the process S121 are allocated to the closest representative value 8 among the temporarily selected 153, 67, 255 and 8. It is. Next, an average value 6 (≈ (8 × 2 + 6 × 1 + 3 × 1) / (2 + 1 + 1)) of the allocated gradation data 6 and 3 and the allocated representative value 8 is calculated. . Since the gradation data is an integer value, the decimal point is rounded off and the average value is also an integer value. Then, the representative value 8 is corrected by replacing the representative value 8 with the average value 6. By executing the processing S121 and the processing S122 in this way, representative values 6, 153, 67, and 255 are selected for the block with 16 pixels shown in FIG. 6A.

  Returning to FIG. 3, next, the tag information generation unit 6122 gives an index indicating the representative value to each of the plurality of representative values selected in the process S12 (S13).

  In the example shown in FIG. 6, as shown on the right side of FIG. 6B, indexes 0, 1, 2, and 3 are assigned to the representative values 6, 153, 67, and 255 selected in the process S12, respectively.

  Returning to FIG. 3, next, the encoding unit 6123 of the compression unit 612 determines the gradation data of each pixel in the block based on the plurality of representative values selected in the processing S12 and the gradation data of the pixel. Then, the gradation data of the pixel is converted into the index assigned in the process S13 (S14). More specifically, for example, for the gradation data of each pixel in the block, the encoding unit 6123 selects the representative value closest to the gradation data of the pixel from the plurality of representative values selected in the process S12. Then, the gradation data of the pixel is converted into the index of the selected representative value. As a result, the gradation data of each pixel in the block is converted into a representative value index. As a result, the encoded image is composed of a plurality of indexes corresponding to the plurality of pixels in the block and converted from the pixel gradation data. Data is generated.

  In the example shown in FIG. 6, as shown on the left side of FIG. 6B, an index of 0 is assigned to pixels whose gradation data is 3, 6 and 8, and an index of 0 is assigned to a pixel whose gradation data is 153 1 is assigned to the pixel whose gradation data is 67, and the index 2 is assigned to the pixel whose gradation data is 255. As a result, the gradation data of each pixel in the block is converted into an index, and the block shown in FIG. 6A becomes the encoded image data shown on the left side of FIG. 6B.

  Returning to FIG. 3, the compressed image writing unit 6124 of the compression unit 612 stores the compressed image data of the original image for one block including the representative value, the index, and the encoded image data in the compressed image storage of the storage element 62. The information is stored in the unit 622 (S15).

  More specifically, for example, as shown in FIG. 7, the compressed image storage unit 622 is set in a predetermined area in the memory area of the storage element 62, and the representative value and index and the encoded image data are in this order. Thus, the predetermined areas are stored in the order of memory addresses. As a result, the representative value and index and the encoded image data are stored in association with each other.

  Then, for example, by storing a representative value and an index indicating the representative value as a set, the index is stored in association with the representative value. In the example shown in FIG. 6B, 6015167722553 is stored. Further, for example, a plurality of representative values are first stored, and an index corresponding to the representative value is stored in the order in which the representative values are stored. In the example shown in FIG. 6B, it is stored as 6153672550123.

  Further, for example, the indices of the respective pixels are stored in the order of the memory addresses according to the order of the pixels, so that the respective indexes are stored in association with the respective pixels.

  Such processing S11 to S15 are sequentially performed on the original image data for each block, so that the original image data is sequentially compressed for each block, and the original compressed image data is sequentially converted for each block. The compressed images are stored in the compressed image storage unit 622 of the storage element 62 in the order of memory addresses.

  As a result, as shown in FIG. 7, the compressed image data of the original image of the block B1 is stored in the storage element 62 from the address a, the compressed image data of the original image of the block B2 is stored in the storage element 62 from the address b, and the block B3 The compressed image data of the original image is stored in the storage element 62 from the address c,..., And the compressed image data of the original image of the block Bn is stored in the storage element 62 from the address n. In each area storing the original compressed image data of each block, as described above, the representative value, the index, and the encoded image data are stored in the order of addresses. The area storing the representative value and index in the compressed image data of the original image of each block constitutes the tag information storage unit 6221, and the area storing the encoded image data in the compressed image data of the original image of each block is encoded. A converted image storage unit 6222 is configured. As described above, the storage element 62 includes a plurality of representative values, a plurality of indexes associated with the plurality of representative values, and encoded image data including a plurality of indexes respectively associated with the plurality of pixels. Has been.

  By operating in this way, the image signal from the external device is received by the IF unit 70, and the original image data generated based on this image signal by the CPU 61 of the control unit 60 is compressed for each block, and for each block. Are stored in the compressed image storage unit 622 in the order of memory addresses.

  In the example shown in FIG. 6, since the original image data before compression is 8 bpp, the block is a 4 × 4 square, the encoded image data is 2 bpp, and the number of representative values is 4, the compression rate is 0.75.

  When an electrostatic latent image is formed on the peripheral surface of the photosensitive drum 22, first, the compressed image reading unit 6131 of the decompressing unit 613 performs a compressed image for one block according to the block order as shown in FIG. Data is read from the compressed image storage unit 622 of the storage element 62 (S21).

  Next, the decoding unit 6132 of the decompression unit 613 replaces the index associated with the pixel for each pixel of the encoded image data with a representative value indicated by the index, thereby compressing the compressed image for one block. The data is decrypted (S22). As a result, the compressed image data for one block is decompressed to become image data (original image data) for one block.

  In the example illustrated in FIG. 6, as illustrated in FIG. 6C, a pixel having an index of 0 is assigned a representative value of 6 as its gradation data, and a pixel having an index of 1 is represented as its gradation data. A pixel with a representative value 153 and an index of 2 is assigned a representative value of 67 as its gradation data, and a pixel with an index of 3 has a representative value of 255 as its gradation data. Is allocated. As a result, the index of each pixel in the block is converted into a representative value, and the encoded image data shown on the left side of FIG. 6B becomes the image data shown in FIG. 6C.

  Returning to FIG. 4, the block writing unit 6133 of the decompression unit 613 develops the image data (original image data) for one decompressed image data used by the exposure unit 24 to add intensity to the laser beam. Is written in the image storage unit 621 in accordance with the block order (S23).

  Then, the control unit 60 gives the intensity of the laser light emitted by the exposure unit 24 using the original image data written in the image storage unit 621, and the exposure unit 24 applies electrostatic latent image to the circumferential surface of the photosensitive drum 22. Form an image.

  Here, after the exposure unit 24 scans the laser beam in the drum axis direction of the photosensitive drum 22 to form an electrostatic latent image for one line, the photosensitive drum 22 rotates by one line, and the exposure unit 24 forms an electrostatic latent image for the next one line. As a result, an electrostatic latent image is formed on the peripheral surface of the photosensitive drum 22. For this reason, it is not necessary to decompress all the blocks at once and develop them in the image storage unit 621. For example, the blocks of original image data required for the exposure unit 24 to form an electrostatic latent image for one line. You just need to thaw. Therefore, the storage capacity of the image storage unit 621 can be reduced.

  FIG. 8 is a diagram for explaining blocks in the case of a line drawing and an image drawing. FIG. 8A shows an example of a block in the case of a line drawing, and FIGS. 8B and 8C show an example of a block in the case of an image drawing.

  The gradation data of the line drawing is generally composed of two values, for example, a value of 0 corresponding to the ground of the document and a value of 255 corresponding to the line portion. For this reason, as shown in FIG. 8A, the values that the gradation data of each pixel in one block can take are binary values of 0 and 255. Therefore, if the block is a 4 × 4 square, the number of representative values is 2, and the image data to be compressed is 1200 dpi and 8 bpp, the image data is compressed by the above-described processing S11 to processing S15. The image data becomes 1 bpp and is compressed at a compression rate of 0.25 while maintaining 1200 dpi. In addition, the gradation data of the pixel is replaced with a representative value as the gradation data, so that it is reversibly compressed. For this reason, a portion with a high resolution and a small number of gradations (number of colors) is compressed by storing the resolution by executing the above-described processing S11 to S15.

  On the other hand, in the case of an image, for example, at 300 dpi, 16 pixels of 4 × 4 in the case of 1200 dpi can be regarded as one pixel. For this reason, as shown in FIG. 8B, the gradation data of each pixel in one block can be, for example, one value of 65, or as shown in FIG. 8C, for each pixel in one block. Since the values that the gradation data can take are, for example, the binary values 65 and 78, the number of values that the gradation data of each pixel can take in one block is not very large. Therefore, when the block is a 4 × 4 square, the number of representative values is 2, and the image data to be compressed is 300 dpi and 8 bpp, the image data is compressed by the above-described processing S11 to processing S15. The image data becomes 1 bpp and is compressed at a compression rate of 0.25 while maintaining 300 dpi. Moreover, since the gradation data of the pixel is highly likely to be replaced with the representative value as the gradation data, it can be compressed with high reversibility (in the example shown in FIGS. 8B and C, it is reversibly compressed). For this reason, the portion having a large number of gradations (number of colors) is compressed by storing the gradation (number of colors) by executing the above-described processing S11 to S15.

  By compressing in the above-described processing S11 to processing S15 as described above, the image data of the compression target image can be compressed while appropriately storing the gradation and the resolution according to the characteristics of the compression target image. In particular, the compression and decompression in the present embodiment is suitable for a printer that prints a line image or an image image.

  Further, in the above-described embodiment, each size in each block is equal to 4 × 4, and the number of representative values in each block is equal to four. For this reason, the data capacities in the compressed image data of each block are equal to each other. Therefore, the compressed image data of each block is stored at equal intervals on the memory address in the compressed image storage unit 622 of the storage element 62 as shown in FIG. 7, so that the compressed image data of an arbitrary block can be easily read out. be able to. Therefore, the compressed image data of an arbitrary block can be decompressed.

  In the above-described embodiment, the block is a square, but may be any shape as long as all image data can be divided into blocks. For example, the block may be a triangle, a diamond, a hexagon, or the like.

  In the above-described embodiment, as shown in FIG. 7, the tag information and the encoded image data are collected for each block and stored in the compressed image storage unit 622. However, the tag information for each block is collected. While being stored in the compressed image storage unit 622, the encoded image data of each block may be collected and stored in the compressed image storage unit 622. Even in such a case, the tag information of each block and the encoded image data of each block can be associated with each other by, for example, storing them in the compressed image storage unit 622 in the memory address order according to the block order. .

  Further, in the above-described embodiment, the compressed image data is stored in the storage element 62. For example, a flexible disk, a CD-R (Compact Disc Recordable), a DVD-RW (Digital Versatile Disc Read Write), a USB memory, etc. May be recorded on the other recording medium.

  In the above-described embodiment, a program such as an image compression program or an image decompression program executed by the control unit 60 may be supplied through a recording medium such as a ROM or a CD-ROM (Compact Disc Read Only Memory). It is also possible to supply through a transmission medium such as The transmission medium is not limited to a wired transmission medium, and may be a wireless transmission medium. The transmission medium includes not only a communication line but also a relay device that relays the communication line, such as a router.

  When the program is supplied through the ROM, the ROM in which the program is recorded is mounted on the control unit 60 and can be used for execution by the control unit 60. When the program is supplied through a CD-ROM, the controller 60 connects the CD-ROM reader and temporarily stores the program in, for example, an EEPROM or a hard disk device (HDD, Hard Disk Drive). Can be used for execution. When the program is supplied through a transmission medium, the program received via the network can be stored in, for example, an EEPROM or an HDD, and can be used for execution by the control unit 60.

  In order to express the present invention, the present invention has been properly and fully described through the embodiments with reference to the drawings. However, those skilled in the art can easily change and / or improve the above-described embodiments. It should be recognized that this is possible. Accordingly, unless the modifications or improvements implemented by those skilled in the art are at a level that departs from the scope of the claims recited in the claims, the modifications or improvements are not limited to the scope of the claims. To be construed as inclusive.

1 is a schematic cross-sectional view mainly showing a mechanical configuration of a color printer in an embodiment. 1 is a block diagram mainly showing an electrical configuration of a color printer in an embodiment. FIG. 3 is a flowchart illustrating a compression operation in the color printer of the embodiment. 6 is a flowchart illustrating an operation of decompression in the color printer of the embodiment. It is a figure for demonstrating the operation | movement which divides | segments image data into a some block. It is a figure for demonstrating the operation | movement of compression and decompression | decompression in the color printer of embodiment. It is a figure for demonstrating the storage state (compressed image format) to the storage element of the representative value in each block, an index, and encoding image data. It is a figure for demonstrating the block in the case of a line drawing and an image drawing.

Explanation of symbols

CP color printer 60 controller 61 CPU
62 storage element 70 interface unit 611 image processing unit 612 compression unit 613 decompression unit 621 image storage unit 622 compressed image storage unit 6121 block reading unit 6122 tag information generation unit 6123 encoding unit 6124 compressed image writing unit 6131 compressed image reading unit 6132 decoding Conversion unit 6133 block writing unit 6221 tag information storage unit 6222 encoded image storage unit

Claims (14)

A blocking unit that divides image data including a plurality of pixels to which multi-value data is allocated into a plurality of blocks each including a plurality of pixels;
A tag information generation unit that selects a plurality of representative values from a range of values that can be taken by the data, and assigns an index indicating the representative value to each of the plurality of representative values;
For each pixel data in the block, an encoding unit that converts the pixel data into the index based on the plurality of representative values and the pixel data,
The tag information generation unit selects a plurality of representative values in descending order of the number of data having the same value among the data of each pixel in the block to be compressed, and sets an index indicating the representative value as the plurality of representative values. image compression apparatus characterized that you grant, respectively. The tag information generation unit selects a plurality of representative values in descending order of the number of data having the same value among the data of each pixel in the block to be compressed, and data of the pixels not selected as the plurality of representative values Is assigned to the nearest representative value from among the plurality of representative values, and the assigned representative value is corrected by an average value of the data of the assigned pixels and the assigned representative value, and the representative value is indicated. The image compression apparatus according to claim 1 , wherein an index is assigned to each of the plurality of representative values. The encoding unit selects a representative value closest to the pixel data from the plurality of representative values for the data of each pixel in the block, and converts the pixel data to an index of the selected representative value. The image compression apparatus according to claim 1, wherein the image compression apparatus is an image compression apparatus. The equal respective sizes of a plurality of blocks, and the image compression apparatus according to any one of claims 1 to 3, wherein the number of the representative value of the plurality of blocks are equal. Dividing image data including a plurality of pixels to which multi-valued data is assigned into a plurality of blocks each including a plurality of pixels;
Selecting a plurality of representative values from a range of values that the data can take;
Providing each of the plurality of representative values with an index indicating the representative value;
Converting the pixel data into the index based on the plurality of representative values and the pixel data for each pixel data in the block, and
Step, among the data of each pixel in the block to be compressed, the image compression method comprising that you select a plurality of representative values in the order number of the data is greater equal a value for selecting a plurality of representative values. In an image compression program to be executed by a computer,
Dividing image data including a plurality of pixels to which multi-valued data is assigned into a plurality of blocks each including a plurality of pixels;
Selecting a plurality of representative values from a range of values that the data can take;
Providing each of the plurality of representative values with an index indicating the representative value;
Converting the pixel data into the index based on the plurality of representative values and the pixel data for each pixel data in the block, and
Step, among the data of each pixel in the block to be compressed, the image compression program characterized that you select a plurality of representative values in the order number of the data is greater equal a value for selecting a plurality of representative values. In a computer-readable recording medium on which an image compression program to be executed by a computer is recorded,
The image compression program is:
Dividing image data including a plurality of pixels to which multi-valued data is assigned into a plurality of blocks each including a plurality of pixels;
Selecting a plurality of representative values from a range of values that the data can take;
Providing each of the plurality of representative values with an index indicating the representative value;
Converting the pixel data into the index based on the plurality of representative values and the pixel data for each pixel data in the block, and
Wherein the plurality of steps of selecting a representative value among the data of each pixel in a block of compressed recording medium characterized that you select a plurality of representative values in the order number of the data is greater equal value. Image data to be compressed including a plurality of pixels to which multi-valued data is assigned is divided into a plurality of blocks each consisting of a plurality of pixels, and for each of the plurality of blocks, a range of values that the data can take A plurality of representative values selected from the above, each of the pixel values in the block to be compressed corresponding to the plurality of representative values selected in descending order of the number of data having the same value A recording apparatus for recording on a recording medium a plurality of indexes attached and indicating the representative value, and encoded image data made up of a plurality of indexes associated with the plurality of pixels and converted from the data of the pixels. Image data to be compressed including a plurality of pixels to which multi-valued data is assigned is divided into a plurality of blocks each consisting of a plurality of pixels, and for each of the plurality of blocks, a range of values that the data can take A plurality of representative values selected from the above, each of the pixel values in the block to be compressed corresponding to the plurality of representative values selected in descending order of the number of data having the same value A recording method for recording, on a recording medium, a plurality of indexes attached and indicating the representative value and encoded image data composed of a plurality of indexes corresponding to the plurality of pixels and converted from the data of the pixels. Image data to be compressed including a plurality of pixels to which multi-valued data is assigned is divided into a plurality of blocks each consisting of a plurality of pixels, and for each of the plurality of blocks, a range of values that the data can take A plurality of representative values selected from the above, each of the pixel values in the block to be compressed corresponding to the plurality of representative values selected in descending order of the number of data having the same value And compressed image data including a plurality of indexes indicating the representative value and encoded image data including a plurality of indexes corresponding to the plurality of pixels and converted from the pixel data, respectively. A computer-readable recording medium. Image data to be compressed including a plurality of pixels to which multi-valued data is assigned is divided into a plurality of blocks each consisting of a plurality of pixels, and for each of the plurality of blocks, a range of values that the data can take A plurality of representative values selected from the above, each of the pixel values in the block to be compressed corresponding to the plurality of representative values selected in descending order of the number of data having the same value And decompressing compressed image data including a plurality of indexes indicating the representative value and encoded image data including a plurality of indexes corresponding to the plurality of pixels and converted from the pixel data. In the image decompression device,
An image decompression apparatus comprising: a decoding unit that converts each index in the encoded image data into a representative value indicated by the index. Image data to be compressed including a plurality of pixels to which multi-valued data is assigned is divided into a plurality of blocks each consisting of a plurality of pixels, and for each of the plurality of blocks, a range of values that the data can take A plurality of representative values selected from the above, each of the pixel values in the block to be compressed corresponding to the plurality of representative values selected in descending order of the number of data having the same value And decompressing compressed image data including a plurality of indexes indicating the representative value and encoded image data including a plurality of indexes corresponding to the plurality of pixels and converted from the pixel data. In the image decompression method,
An image decompression method comprising: for each index in the encoded image data, converting the index into a representative value indicated by the index. Image data to be compressed including a plurality of pixels to which multi-valued data is assigned is divided into a plurality of blocks each consisting of a plurality of pixels, and for each of the plurality of blocks, a range of values that the data can take A plurality of representative values selected from the above, each of the pixel values in the block to be compressed corresponding to the plurality of representative values selected in descending order of the number of data having the same value And decompressing compressed image data including a plurality of indexes indicating the representative value and encoded image data including a plurality of indexes corresponding to the plurality of pixels and converted from the pixel data. In an image decompression program for causing a computer to execute image decompression processing,
An image decompression program comprising: converting each index into a representative value indicated by the index for each index in the encoded image data. Image data to be compressed including a plurality of pixels to which multi-valued data is assigned is divided into a plurality of blocks each consisting of a plurality of pixels, and for each of the plurality of blocks, a range of values that the data can take A plurality of representative values selected from the above, each of the pixel values in the block to be compressed corresponding to the plurality of representative values selected in descending order of the number of data having the same value And decompressing compressed image data including a plurality of indexes indicating the representative value and encoded image data including a plurality of indexes corresponding to the plurality of pixels and converted from the pixel data. In a computer-readable recording medium on which an image decompression program for causing a computer to execute image decompression processing is recorded ,
A recording medium comprising the step of converting the index into a representative value indicated by the index for each index in the encoded image data.

Images