JP2008235966A - Image compression apparatus, image forming apparatus, and still image compression method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image compression apparatus or the like capable of outputting the images of high quality by effectively utilizing compression resources. <P>SOLUTION: The image compression apparatus or the like includes: a ratio setting means for setting the ratio of an area to perform lossless compression to input image data; an area setting means for setting a lossless compression area which is the application area of the lossless compression and a lossy compression area which is the application area of lossy compression to the image data according to the ratio; a lossless compression means for performing lossless compression of the lossless compression area; a lossless compression rate calculation means for calculating the compression rate of the lossless compression area by the lossless compression means; a scheduled compression rate calculation means for calculating a scheduled compression rate to be applied to the lossy compression area on the basis of the compression rate of the lossless compression area; and a lossy compression means for performing lossy compression of the lossy compression area on the basis of the calculated schedule compression rate. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a digital copying machine, a printer, and a scanner, an image compressing apparatus provided in the image forming apparatus, and a still image compressing method used in the image forming apparatus. The present invention relates to an image forming apparatus that can provide a high-quality compressed image.

  In recent years, full-color image forming apparatuses capable of outputting full-color images are increasing instead of monochrome image-forming apparatuses that output monochrome images. Full-color images look better than monochrome images, and because they can represent points that could not be represented by monochrome images, they are increasing their share.

  On the other hand, a full-color image has a problem that the size of image data per sheet becomes large. Therefore, the size of the image data is reduced by compressing the image data, thereby ensuring a sufficient number of sheets that can be handled by the image forming apparatus. In the case of a low compression rate, the amount, scale, etc. of resources used for image processing in the image forming apparatus become large, leading to an increase in cost. For this reason, it is desirable to highly compress the image data. However, since high compression causes degradation of the output image, it is necessary to avoid unnecessary compression.

  JP-A-9-149260 (Patent Document 1) discloses a technique for changing the compression rate by constantly monitoring the compression rate.

  Japanese Patent Laying-Open No. 2003-037739 (Patent Document 2) discloses a technique for simultaneously compressing a plurality of compression methods and selecting the most appropriate compressed data.

Japanese Patent Laid-Open No. 8-13938 (Patent Document 3) discloses a technique for classifying image areas and applying an optimum compression method to each classified area.
JP-A-9-149260 JP 2003-037739 A JP-A-8-139938

  However, in the technique disclosed in Patent Document 1, since the compression rate is changed for each pixel, a region to which lossless compression is applied and a region to which lossy compression are applied are mixed. There is a problem that the image quality is clearly deteriorated in a region where the applied portions are concentrated. Further, since it is assumed that reversible compression and irreversible compression are always switched, there is a problem that the circuit scale becomes large.

  Further, in the technique disclosed in Patent Document 2, it is necessary to operate a plurality of compression circuits at the same time for selection of the compression ratio, and there is a problem that the circuit scale becomes large as in Patent Document 1. Further, it can be predicted that the image quality changes for each region.

  Still further, the technique disclosed in Patent Document 3 requires a circuit for classifying regions according to their characteristics in addition to data compression, which increases the circuit scale.

  The above prior art is intended to obtain image data with high quality and high compression rate, and does not consider the cost of the apparatus.

  When cost is considered, the following problems also arise. That is, in an image compression technique having sufficient quality and speed, the size of image data after compression varies greatly depending on the features of the image data. That is, the amount of compressed image data is determined only after the image data is compressed. In consideration of this point, when applying the compression technique to the image processing apparatus, it is necessary to provide each resource so as to withstand the worst case with the lowest compression rate. Preparing for such a worst case means that in a normal case, there is a surplus of resources. In other words, even if the high compression processing is not used, providing for the worst case causes a cost increase.

  SUMMARY An advantage of some aspects of the invention is that it provides an image compression apparatus and the like that can output a high-quality image by effectively using compression resources.

  The present invention employs the following means in order to achieve the above object. That is, in the image compression apparatus or the like according to the present invention, ratio setting means for setting the ratio of the area for performing reversible compression on the input image data, and the reversible compression area that is the application area of the reversible compression according to the ratio and non A region setting means for setting a lossy compression region, which is a lossless compression application region, to the image data, a lossless compression device for lossless compression of the lossless compression region, and a compression ratio of the lossless compression region by the lossless compression unit. A lossless compression ratio calculating means, a scheduled compression ratio calculating means for calculating a scheduled compression ratio to be applied to the irreversible compression area based on the compression ratio of the lossless compression area, and an irreversible compression area based on the calculated scheduled compression ratio And irreversible compression means for irreversibly compressing.

  In addition, an irreversible compression ratio calculating means for calculating a compression ratio of the irreversible compression area after compression, and an image of the irreversible compression area that has been irreversibly compressed based on the compression ratio of the irreversible compression area and the scheduled compression ratio There is a configuration including a determination unit that determines whether or not data can be adopted.

  Further, the lossless compression by the lossless compression means, the calculation of the scheduled compression ratio by the expected compression ratio calculation means, the lossy compression by the lossy compression means, and the determination by the determination means are constituted by a plurality of dot data and the lossless compression described above. The minimum unit of image compression by the unit and the lossy compression unit may be performed for each line of the minimum unit of the image data arranged in a square.

  Still further, the area setting means may be configured to set the areas in the unit area according to a pattern having a regular ratio between the lossless compression area and the lossy compression.

  Furthermore, an image forming apparatus having such an image compression apparatus and a still image compression method realized by the processing procedure of the apparatus are also provided.

  Since the ratio of the lossless compression area is set based on the setting condition set by the user, the required minimum image quality can be guaranteed regardless of the characteristics of the image data.

  In addition, after the lossless compression ratio is determined, the setting value of the compression ratio of the irreversible area is calculated, that is, the remaining resources are allocated to the irreversible compression, so the compression ratio of the irreversible area can be set to the upper limit of the remaining resources. Thus, it becomes possible to compress the lossy compression area by using the compression resources to the maximum. For this reason, the utilization efficiency of compressed resources can be increased, and as a result, the cost of the apparatus can be reduced.

  Furthermore, when the lossy-compressed image data is equal to or higher than the scheduled compression rate, the lossless compression region is complemented by the lossy compression region, so that high-quality output can be expected with conventional resources.

  Further, compression processing is performed for each line of the compression unit data, and at this time, a compression pattern having regularity in which the reversible compression area and the irreversible compression are equally arranged is adopted. For this reason, the compression process of one cycle is simplified, the working memory during the compression process can be minimized, and the occurrence of unevenness in resolution can be prevented in the entire image data.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings for understanding of the present invention. In addition, the following embodiment is an example which actualized this invention, Comprising: It is not the thing of the character which limits the technical scope of this invention.

  The image forming apparatus 101 according to the present invention will be described below.

  FIG. 1 is a schematic diagram of the image forming apparatus 100. However, details of each part not directly related to the present invention are omitted.

  The image forming apparatus 100 according to the present invention corresponds to, for example, a printer, a single scanner, or a multifunction machine including a printer, a copy, a scanner, a fax machine, and the like.

  As an example, the operation of the image forming apparatus when copying a document using a multifunction machine will be briefly described.

  For example, when a user prints a document using the multifunction device, the document is placed on the document table 103 or the table 105 shown in FIG. 1, and a print instruction is given to the operation panel provided near the document table. Do. When the instruction is given, printing is performed by operating the following units (drive units).

  That is, as shown in FIG. 1, the image forming apparatus 100 according to the present embodiment includes a main body 101 and a platen cover 102 attached above the main body 101. A document table 103 is provided on the upper surface of the main body 101, and the document table 103 is opened and closed by a platen cover 102. The platen cover 102 is provided with an automatic document feeder 104, a placing table 105, and a sheet discharging table 109.

  The automatic document feeder 104 includes a document conveyance path 108 formed inside the platen cover 102, a pickup roller 106 and a conveyance roller 107 provided inside the platen cover 102, and the like. The document conveyance path 108 is a document conveyance path that leads from the placement table 105 to the sheet discharge table 109 via a reading position P where reading is performed by the reading unit 110 provided in the main body 101.

  The automatic document feeder 104 pulls out each document placed on the placing table 105 to the inside of the transport path 108 by the pickup roller 106 and passes the document pulled out by the transport roller 107 and the like through the reading position P. The paper is discharged onto the paper base 109. When the document passes the reading position P, the document is read by the reading unit 110.

  The reading unit 110 is provided below the document table 103, and its details are shown in FIG. The reading unit 110 includes a first light source 111 that illuminates the document table 103 in the main scanning direction, a slit 116 that selectively passes light from the document table, and a mirror 112 that guides light from the document table. The movable carriage 117, the second movable carriage 118 including mirrors 113A and 113B that reflect the reflected light from the first movable carriage 117 again, and the lens group 119 that optically corrects the light guided by the mirror, An image sensor 115 that receives the light corrected by the lens group 119, and an image data generation unit 114 that converts the light received by the image sensor into an electrical signal and performs correction / correction as necessary. .

  When reading a document on the automatic document feeder 104, the light source 111 moves to a position where the reading position P can be irradiated and emits light. Light from the light source 111 is reflected by a document that passes through the document table 103 and passes through the reading position P, and is guided to the image sensor 115 by the slit 116, mirrors 112, 113A, and 113B, and the lens group 119. The image sensor 115 converts the received light into an electrical signal and transmits it to the image data generation unit 114. The light received by the image sensor 115 is input to the image data generator 114 as analog electrical signals of R (red), G (green), and B (blue), where analog-to-digital conversion is performed. Digitized. Further, the image data generation unit 114 generates digital image data including a plurality of minimum unit data by using the sequentially converted digital signal as minimum unit data (dot data) and correcting or correcting the minimum unit data.

  The reading unit 110 can read not only the document conveyed by the automatic document feeder 104 but also the document placed on the document table 103. When reading a document placed on the document table 103, the first carriage 112 moves in the sub-scanning direction while emitting light from the light source 111, so that the optical path length from the light source 111 to the image sensor 115 is constant. The second moving carriage 118 moves in the direction of the image sensor 115 at a half speed of the first moving carriage 117.

  The image sensor 115 electrically outputs light from the document placed on the document table 103 based on the light guided to the mirrors 112, 113 </ b> A, 113 </ b> B, as in the case of the document conveyed to the automatic document feeder 104. The signal is converted into a signal, and based on this, the image data generation unit 114 generates image data.

  A printing unit 120 that prints image data is provided below the reading unit 110 of the main body 101. Image data that can be printed by the printing unit 120 is generated by the image data generation unit 114 as described above, or transmitted from a terminal such as a personal computer connected to the image forming apparatus 100 and a network such as a LAN. It is.

  As a printing method performed by the printing unit 120, an electrophotographic method is used. That is, the photosensitive drum 121 is uniformly charged by the charger 122, and then the photosensitive drum 121 is irradiated by the laser 123 to form a latent image on the photosensitive drum 121, and toner is attached to the latent image by the developing device 124. In this method, a visual image is formed and the visible image is transferred onto a sheet by a transfer roller.

  Note that in the image forming apparatus corresponding to the full-color image, the developing device (rotary developing device) 124 is rotated in the circumferential direction around a rotation axis configured in a direction perpendicular to the paper surface of FIG. A developing unit in which color toner is stored is disposed at a position facing the photosensitive drum 121. In this state, the latent image on the photosensitive drum 121 is developed with toner stored in the developing device 124 and transferred to the intermediate transfer belt 125A. The developing device 124 includes four developing units 124 (Y), (C), (M), and yellow (Y), cyan (C), magenta (M), and black (K). (K). By repeating the transfer to the intermediate transfer belt 125A for each color, a full color image is formed on the intermediate transfer belt 125A.

  The paper on which the visible image is printed is placed on a paper feed tray such as the manual feed tray 131 and the paper feed cassettes 132, 133, and 134.

  When the printing unit 120 performs printing, one sheet of paper is pulled out from any one of the paper feed trays using the pickup roller 135, and the pulled-out paper is transferred to the intermediate transfer belt 125 </ b> A by the transport roller 137 or the registration roller 138. Feed between rollers 125B.

  When the visible image on the intermediate transfer belt 125 is transferred onto the sheet fed between the intermediate transfer belt 125 and the transfer roller 125, the printing unit 120 uses the conveying belt 126 to fix the visible image. Send paper to 127. The fixing device 127 includes a heating roller 128 with a built-in heater and a pressure roller 129 pressed against the heating roller 128 with a predetermined pressure. When the sheet passes between the heating roller 128 and the pressure roller 129, the visible image is fixed to the sheet by heat and the pressing force to the sheet. The printing unit 120 discharges the sheet that has passed through the fixing device 127 to the discharge tray 130.

  The basic copy service processing in the image forming apparatus 100 has been described above.

  In the image forming apparatus 100, as shown in the schematic configuration diagram of FIG. 3, a central processing unit (CPU) 301, a random access memory (RAM) 302, a read only memory (ROM) 303, and a hard disk drive (HDD). 304 and a driver 305 corresponding to each drive unit in the printing process are connected via an internal bus 306. The CPU 301 uses, for example, the RAM 302 as a work area, executes a program stored in the ROM 303, the HDD 304, and the like, and exchanges data and commands with the driver 305 based on the execution result, thereby performing the above-described FIG. 2 controls the operation of each driving unit 307 shown in FIG.

  Next, details of the image compression unit 400 according to the present invention will be described.

  The image compression unit 400 can be provided as an image compression apparatus provided in the image data generation unit 114 or connected to the image data generation unit 114, for example.

  The image data input unit 401 constituting the image compression unit 400 receives the image data generated by the image data generation unit 114 (FIG. 6: S601). The image data has a resolution of, for example, 1200 dpi, and may be converted to a resolution of, for example, 600 dpi in accordance with the output capability of the image processing apparatus 100. Here, description will be made assuming that 600 dpi image data is processed for one page.

  When the image data is received, the ratio setting unit 403 that has received a notification to that effect acquires the ratio of the area to be subjected to lossless compression from the user setting storage unit 402. Here, the ratio is stored in the user setting storage unit 402 by the user setting in advance from the operation panel, for example. Specifically, when the user desires high-quality printing, “high quality” is set in advance for the image forming apparatus 100. It is also possible to set “low image quality” which is inferior to “high image quality” and “normal image quality” which is an intermediate image quality. By setting “high image quality”, the compressed image data is compressed so as to have information close to the original image of 600 dpi. However, in this case, the size of the image data after compression increases because the lossless compression area described later increases, and the number of pages of image data that can be handled (for example, stored) by the image forming apparatus 100. Decrease. On the other hand, when “normal image quality” or “low image quality” is set, the area to be reversibly compressed is reduced, so that the size of the compressed image data is reduced. However, the number of pages of image data that can be handled by the image forming apparatus 100 is increased compared to the case of “high image quality”.

  Assuming that the user has set “low image quality”, the preset ratio is, for example, “25%”. The ratio setting unit 403 receives the ratio 25%, and sets the ratio of the area to be subjected to lossless compression to 25% (FIG. 6: S602). Note that the lossless compression referred to here is compression that can restore 100% of the original data before compression from the data after compression, and has a feature that the compression ratio is low without causing image quality deterioration.

  When the ratio of the areas to be subjected to the lossless compression is 25%, the area setting unit 404 employs the pattern A corresponding to 25% (701) in FIG. 7, for example. Here, each black circle and white circle shown in FIG. 7 is a set of a plurality of dot data (minimum unit data), and is composed of, for example, 8 × 8 dots. These black circles and white circles are the minimum unit for compressing an image, that is, compression unit data, and compression processing is performed using one black circle or white circle as a unit of compression. Since the four compression unit data included in the dotted line 704 are allocated to one lossless compression region and three lossy compression regions, the region where lossless compression is performed can be said to be 25%. That is, the area setting means 404 assigns or sets one compression unit data to the lossless compression area based on 25% pattern A for each minimum unit data of the input image data, and the remaining three The compression unit data is set in the lossy compression area (FIG. 6: S603). 25% of the image data input by the above processing is a target of lossless compression processing, and 75% which is not a target of lossless compression is a target of lossy compression processing. Note that the plurality of patterns shown in FIG. 7 prevent the occurrence of uneven spots in the resolution of the entire image data by having the lossless compression area and the lossy compression in an equal ratio and regularity.

  Subsequently, based on the information of the lossless compression area and the information of the lossy compression area set by the area setting unit 404, the compression processing (FIG. 6: S604) performed by the lossless compression means 405 and the lossy compression means 408. Details will be described. When using the 25% pattern A, since different compression processing is repeated a plurality of times for two lines (two lines of compression unit data in the side direction in the image data constituting the square), two lines are regarded as one process. explain. In FIG. 5, the input image data 501 is displayed as the image data for the two lines, and the data size is assumed to be 100.

  First, the area setting unit 404 determines whether or not there is a lossless compression area in one line of the compression unit data in the image data (FIG. 8: S801). Specifically, it is determined whether or not a black circle indicating a lossless compression area exists in one line 705 of the 25% pattern A in FIG. Here, since the reversible compression area exists, the reversible compression means 405 reversibly compresses the minimum unit data corresponding to the first line of the image data and the minimum unit data corresponding to the reversible compression area. Is transmitted (FIG. 8: S801 YES).

  The lossless compression unit 405 that has received the above command performs lossless compression on the compression unit data corresponding to the one line of the lossless compression region based on the image data and the information on the lossless compression region set by the region setting unit 404. (FIG. 8: S802).

  By this process, the minimum unit data (size 25) corresponding to 25% of the input image data 501 (size 100) for two lines shown in FIG. 5 is losslessly compressed, and lossless compressed data 502 is generated.

  When the reversible compression is completed, the compression unit data after the reversible compression is transmitted to the compressed image forming unit 411. Further, the size of the compression unit data after the lossless compression is transmitted to the lossless compression rate calculation unit 406, and the lossless compression rate calculation unit 406 includes the size of the compression unit data before the compression and the compression unit after the lossless compression. Based on the data size, the lossless compression rate is calculated (FIG. 8: S803). Here, assuming that the lossless compression rate is 70%, the size of the lossless compressed image data 502 is 17.5. The lossless compression rate is a value that can be calculated only after compression.

  When the lossless compression rate is calculated, the scheduled compression rate calculation unit 407 calculates the scheduled compression rate 504 based on the lossless compression rate and the maximum allowable size 503 of the compressed image data. Here, the maximum allowable size indicates the maximum size in which the compressed image data size is allowed. For example, when the image forming apparatus 100 has the ability to store 1000 pieces of image data as the performance, the maximum allowable size is less than 1/1000 of the storage memory (resource) included in the image forming apparatus 100. It needs to be a size. Further, assuming that the maximum capacity of work memory (resource) that can be used for compression processing in the image forming apparatus 100 is 100, the image data size for at least one page generated by compression, or work used in the compression process. The total size of the memory (resources) needs to be within the maximum capacity 100. Since the value of the maximum allowable size 503 varies for each image forming apparatus 100 and further for each setting condition in the apparatus, the scheduled compression rate calculation unit 407 may calculate it whenever necessary. The maximum allowable size 503 of the compressed image data set under such a plurality of conditions is 30 here.

  The scheduled compression rate calculation means 407 calculates a scheduled compression rate to be achieved by irreversible compression based on the lossless compression rate and the maximum allowable size 503. Specifically, since the lossless compression rate is 70%, the size of the lossless compressed image data is 17.5 by integrating with the data amount (25) of the minimum unit data corresponding to the lossless compression area. On the other hand, since the maximum allowable size 503 is 30, the image data size generated by irreversibly compressing the irreversible compression area by allocating all remaining resources to the irreversible compression processing is 12.5. Calculated. Therefore, it is necessary to compress the data size (75) of the uncompressed area to the compressed data size (12.5), and the scheduled compression rate is set to 84% (FIG. 8: S804).

  Subsequently, the area setting unit 404 determines whether or not there is an irreversible compression area in the line for one line of the compression unit data in the image data (FIG. 8: S805). Specifically, it is determined whether or not a white circle indicating an irreversible compression area exists in one line 705 of the 25% pattern A in FIG. Here, since the lossy compression area exists, the minimum unit data corresponding to the first line of the image data and the minimum unit data corresponding to the lossy compression area are not transferred to the lossy compression unit 408. A command for reversible compression is transmitted (FIG. 8: S805 YES).

  The lossy compression unit 408 that has received the command is based on the image data, the information of the lossy compression region (size 25) of the first line set by the region setting unit 404, and the calculated scheduled compression rate. Thus, the compression unit data corresponding to the irreversible compression area is irreversibly compressed (FIG. 8: S806). Here, in the irreversible compression process, since the compression rate can generally be set as a parameter, the scheduled compression rate of 84% is applied to the compression rate. By setting the parameter, a compression rate close to the parameter can be expected in lossy compression.

  By this processing, the minimum unit data (size 25) corresponding to the irreversible compression area of the first line in the input image data 501 (size 100) for two lines shown in FIG. 5 is irreversibly compressed. Data 505 is generated.

  When the irreversible compression of the first line is completed, the size of the irreversible compression data 505 is transmitted to the irreversible compression rate calculation unit 410. The irreversible compression rate calculation unit 410 determines the size of the compression unit data before compression and the size of the compression unit data. Based on the size of the lossless compression data 505 (compression unit data after lossy compression), the lossy compression rate is calculated (FIG. 8: S807). Here, it is assumed that the lossy compression ratio is 80%.

  Subsequently, the scheduled compression rate calculated by the scheduled compression rate calculation unit 407, the irreversible compression rate calculated by the irreversible compression rate calculation unit 410, and the compression unit data after irreversible compression are determined. 409.

  Based on the received scheduled compression rate and irreversible compression rate, the determination unit 409 determines whether or not the compression unit data after irreversible compression can be adopted (utilized) (FIG. 8: S808).

  Here, since the scheduled compression rate is 84%, the irreversible compression rate of the first line is 80%, so the determination unit 409 discards the irreversible compression data (FIG. 8: S808 NO → S810). .

  Thus, the compression process for the compression unit data on the first line is completed.

  Subsequently, the image compression unit 400 performs processing for the second line. The second line is different from the first line in that there is no lossless compression area on the second line. In this case, in step S801 of the compression process 604, lossy compression is applied without lossless compression (FIG. 8: S801 NO → S806). The processing content is as described above, but the calculated compression rate is calculated on the first line. That is, the region setting unit 404 performs irreversible compression on the irreversible compression unit 408 with the minimum unit data corresponding to the second line of the image data and the minimum unit data corresponding to the irreversible compression region. Send the command.

  The lossy compression means 408 that has received the above command is calculated by processing the image data, the information of the lossy compression area (size 50) of the second line set by the area setting means 404, and the processing of the first line. Based on the scheduled compression rate, the compression unit data corresponding to the irreversible compression area is irreversibly compressed (FIG. 8: S806).

  By this processing, the minimum unit data (size 50) corresponding to the irreversible compression area of the second line in the input image data 501 (size 100) for two lines shown in FIG. 5 is irreversibly compressed. Data 506 is generated.

  When the irreversible compression of the second line is completed, the size of the irreversible compression data 506 is transmitted to the irreversible compression rate calculation unit 410. The irreversible compression rate calculation unit 410 determines the size of the compression unit data before compression and the size of the compression unit data. Based on the size of the lossless compression data 506, the lossy compression rate is calculated (FIG. 8: S807). Here, it is assumed that the lossy compression ratio is 90%.

  Subsequently, the scheduled compression rate calculated in the processing of the first line, the irreversible compression rate calculated by the irreversible compression rate calculation unit 410, and the compression unit data after the irreversible compression are determined. 409.

  Based on the received scheduled compression rate and irreversible compression rate, the determination unit 409 determines whether or not the compression unit data after irreversible compression can be used (FIG. 8: S808).

  Here, since the scheduled compression rate is 84%, the irreversible compression rate of the second line is 90%, so the determination unit 409 employs irreversible compression data (FIG. 8: S808 YES → S811). . If it is determined to be adopted, the lossy compressed data is transmitted to the compressed image forming unit 411.

  By repeating the above processing for all lines forming the image forming data, the compression of all the image data is completed. Each piece of compressed unit data after compression is formed into one compressed image data by the compressed image forming unit 411 and output from the image compressing unit 400.

  As described above, since the ratio of the lossless compression area is set based on the setting condition set by the user, the required minimum image quality can be guaranteed regardless of the characteristics of the image data.

  In addition, after the lossless compression ratio is determined, the setting value of the compression ratio of the irreversible area is calculated, that is, the remaining resources are allocated to the irreversible compression, so the compression ratio of the irreversible area can be set to the upper limit of the remaining resources. Thus, it becomes possible to compress the lossy compression area by using the compression resources to the maximum. For this reason, the utilization efficiency of compressed resources can be increased, and as a result, the cost of the apparatus can be reduced.

  Further, compression processing is performed for each line of the compression unit data, and at this time, a compression pattern having regularity in which the reversible compression area and the irreversible compression are equally arranged is adopted. For this reason, the compression process of one cycle is simplified, the working memory during the compression process can be minimized, and the occurrence of unevenness in resolution can be prevented in the entire image data.

  Note that when the determination unit 409 determines that the irreversible compressed data is not adopted, the compressed image forming unit 411 may apply linear interpolation processing to the application area of the irreversible compressed data.

  Moreover, although the example which employ | adopted 25% pattern A was demonstrated in the said embodiment, even if it employ | adopts 33% pattern and 50% pattern, it is the same. For the 25% pattern A, the processing in two lines is one cycle. For example, 50% (703) pattern B, 50% (703) pattern C, 33% (702) pattern B, 33% (702) In the pattern C, one line of processing can be applied to the above-described processing as one cycle. In the case of 33% (702) pattern A, the processing for three lines may be one cycle.

  Since the image compression apparatus and the like according to the present invention can output high-quality images by effectively using compression resources, it is useful as an image compression apparatus that achieves both cost and image quality.

1 is a schematic diagram of an image forming apparatus according to the present invention. The enlarged view of a reading part. 1 is a schematic configuration diagram of an image forming apparatus according to the present invention. 1 is a schematic functional block diagram of an image compression apparatus according to the present invention. The figure which shows transition of a compression process. 6 is a flowchart showing processing of the image compression apparatus. The figure which shows the example of a setting pattern. The flowchart which shows the detail of a compression process.

Explanation of symbols

400 image compression means 401 image data input means 402 user setting storage means 403 ratio setting means 404 area setting means 405 reversible compression means 406 reversible compression rate calculation means 407 scheduled compression rate calculation means 408 lossy compression means 409 determination means 410 lossy compression Rate calculating means 411 Compressed image forming means

Claims (6)

A ratio setting means for setting a ratio of an area for performing reversible compression on input image data;
An area setting means for setting a reversible compression area that is an application area of lossless compression and an irreversible compression area that is an application area of irreversible compression in the image data according to the ratio;
Reversible compression means for reversibly compressing the reversible compression region;
Reversible compression rate calculation means for calculating the compression rate of the reversible compression area by the reversible compression means;
A planned compression rate calculation means for calculating a planned compression rate to be applied to the lossy compression region based on the compression rate of the lossless compression region;
Irreversible compression means for irreversibly compressing the irreversible compression region based on the calculated scheduled compression rate;
An image compression apparatus comprising: further,
Irreversible compression rate calculation means for calculating the compression rate of the irreversible compression region after compression;
A determination means for determining whether or not to adopt the image data of the irreversible compression area based on the compression ratio of the irreversible compression area and the scheduled compression ratio;
The image compression apparatus according to claim 1, further comprising: Reversible compression by the reversible compression means;
Calculation of the planned compression ratio by the above-mentioned planned compression ratio calculation means,
Irreversible compression by the irreversible compression means;
The determination by the determination means is
The minimum unit of image compression constituted by a plurality of dot data by the lossless compression unit and the lossy compression unit is performed for each line of the minimum unit of the image data arranged in a square. Image compression device. The area setting means includes
The image compression apparatus according to any one of claims 1 to 3, wherein in the unit area, the reversible compression area and the irreversible compression are set in accordance with a pattern having an equal ratio and regularity.   An image forming apparatus comprising the image compression apparatus according to claim 1. Setting a ratio of areas for lossless compression with respect to input image data;
A step of setting a reversible compression area that is an application area of lossless compression and an irreversible compression area that is an application area of irreversible compression in the image data according to the ratio;
Reversibly compressing the reversible compression region;
Calculating a compression ratio of the lossless compression region;
Calculating a scheduled compression ratio to be applied to the lossy compression area based on the compression ratio of the lossless compression area;
Irreversibly compressing the irreversible compression region based on the calculated scheduled compression rate;
A still image compression method.

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