JP2016119528A - Image processor, program and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable the generation of a compressed image of high quality by reducing a deterioration in the image quality of a boundary of attributes during performing compression by an irreversible compression system.SOLUTION: The image processor performs compression processing of color information of each attribute by the irreversible compression system, and performs compression processing of attribute information by a reversible compression system and includes an attribute information detection part for detecting prescribed attribute information from image data, a color information separation part for separating color information from the image data in each attribute, a block extraction part for dividing the color information of each attribute into prescribed image processing units, a replacement determination part for determining whether to replace the color information of each attribute in each image processing unit about the color information of each attribute, and a replacement part for replacing the color information of each attribute in each image processing unit with a prescribed value obtained from color information of the same attribute in the image processing unit.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image processing device, a program, and a method, and can be applied to, for example, an image processing device, a program, and a method that generate a compressed image by performing compression processing on image data.

  Since image data has a large amount of information, there are various image compression techniques for compressing image data to reduce the amount of information. In recent years, along with the popularization and standardization (ISO 32000-1) of PDF (Portable Document Format) files, there is an image compression process that uses MRC (Mixed Raster Content) to compress image data and generate PDF files. In order to compress the image data at a high compression rate, the image is separated into layers of a multilayer structure, compressed for each layer using an image compression method having a different compression rate, and the compressed layers are combined. A compressed image is obtained.

  A conventional image processing apparatus separates pixels belonging to a character region such as characters and diagrams as character attributes and pixels belonging to a non-character region as non-character attributes based on the pixel value of each pixel of image data. . In order to compress the image data at a high compression rate, the character attribute color information or the non-character attribute color information is compressed by the lossy compression method. In addition, when a conventional image processing apparatus compresses each color information by a lossy compression method, the pixel values of all the pixels in each attribute block are replaced with representative values or the like (see Patent Document 1). .

JP 2014-072556 A

  However, since the attribute information of each pixel may not be detected properly, when a color information image compressed by the lossy compression method is combined to generate a compressed image, for example, the character attribute and the non-character attribute In some cases, the image quality may deteriorate at the boundary between the two.

  For this reason, there is a need for an image processing apparatus, program, and method that can reduce deterioration in image quality at the boundary between attributes and generate a high-quality compressed image when compression is performed using a lossy compression method.

  In order to solve this problem, an image processing apparatus according to a first aspect of the present invention includes (1) an attribute information detection unit that detects predetermined attribute information from image data, and (2) color information from the image data for each attribute. A color information separating unit that separates the color information into a predetermined image processing unit; and (4) color information for each attribute. For each of the image processing units, for each image processing unit, a replacement determination unit that determines whether or not the color information for each attribute in each image processing unit is replaced with a predetermined value, and (5) each of the color information for each attribute The color information for each attribute in each image processing unit is replaced with a predetermined value obtained from the color information of the same attribute in the image processing unit for each image processing unit according to the replacement determination result of the replacement determination unit. A substitution part, and (6) a genus obtained by the substitution part A irreversible compression unit that performs compression processing on each color information by a lossy compression method; and (7) a lossless compression unit that performs compression processing on the attribute information obtained by the attribute information detection unit by a lossless compression method. It is characterized by providing.

  An image processing program according to a second aspect of the present invention includes: (1) an attribute information detection unit that detects predetermined attribute information from image data; and (2) color information that separates color information from image data for each attribute. A separation unit; (3) a block extraction unit that divides each color information for each attribute separated by the color information separation unit into predetermined image processing units; and (4) an image for each color information for each attribute. For each processing unit, a replacement determination unit that determines whether or not the color information for each attribute in each image processing unit is replaced with a predetermined value, and (5) the replacement determination unit for each color information for each attribute. A replacement unit that replaces the color information for each attribute in each image processing unit with a predetermined value obtained from the color information of the same attribute in the image processing unit, for each image processing unit, according to the replacement determination result; 6) For each attribute obtained by the replacement part Each of the information is made to function as an irreversible compression unit that performs compression processing by the irreversible compression method, and (7) a lossless compression unit that performs compression processing by the lossless compression method on the attribute information obtained by the attribute information detection unit. Features.

  In the image processing method according to the third aspect of the present invention, (1) the attribute information detection unit detects predetermined attribute information from the image data, and (2) the color information separation unit extracts color information from the image data for each attribute. (3) The block extraction unit divides each color information for each attribute separated by the color information separation unit into predetermined image processing units, and (4) the replacement determination unit performs color information for each attribute. For each of the image processing units, it is determined whether or not the color information for each attribute in each image processing unit is replaced with a predetermined value, and (5) the replacement unit is configured for each piece of color information for each attribute. The color information for each attribute in each image processing unit is replaced with a predetermined value obtained from the color information of the same attribute in the image processing unit for each image processing unit according to the replacement determination result of the replacement determination unit. (6) Color information for each attribute obtained by the irreversible compression unit by the replacement unit Each performs compression process with lossy compression method, (7) a reversible compression unit, characterized in that the attribute information obtained by the attribute information detection unit performs compression processing by the reversible compression method.

  ADVANTAGE OF THE INVENTION According to this invention, when compressing by an irreversible compression system, deterioration of the image quality of an attribute boundary can be reduced and a high quality compressed image can be produced | generated.

It is a block diagram which shows the functional structure of the image processing apparatus which concerns on 1st Embodiment. It is a figure which shows the example of the data of the attribute information which concerns on 1st Embodiment. 4 is a flowchart illustrating an operation of compression processing in the image processing apparatus according to the first embodiment. It is a flowchart which shows the operation | movement of the replacement determination process which concerns on 1st Embodiment. It is explanatory drawing explaining the presence or absence of the separation area | region in each block which concerns on 1st Embodiment. It is explanatory drawing explaining the replacement determination process which concerns on 1st Embodiment. It is explanatory drawing explaining the image compression, expansion | extension, and composition by the conventional image processing apparatus. It is explanatory drawing explaining the image compression by the image processing apparatus which concerns on 1st Embodiment, expansion | extension, and a synthesis | combination.

(A) First Embodiment Hereinafter, a first embodiment of an image processing apparatus, a program, and a method according to the present invention will be described in detail with reference to the drawings.

(A-1) Configuration of First Embodiment FIG. 1 is a block diagram illustrating a functional configuration of an image processing apparatus according to the first embodiment. In FIG. 1, an image processing apparatus 100 according to the first embodiment is connected to a scanner 200 as an input unit for inputting image data and a display 300 as an output unit for outputting an image based on the image data. . The image processing apparatus 100 includes a storage unit 400, a compression unit 500, and an expansion unit 600.

  The image processing apparatus 100 compresses the image data based on the read signal supplied from the scanner 200 to generate a compressed image, or decompresses the compressed image data and displays it on the display 300.

  The image processing apparatus 100 may be a control device having a CPU, a ROM, a RAM, an EEPROM, an input / output interface unit, and the like in hardware. For example, the image processing apparatus 100 is a scanner device physically integrated with the scanner 200. For example, in addition to the scanning function by the scanner 200 that reads image data, a multi-function peripheral (MFP) having a printing function, a copying function, an electronic mail function, and the like can be applied.

  Further, the image processing apparatus 100 may realize the image processing function as a part or combination of circuits for performing signal processing, or may realize the image processing function by software operating on a general-purpose computer. good. Furthermore, an image processing function may be constructed by installing an image processing program in a computer such as a PC or a workstation.

  The storage unit 400 stores an image processing program, data necessary for image processing, image data, image data after compression processing, and the like. The storage unit 400 includes, for example, a volatile memory RAM, and stores image data input from the scanner 200 as an input unit and image data compressed by the compression unit 500.

  The compression unit 500 performs a predetermined image compression process on the image data input from the scanner 200 or the image data stored in the storage unit 400. The compression unit 500 includes an attribute detection unit 501, a color information separation unit 502, a block extraction unit 503, a first replacement determination unit 504, a first replacement unit 506, a first lossy compression unit 508, a second replacement determination unit 505, 2 replacement unit 507, second irreversible compression unit 509, and reversible compression unit 510.

  The attribute detection unit 501 separates character regions such as characters and line drawings from non-character regions other than characters and line drawings from the image data read from the storage unit 400, and sets attribute information for each pixel of the image data. Give.

  Here, the attribute information is information indicating whether the area to which each pixel of the image data belongs is a character area or a non-character area. “Character attribute” refers to an attribute indicating that an area in an image is an area of a character or a line drawing. The “non-character attribute” refers to an attribute indicating that an area in an image is an area other than a character or a line drawing, and includes, for example, a photograph area, a natural image area, and a background area.

  FIG. 2 is a diagram illustrating an example of attribute information data according to the first embodiment. FIG. 2 exemplifies attribute information of each pixel in the image data of vertical 12 pixels × horizontal 12 pixels. The attribute information can be, for example, 1-bit binary data. In FIG. 2, “1” indicates a character attribute, and “0” indicates a non-character attribute.

  Based on the attribute information detected by the attribute detection unit 501, the color information separation unit 502 uses image data indicating character attribute color information (hereinafter referred to as character image data) from the image data stored in the storage unit 400. And image data indicating color information for non-character attributes (hereinafter also referred to as non-character image data).

  Here, “color information” is information representing the color of each pixel. For example, when the image data is color image data, and each color of R (red), G (green), and B (blue) of the RGB color system is expressed with 256 gradations, the color information of each pixel is expressed. The color information represents the gradation of each color as 8-bit data. More specifically, when the color information of the pixel is red with the maximum luminance, the pixel value indicating the color information of the pixel is “255, 0,” in the order of R (red), G (green), and B (blue). The data is “0”. Further, for example, when the image data is monochrome image data, it can be data indicating brightness of black and white (for example, 8-bit data).

  The block extraction unit 503 performs predetermined image processing on the attribute information of each pixel detected by the attribute detection unit 501 and the character image data and non-character image data generated by the color information separation unit 502. Divide into units.

  Here, the predetermined image processing unit divided by the block extraction unit 503 can be, for example, a block (area) of vertical m pixels × horizontal n pixels. In this embodiment, a case of 8 × 8 blocks is exemplified, but the block size indicating the image processing unit is not particularly limited.

  The first replacement determination unit 504, the first replacement unit 506, and the first irreversible compression unit 508 are processing units that perform image processing on the character image data, and the second replacement determination unit 505, the second replacement unit 507, and the second replacement unit 507. The 2 lossy compression unit 509 is a processing unit that performs image processing on non-character image data.

  Based on the attribute information detected by the attribute detection unit 501, the first replacement determination unit 504 calculates pixel values of pixels in each block of the character image data for all blocks extracted by the block extraction unit 503. Then, it is determined whether or not the pixel value of the pixel belonging to the character attribute in the block may be replaced with a representative value or an average value. The detailed description of the replacement determination method by the first replacement determination unit 504 will be described in detail in the operation section.

  Based on the attribute information detected by the attribute detection unit 501, the second replacement determination unit 505 performs pixel values of pixels in each block of the non-character image data for all blocks extracted by the block extraction unit 503. Is replaced with a representative value or an average value of pixel values of pixels belonging to the non-character attribute in the pixel block. Note that the detailed description of the replacement determination method by the second replacement determination unit 505 will also be described in detail in the operation section.

  The first replacement unit 506 sets the pixel values of the pixels in each block of the character image data for all the blocks of the character image data in accordance with the replacement determination result by the first replacement determination unit 504. The pixel value is replaced with a representative value or an average value of the pixel values belonging to the attribute.

  That is, when it is determined by the first replacement determination unit 504 that the replacement is performed, the first replacement unit 506 replaces the pixel value of the pixel in each block of the character image data with the representative value or the average value. On the other hand, when the first replacement determining unit 504 determines not to replace, the first replacing unit 506 does not replace the pixel value of the pixel in each block of the character image data with the representative value or the average value.

  The second replacement unit 507 sets the pixel values of the pixels in each block of the non-character image data in all the blocks of the non-character image data according to the replacement determination result by the second replacement determination unit 505. Are replaced with a representative value or an average value of pixel values of pixels belonging to the non-character attribute.

  That is, when it is determined by the second replacement determination unit 505 that the replacement is performed, the second replacement unit 507 replaces the pixel value of the pixel in each block of the non-character image data with the representative value or the average value. On the other hand, when the second replacement determining unit 505 determines not to replace, the second replacing unit 507 does not replace the pixel value of the pixel in each block of the non-character image data with the representative value or the average value. .

  The first irreversible compression unit 508 performs compression processing on all blocks of the character image data replaced by the first replacement unit 505 by the irreversible compression method, and stores the compressed data in the storage unit 400. To do. Here, the lossy compression method is a compression method in which the compressed data and the decompressed data do not completely match, but the compression rate is higher than that of the lossless compression method. For example, JPEG or the like may be used. it can.

  The second lossy compression unit 509 performs compression processing on all blocks of the non-character image data replaced by the second replacement unit 506 using the lossy compression method, and stores the compressed data in the storage unit 400. Remember. Similarly to the first irreversible compression unit 508, the second irreversible compression unit 509 can use JPEG or the like.

  The lossless compression unit 510 performs compression processing on the attribute information detected by the attribute detection unit 501 using the lossless compression method, and stores the data after the lossless compression processing in the storage unit 400. Here, the lossless compression method is a compression method in which the compression rate is lower than that of the lossy compression method, but the compressed data and the decompressed data can be matched. In this embodiment, the case where MMR (Modified Modified READ) etc. are used as a reversible compression system is illustrated.

  The decompression unit 600 decompresses each of the character image data, the non-character image data, and the attribute information data that has been subjected to the compression processing stored in the storage unit 400, and combines the decompressed data. Image data is generated. The decompression unit 400 stores the generated image data in the storage unit 400. As illustrated in FIG. 1, the decompression unit 600 includes a first irreversible decompression unit 601, a second irreversible decompression unit 602, a reversible decompression unit 603, and a synthesis unit 604.

  The first irreversible decompression unit 601 performs a decompression process on the data compressed by the first irreversible compression unit 508.

  The second lossy decompression unit 602 performs decompression processing on the data compressed by the second lossy compression unit 508.

  The lossless decompression unit 603 performs decompression processing on the data compressed by the lossless compression unit 510.

  The synthesizing unit 604 determines whether the attribute of each pixel is a character attribute or a non-character attribute based on the attribute information expanded by the reversible expansion unit 603, and the first irreversible expansion unit 601 or second The pixel value of the character attribute or non-character attribute expanded by the irreversible expansion unit 602 is selected for each pixel, and the image data is synthesized. Further, the synthesis unit 604 stores the synthesized image data in the storage unit 400.

  The display 300 reads the decompression unit 600 stored in the storage unit 400 of the image processing apparatus 100 and outputs an image based on the image data to the display screen.

  Although not shown in FIG. 1, the image processing apparatus 100 may include a network interface that is connected to a communication network and performs data communication with other apparatuses connected to the communication network. The image processing apparatus 100 may receive image data transmitted from another apparatus via a network interface, and execute a compression process on the received image data.

(A-2) Operation of the First Embodiment FIG. 3 is a flowchart showing the operation of compression processing in the image processing apparatus 100 according to the first embodiment.

  First, in the image processing apparatus 100, the compression unit 500 determines whether there is a request for compression processing on image data. If there is a request for compression processing, the compression unit 500 executes compression processing on the image data stored in the storage unit 400. Hereinafter, the image data that the compression unit 500 performs compression processing will be referred to as original image data.

[Step S100]
In the compression unit 500, the attribute detection unit 501 reads the original image data stored in the storage unit 400, and based on a known region separation algorithm from the read original image data, character regions such as characters and line drawings, Detect and separate non-character areas other than characters and line drawings. Then, the attribute detection unit 501 assigns attribute information indicating either a character attribute or a non-character attribute to each pixel of the original image data (see FIG. 2).

  Here, various methods are applied to the method for detecting and separating the character area (character attribute) and the non-character area (non-character attribute) by the attribute detection unit 501. For example, in the case of a monochrome image, the pixel value of a certain pixel is compared with a threshold value. If the pixel value exceeds the threshold value, the pixel belongs to the character area, and if the pixel value is less than the threshold value, the pixel is a non-character. You may make it judge that it belongs to an area | region. In addition, for example, the difference between the pixel value of the pixel and the pixel value of the pixel adjacent to the pixel or the pixel value of the peripheral pixel located around the pixel (for example, the average value of the pixel values of the peripheral pixels) is calculated. On the other hand, when the difference value exceeds the threshold value, it may be determined that the pixel belongs to the character area, and when the difference value is equal to or less than the threshold value, it may be determined that the pixel belongs to the non-character area.

[Step S200]
The color information separation unit 502 generates character image data and non-character image data from the original image data read in step S <b> 100 based on the attribute information given by the attribute detection unit 501. Here, for example, the character image data and the non-character image data may be the same image data as the original image data read in step S100, or the original image data may be processed by known image processing, for example. Alternatively, the image data may be subjected to predetermined processing.

[Step S300]
The block detection unit 503 classifies the character image data and the non-character image data generated in step S200 into blocks each having an image size of, for example, 8 pixels vertically × 8 pixels horizontally. Also, the block detection unit 503 classifies the attribute information of each pixel generated by the attribute detection unit 501 into the image size of the segmented block size (8 × 8 pixels). This block division is performed on the previous pixel.

[Step S400]
The first replacement determination unit 504 determines the pixel value of each pixel in the block of the character image data from the pixel value of each pixel belonging to the character attribute based on the block-divided attribute information obtained by the block extraction unit 503. It is determined whether or not to replace the obtained representative value or average value. The process of step S400 is performed on all the blocks extracted by the block extraction unit 503.

  Here, the representative value may be the maximum value or the minimum value of the pixel values of each pixel of the image data (for example, character image data), or a preset value regardless of the image data. It may be. The average value may be an average value obtained by arithmetically averaging the pixel values of each pixel in the block of image data.

[Step S450]
The second replacement determination unit 505 determines the pixel value of each pixel in the block of the non-character image data based on the block-divided attribute information obtained by the block extraction unit 503, and the pixel value of each pixel belonging to the non-character attribute. It is determined whether or not the value is replaced with a representative value or an average value obtained from the value. The process of step S450 is performed on all the blocks extracted by the block extraction unit 503.

[Step S500]
If it is determined that the replacement is performed based on the replacement determination result obtained in step S400, the first replacement unit 506 uses the pixel value of the pixel belonging to the character attribute in each block of the character image data obtained in step S200. The representative value or average value in the block of the character image data is calculated. Then, the first replacement unit 506 replaces the pixel value of each pixel of the block of the character image data with the calculated representative value or average value. Thereby, the processed character image data can be obtained.

  Similarly, when the second replacement unit 507 performs replacement based on the replacement determination result obtained in step S450, the pixel belonging to the non-character attribute in each block of the non-character image data obtained in step S200. From the pixel value, a representative value or an average value of the pixel values of the pixels belonging to the non-character attribute in the block of the non-character image data is calculated. Then, the second replacement unit 507 replaces the pixel value of each pixel of the block of the non-character image data with the calculated representative value or average value. Thus, processed non-character image data can be obtained.

[Step S600]
The first lossy compression unit 508 performs JPEG compression processing on the processed character image data obtained in step S500. As a result, JPEG-compressed character image data can be generated, and the first lossy compression unit 508 stores the generated JPEG-compressed character image data in the storage unit 400.

  The second lossy compression unit 509 performs JPEG compression processing on the processed non-character image data obtained in step S500. Thus, JPEG-compressed non-character image data can be generated, and the second lossy compression unit 509 stores the generated JPEG-compressed non-character image data in the storage unit 400.

  The lossless compression unit 510 performs MMR compression processing on the attribute information obtained in step S100. Thereby, attribute information compressed by MMR can be generated, and the lossless compression unit 510 stores the generated attribute information compressed by MMR in the storage unit 400. In this embodiment, MMR compression is used as the lossless compression method, but various lossless compression methods can be applied as long as the method is a lossless compression method for binary data such as JB1G2.

  FIG. 4 is a flowchart showing the operation of the replacement determination process according to the first embodiment. Both the first replacement determination unit 504 and the second replacement determination unit 505 basically perform the processing illustrated in FIG. Hereinafter, the processing of the second replacement determination unit 505 that determines whether or not to perform pixel value replacement on non-character image data will be described as an example.

[Step S401]
First, the second replacement determination unit 505 determines in each block divided by the block extraction unit 503 whether the pixel region belonging to the non-character attribute is separated into two or more regions based on the attribute information of each pixel. Determine whether or not. When there are two or more pixel regions belonging to the non-character attribute (when there are two or more separation regions), the process proceeds to S404, and otherwise, the process proceeds to S402.

  FIG. 5 is an explanatory diagram illustrating the presence / absence of a separation region in each block according to the first embodiment. In FIG. 5, in order to facilitate the description, in a block of 8 vertical pixels × 8 horizontal pixels, the attribute information “1: character attribute” is represented by “black”, and the attribute information “0: non-character attribute” is represented by “white”. ".

  FIG. 5A illustrates a case where there are no two or more separation regions. As shown in FIG. 5A, pixels belonging to non-character attributes (white pixels) have the same attribute information of surrounding pixels, and pixel areas belonging to non-character attributes are connected in the block. On the other hand, FIG. 5B illustrates a case where there are two or more textual areas. As shown in FIG. 5B, a white pixel (white pixel) belonging to a non-character attribute is separated into two or more of a separation region BL1 and a separation region BL2 in the block.

[Step S402]
When two or more regions (separation regions) belonging to the non-character attribute are separated, the second replacement determination unit 505 obtains an average value of the pixel values of the pixels belonging to each separation region. In addition, the second replacement determination unit 505 takes the difference between the average values of the pixel values in each separation region, and compares the difference value with a threshold value. If the difference value is greater than the threshold value, the process proceeds to S403. If the difference value is equal to or less than the threshold value, the process proceeds to S404. That is, the second replacement determination unit 505 obtains the average value of the pixel values of all the pixels that are connected to each other and belong to the separation region, and whether or not the difference value of the average value of the pixel values between the separation regions exceeds the threshold value. Determine.

  FIG. 6 is an explanatory diagram for explaining the replacement determination process according to the first embodiment. In FIG. 6, a block of 8 vertical pixels × 8 horizontal pixels is extracted from the original image data, and attribute information in the extracted block and non-character attribute image data corresponding to the attribute information block are shown.

  In this example, as shown in FIG. 6A, the original image data is a monochrome image that is “E”, which is a black bold letter, on a white background. Further, the block extracted by the block extraction unit 503 is assumed to be an edge portion of the character “E” as shown in FIG. Also, pixels belonging to the character attribute are represented in black, and pixels belonging to the non-character attribute are represented in white.

  At this time, it is assumed that the attribute detection unit 501 detects attribute information of each pixel as shown in FIG. 6C from a block (see FIG. 6B) extracted from the original image data.

  That is, normally, it should be detected that the area from the fourth column to the eighth column from the left is a character attribute, as in the block of 8 vertical pixels × 8 horizontal pixels in FIG. It is. However, here, as shown in FIG. 6C, it is detected that the areas in the fourth and fifth columns have character attributes and the areas in the sixth to eighth columns have non-character attributes. It shall be assumed. This is because the attribute detection unit 501 determines the attribute information by comparing the difference value between the pixel value of the pixel and the pixel value of the pixel adjacent to or around the pixel and the threshold value. This is because the attribute information may not be detected correctly depending on the size.

  FIG. 6D shows the non-character image data generated by the color information separation unit 502.

  Based on the attribute information of FIG. 6C, the second replacement determination unit 505 determines that the region BL1 in the first column to the third column and the region BL2 in the sixth column to the eighth column from the left are Judged as a non-character attribute separation region. Therefore, the second replacement determination unit 505 obtains the average value of the pixel values of all the pixels belonging to the separation region BL1 and the average value of the pixel values of all the pixels belonging to the separation region BL2.

  Then, the second replacement determination unit 505 calculates a difference between the average value of the pixel values in the separation region BL1 and the average value of the pixel values in the separation region BL2, and determines whether or not the difference value is larger than the threshold value.

  Here, the average value of the pixel values in the separation region will be described. For example, when the original image data is color data (that is, when the non-character image data is color data), the average value of the pixel values (RGB three-channel pixel values) of the pixels belonging to the separation region is obtained. When the difference value of the average value of the pixel values of the three channels and the threshold value are compared for each channel between the separation regions, and the difference value is larger than the threshold value even in one channel, the difference in the pixel value between the separation regions is large. To do. On the other hand, in the case of monochrome data, the average value of the pixel values of only one channel is obtained, the difference value of the average value is compared with the threshold value, and if the difference value is greater than the threshold value, the difference in pixel value between the separation regions Is assumed to be large.

[Step S403]
If the difference value of the average value of the pixel values is larger than the threshold value in step S402, the second replacement determination unit 505 gives a determination result that the pixel block is not replaced. If the determination result is given, the process of step S400 is terminated.

[Step S404]
If the non-character attribute is not separated in step S401, or if the difference value of the average value of the pixel values of the non-character image data between the separated regions is smaller than the threshold value in step S402, the second replacement determination unit 505 Gives the result of the replacement for the block. If the determination result is given, the process of step S400 is terminated.

  In the process of step 450 in FIGS. 4 and 3, the operation of the replacement determination process has been described focusing on one block. However, the first replacement determination unit 504 and the second replacement determination unit 505 perform replacement determination results for all blocks extracted from the original image data.

  Next, the operation of image expansion processing by the expansion unit 600 according to the first embodiment will be described.

  When there is a request for decompression processing, the decompression unit 600 performs decompression processing on the image data compressed by the compression unit 500.

  The first lossy decompression unit 601 performs JPEG decompression processing on the JPEG-compressed character image data obtained in step S600. Thereby, JPEG decompressed character image data can be generated.

  The second lossy decompression unit 602 performs JPEG decompression processing on the JPEG-compressed non-character image data obtained in step S600. As a result, JPEG decompressed non-character image data can be generated.

  The MMR decompression unit 603 performs an MMR decompression process on the compressed attribute information obtained in step S600. Thereby, the attribute information expanded by MMR can be generated.

  The combining unit 604 combines the expanded character image data and non-character image data based on the expanded attribute information, and outputs one piece of image data.

  Here, in the composition method by the composition unit 604, when the pixel has the character attribute based on the attribute information, the pixel value of the corresponding pixel of the expanded character image data is extracted, and the pixel has the non-character attribute. If there is, the pixel value of the corresponding pixel of the decompressed non-character image data is extracted, and one image is generated by using the pixel value for the corresponding pixel. The composite image data generated in this way is stored in the storage unit 400.

  Further, the display 300 displays the composite image data stored in the storage unit 400 on the screen.

  FIG. 7 is an explanatory diagram for explaining image compression, decompression, and composition by a conventional image processing apparatus, and FIG. 8 is an explanation for explaining image compression, decompression, and composition by the image processing apparatus 100 according to this embodiment. FIG.

  Here, image data generated when compression, expansion, and composition processing is performed according to the image processing according to the first embodiment is compared with image data generated according to conventional image processing.

  7 and 8 exemplify a case where the pixel attribute information in the block is not correctly detected, as in the example of FIG. 6 (see FIGS. 7C and 8C).

  In the conventional image processing of FIG. 7, the character image data is replaced with black pixels (character attributes) which are representative values or average values (hereinafter referred to as representative values) (FIG. 7 (d1) and FIG. 7). (See (d2)). Further, the non-character image data is also replaced with white pixels (non-character attributes) which are representative values and the like (FIG. 7 (e1) and FIG. 7 (e2)). Thus, by replacing the pixel values in the pixel block with uniform pixel values, the compression effect is high when JPEG compression is performed. However, as shown in FIGS. 7F and 7G, on the other hand, when the composition process is performed, a fatal image quality deterioration occurs in which the inside of the character “E” is blanked out.

  On the other hand, in FIG. 8, the image processing apparatus 100 according to the first embodiment determines that the pixel value of each pixel of the character image data may be replaced by the first replacement determination unit 504 and performs the first replacement. A unit 506 replaces the pixel value of each pixel of the character image data with a representative value or the like. On the other hand, the second replacement determination unit 505 determines that the replacement is not performed when it is determined that the difference value of the average value of the pixel values between the separation regions of the attribute information is larger than the threshold value. Therefore, the second replacement unit 507 does not replace the representative value or the like. Therefore, as shown in FIG. 8 (e2), in the non-character image data that has been subjected to the compression process, the pixel value in which each pixel is not replaced is maintained. As a result, it is possible to obtain an image in which white spots do not occur inside the character “E” when the composition processing is performed.

(A-3) Effects of the First Embodiment As described above, according to the first embodiment, by performing replacement determination when performing pixel value replacement, the boundary between attribute information as in the past is achieved. Thus, the fatal image quality degradation that may occur is not generated, and the effect of improving the image quality is obtained.

(B) Other Embodiments Although various modified embodiments have been mentioned in the above-described embodiments, the present invention can also be applied to the following modified embodiments.

  In the embodiment described above, the first replacement determination unit and the second replacement determination unit determine whether or not there is a separation region in the block, obtain an average value of pixel values of pixels belonging to each separation region, and separate the separation region The case where it is determined whether or not the difference value of the average value between them is larger than the threshold value is illustrated. This is to determine whether the pixel in the separation area is a character area or a non-character area. In this modified embodiment, the average value of the pixel values of each separation area is compared with a threshold value for separating the character area or the non-character area to determine whether each separation area is a character area or a non-character area. You may make it do. In this case, when any of the plurality of separation regions exceeds the threshold, the first replacement determination unit or the second replacement determination unit may determine that the replacement is not performed.

  DESCRIPTION OF SYMBOLS 100 ... Image processing apparatus, 200 ... Scanner, 300 ... Display, 500 ... Compression part, 501 ... Attribute detection part, 502 ... Color information separation part, 503 ... Block extraction part, 504 ... 1st replacement determination part, 505 ... 2nd Replacement determination unit, 506... First replacement unit, 507... Second replacement unit, 508... First lossy compression unit, 509... Second lossy compression unit, 510. 1 irreversible decompression unit, 602... Second irreversible decompression unit, 603... Reversible decompression unit, 604.

Claims (9)

An attribute information detector for detecting predetermined attribute information from the image data;
A color information separation unit that separates color information from the image data for each attribute;
A block extraction unit that divides each color information for each attribute separated by the color information separation unit into predetermined image processing units;
For each of the color information for each attribute, for each image processing unit, a replacement determination unit that determines whether or not to replace the color information for each attribute in each image processing unit with a predetermined value;
For each color information for each attribute, the color information for each attribute in each image processing unit is the same in the image processing unit for each image processing unit according to the replacement determination result of the replacement determination unit. A replacement unit for replacing with a predetermined value obtained from the color information of the attribute;
Each of the color information for each attribute obtained by the replacement unit, a lossy compression unit that performs compression processing in a lossy compression method,
An image processing apparatus comprising: a lossless compression unit that compresses the attribute information obtained by the attribute information detection unit using a lossless compression method. The replacement determination unit
For each image processing unit, based on the attribute information, determine whether or not areas belonging to the same attribute are separated within the image processing unit,
When areas belonging to the same attribute are separated, the average value of the color information of the attribute belonging to each separation area is obtained for each separation area, and the difference value of the average value between the separation areas is greater than a predetermined threshold value. It is determined whether it is large. The image processing apparatus of Claim 1 characterized by the above-mentioned. The replacement determination unit
When the difference value of the average value between the separation regions is larger than a predetermined threshold, it is determined not to replace the color information of the attribute in the image processing unit with the predetermined value,
3. The image according to claim 2, wherein when the difference value of the average value between the separation regions is equal to or less than a predetermined threshold value, it is determined that the color information of the attribute in the image processing unit is replaced with the predetermined value. Processing equipment. The attribute information includes a character attribute or a non-character attribute;
The replacement unit is
For the color information of the character attribute segmented by the block extraction unit, the representative value calculated from the pixel value of each pixel in the image processing unit based on the pixel value of each pixel belonging to the character attribute in the image processing unit Is replaced with
For the non-character attribute color information divided by the block extraction unit, the pixel value of each pixel in the image processing unit is calculated based on the pixel value of each pixel belonging to the non-character attribute in the image processing unit. The image processing apparatus according to claim 1, wherein the image processing apparatus substitutes a representative value.   The image processing apparatus according to claim 4, wherein the representative value is an average value of pixel values of pixels belonging to a character attribute or a non-character attribute in each image processing unit.   The image processing apparatus according to claim 1, wherein the irreversible compression unit compresses the color information for each attribute obtained by the replacement unit using a JPEG method. An irreversible decompression unit that decompresses color information for each attribute compressed by the irreversible compression unit;
A lossless decompression unit that decompresses the attribute information compressed by the lossless compression unit;
A combining unit that determines an attribute of each pixel based on the attribute information expanded by the lossless expansion unit, and selects and combines color information expanded by the irreversible expansion unit for each pixel according to the determined attribute; The image processing apparatus according to claim 1, further comprising: An attribute information detection unit for detecting predetermined attribute information from image data;
A color information separation unit that separates color information from the image data for each attribute;
A block extraction unit that divides each color information for each attribute separated by the color information separation unit into predetermined image processing units;
For each of the color information for each attribute, for each image processing unit, a replacement determination unit that determines whether or not to replace the color information for each attribute in each image processing unit with a predetermined value;
For each color information for each attribute, the color information for each attribute in each image processing unit is the same in the image processing unit for each image processing unit according to the replacement determination result of the replacement determination unit. A replacement unit for replacing with a predetermined value obtained from the color information of the attribute;
Each of the color information for each attribute obtained by the replacement unit, a lossy compression unit that performs compression processing in a lossy compression method,
An image processing program that causes the attribute information obtained by the attribute information detection unit to function as a lossless compression unit that performs compression processing using a lossless compression method. The attribute information detection unit detects predetermined attribute information from the image data,
A color information separating unit for separating color information for each attribute from the image data;
The block extraction unit divides each color information for each attribute separated by the color information separation unit into predetermined image processing units,
For each of the color information for each attribute, a replacement determination unit determines, for each image processing unit, whether to replace the color information for each attribute in each image processing unit with a predetermined value,
For each of the color information for each attribute, the replacement unit converts the color information for each attribute in each image processing unit for each image processing unit according to the replacement determination result of the replacement determination unit. Replace with the predetermined value obtained from the color information of the same attribute in
The irreversible compression unit performs compression processing of each color information for each attribute obtained by the replacement unit in an irreversible compression method,
An image processing method, wherein a lossless compression unit compresses the attribute information obtained by the attribute information detection unit by a lossless compression method.

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