JP2016127346A - Image processing apparatus, image forming apparatus, method for controlling image processing apparatus, and control program of image processing apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image processing apparatus capable of maintaining gradation of image data and performing position correction even with a simple hardware configuration.SOLUTION: The image processing apparatus performs compression processing of an image of a processing object, and generates compressed data B12, B13, B14 of each input image B11 having a prescribed first size constituting the image of the processing object. The image processing apparatus determines whether to be a high resolution part or a low resolution part in each area of the input image B11. The image processing apparatus discriminates respective gradation of pixels belonging to high resolution parts, and determines the maximum gradation and the minimum gradation in the input image. The image processing apparatus patterns each of the high resolution parts to a prescribed shape pattern on the basis of the gradation and arrangement states of pixels included in the area. The image processing apparatus generates compressed data B12, B13, B14 about the input image B11 on the basis of information corresponding to the maximum gradation and the minimum gradation, and a code corresponding to the shape pattern.SELECTED DRAWING: Figure 5

Description

  The present invention relates to an image processing apparatus, an image forming apparatus, a control method for the image processing apparatus, and a control program for the image processing apparatus, and more particularly to an image processing apparatus, an image forming apparatus, and an image processing apparatus that perform position correction by compressing image data. The present invention relates to a control method for a processing apparatus and a control program for an image processing apparatus.

  Image data in image forming apparatuses such as MFPs (Multi Function Peripherals), facsimile machines, copiers, and printers having a scanner function, a facsimile function, a copying function, a printer function, a data communication function, and a server function An image processing apparatus that performs this correction processing is used. The image processing apparatus corrects the position of the image data based on the state of the image forming apparatus in order to stabilize the output of the image forming apparatus. As the position correction, for example, skew correction or print position deviation correction is performed.

  Image data correction processing is performed before screen processing. At this time, image data having a high gradation such as 10 bits is used. If position correction is to be performed on such high gradation image data, there is a problem that a large capacity memory is required. On the other hand, for example, when a page memory using a DDR (Double Data Rate) system is used, a memory capacity can be secured. However, there is a problem that a very large transfer bandwidth is required. Therefore, the position correction of the image data is performed in a state where the high gradation image data is compressed and the data amount is reduced.

  Japanese Patent Application Laid-Open Publication No. 2004-228561 discloses a method for compressing image data when performing position correction by storing screen-processed data in a page memory in an image forming apparatus. In this compression method, position correction is performed by address control.

  Patent Document 2 below discloses an image processing apparatus that divides one image into blocks, performs fixed-length compression, and performs position correction.

  Patent Document 3 below describes that in an image processing apparatus that performs contour processing, gradation is quantized by performing BTC compression, degeneration compression, or the like in units of blocks. The compression method is changed depending on whether or not the attribute data attached to the image data is a photographic image.

JP 2008-148291 A JP 2000-280525 A JP 2011-24162 A

  By the way, in the method as described in Patent Document 1, if position correction is performed in a state where screen processing is performed, the screen shape may be broken. If the screen shape is broken, streaks or unevenness may occur and image quality may deteriorate.

  In addition, in the methods described in Patent Document 2 and Patent Document 3, the gradation of the image is quantized. Then, there is a problem that the significance of correcting high gradation image data is diminished.

  The present invention has been made to solve such a problem, and can maintain the gradation of image data, and can perform position correction with a simple hardware configuration and image formation. It is an object of the present invention to provide an image processing apparatus, an image processing apparatus control method, and an image processing apparatus control program.

  In order to achieve the above object, according to one aspect of the present invention, image processing is performed for performing compression processing on an image to be processed and generating compressed data for each input image having a predetermined first size constituting the image to be processed. A first determination unit configured to determine, for each predetermined second size region of the input image, whether the region is a high-resolution part or a low-resolution part that is not a high-resolution part; Second determination means for determining the gradation of each pixel belonging to the region determined to be the high resolution portion by the determination means, and determining the maximum gradation and the minimum gradation in the input image; Patterning means for patterning each area determined to be a high-resolution part by one determination means into a predetermined shape pattern based on the gradation and arrangement state of pixels included in the area; and a second determination As determined by the means Generating means for generating compressed data for the input image based on the information corresponding to the gradation and the minimum gradation and the code corresponding to the shape pattern patterned by the patterning means. The converting means includes a pixel in the area determined to be a high resolution portion by the first determining means, a pixel in the first section that refers to the maximum gradation, and a pixel in the second section that refers to the minimum gradation. Divide the pixel into any one of the pixels of the third division that refers to the gradation of the pixel and the area determined to be the low-resolution portion around the pixel, and pattern the pixel based on the arrangement state of the pixel of each division I do.

  Preferably, the generation unit calculates an average value obtained by averaging the gradations of pixels included in the region determined by the first determination unit as the low resolution portion, and sets the calculated average value to the calculated average value. Based on this, compressed data is generated.

  Preferably, when the generation unit includes at least one of a pixel in the first section and a pixel in the second section with respect to the region determined to be the high resolution portion by the first determination unit, the generation unit A code reflecting the gradation is included in the compressed data.

  Preferably, the image processing apparatus further includes a decompression unit that decodes an image to be processed based on the compressed data generated by the generation unit, and the decompression unit includes, for each input image, an area corresponding to the low resolution portion. The gradation of the pixel is determined as the gradation corresponding to the code included in the compressed data, and the shape pattern corresponding to the code included in the compressed data, the maximum gradation, and the minimum The gradation of each pixel is determined based on the information corresponding to the gradation and the gradation of the low resolution portion.

  Preferably, the image processing apparatus further includes a position correction unit that performs a position correction process using the compressed data generated by the generation unit, and the decompression unit decodes the compressed data after the position correction unit is performed. Do.

  According to another aspect of the present invention, an image forming apparatus includes any of the image processing apparatuses described above and an image forming unit that forms an image on a sheet based on an image processed by the image processing apparatus.

  According to still another aspect of the present invention, a method of controlling an image processing apparatus that performs compression processing on an image to be processed and generates compressed data for each input image having a predetermined first size constituting the image to be processed A first determination step for determining, for each predetermined second size region of the input image, whether the region is a high-resolution part or a low-resolution part that is not a high-resolution part, and a first determination A second determination step of determining a gradation of each pixel belonging to the region determined to be a high-resolution part by the step, and determining a maximum gradation and a minimum gradation in the input image; A patterning step of patterning each of the regions determined to be high-resolution portions by the determination step into a predetermined shape pattern based on the gradation and arrangement state of the pixels included in the region; and a second determination step A generation step for generating compressed data for the input image based on the information corresponding to the maximum gradation and the minimum gradation determined more and the code corresponding to the shape pattern patterned by the patterning step And the patterning step refers to the pixels in the region determined to be the high resolution portion in the first determination step, the pixels in the first section that refers to the maximum gradation, and the minimum gradation. The pixel is divided into any one of the second division pixel and the third division pixel that refers to the gradation of the area determined to be the low resolution portion around the second division pixel, and the arrangement state of the pixels of each division Patterning is performed based on

  According to still another aspect of the present invention, a control program for an image processing device that performs compression processing on an image to be processed and generates compressed data for each input image having a predetermined first size constituting the image to be processed A first determination step for determining, for each predetermined second size region of the input image, whether the region is a high-resolution part or a low-resolution part that is not a high-resolution part, and a first determination A second determination step of determining a gradation of each pixel belonging to the region determined to be a high-resolution part by the step, and determining a maximum gradation and a minimum gradation in the input image; A patterning step for patterning each of the regions determined to be a high-resolution portion by the determination step into a predetermined shape pattern based on the gradation and arrangement state of the pixels included in the region; and a second determination step Compressed data for the input image is generated based on information corresponding to the maximum gradation and the minimum gradation determined by the mapping, and a code corresponding to the shape pattern patterned by the patterning step. And the patterning step includes a pixel in a region determined to be a high-resolution part in the first determination step, a pixel in the first section that refers to the maximum gradation, and a minimum gradation. The pixel of the second section to be referred to and the pixel of the third section to refer to the gradation of the area determined to be the low resolution portion in the vicinity thereof are divided into pixels of each section Patterning is performed based on the arrangement state.

  According to these inventions, compressed data for the input image is generated based on the information corresponding to the maximum gradation and the minimum gradation and the code corresponding to the shape pattern patterned by the patterning step. The Therefore, an image processing apparatus, an image forming apparatus, a control method for the image processing apparatus, and a control program for the image processing apparatus capable of maintaining the gradation of the image data and performing position correction with a simple hardware configuration. Can be provided.

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an example of an embodiment of the present invention. 2 is a functional block diagram of the image forming apparatus. FIG. 6 is a flowchart illustrating a processing procedure of image forming processing performed in the image forming apparatus. It is a figure explaining the structure of an image process part. It is a figure explaining the compression compression data. It is a figure explaining compression processing. It is a figure which shows an example of the encoding pattern for high resolution parts. It is a figure which shows an example of a MAX / MIN encoding pattern. It is a 1st flowchart which shows a compression process. It is a 2nd flowchart which shows a compression process. It is a 1st flowchart which shows a high resolution part encoding process. It is a 2nd flowchart which shows a high resolution part encoding process. It is a 3rd flowchart which shows a high resolution part encoding process. It is a figure explaining the 1st example of a process in case there are four types of pixels which refer to a gradation from the surrounding low resolution part in one block. It is a figure explaining the 2nd example of a process in case there are four types of pixels which refer to a gradation from the surrounding low-resolution part in one block. It is a figure explaining restoration | restoration of the pixel which refers a gradation from the surrounding low resolution part. It is a 1st figure explaining the specific example of a compression process. It is a 2nd figure explaining the specific example of a compression process. It is a 3rd figure explaining the specific example of a compression process.

  Hereinafter, an image forming apparatus including an image processing apparatus according to an embodiment of the present invention will be described.

  The image forming apparatus is an MFP (Multi Function Peripheral) having a scanner function, a copying function, a printer function, a facsimile function, a data communication function, and a server function. The scanner function is a function for reading an image of a set original and storing it in an HDD (Hard Disk Drive) or the like. The copying function is a function of printing (printing) it on paper or the like. The function as a printer is a function for printing on a sheet based on an instruction received from an external terminal such as a PC. The facsimile function is a function for receiving facsimile data from an external facsimile machine or the like and storing it in an HDD or the like. The data communication function is a function for transmitting / receiving data to / from a connected external device. The server function is a function that allows a plurality of users to share data stored in the HDD or the like.

  The image forming apparatus performs image processing on an image to be printed on paper when executing a copying function, a function as a printer, and a facsimile function. That is, the image forming apparatus functions as an image processing apparatus.

  [Embodiment]

  FIG. 1 is a diagram showing a schematic configuration of an image forming apparatus according to an example of an embodiment of the present invention.

  As shown in FIG. 1, an image forming apparatus (an example of an image processing apparatus) 1 includes a main body 10 and an image reading device 40. The main body 10 forms an image on a sheet. The image reading device 40 reads an image on a sheet on which an image is formed. Hereinafter, an image generated for image formation by the main body 10 may be referred to as a first image. An image generated by reading an image on a sheet by the image reading device 40 may be referred to as a second image.

  Between the main body 10 and the image reading device 40, a transport unit 10a that transports paper from the main body 10 to the image reading device 40 is disposed.

  The main body 10 is provided with an image forming unit 20 and a scanner unit 31. A transport unit 26 is provided inside the main body 10. The transport unit 26 transports the paper fed from the paper feed tray 25 to the image forming unit 20 along the paper transport path. The transport unit 26 includes a plurality of transport rollers 26a. The transport roller 26a is provided at a plurality of locations in the paper transport path. The conveyance roller 26a includes a registration roller 26b and a paper discharge roller 26c.

  FIG. 2 is a functional block diagram of the image forming apparatus.

  In FIG. 2, the main configurations of the main body 10 and the image reading device 40 are shown for each function.

  As shown in FIG. 2, the main body 10 includes a control unit 11, a storage unit 12, an operation unit 13, a display unit 14, a communication unit 15, an image generation unit 30, an image processing unit 17, an image forming unit 20, and a history storage unit. 19 is provided. The main body 10 is connected to an external device 50 on the network. The main body 10 can communicate with the external device 50 through the communication unit 15.

  The control unit 11 reads the control program 12 a stored in the storage unit 12. The control unit 11 controls each unit of the main body 10 by executing the read control program 12a. The control unit 11 can be configured by a CPU (Central Processing Unit), a RAM (Random Access Memory), and the like.

  The control unit 11 executes a print job, a copy job, a scan job, and the like. For example, when executing a print job or a copy job, the control unit 11 causes the image processing unit 17 to perform image processing on the image generated by the image generation unit 30. The control unit 11 causes the image forming unit 20 to form an image on a sheet according to the gradation value of each pixel of the image after image processing.

  The storage unit 12 stores a control program 12a, data used when the control program 12a is executed, and the like. These control programs 12a and information can be read by the control unit 11.

  The storage unit 12 can store attribute information, a second image, and the like. The attribute information is generated by the image generation unit 30, for example. The second image is generated by the image reading device 40.

  As the storage unit 12, a large-capacity memory such as a hard disk drive can be used.

  As shown in FIG. 1, the operation unit 13 and the display unit 14 are provided as a user interface of the main body 10.

  The operation unit 13 generates an operation signal corresponding to a user operation. The operation unit 13 outputs the generated operation signal to the control unit 11. Examples of the operation unit 13 include a key and a touch panel. The touch panel is configured integrally with the display unit 14.

  The display unit 14 displays an operation screen or the like according to instructions from the control unit 11. As the display unit 14, an LCD (Liquid Crystal Display), an OELD (Organic Electro Luminescence Display), or the like can be used.

  As shown in FIG. 2, the communication unit 15 communicates with an external device 50 on the network. The external device 50 is, for example, a user terminal, a server, or another image forming apparatus.

  The communication unit 15 receives data from the external device 50 that is a user terminal, for example, via a network. At the time of execution of a print job, the communication unit 15 receives PDL data described in a page description language (PDL: Page Description Language). Further, the communication unit 15 can transmit a management image for history management to the external device 50. The management image or the like is generated in the history storage unit 19.

  The image generation unit 30 generates a first image when executing a print job. The image generation unit 30 rasterizes the PDL data received by the communication unit 15 and generates a first image. The first image is a bitmap format image having a gradation value for each pixel. The image generation unit 30 generates a first image for each color of C (cyan), M (magenta), Y (yellow), and K (black). The gradation value is a data value representing the density of the image. For example, an 8-bit data value represents the gradation of gradation from 0 to 255.

  The image generation unit 30 generates attribute information indicating the attribute of each pixel of the first image when generating the first image. For example, the image generation unit 30 determines the attribute of each pixel drawn according to the character code described in the PDL data as a character (Text). The attribute of each pixel of the image such as kana, alphabet, number, etc. is determined as a character. The image generation unit 30 determines the attribute of each pixel drawn according to the description of the vector format (DXF, SVG, WMF, etc.) as a graphic (Graphics). The attribute of each pixel of the image, such as ruled lines, polygons, and circles, is determined as a figure. Further, the image generation unit 30 determines the attribute of an image such as a photograph drawn by a file such as JPEG as a photograph.

  As shown in FIG. 1, the image generation unit 30 includes a scanner unit 31 used for a copying function. That is, the image generation unit 30 reads an image of a document set by the user with the scanner unit 31 when executing a copy job or a scan job. The image generation unit 30 acquires images of each color of R (red), G (green), and B (blue) by reading with the scanner unit 31. The image generation unit 30 can also generate an image of each color of C, M, Y, and K by performing color conversion on the image of each color.

  The image processing unit 17 performs image processing on the first image generated by the image generation unit 30. Image processing includes, for example, gradation processing and halftone processing.

  The gradation process is a process for converting the gradation value of each pixel of the image into a corrected gradation value. The correction is performed so that the density characteristic of the image formed on the paper matches the target density characteristic.

  The halftone processing is, for example, error diffusion processing, screen processing using a systematic dither method, or the like.

  The image forming unit 20 forms an image having a plurality of colors on a sheet according to the gradation value of each pixel of the first image subjected to image processing by the image processing unit 17 when executing a print job or a copy job. .

  As shown in FIG. 1, the image forming unit 20 includes four writing units 21 (21Y, 21M, 21C, and 21K), an intermediate transfer belt 23a, a secondary transfer roller 23b, a fixing device 24, and a paper feed tray 25. ing. Each writing unit 21 is arranged in series along the belt surface of the intermediate transfer belt 23a. The intermediate transfer belt 23a is wound and rotated by a plurality of rollers. One of the plurality of rollers constitutes a secondary transfer roller 23b.

  The image forming unit 20 includes a reversing mechanism 27 in addition to a transport unit 26 that transports paper from the paper feed tray 25. The transport unit 26 includes transport rollers 26a provided at a plurality of locations on the paper transport path. The paper feed tray 25 accommodates paper. The transport unit 26 transports paper from the paper feed tray 25 by a plurality of transport rollers 26a. A secondary transfer roller 23b and a fixing device 24 are disposed on the sheet conveyance path.

  The four writing units 21C, 21M, 21Y, and 21K form images of C, M, Y, and K colors, respectively. The configuration of each writing unit 21 is the same. That is, the writing unit 21 includes an exposure unit 22a, a photoreceptor 22b, a development unit 22c, a charging unit 22d, and a cleaning unit 22e.

  Each writing unit 21 forms an image of each color as follows. That is, the charging unit 22d applies a voltage to the photoconductor 22b to charge it. The exposure unit 22a emits a laser beam according to the gradation value of each pixel of each color C, M, Y, and K image to expose the photoconductor 22b. The developing unit 22c supplies a color material such as toner to the photoconductor 22b and develops the electrostatic latent image formed on the photoconductor 22b. Then, an image of each color is formed on the photoconductor 22b of each writing unit 21.

  The image on each photoconductor 22b is sequentially transferred onto the intermediate transfer belt 23a, and an image having a plurality of colors is formed on the intermediate transfer belt 23a. After the transfer of the image to the intermediate transfer belt 23a, each writing unit 21 removes the color material remaining on the photoreceptor 22b by the cleaning unit 22e.

  Paper is fed by the paper feed tray 25. The paper is transported along the paper transport path by the transport unit 26. The secondary transfer roller 23b transfers an image composed of a plurality of colors on the intermediate transfer belt 23a onto a sheet. The sheet is conveyed to the fixing device 24. The fixing device 24 heats and pressurizes the paper. As a result, the image is fixed on the sheet. Thereafter, the sheet is sent to the transport unit 10a by the discharge roller 26c.

  When images are formed on both sides of the paper, the paper is conveyed to the reversing mechanism 27 after the image is fixed. The reversing mechanism 27 includes a conveyance roller 27a and the like. The reversing mechanism 27 reverses the sheet surface by the conveying roller 27a and conveys the sheet to the secondary transfer roller 23b again. As a result, an image is formed on the opposite side of the sheet.

  A transport unit 28 is provided in the transport unit 10a. The transport unit 28 includes transport rollers 28a disposed at a plurality of locations on the paper transport path. The paper sent to the transport unit 10 a is transported by the transport unit 28 and sent to the image reading device 40.

  The history storage unit 19 uses the second image generated by reading the image on the sheet by the image reading unit 41 to generate an image representing the history of the image formation performed and stores the image in the storage unit 12.

  The image reading device 40 includes an image reading unit 41 and a transport unit 42. The transport unit 42 includes transport rollers 42 a disposed at a plurality of locations on the paper transport path. The image reading device 40 conveys the sheet on which the image is formed to the image reading unit 41 by the conveyance unit 42. The image reading unit 41 reads the conveyed paper as an image. The read paper is transported by the transport unit 42 and discharged from the image reading device 40 to the outside.

  The transport unit 42 is provided with a paper reversing mechanism. When reading both sides of a sheet, after reading one side of the sheet, the sheet reversed by the reversing mechanism is conveyed to the image reading unit 41.

  The image reading unit 41 is a line sensor arranged on the paper transport path. The image reading unit 41 reads an image on a sheet conveyed from the main body 10 by the conveying unit 10a, and generates an image in a bitmap format as a second image. The image reading unit 41 may be an area sensor.

  An image transfer path using an interface such as PCI express is provided between the image reading device 40 and the main body 10. The second image generated by the image reading unit 41 is transferred to the main body 10 via this image transfer path. The main body 10 stores the transferred second image in the storage unit 12.

  As described above, the external device 50 can be a user terminal, a server, another image forming apparatus, or the like. As shown in FIG. 2, the external device 50 includes a storage unit 51.

  Similar to the storage unit 12 of the main body 10, the storage unit 51 can store attribute information generated by the image generation unit 30 and information generated by the history storage unit 19. As the storage unit 51, a large-capacity memory such as a hard disk drive can be used.

  FIG. 3 is a flowchart illustrating a processing procedure of image forming processing performed in the image forming apparatus 1.

  When the PDL data is transmitted to the image forming apparatus 1, the image generation unit 30 executes a rasterization process of the PDL data and generates a first image for each page (step S11). An image forming process is performed for each page.

  The image generation unit 30 generates attribute information indicating the attribute of each pixel of the first image, and stores the generated attribute information in the storage unit 12 (step S12).

  When the image generation unit 30 generates an image of character attributes in the first image, the image generation unit 30 generates color information of the characters and stores the character color information in association with the attribute information in the storage unit 12 (step S13).

  An image of each color of Y, M, C, and K is generated by the rasterizing process. Therefore, Y, M, C, and K gradation values of each pixel constituting the character can be used as color information. Further, R, G, and B gradation values described as character colors in the PDL data can be used as color information. Since characters often have a single color, one color information may be generated not in units of pixels but in units of characters or character strings to reduce the data amount of color information.

  When the first image is generated, the image processing unit 17 performs image processing on the first image. Examples of the image processing include gradation processing and halftone processing. The image processing unit 17 acquires attribute information generated together with the first image from the storage unit 12. The image processing unit 17 can perform image processing under different conditions according to attributes. For example, the image processing unit 17 can perform image processing so that the number of screen lines differs for each attribute indicated by the attribute information.

  Further, the image processing unit 17 can perform image processing according to application setting for image formation. The image processing unit 17 can change the position and color of the first image, add, delete, convert, enlarge, and reduce the image. Application settings include page allocation, page insertion, magnification change, repeat, centering, binding margin, image editing, stamp, color adjustment, negative / positive inversion, mirror image, frame erase, and the like. Page allocation is a process of reducing and arranging a plurality of pages of images on one page. Page insertion is a process of adding an image of one page. The magnification change is a process for enlarging or reducing the image. Repeat is a process of arranging the same image on a plurality of pages. Centering is a process of shifting the image to the center position of the page. The binding margin is a process of providing a binding area by shifting the position of the image. Image editing is processing for adding characters such as date and number of pages. Stamping is a process of adding an image such as a watermark or a logo mark. Negative / positive inversion is a process of inverting the brightness of an image. A mirror image is a process of converting an image into a mirror image. Frame erasing is processing for deleting a frame in an image.

  The image forming unit 20 forms an image on the paper according to the gradation value of each pixel of the first image after image processing (step S14). The sheet on which the image is formed is conveyed to the image reading device 40 by the conveyance unit 10a.

  In the image reading device 40, the image reading unit 41 reads an image on a sheet (step S15). Thereby, the second image is generated. The generated second image is transferred to the storage unit 12 of the main body 10 and stored as a history image (step S16).

  [Description of image processing]

  The image processing unit 17 executes position correction processing such as skew correction on the image in a state where the image to be processed is compressed. Then, after position correction, the image is expanded, and outline processing and screen processing are performed.

  In the present embodiment, the image processing unit 17 generates compressed data for each input image constituting the processing target image. That is, for each input image, the compressed and compressed image data is temporarily expanded and then fixed-length compression is performed. At this time, in each input image, it is determined whether the predetermined unit area is a high resolution portion or a low resolution portion, and the compression method is switched according to the determination result. Then, the data of the MAX gradation (maximum gradation) and the MIN gradation (minimum gradation) of the high resolution portion is encoded and included in the compressed data after compression. Here, high gradation is maintained in the low resolution portion. For the area between the MAX gradation and the MIN gradation in the high resolution portion, the gradation is referred from the low resolution portion around the high resolution portion.

  As a result, it is possible to reduce the data amount while maintaining the maximum gradation of the image data having a high gradation and maintaining the shape of the high resolution portion. Therefore, it is possible to reduce the processing load on the image forming apparatus 1 when performing the position correction process on the compressed data while maintaining the image quality as much as possible.

  FIG. 4 is a diagram illustrating the configuration of the image processing unit 17.

  In FIG. 4, the resolution and gradation of the image processed by the image processing unit 17 are shown together with the functional blocks of the image processing unit 17.

  The image processing unit 17 includes a system control ASIC (Application Specific Integrated Circuit) 110, a degeneration / expansion unit 111, a toner amount limiting unit 112, a color conversion processing unit 113, a density balance unit 114, a compression processing unit (first processing unit). An example of a determination unit, an example of a second determination unit, an example of a patterning unit) 115, a position correction unit (an example of a position correction unit) 116, an expansion outline processing unit (an example of an expansion unit) 117, and a screen processing unit 118 and the like. Each unit of the image processing unit 17 performs processing as follows based on control of the control unit 11.

  In the following description, the depth and resolution of the gradation, the number of pixels in the region, and the like are examples, and are not limited thereto.

  The image data is subjected to degeneracy compression processing. As a result, 600 dpi / 4 bit image data of each color that has been compressed and compressed is input from the system control ASIC 110.

  FIG. 5 is a diagram for explaining the compressed compression data.

  In FIG. 5, an input image B11, reduced compression data B12, B13, B14, and an expanded image B15 are illustrated. The degenerate compressed data includes MAX / MIN gradation data B12, identification flag data B13, and code data B14. The input image B11 and the expanded image B15 are 8 × 8 pixel data.

  In the compression / decompression process, 1200 dpi / 8-bit image data is compressed into 600 dpi / 4-bit image data (degraded compression data B12, B13, B14). At this time, the image is compressed after being divided into 2 × 2 pixel unit areas of a portion to be processed with shape priority and a portion to be processed with gradation priority.

  The compression / decompression unit 111 performs decompression processing on the input compression data B12, B13, B14. When the decompression process is performed, a decompressed image B15 of 1200 dpi / 8 bits is output. In the expanded image B15, the shape-priority portion (the region where the identification flag data B13 is “H”) has two gradations, that is, the MAX gradation and the MIN gradation. In the gradation priority portion (region where the identification flag data B13 is “L”), the same gradation is obtained in each region of 2 × 2 pixels.

  Returning to FIG. 4, the color conversion processing unit 113 and the density balance unit 114 perform inter-color processing on the expanded image B15. As a result, the expanded image B15 is converted into image data of 1200 dpi / 10 bits. The inter-color processing includes each processing such as toner amount limitation, color conversion processing, and density balance adjustment.

  The compression processing unit 115 converts the 1200 dpi / 10-bit image data after inter-color processing into 600 dpi / 16-bit image data (compression processing). The image data includes 12-bit color data and a 4-bit attribute signal. That is, the attribute signal is put in the compressed data of each color. For this reason, the image data that has previously included four colors of YMCK and attribute signals becomes data of four colors of YMCK.

  When the compression process is performed, the compressed data is written into a working memory (sometimes simply referred to as a memory) such as DDR.

  The position correction unit 116 performs position correction based on the measured positional deviation information. For example, an address read from the memory is controlled so that a shift amount of 4 pixels or more at 600 dpi is a shift amount within 4 pixels.

  The decompression outline processing unit 117 decodes the compressed data read from the memory (decompression processing). The decompression process is performed as described below. An outline process is performed on the decompressed data. Thereby, edge tag data is generated.

  The screen processing unit 118 performs resolution conversion on the decompressed data and expands it to 2400 dpi data. The resolution-converted image data is stored in the line buffer. By controlling the address read from the line buffer, the position can be finely adjusted.

  [Description of compression processing]

  The compression processing unit 115 performs compression processing by the following method.

  FIG. 6 is a diagram for explaining compression processing.

  FIG. 6 illustrates an image (input image) B21 after inter-color processing, compressed data B22, B23, B24, and an expanded image B25. In the compression process, an input image B21 in the range of 8 × 8 pixels (an example of a predetermined first size) is processed as a unit. When compression is performed, the input image B21 becomes data in units of 4 × 4 pixels. In addition, processing is performed by setting a 2 × 2 pixel range (an example of a predetermined second size) in the input image B21 as one unit region (hereinafter, also referred to as a block).

  The compressed data includes MAX / MIN gradation data B22, identification flag data B23, and code data B24. The attribute signal is not compressed and is loaded on the compressed data of each color as it is.

  The MAX / MIN gradation data B22 is generated in the same manner as the compression / decompression process. That is, for each input image B21, information on the maximum gradation and information on the minimum gradation are included. Specifically, information of upper 8 bits is included as shown in the figure among 10-bit information representing MAX gradation and MIN gradation. The lower 2 bits correspond to the code data B24.

  The identification flag data B23 is 1-bit information for identifying the high resolution portion and the low resolution portion for each block. If the gradation difference in the 2 × 2 pixel area is smaller than the set threshold value THa1 in the input image B21 to be compressed, it becomes a low resolution portion. The other area is a high resolution part.

  When the threshold value THa1 is set to 0, a high resolution portion is obtained except when the gradations are all equal.

  The code data B24 includes codes given by different methods depending on whether the block is a high-resolution part or a low-resolution part.

  For the block of the low resolution part, the gradation of the original pixel is encoded as it is.

  On the other hand, for the block of the high resolution portion, a predetermined high resolution portion coding pattern (sometimes referred to as a first coding pattern) P1 and a MAX / MIN coding pattern (sometimes referred to as a second coding pattern). Encoding is performed based on P2. The high-resolution block is encoded such that the upper 7 bits correspond to the first encoding pattern P1 and the lower 3 bits correspond to the second encoding pattern P2.

  FIG. 7 is a diagram illustrating an example of an encoding pattern for a high resolution portion.

  As shown in FIG. 7, in the first encoding pattern P1, for each pixel of each block, the gradation of the pixel is classified into three types. In the first coding pattern P1, a 7-bit shape pattern is determined based on the arrangement state (sometimes referred to as a shape) of pixels in each section included in the processing target block.

  The pixels of each block are roughly divided into a first section of pixels referring to the MAX gradation, a second section of pixels referring to the MIN gradation, and a third section referring to the surrounding low resolution portion. It is divided into pixels. When there are a plurality of pixels in which the gradation of the low resolution portion referred to for one block is different from each other, the pixel of the third section that refers to the gradation from the surrounding low resolution portion is further divided into portions to form a shape pattern. Is expressed.

  FIG. 8 is a diagram illustrating an example of the MAX / MIN encoding pattern.

  As shown in FIG. 8, in the second coding pattern P2, codes for 3 bits corresponding to the lower 2 bits of the MAX gradation and the lower 2 bits of the MIN gradation are defined. The second coding pattern P2 includes only the pixels in the first case where the pixels of the block include pixels that reference the MAX gradation and pixels that reference the MIN gradation, and pixels that reference the MAX gradation. This is defined for each of the second case and the third case in which only the pixels referring to the MIN gradation are included.

  In the second case and the third case, values corresponding to the lower two bits of the gradation correspond to each.

  In the first case, a combination of the lower 2 bits of the MAX gradation and the lower 2 bits of the MIN gradation is defined within a range represented by 3 bits.

  In the present embodiment, when an adjacent block is a low resolution portion and the gradation difference is smaller than a predetermined threshold THa2, the pixel is determined as a pixel that refers to the gradation from the surrounding low resolution. Other pixels are classified into pixels that reference the MAX gradation or pixels that reference the MIN gradation.

  In the MAX / MIN gradation data B22, information on the MAX gradation and the MIN gradation is embedded from the pixels assigned to the high resolution portion in the input image B21. That is, the upper 8 bits of the highest density gradation and the upper 8 bits of the lowest density gradation are embedded.

  For the lower 2 bits of each of the MAX gradation and the MIN gradation, a code is selected so that the error is reduced. The code is selected based on the first coding pattern and the second coding pattern. If all the input images B41 have a low resolution, both the lower 2 bits of the MAX gradation and the lower 2 bits of the MIN gradation are set to 0.

  FIG. 9 is a first flowchart showing the compression processing. FIG. 10 is a second flowchart showing the compression process.

  In step S111, an input image B21 of 1200 dpi / 10 bits of 8 × 8 pixels is input.

  In step S112, the input image B21 is divided into blocks each having 2 × 2 pixels. Then, it is confirmed whether or not the gradation of the pixels is equal in each block.

  If they are not equal in step S112, the process of step S113 is performed for the block. In step S113, the MAX gradation pixel and the MIN gradation pixel in the block are detected.

  In step S114, it is confirmed whether or not the difference between the detected MAX gradation and MIN gradation is equal to or less than a predetermined threshold THa1.

  When all the gradations of the pixels in the block are equal in step S112, and when the gradation difference is equal to or less than the threshold value THa1 in step S114, the process of step S115 is performed. In step S115, the identification flag is set to “0”. That is, the block is set to be a low resolution portion.

  On the other hand, when the gradation difference is larger than the threshold value THa1 in step S114, the identification flag is set to “1” in step S116. That is, the block is set to be a high resolution portion.

  In step S117, when all blocks have been identified for the input image B21, the process proceeds to step S118. In step S118, the gradations of the images in the block identified as the low resolution portion are averaged to form a one-pixel block.

  In step S119, a high resolution part encoding process is performed. Processing is performed as described below for the pixels in the block identified as the high resolution portion.

  In step S120, the process for each input image B21 is performed until the process is performed up to the end of the image. When the processing is performed up to the end of the image, the compression processing ends.

  FIG. 11 is a first flowchart showing the high-resolution part encoding process. FIG. 12 is a second flowchart showing the high-resolution part encoding process. FIG. 13 is a third flowchart showing the high-resolution part encoding process.

  When the high resolution part encoding process is started, the pixels of the high resolution part are searched for in step S131.

  In step S132, it is determined whether or not the gradation difference between the pixel and the low-resolution block adjacent to the pixel is smaller than a predetermined threshold THa2. If it is small, the pixel is treated as a pixel that refers to the gradation of the surrounding low resolution portion. If larger, the process proceeds to step S133.

  In step S133, it is confirmed whether or not the gradation of the pixel is greater than the MAX gradation at that time for the input image B21. If not, the process proceeds to step S135.

  If it is larger than the MAX gradation, in step S134, the MAX gradation for the input image B21 is updated with the gradation of the pixel.

  In step S135, it is confirmed whether or not the gradation of the pixel is smaller than the MIN gradation at that time for the input image B21.

  If it is smaller than the MIN gradation, in step S136, the MIN gradation for the input image B21 is updated with the gradation of the pixel.

  When the identification is completed for all the pixels included in the block determined to be the high resolution portion of the input image B21 in step S137, the process proceeds to step S138.

  In step S138, MAX / MIN gradation data B22 for the input image B21 is generated. That is, the upper 8 bits of the MAX gradation and the upper 8 bits of the MIN gradation are embedded in the 11th bit of the compressed data.

  Here, the MAX gradation and the MIN gradation are reset for each input image B21. That is, in each input image B21, the gradation of an image in which the gradation difference from the adjacent low resolution portion is larger than the threshold THa2 is set as the MAX gradation and the MIN gradation. Thereafter, if there is a pixel whose gradation difference is larger than the threshold THa2, it is confirmed whether or not the gradation is the MAX gradation or the MIN gradation.

  In step S139, processing is performed on pixels other than the pixels that are referred to the gradations of the surrounding low resolution portions. That is, processing is performed for the pixels that are determined to be NO in step S132. Each pixel is assigned to either a pixel that refers to the MAX gradation or a pixel that refers to the MIN gradation, depending on whether it is larger or smaller than the intermediate value between the MAX gradation and the MIN gradation.

  In step S140, the upper 7 bits of the code data are determined based on the reference destination of the gradation of each pixel included and the first coding pattern P1 for each block.

  In step S141, for each block, it is determined whether or not pixels that refer to the MAX gradation and pixels that refer to the MIN gradation are mixed.

  If not, the process of step S142 is performed. That is, the lower 2 bits of the gradation to be referenced are embedded in the code 3 bits.

  If they are mixed, the process of step S143 is performed. That is, whether or not to give priority to the MAX gradation is confirmed.

  When priority is given to the MAX gradation (MAX priority), the process of step S144 is performed. That is, in the second coding pattern P2, a combination code that minimizes the error of the MIN gradation is selected from among those in which the lower 2 bits of the MAX gradation match.

  For example, in the case where priority is given to the MAX gradation, it is assumed that the lower 2 bits of the MAX gradation are “3”. At this time, if the lower 2 bits of the MIN gradation are “0” or “1”, the code is “7”. On the other hand, if the lower 2 bits of the MIN gradation are “2” or “3”, the code is “4”.

  On the other hand, if the MAX gradation is not prioritized, the process of step S145 is performed. That is, in the second coding pattern P2, a code having a combination in which the error of the MAX gradation is the smallest among the two lower bits of the MIN gradation that match is selected.

  Here, up to four types of pixels that refer to gradations from surrounding low-resolution portions can be classified within one block. When the pixels in one block are classified into these four types, the low resolution part to be referred to may be determined uniformly depending on whether the third bit of the code is 0 or 1.

  FIG. 14 is a diagram for describing a first example of processing in the case where there are four types of pixels that refer to gradations from one peripheral low-resolution part in one block.

  FIG. 14 shows an example in which the upper 7 bits of the compressed data in the central block are “0011100”. Each of the upper, lower, left and right blocks of the central block is a low resolution portion.

  At this time, the upper left pixel refers to the gradation of the upper block (number 1). The lower right pixel refers to the gradation of the right block (number 2). The lower left pixel refers to the gradation of the lower block (number 3). The lower right pixel refers to the gradation of the left block (number 4).

  FIG. 15 is a diagram for describing a second example of processing in the case where there are four types of pixels in one block that refer to gradations from the peripheral low resolution portion.

  FIG. 15 shows an example in which the upper 7 bits of the compressed data in the central block are “0011101”. Each of the upper, lower, left and right blocks of the central block is a low resolution portion.

  At this time, the upper left pixel refers to the gradation of the left block (number 4). The upper right pixel refers to the gradation of the upper block (number 1). The lower left pixel refers to the gradation of the right block (number 2). The lower right pixel refers to the gradation of the lower block (number 3).

  [Explanation of decompression processing]

  The compressed data B22, B23, and B24 are expanded as follows.

  The low resolution part is restored based on the identification flag data B23. That is, by copying the gradation of the block and expanding the pixel, a 2 × 2 pixel block in 1200 dpi data is restored.

  The high resolution portion is restored based on the first coding pattern P1, the second coding pattern P2, and the code data B24. That is, the high-resolution part restores a block having a shape based on the first coding pattern P1 from the upper 7 bits of the code. Then, if necessary, the pixel that refers to the MAX gradation and the pixel that refers to the MIN gradation are restored based on the lower 3 bits and the MAX / MIN gradation data B22.

  That is, the pixel that refers to the MAX gradation is restored based on the MAX gradation 8 bits of the MAX / MIN gradation data B22 and the lower 2 bits corresponding to the MAX gradation based on the lower 3 bits of the code data B24. .

  The pixel that refers to the MIX gradation is restored based on the MIN gradation 8 bits of the MAX / MIN gradation data B22 and the lower 2 bits corresponding to the MIN gradation based on the lower 3 bits of the code data B24.

  Pixels that refer to gradations from the surrounding low resolution portions are weighted from adjacent low resolution portions to determine the gradations. Decisions are made by majority vote.

  FIG. 16 is a diagram for explaining restoration of a pixel that refers to a gradation from a peripheral low resolution portion.

  In FIG. 16, it is assumed that the gradation of the pixel of interest 231 at the upper left of the central block is determined. Blocks (numbers 1-8) around the central block are low resolution portions.

  The gradation of the target pixel 231 is determined by majority decision based on the gradations of the upper left block (number 1), the upper block (number 2), and the left block (number 4). At this time, the gradation of the upper left block and the gradation of the upper block are the same, but the gradation of the left block is different from them. That is, of the blocks adjacent to the pixel of interest 231, the gradations of the two blocks of the upper left block (number 1) and the upper block (number 2) are referred to as the gradation of the pixel of interest 231. It should be noted that the blocks located at the top, bottom, left and right of the pixel (numbers 2 and 4 in this example) are weighted more heavily than the block located diagonally (number 1 in this example) when considering gradation. Also good.

  [Description of specific examples of compression processing and decompression processing]

  FIG. 17 is a first diagram illustrating a specific example of compression processing. FIG. 18 is a second diagram illustrating a specific example of compression processing. FIG. 19 is a third diagram illustrating a specific example of the compression process.

  17, FIG. 18, and FIG. 19 show an input image B41 for compression processing, compressed data B42, B43, B44, and a decompressed image B45. For each image, the right image (B41a, B42a, B43a, B44a, B45a) shows the contents (values) of each pixel or block. This specific example corresponds to that shown in FIG.

  In the example described below, the input image B41 is composed of 8 × 8 pixels. A threshold THa1 for gradation difference in one block (2 × 2 pixels) is set to 4. Further, the threshold THa2 for the gradation difference when referring to the gradation from the adjacent low resolution part is set to 8. Further, the lower 2 bits of MAX / MIN are given priority to MAX.

  In the input image B41, the gradation of a 2 × 2 pixel block composed of pixels a11, a12, a21, and a22 is seen. Then, in this block, the MAX gradation is “540” and the MIN gradation is “539”. Since the gradation difference between the MAX gradation and the MIN gradation is smaller than 4, this block is identified as a low resolution portion. Therefore, in the identification flag data B13, the block b11 corresponding to the pixels a11, a12, a21, and a22 is “0” corresponding to the low resolution portion.

  Similarly, the gradation is confirmed for each 2 × 2 pixel block in the 8 × 8 pixel input image B41 to be compressed. Each block is “0” for the high resolution portion and “1” for the high resolution portion.

  In this way, identification flag data B43 (B43a) when the input image B41 is compressed is generated.

  When the determination regarding the identification flag is completed for each block of the input image B41, the averaged block of the identified block which is the low resolution portion is performed.

  The average of the pixels a11, a12, a21, a22 corresponding to the block b11 is “540”. (Round after the decimal point) Similarly, averaging of each block identified as the low resolution portion in the input image B41 is performed.

  When the low resolution part is averaged, the gradation of the high resolution part is compared with the gradations of the peripheral low resolution part.

  For example, among the pixels a15, a16, a25, and a26 corresponding to the block b13, the pixels a15, a16, and a25 have a gradation difference smaller than 8 from the gradation “540” of the block b12. For this reason, the pixels a15, a16, and a25 are pixels that refer to the gradation from the peripheral low resolution portion (block b12). The pixel a26 has a gradation difference smaller than 8 from the gradation “645” of the block b23. For this reason, the pixel is referred to the gradation from the peripheral low resolution portion (block b23). However, the gradation (“538”) of the pixels a15, a16, and a25 and the gradation (“641”) of the pixel a26 are different from each other.

  On the other hand, for example, the pixels a17, a18, a27, and a28 corresponding to the block b14 have a gradation difference larger than 8 with the surrounding low resolution portions b23 and b24. Therefore, it is not a pixel that refers to the gradation from the surrounding low resolution part.

  The pixels a17 and a18 have the gradation “321”. Since the MAX gradation and the MIN gradation are not yet determined, these gradations are set as the MAX gradation and the MIN gradation in the input image B41.

  Next, the gradation “756” of the pixels a27 and a28 is larger than the MAX gradation “321” at this time. Therefore, the MAX gradation in the input image B41 is changed to “756”.

  In all the high resolution portions in the input image B41, the gradation is confirmed in this way for all pixels that are not pixels that reference the gradation from the surrounding low resolution portions. As a result, the MAX gradation is “760” and the MIN gradation is “321”. If “760” is converted into a binary number, “1011111000”, the upper 8 bits are set as a value representing the MAX gradation. On the other hand, when “321” is converted into a binary number, “0101000001”, the upper 8 bits are set as a value representing the MIN gradation. Thus, MAX / MIN gradation data B42 (B42a) is generated.

  The code data B44 is as follows.

  Since the block c11 (corresponding to the block B11) is a low resolution portion, the averaged gradation “540” is obtained. Similarly, in the other low resolution portions, the average gradation is used as the code data B44.

  The block c13 is a high resolution part. Therefore, the upper 7 bits are “26” based on the first coding pattern P1. In the block c13, there are no pixels that refer to the MAX gradation or pixels that refer to the MIN gradation. In this case, the lower 3 bits are “0”. As a result, the code of the block c13 becomes “208”.

  The block c14 is a high resolution part. Therefore, the upper 7 bits are “33” based on the first coding pattern P1. In the block c14, pixels that refer to the MAX gradation and pixels that refer to the MIN gradation are mixed. In this example, MAX priority is given. Since the MAX gradation is “760” and the gradations of the pixels a27 and a28 are “756”, the lower 2 bits are “0”. Since the MIN gradation is “320” and the gradations of the pixels a17 and a18 are “321”, the lower 2 bits are “0” with little error. Therefore, the lower 3 bits are “0” based on the second coding pattern P2. As a result, the code of the block c14 becomes “264”.

  When processing is performed for each block in this way, code data B44 (B44a) obtained when compression processing is performed on the input image B41 is obtained.

  Next, decompression of the compressed data B42, B43, B44 compressed in this way will be described.

  The pixels d11, d12, d21, and d22 have identification flags “0” and are low resolution portions. The block c11 is copied and the gradation is set to “540”.

  The pixels d33, d34, d43, and d44 have the identification flag “1” and are high-resolution portions. Therefore, gradation processing is performed based on the upper 7 bits of the code and the first coding pattern P1. Different gradations are restored for the upper left pixel d33 and the other pixels d34, d43, and d44 with reference to the gradations of the surrounding low resolution portions.

  That is, for the pixel d33, the gradations of the adjacent blocks c11, c12, c21 are all “540”. Therefore, the gradation of the pixel d33 is “540”.

  Regarding the pixels d34, d43, and d44, the gray levels of the adjacent blocks c23, c32 and c33 are different from “645” and “647”, respectively. In this case, there are more blocks with gradation of “645”. Therefore, the gradations of the pixels d34, d43, and d44 are “645”.

  The pixels d51, d52, d61, and d62 have identification flags of “1” and are high resolution portions. Therefore, gradation processing is performed based on the upper 7 bits of the code and the first coding pattern P1. The upper left pixel d51 and the lower left pixel d61 have a MIN gradation. The upper right pixel d52 is a pixel that refers to the gradation from the surrounding low resolution portion. The lower right pixel d62 has a MAX gradation.

  Pixels d51 and d61 are MIN gradations. The upper 8 bits of the MIN gradation based on the MAX / MIN gradation data B42a are “01010000”. Since the code data B44a is “262”, its lower 3 bits are “6”. From the second coding pattern P2, the lower 2 bits of the MIN gradation corresponding to “6” when the MAX gradation and the MIN gradation are mixed are “3”. Therefore, the gradation is “323 (0b0101000011)” from the upper 8 bits “01010000” and the lower 2 bits “11”.

  In the pixel d52, the gradations of the blocks c21 and c32 in the adjacent low resolution portion are different between “540” and “645”, respectively. At this time, the gradation of the pixel d43, which is a pixel that refers to the gradation of the peripheral low resolution portion, is “645”. Since there are two gradations “645” in the block C32 and the pixel d43, the gradation of the pixel d52 is “645”.

  The pixel d62 has a MAX gradation. The upper 8 bits of the MAX gradation based on the MAX / MIN gradation data B42a are “10111110”. Since the lower 3 bits of the code data B44a are “6”, the lower 2 bits of the MAX gradation corresponding to “6” are “0” from the second coding pattern P2. Therefore, the gradation is “760 (0b1011111000)” from the upper 8 bits “10111110” and the lower 2 bits “00”.

  In this way, decompression is performed based on the compressed data B42, B43, and B44, whereby a decompressed image B45 (B45a) is obtained.

  [Effects of the embodiment]

  In the image forming apparatus configured as described above, whether an area is a high-resolution part or a low-resolution part is determined for each 2 × 2 pixel block in the input image. Then, the compression method is switched according to the determination result. For the low resolution portion, the gradation of each pixel is maintained based on the average value of the gradation of the pixels included in the block. Therefore, high gradation is maintained for the low resolution portion. For the high resolution part, the shape pattern is maintained according to the original gradation. Then, the gradation of each pixel in the high resolution part is determined by referring to the gradation of the surrounding low resolution part according to the original pixel. Therefore, the gradation can be maintained at a high level while maintaining the shape of the high resolution portion.

  The compressed data includes MAX / MIN gradation data and code data corresponding to the shape pattern for the high resolution portion. As a result, the amount of compressed data can be effectively reduced. The position correction is performed based on the compressed data. Therefore, memory such as a line buffer necessary for position correction can be reduced. In addition, it is possible to reduce the system bandwidth necessary for reading / writing data from / to the image memory. Since the system band can be reduced, the operating frequency can be lowered and the power consumption of the image forming apparatus can be lowered. Further, since the system bandwidth can be reduced, the image memory can be shared with other processes. In other words, the capacity of the image memory can be reduced, and the configuration of the image forming apparatus 1 can be simplified and the manufacturing cost can be reduced.

  [Others]

  The processing unit of the compression process is not limited to the above. For example, for a unit area in the main scanning direction (corresponding to the direction perpendicular to the paper transport direction) N dots (N is an integer) and in the sub-scanning direction (corresponding to the paper transport direction) M dots (M is an integer) May be determined as a high-resolution part or a low-resolution part, or subsequent processing may be performed. Similarly, the size of the input image is not limited to the above-described size.

  In the image processing performed by the image processing unit, the resolution and bit depth of the image at each stage are not limited to those described above.

  The image forming apparatus may perform a compression process on a monochrome input image. Even in this case, the compression process and the expansion process can be performed as described above.

  The image processing apparatus may be a monochrome / color copying machine, a printer, a facsimile machine, or a multifunction machine (MFP) thereof. It is not limited to the one that forms an image by an electrophotographic method, and may be one that forms an image by a so-called inkjet method, for example.

  The hardware configuration of the image processing apparatus is not limited to the above, and the image processing may be performed by various control circuits.

  Further, the image processing apparatus according to the present invention is not limited to that used in the image forming apparatus. For example, the present invention can be applied to image processing apparatuses used in various apparatuses such as a scanner apparatus that reads image data, an imaging apparatus, and an image data transmission / reception apparatus.

  The processing in the above embodiment may be performed by software or by using a hardware circuit.

  A program for executing the processing in the above-described embodiment can be provided, or the program can be recorded on a recording medium such as a CD-ROM, a flexible disk, a hard disk, a ROM, a RAM, or a memory card and provided to the user. It may be. The program may be downloaded to the apparatus via a communication line such as the Internet. The processing described in the text in the above flowchart is executed by the CPU according to the program.

  The above embodiment should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10 Main body 11 Control part 12 Storage part 12a Control program 13 Operation part 14 Display part 17 Image processing part 20 Image forming part 30 Image generation part 115 Compression processing part (an example of a 1st determination means, an example of a 2nd determination means) An example, an example of patterning means)
116 Position correction unit (an example of position correction means)
117 Extension outline processing unit (an example of extension means)

Claims (8)

An image processing apparatus that performs compression processing on an image to be processed and generates compressed data for each input image having a predetermined first size that constitutes the image to be processed.
First determination means for determining, for each predetermined second size region of the input image, whether the region is a high-resolution part or a low-resolution part that is not the high-resolution part;
A second determination for determining each gradation of pixels belonging to the region determined to be a high-resolution part by the first determination unit, and determining a maximum gradation and a minimum gradation in the input image; Means,
Patterning means for patterning each of the areas determined to be high-resolution portions by the first determination means into a predetermined shape pattern based on the gradation and arrangement state of the pixels included in the area;
On the basis of the information corresponding to the maximum gradation and the minimum gradation determined by the second determination means and the code corresponding to the shape pattern patterned by the patterning means, Generating means for generating compressed data,
The patterning unit refers to a pixel in a region determined to be a high resolution portion by the first determination unit, a pixel in a first section that refers to the maximum gradation, and the minimum gradation. The pixel of the second division and the pixel of the third division that refers to the gradation of the area determined to be the low resolution portion around the second division, and the arrangement of the pixels of each division An image processing apparatus that performs the patterning based on a state. The generating means includes
For each region determined to be a low-resolution part by the first determination unit, an average value obtained by averaging the gradations of pixels included in the region is calculated,
The image processing apparatus according to claim 1, wherein the compressed data is generated based on the calculated average value.   When the generation unit includes at least one of the pixel of the first section and the pixel of the second section for the region determined to be the high resolution portion by the first determination unit, the pixel The image processing apparatus according to claim 1, wherein a code reflecting the gradation of the image is included in the compressed data. Further comprising decompression means for decoding the processing target image based on the compressed data generated by the generation means;
The decompression means for each input image,
Determining the gradation of the pixels in the region corresponding to the low resolution portion to a gradation corresponding to a code included in the compressed data;
Based on the shape pattern corresponding to the code included in the compressed data, the information corresponding to the maximum gradation and the minimum gradation, and the gradation of the low resolution part for the region corresponding to the high resolution part The image processing apparatus according to claim 1, wherein the gradation of each pixel is determined. Position correction means for performing position correction processing using the compressed data generated by the generation means;
The image processing apparatus according to claim 4, wherein the decompression unit performs the decoding on the compressed data after the position correction unit is performed. An image processing apparatus according to any one of claims 1 to 5,
An image forming apparatus comprising: an image forming unit that forms an image on a sheet based on an image processed by the image processing apparatus. A control method of an image processing apparatus that performs compression processing on an image to be processed and generates compressed data for each input image having a predetermined first size that constitutes the image to be processed.
A first determination step for determining, for each predetermined second size region of the input image, whether the region is a high-resolution part or a low-resolution part that is not the high-resolution part;
A second determination for determining a gradation of each of the pixels belonging to the region determined to be a high-resolution portion by the first determination step, and determining a maximum gradation and a minimum gradation in the input image; Steps,
A patterning step of patterning each of the regions determined to be high-resolution portions by the first determination step into a predetermined shape pattern based on the gradation and arrangement state of pixels included in the region;
Based on the information corresponding to the maximum gradation and the minimum gradation determined by the second determination step and the code corresponding to the shape pattern patterned by the patterning step, the input image A generating step for generating compressed data;
The patterning step refers to a pixel in a region determined to be a high resolution portion by the first determination step, a pixel in a first section that refers to the maximum gradation, and the minimum gradation. The pixel of the second division and the pixel of the third division that refers to the gradation of the area determined to be the low resolution portion around the second division, and the arrangement of the pixels of each division A method for controlling an image processing apparatus, wherein the patterning is performed based on a state. A control program for an image processing apparatus that performs compression processing on an image to be processed and generates compressed data for each input image having a predetermined first size that constitutes the image to be processed.
A first determination step for determining, for each predetermined second size region of the input image, whether the region is a high-resolution part or a low-resolution part that is not the high-resolution part;
A second determination for determining a gradation of each of the pixels belonging to the region determined to be a high-resolution portion by the first determination step, and determining a maximum gradation and a minimum gradation in the input image; Steps,
A patterning step of patterning each of the regions determined to be high-resolution portions by the first determination step into a predetermined shape pattern based on the gradation and arrangement state of pixels included in the region;
Based on the information corresponding to the maximum gradation and the minimum gradation determined by the second determination step and the code corresponding to the shape pattern patterned by the patterning step, the input image A generating step for generating compressed data;
The patterning step refers to a pixel in a region determined to be a high resolution portion by the first determination step, a pixel in a first section that refers to the maximum gradation, and the minimum gradation. The pixel of the second division and the pixel of the third division that refers to the gradation of the area determined to be the low resolution portion around the second division, and the arrangement of the pixels of each division A control program for an image processing apparatus, which performs the patterning based on a state.

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