JP4235583B2 - Image processing apparatus, image processing program, and storage medium - Google Patents

Description

  The present invention relates to an image processing apparatus, an image processing program, and a storage medium that can greatly reduce the file size without significantly reducing the image quality of a multi-value image that is a processing target image.

  In general, a color image has a large file size, which may be inconvenient when communicating or accumulating. Therefore, a technique for reducing the file size without reducing the image quality as much as possible is required.

  Currently, a method of compressing an image by performing JPEG compression or the like is widespread. This compression is an excellent method for compressing natural images such as photographs, but is not very suitable for compressing document images containing characters. This is because a characteristic noise called mosquito noise is generated in a portion where an abrupt color change occurs such as an edge portion of a character. In addition, the compression efficiency is not so good for an image such as a document image in which many such rapid color changes occur. Although it is possible to forcibly improve the compression rate, in this case, the edge portion of the character is crushed and the visibility of the character is greatly reduced.

  Therefore, a method as shown in Patent Document 1 has been proposed. In this method, a processing target image is divided into blocks having a predetermined size, and each block is classified into a gradation portion and a character portion. Two-dimensional discrete cosine transform is performed on the gradation part and encoding is performed using a quantization table, and the character part is composed of only a luminance signal and an identification color code and is compressed and encoded. . Since the gradation part has little color change, a compression method using discrete cosine transform such as JPEG compression functions effectively, and the compression part and the image quality are at a high level by using another method for the character part. Can be balanced.

Japanese Patent No. 3095804

  However, since the method of Patent Document 1 distinguishes the character portion and the gradation portion in units of blocks, depending on the size of the block, the character and the gradation portion may be mixed inside the block. In this case, the image quality of either the character or the gradation portion is degraded in the block. If the block is made smaller, information for determining whether it is a character portion or a gradation portion is reduced, so that the possibility of a determination error increases, which also leads to a decrease in accuracy.

  An object of the present invention is to efficiently reduce the file size of an image while maintaining the image quality of a multi-valued image to be processed.

The image processing apparatus according to the present invention includes a multi-value image acquisition unit that acquires a multi-value image as a processing target image, a binary image acquisition unit that acquires a binary image generated based on the processing target image, and the processing target. Specific attribute pixel specifying means for specifying a pixel having a specific attribute from the image, white pixel replacement means for replacing a pixel not having the specific attribute in the binary image with a white pixel, and the specific attribute Specific attribute pixel image generation means for generating one or a plurality of images composed only of a pixel portion, and a specific attribute pixel-erased multi-value image for generating a multi-value image in which pixels having the specific attribute are filled with a background color Generating means and image encoding means for encoding each of the plurality of images generated by these image generating means, and the specific attribute pixel specifying means has a specific attribute based on the binary image. To identify the pixel.

  Accordingly, a multi-valued image as an original image and a binary image based on the multi-valued image are prepared, pixels having a specific attribute such as a character are specified based on the binary image, and the presence or absence of such a specific attribute is determined. In response, a single or a plurality of binary images composed only of a pixel portion having a specific attribute are generated, and a multi-value image in which pixels having a specific attribute are filled with a background color is generated, By encoding the file into a file, the pixel size of a pixel having a specific attribute can be greatly reduced without significantly reducing the image quality of the multi-valued image to be processed while ensuring the visibility. It becomes possible.

In the image processing apparatus, the pixel having the specific attribute specified by the specific attribute pixel specifying unit includes a pixel constituting a character, a ruled line, or a line drawing.

  Therefore, the compression rate is reduced so that the file size can be reduced without degrading the visibility of the character image by targeting the pixels of the character image, such as characters, ruled lines or line drawings, as pixels having specific attributes. It is possible to increase the processing.

In the image processing apparatus, the pixel having the specific attribute specified by the specific attribute pixel specifying unit includes a pixel constituting an area that can be considered as a single color.

  Therefore, since a mark composed of a single color is not a character, it is better to binarize the image quality and compression rate. Therefore, not only a character etc. but also a region that can be regarded as a single color is targeted as a specific attribute. Thus, proper processing can be performed.

In the image processing apparatus, the region that can be regarded as a single color includes a means for extracting a connected component of black pixels from the binary image, and a multi-valued image as the processing target image corresponding to the black pixels constituting the connected component. Means for acquiring the color information, and means for assuming that the region corresponding to the connected component of the black pixel is a single color when the variation of the acquired color information is less than a predetermined value.

Thus, in realizing the invention, it is possible to properly carry out the determination of the area to monochromatic regarded to be treated as a specific attribute.

The image processing apparatus according to the present invention includes a multi-value image acquisition unit that acquires a multi-value image as a processing target image, a binary image acquisition unit that acquires a binary image generated based on the processing target image, and the processing target. Specific attribute pixel specifying means for specifying a pixel having a specific attribute from the image, white pixel replacement means for replacing a pixel not having the specific attribute in the binary image with a white pixel, and the specific attribute Specific attribute pixel image generation means for generating one or a plurality of images composed only of a pixel portion, and a specific attribute pixel-erased multi-value image for generating a multi-value image in which pixels having the specific attribute are filled with a background color Generating means and image encoding means for encoding each of the plurality of images generated by these image generating means, and the specific attribute pixel elimination multi-value image generating means does not have the specific attribute Means for extracting a connected component of black pixels from a binary image in which elements are replaced with white pixels, means for acquiring a pixel value around the connected component of black pixels, and a connected component based on the surrounding pixel values Means for calculating a background color corresponding to the position.

  Therefore, a multi-valued image that is an original image and a binary image based on the multi-valued image are prepared, pixels having specific attributes such as characters are specified, and a specific image is specified according to the presence or absence of such specific attributes. Generate single or multiple images consisting only of pixel parts with attributes, and generate multi-valued images with pixels with specific attributes filled with background color, and encode each file into a file As a result, it is possible to significantly reduce the file size of the pixel having a specific attribute without significantly reducing the image quality of the multi-valued image as the processing target image while ensuring the visibility. At this time, in order to generate a multi-value image in which pixels having a specific attribute are filled with a background color, a connected component of black pixels is extracted from a binary image in which pixels having no specific attribute are replaced with white pixels. In addition, by acquiring the pixel values around the connected components of the black pixels and calculating the background color corresponding to the position of the connected components based on the surrounding pixel values, it is possible to perform appropriate processing.

The image processing apparatus further includes means for generating a binary image in which a black pixel portion is thickened by a predetermined value from a binary image in which pixels having no specific attribute are replaced with white pixels, and connecting the black pixels The means for extracting a component calculates a connected component of black pixels from the thick binary image.

  Therefore, there are cases where the pixel value is gently changing at the boundary between the character or the like in the multi-valued image and the background, and there is a possibility that the character color is mixed in the background. By performing the thickening process, it is possible to reduce the possibility that these boundary portions are also to be erased wider and the character color remains unerased at the boundary portions.

In the image processing apparatus, the means for obtaining the pixel values around the connected component of the black pixels does not use the black pixel portion in the binary image that is the target for calculating the connected component as the surrounding pixel value.

  Therefore, it is highly likely that a black pixel portion in a binary image is a portion that constitutes a character or the like, not a background. However, by not including such a black pixel portion as a surrounding pixel value, a specific pixel can be obtained. Appropriate processing can be performed in generating a multi-valued image in which pixels having attributes are filled with a background color.

In the image processing apparatus, the means for obtaining pixel values around the connected components of the black pixels comprises means for calculating an average value of pixels at the periphery of the circumscribed rectangle of the connected components.

Therefore, in realizing the above- described invention, it is possible to appropriately perform processing for obtaining pixel values around the connected components of black pixels.

In the image processing apparatus, the specific attribute pixel erasure multilevel image generation unit includes a unit that replaces the pixel value at the position of the multilevel image corresponding to the position of the connected component with the calculated background color.

  Therefore, an image in which an image having a specific attribute such as a character is erased can be reliably generated on the multi-valued image.

The image processing apparatus according to the present invention includes a multi-value image acquisition unit that acquires a multi-value image as a processing target image, a binary image acquisition unit that acquires a binary image generated based on the processing target image, and the processing target. Specific attribute pixel specifying means for specifying a pixel having a specific attribute from the image, white pixel replacement means for replacing a pixel not having the specific attribute in the binary image with a white pixel, and the specific attribute Specific attribute pixel image generation means for generating one or a plurality of images composed only of a pixel portion, and a specific attribute pixel-erased multi-value image for generating a multi-value image in which pixels having the specific attribute are filled with a background color Generating means and image encoding means for encoding each of the plurality of images generated by these image generating means, wherein the specific attribute pixel image generating means is a binary image having the specific attribute. A means for obtaining a pixel value of a pixel in a corresponding multi-valued image, a means for calculating a representative color from the obtained pixel value, and a pixel value having the specific attribute as any of the calculated representative colors. And means for generating one or a plurality of images having only the calculated representative color as a constituent pixel color in accordance with the result of assigning the pixel value.

  Therefore, a multi-valued image that is an original image and a binary image based on the multi-valued image are prepared, pixels having specific attributes such as characters are specified, and a specific image is specified according to the presence or absence of such specific attributes. Generate single or multiple images consisting only of pixel parts with attributes, and generate multi-valued images with pixels with specific attributes filled with background color, and encode each file into a file As a result, it is possible to significantly reduce the file size of the pixel having a specific attribute without significantly reducing the image quality of the multi-valued image as the processing target image while ensuring the visibility. At this time, in generating one or a plurality of images composed only of pixel portions having specific attributes, the pixel values in the corresponding multivalued image of the pixels on the binary image having the specific attributes are calculated. Obtain and calculate a representative color from the pixel value, while assigning a pixel value having a specific attribute to one of the calculated representative colors, and using only the calculated representative color as a constituent pixel color By generating the image according to the result of assigning the pixel value, it can be appropriately assigned as a reduced color image, and the image quality and compression efficiency can be improved.

In the image processing apparatus, the means for calculating the representative color includes a means for creating a histogram of pixel values, a means for selecting a representative color candidate having a higher priority from a higher frequency of the histogram, and the representative color candidate Means for determining whether or not the color is an achromatic color, means for excluding from the representative color candidates the achromatic color representative color candidates having a higher priority than the first predetermined number of achromatic color representative color candidates; And a means for selecting a second predetermined number of representative colors from the representative color candidates having a high number as representative colors.

Thus, in realizing the invention, properly performed by using the priority-based processing for calculating the representative color in the histogram.

In the image processing apparatus, the means for calculating the representative color includes a means for creating a histogram of pixel values, a means for selecting a representative color candidate having a higher priority from the higher frequency of the histogram, and a representative having a higher priority. Means for leaving a first predetermined number of color candidates; means for determining whether or not the representative color candidate is an achromatic color; and more achromatic color representative color candidates having a higher priority than the second predetermined number Means for excluding achromatic representative color candidates from representative color candidates; means for calculating a color difference between representative color candidates; and a representative color candidate having the lowest color difference, the one having the lowest priority. The means for excluding the representative color candidates and the representative color candidates remaining after repeating the exclusion from the representative color candidates from the calculation of the degree of color difference between the representative color candidates until the number of representative color candidates reaches the third predetermined number And means for selecting as a color.

Thus, in realizing the invention, it is possible to properly carry out the calculation processing of the representative color. In particular, since the number of achromatic colors that are representative colors is limited, it is possible to prevent characters and the like from being composed of only achromatic colors.

In the image processing apparatus, means for assigning a pixel value having the specific attribute to any one of the calculated representative colors includes means for extracting a connected component of pixels having a specific attribute, and the representative color Means for assigning to each connected component.

Thus, in realizing the invention, it is possible to properly carry out the calculation processing of the representative color. In particular, it is effective to reduce the size of the generated file by performing it in units of connected components.

In the image processing apparatus, the means for assigning a pixel value having the specific attribute to any of the calculated representative colors comprises means for assigning the representative color in units of pixels.

Thus, in realizing the invention, the pixel values having a specific attribute is assigned to any one of the calculated representative color processing can be appropriately performed. In particular, by performing it in units of pixels, it is possible to cope with fine fluctuations in pixel values and improve the appearance of the generated image.

The image processing apparatus further includes means for changing the resolution of the image.

  Therefore, for example, by changing the resolution so as to reduce the resolution and then performing the encoding / compression processing, the file size can be further reduced.

The computer-readable image processing program according to the present invention includes a multi-value image acquisition function for acquiring a multi-value image as a processing target image, and a binary image acquisition for acquiring a binary image generated based on the processing target image. A specific attribute pixel specifying function for specifying a pixel having a specific attribute from the processing target image, a white pixel replacement function for replacing a pixel not having the specific attribute with a white pixel in the binary image, A specific attribute pixel image generation function that generates one or a plurality of images composed only of a pixel portion having a specific attribute, and a specification that generates a multi-value image in which pixels having the specific attribute are filled with a background color The specific pixel attribute causing the computer to execute an attribute pixel elimination multi-value image generation function and an image encoding function for encoding each of a plurality of images generated by these image generation functions Containing specific function, determining the pixel having a specific attribute on the basis of the binary image.

Therefore, the same effect as the above-described invention can be achieved.

The computer-readable image processing program according to the present invention includes a multi-value image acquisition function for acquiring a multi-value image as a processing target image, and a binary image acquisition for acquiring a binary image generated based on the processing target image. A specific attribute pixel specifying function for specifying a pixel having a specific attribute from the processing target image, a white pixel replacement function for replacing a pixel not having the specific attribute with a white pixel in the binary image, A specific attribute pixel image generation function that generates one or a plurality of images composed only of a pixel portion having a specific attribute, and a specification that generates a multi-value image in which pixels having the specific attribute are filled with a background color The specific pixel attribute causing the computer to execute an attribute pixel elimination multi-value image generation function and an image encoding function for encoding each of a plurality of images generated by these image generation functions The elementary erasure multi-value image generation function includes a function of extracting a black pixel connected component from a binary image in which pixels having no specific attribute are replaced with white pixels, and pixel values around the black pixel connected component And a function of calculating a background color corresponding to the position of a connected component based on the surrounding pixel values.

  Therefore, the same effect as the above-described invention can be achieved.

The computer-readable image processing program according to the present invention includes a multi-value image acquisition function for acquiring a multi-value image as a processing target image, and a binary image acquisition for acquiring a binary image generated based on the processing target image. A specific attribute pixel specifying function for specifying a pixel having a specific attribute from the processing target image, a white pixel replacement function for replacing a pixel not having the specific attribute with a white pixel in the binary image, A specific attribute pixel image generation function that generates one or a plurality of images composed only of a pixel portion having a specific attribute, and a specification that generates a multi-value image in which pixels having the specific attribute are filled with a background color The specific pixel attribute causing the computer to execute an attribute pixel elimination multi-value image generation function and an image encoding function for encoding each of a plurality of images generated by these image generation functions The elementary image generation function includes a function of acquiring a pixel value in a corresponding multi-valued image of a pixel on the binary image having the specific attribute, a function of calculating a representative color from the acquired pixel value, A function of assigning a pixel value having a specific attribute to one of the calculated representative colors, and a result of assigning the pixel value to one or a plurality of images having only the calculated representative color as a constituent pixel color And the function to be generated in accordance with the above-mentioned computer.

Accordingly, the same effect as that of the above-mentioned light is achieved.

Computer-readable storage medium of the present invention stores the image processing program.

Therefore, the same effect as the above-described invention can be achieved.

In the image processing apparatus, means for assigning a pixel value having the specific attribute to any one of the calculated representative colors includes means for obtaining an average value of the pixel values, and the obtained average value and representative color. And a means for selecting the closest representative color by obtaining the distance between the first and second colors.

  Therefore, it is possible to assign representative colors with little difference from the original image.

In the image processing apparatus, means for assigning a pixel value having the specific attribute to one of the calculated representative colors includes means for obtaining a mode value of the pixel value, Means for obtaining a distance from the representative color and selecting the closest representative color.

  Therefore, it is possible to assign representative colors with little difference from the original image.

In the image processing apparatus, the means for assigning a pixel value having the specific attribute to any one of the calculated representative colors includes a means for obtaining a mode value of the pixel value, and a mode value obtained In the case of an achromatic color, a means for performing a correction for substituting the mode value with a blacker color by a subtraction process using a predetermined correction value, and obtaining the distance between the corrected mode value and the representative color to obtain the closest representative Means for selecting a color.

  Therefore, when the mode value is an achromatic color, the mode value is corrected to a darker color and then compared with the representative color to select the closest one, so a good-looking process that gives a deep impression Is possible.

In the image processing apparatus, means for assigning a pixel value having the specific attribute to any one of the calculated representative colors includes means for obtaining a mode value of the pixel value, and determining the mode value. On the other hand, a means for performing a correction for replacing the mode with a darker color by a multiplication process using a predetermined correction value, and obtaining the distance between the corrected mode and the representative color and selecting the closest representative color Means.

  Therefore, regardless of whether the mode value is an achromatic color or a chromatic color, the mode value is corrected to a darker color and then compared with the representative color to select the closest one. It is possible to give a good-looking process.

According to the image processing device of the present invention, a multi-value image that is an original image and a binary image based on the multi-value image are prepared, and pixels having specific attributes such as characters are specified based on the binary image, Depending on the presence or absence of such a specific attribute, one or a plurality of binary images composed only of pixel portions having the specific attribute are generated, and pixels having the specific attribute are filled with a background color. Since a multi-value image is generated and each is encoded and filed, the image quality of the multi-value image that is the processing target image is greatly reduced while ensuring the visibility of pixels having specific attributes. The file size can be greatly reduced without causing the change.

According to the present invention, the image processing apparatus, a character, that the target pixel having a specific attribute pixels of the so-called character-based image such as borders or line drawing, without reducing the visibility of the character-based image The compression rate can be increased so that the file size is reduced.

According to the present invention, in the image processing apparatus, the mark composed of a single color such as image quality better to not but binarizing the character, since it may be a compression rate, as a specific attribute, not only characters and the like, a single color Appropriate processing can be performed by targeting a region that can be considered as a target.

According to the present invention, in realizing the above- described invention, it is possible to appropriately determine a region that can be regarded as a single color treated as a specific attribute.

According to the image processing apparatus according to the present invention, prepared and multivalued image becomes the original image and the binary image based on this, for example, to identify the pixel having a specific attribute such as a character, of such a specific Depending on the presence or absence of an attribute, generate one or more images consisting only of pixel parts with a specific attribute, and generate a multivalued image with pixels with a specific attribute filled with a background color. By encoding each file into a file, the file size can be greatly reduced without significantly degrading the image quality of the multi-valued image to be processed while ensuring the visibility of pixels with specific attributes. In this case, when generating a multi-valued image in which pixels having a specific attribute are filled with a background color, a black image is generated from a binary image in which pixels having no specific attribute are replaced with white pixels. Extract connected components of pixels Obtains the pixel values of the surrounding connected components of black pixels, by calculating the background color corresponding to the position of the connected component based on the surrounding pixel values, it is possible to allow for proper processing.

According to the present invention, in the image processing apparatus, the boundary between the characters and the like and the background or the like in the multivalued image may pixel values change gently, character color is mixed into the background section Although there is a possibility, since the processing for thickening the binary image is performed, these boundary portions are also to be erased wider, and the possibility that the character color remains unerased at the boundary portions can be reduced.

According to the present invention, the image processing apparatus, the portion that is a black pixel in the binary image has a high possibility of being a part constituting a character or the like instead of the background, ambient such black pixel portion Since the pixel values are not included, it is possible to perform appropriate processing when generating a multi-value image in which pixels having specific attributes are filled with a background color.

According to the present invention, in realizing the above- described invention, it is possible to appropriately perform a process of acquiring pixel values around the connected components of black pixels.

According to the present invention, in the image processing apparatus, on the multi-valued image, the image which the image is erased with a specific attribute such as a character can be reliably generated.

According to the image processing apparatus of the present invention, a multi-value image serving as an original image and a binary image based on the multi-value image are prepared, pixels having specific attributes such as characters are specified, and such specific attributes are specified. Depending on the presence or absence, generate one or more images composed only of pixel parts with a specific attribute, and generate a multi-value image in which pixels with a specific attribute are filled with a background color, By encoding each file into a file, it is possible to significantly reduce the file size without degrading the image quality of the multi-valued image to be processed, while ensuring the visibility of pixels with specific attributes. In this case, in generating one or a plurality of images composed only of pixel portions having specific attributes, the corresponding multivalues of the pixels on the binary image having the specific attributes Get the pixel value in the image While calculating a representative color from the pixel value, a pixel value having a specific attribute is assigned to any of the calculated representative colors, and one or more images having only the calculated representative color as a constituent pixel color Since the pixel value is generated according to the result of the assignment, it can be properly assigned as a reduced color image, and the image quality and compression efficiency can be improved.

According to the present invention, in realizing the above- described invention, the process of calculating the representative color can be appropriately performed by using the priority based on the histogram.

According to the present invention, in realizing the above- described invention, the representative color calculation process can be appropriately performed. In particular, since the number of achromatic colors that are representative colors is limited, characters and the like are only achromatic colors. Can be prevented.

According to the present invention, in realizing the above- described invention, the representative color calculation process can be appropriately performed. In particular, it is effective for reducing the size of the generated file by performing it in units of connected components. Become.

According to the present invention, it is possible to appropriately perform a process of assigning a pixel value having a specific attribute to any one of the calculated representative colors in order to realize the above- mentioned brightness. Thus, it is possible to cope with fine fluctuations of the pixel value and improve the appearance of the generated image.

According to the present invention, in the image processing apparatus, for example, from by changing the resolution to reduce the resolution, by causing the coding and compressing process, it is possible to further reduce the file size.

According to the computer readable image processing program of the present invention, it is possible to achieve the same effect as the invention.

According to the computer readable image processing program of the present invention, it is possible to achieve the same effect as the invention.

According to the computer readable image processing program of the present invention, it is possible to achieve the same effect as the invention.

According to the computer-readable storage medium of the present invention, it is possible to achieve the same effect as the above-mentioned bright.

According to the present invention, in the image processing apparatus, it is possible to perform the allocation of fewer representative color of the difference between the original image.

According to the present invention, in the image processing apparatus, it is possible to perform the allocation of fewer representative color of the difference between the original image.

According to the present invention, in the image processing apparatus, when the mode value of the achromatic, since selecting the closest performing comparison between the representative color after correction the mode in darker colors, It is possible to perform a good-looking process that gives an impressive impression.

According to the present invention, the image processing apparatus, the mode is both the achromatic-chromatic, closest performing comparison between the representative color after correction the mode in darker Since this is selected, it is possible to perform a good-looking process that gives an impressive impression.

  An embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 is a block diagram showing an electrical connection of the image processing apparatus 1 according to the present embodiment. As shown in FIG. 1, the image processing apparatus 1 is a computer such as a PC, and performs various calculations and centrally controls each part of the image processing apparatus 1, and a memory 3 including various ROMs and RAMs. Are connected by a bus 4.

  A bus 4 includes a magnetic storage device 5 such as a hard disk, an input device 6 such as a keyboard and a mouse, a display device 7, and a storage medium reader 9 that reads a storage medium 8 such as an optical disk via a predetermined interface. An image reading apparatus 10 that reads an image is connected, and a predetermined communication interface 12 that communicates with the network 11 is connected. As the storage medium 8, various media such as an optical disc such as a CD and a DVD, a magneto-optical disc, and an FD can be used. Further, as the storage medium reading device 18, specifically, an optical disk drive device, a magneto-optical disk drive device, an FDD device, or the like is used according to the type of the storage medium 17.

  The image processing apparatus 1 reads the image processing program 13 for executing the program of the present invention from the storage medium 8 for executing the storage medium of the present invention, and installs it in the magnetic storage device 5. These programs may be downloaded and installed via the network 11 such as the Internet. With this installation, the image processing apparatus 1 is in a state in which predetermined processing described later can be executed. Note that the image processing program 13 may operate on a predetermined OS.

  In the present embodiment, by using the image processing program 13, the multi-valued image as the processing target image (original image) can be significantly reduced without sacrificing the character visibility. Here, the outline of the process of the present embodiment will be described with reference to the schematic flowchart of FIG. 2 showing the outline of the process and the conceptual diagram of the process shown in FIG.

  First, a multi-valued image to be processed as shown in FIG. 3A is acquired using an image reading device 10 such as an image scanner (step S1). Then, by binarizing such a multi-valued image, a binary image as shown in FIG. 3B is acquired (S2). Thereafter, an area having a specific attribute such as a character area is searched (S3). Then, as shown in FIG. 3 (c), white pixel processing is performed to replace pixels having no specific attribute in the binary image with white pixels so as to leave only characters (S4), as shown in FIG. 3 (d). Thus, a color-reduced image of the character part is created (S5).

  On the other hand, the multi-valued image is an image in which a specific attribute portion is filled with a background color, and is an image from which characters are erased as shown in FIG. 3E (S6). Such an image filled with background color is regarded as having little important information, and is highly encoded (lossy compression in JPEG format, etc.), that is, the resolution is reduced as shown in FIG. (S7).

  Also, the pixels constituting the character are encoded with a reduced number of colors (reversible compression in PNG format, etc.), or a binary (two-color) image is generated for the number of colors and encoded (reversible compression in MMR format, etc.) (S7).

  Thereafter, the background image and the character image are combined into a format (for example, PDF) that can be superimposed and displayed while maintaining the same positional relationship as the original image (S8). The resulting file has a significantly smaller file size than the original image.

  Details of the processing procedure will be described in detail with reference to FIG. 4 showing a functional block diagram of functions realized by the image processing apparatus 1 based on the image processing program 13.

1. Acquire a multi-value image as a processing target image and a binary image based on the multi-value image. The multi-value image acquisition unit 21 and the binary image acquisition unit 22 acquire a multi-value image and a binary image (S1, S2). It is assumed that the binary image is generated based on the multi-value image. As a binarization method, a fixed threshold value may be used. For example, a pixel brighter than the threshold value may be a white pixel, and a dark pixel may be a black pixel. The binary image and the multi-value image may have different resolutions. For example, after a binary image is generated by the above-described method, the resolution of the multi-valued image may be reduced by performing a thinning process, and this may be acquired as a multi-value image to be processed. Furthermore, the binary image generation may be performed by another device and the generated image file may be acquired.

2. Acquire Character Area The specific attribute pixel specifying means 24 determines the position where the character exists on the image (S3). It may be acquired from a multi-valued image or a binary image. In the case of obtaining from a multi-valued image, a character region extraction technique that has already been disclosed may be used, such as Japanese Patent Application Laid-Open No. 2002-288589, and in the case of obtaining from a binary image, Japanese Patent Application Laid-Open No. 6-20092. In the present embodiment, it is assumed that pixels constituting a character are acquired as pixels having specific attributes based on a binary image.

3. Replace non-character with white pixel The white pixel replacing means 25 replaces a pixel other than the character area (a pixel having no specific attribute) in the binary image with a white pixel (S4).

4). Create a color-reduced image with only character pixels. This is a process of generating an image having color information composed of the black pixel portions remaining in the process (process by the specific attribute pixel image generation means 26; S5).

  This will be described with reference to FIG. First, pixel values of pixels having specific attributes are acquired (S11), and representative colors of those pixels are calculated (S12). That is, the color information is obtained from the multi-valued image, but the pixel values at the corresponding positions are not used as they are, but about several to several tens of representative colors are calculated from these pixel values. Then, each black pixel is assigned to one of the colors (S13), and an image of several to several tens of colors is created (S14). The image generated here may be one image of several colors to several tens of colors, or several to several tens of binary (two colors) images having a character color and a transparent background color may be generated. Is also possible. In any case, since the number of colors used in the character portion is reduced compared to the multi-value image that is the processing target image, this image will be referred to as a “reduced color image” here.

  Here, details of the means (S12) for calculating the representative color will be described. FIG. 6 is a schematic flowchart showing an example of a representative color calculation method.

  (1) A pixel value at a position on the multi-value image corresponding to the black pixel of the binary image is obtained, and a histogram of pixel values is generated (S21). For example, the RGB space may be equally divided into 4 × 4 × 4 blocks, where the pixel of interest applies in the block, and 1 may be added to the frequency value of the corresponding space.

  (2) A block having a high frequency is obtained, the frequency is regarded as a high priority, and a priority is assigned from the frequency value (S22). These blocks are called “representative color candidate blocks”.

  (3) It examines in order from a block with a high priority, and judges whether the said block is an achromatic color (S23). If the RGB representative value of the block (such as the RGB median value of the block) is almost the same value, it is an achromatic color.

  (4) If it is not an achromatic color (N in S23), the process proceeds to examination of a block having the next priority (S27).

  (5) If it is an achromatic color (Y of S23), it will examine how much achromatic color has existed in the top candidates so far (S24). If the achromatic color has reached a predetermined value (referred to herein as the predetermined number 1), the corresponding block is excluded from the representative color candidates (S26), and if not, 1 is added to the achromatic color number. The following process is performed (S25).

(6) Steps S22 to S26 are repeated until all representative color candidate blocks have been examined (S27).
(7) Of the representative color candidate blocks remaining without being excluded, the second predetermined number from the higher priority is output as the representative color (S28).

  Further, as a representative color calculation method, a method as shown in FIG. 7 is also conceivable.

  (1) A pixel value at a position on a multi-value image corresponding to a black pixel of a binary image is obtained, and a histogram of pixel values is generated (S31). The method may be the same as the method described above with reference to FIG.

  (2) A block having a high frequency is obtained, the frequency is regarded as a high priority, and a priority is assigned from the frequency value (S32).

  (3) In order from the block with the highest priority, the first predetermined number is left and others are excluded from the candidates (S33).

  (4) Examining in order from the block with the highest priority, it is determined whether or not the block is achromatic (S34).

  (5) If it is not an achromatic color (N in S34), the process proceeds to examination of a block having the next priority (S38).

  (6) If it is an achromatic color (Y in S34), it is examined how many achromatic colors have been found in the top candidates so far (S35). If the achromatic color has reached a predetermined value (referred to herein as the predetermined number 1) (Y in S35), the corresponding block is excluded from the representative color candidates (S37), and if not reached (S35). N), 1 is added to the number of achromatic colors, and the following processing is performed (S36).

  (7) Steps S33 to S37 are repeated until all representative color candidate blocks have been examined (S38).

  (8) Among the representative color candidates, the closest colors are selected (S39). The closeness of color is calculated using the sum of squares of differences between RGB components.

  (9) Of the two selected representative color blocks, the one with the lower frequency value is excluded from the candidates (S40).

  (10) The processes (8) and (9) are repeated until the third predetermined number or less is reached (S41).

  (11) The representative color candidate block remaining without being excluded is output as a representative color (S42).

  In the process shown in FIG. 7, it is possible to prevent a character from being composed of only achromatic colors by limiting the number of achromatic colors that are representative colors.

  Next, details of the means (S13) for assigning a pixel value having a specific attribute such as a character to one of the calculated representative colors will be described with reference to FIG.

  (1) Extract the connected components of black pixels from the binary image (S51).

  (2) The position on the multi-value image corresponding to the position of the connected component is calculated (S52).

  (3) The average value of the pixel values at the corresponding position is obtained. The mode value may be obtained instead of the average value. The method for obtaining the mode value may be the same as the method for obtaining the pixel value histogram described above. Here, the mode value is used (S53).

  (4) The distance between the mode and the representative color is obtained, and the closest one is selected (S54).

  (5) The entire connected component is regarded as having a pixel value of the representative color and is written out as a reduced color image (S55). If the subtractive color image is a binary image defined for each color, the connected component is written to the binary image representing the corresponding color. If the color-reduced image is a multi-valued image, color information and connected components are written into the color-reduced image.

  (6) The processes (2) to (5) described above are performed for all connected components (S56).

  Here, allocation to the representative color is performed in units of connected components, but may be performed in units of pixels. When done in pixel units, the generated file size tends to increase, and the processing time slightly increases. However, the generated image looks better because it can cope with fine fluctuations in pixel values compared to the connected component unit. May be.

  The assignment may be in units of characters, but in this case, a new process for determining how far the characters are is required. Also, depending on the accuracy of the process for determining how far the character is, there is a possibility that the character breaks and the color change do not match, resulting in an unnatural character reproduction.

  By the way, when the distance between the mode and the representative color is obtained and the closest representative color is selected as in step S54 described above with reference to FIG. 8, the difference from the original image is reduced, but the appearance is not so good. is there. In particular, it is often the case that black characters are more “squeezed” to the human eye when the black color is selected.

  Therefore, when the most frequent color is an achromatic color, it is preferable to replace it with a little black color, compare the replaced color with the representative color, and select the closest one.

  The specific procedure is as follows.

  (1) First, as a process corresponding to the process of obtaining the mode value in step S53, the mode color is obtained. The obtained most frequent colors are R, G, and B.

(2) When the obtained most frequent colors R, G, B are smaller than a predetermined threshold Diff, it is determined that the color is an achromatic color. That is,
| R−G | <Diff and | GB | <Diff and | B−R | <Diff
In this case, it is determined that the color is achromatic.

(3) When the most frequent color is determined to be an achromatic color, color correction is performed to improve the appearance by expressing black characters more black. If the corrected color is R ′, G ′, B ′ and the predetermined correction value is Rt, Gt, Bt,
R ′ = max (R−Rt, 0)
G ′ = max (G−Gt, 0)
B ′ = max (B−Bt, 0)
A subtraction process is performed. Here, max (a, b) indicates that the larger value of a and b is selected. That is, the character color is intended to be darkened (blackened) by reducing a predetermined correction value. Since a negative value is not allowed as the pixel value, the minimum value is set to 0 so as not to become negative when subtraction is performed.

  (4) As in step S54, a representative color closest to the corrected mode value (R ', G', B ') is searched and selected.

  The reason for limiting the processing to an achromatic color in this processing example is that the hue changes when the subtraction processing (3) is performed in the case of a chromatic color. In this example, chromatic color correction processing is not performed, and reproduction is performed with colors close to the original image.

Incidentally, when it is desired to darken the colors including chromatic colors, the mode values (R, G, B) may be subjected to multiplication processing instead of subtraction processing. That is, using predetermined correction values Ru, Gu, Bu (values of 0 or more and less than 1),
R ′ = R × Ru
G ′ = G × Gu
B ′ = B × Bu
And it is sufficient. If the same value is given to the correction values Ru, Gu, Bu, the hue does not change greatly. According to this method, it is possible to darken a color regardless of a chromatic color or an achromatic color.

  Here, the processing in the case of assigning the representative color to the connected component unit has been described, but the same processing may be performed in pixel units as in the case described above with reference to FIG. Color correction (darkening) may be performed, and the color closest to the representative color may be selected using the corrected color.

5. Character-free multi-value image generation The specific attribute pixel elimination multi-value image generation means 23 performs the above-mentioned processing The character portion of the multi-value image corresponding to the remaining black pixel portion is filled with the background color to create a multi-value image without characters (S6). Details will be described with reference to a schematic flowchart shown in FIG.

  (1) First, the binary image is thickened (S61). The boundary between the character and the background in the multivalued image may have a gentle change in pixel value. In this case, the character color may be mixed in the background. By performing the thickening process, the boundary between the character and the background is also subject to erasure so that the possibility of the character color remaining at the boundary can be reduced.

  (2) Extract connected components of black pixels from the thickened image (S62).

  (3) For one connected component, pixel values around the corresponding multi-valued image (pixel values at the periphery of the circumscribed rectangle of the connected component) are obtained, and these are averaged and considered as the background color. However, since the portion that is a black pixel in the binary image is likely to be a portion that constitutes a character rather than a background, it is not included in the average value calculation. (S63).

  (4) The pixel portion of the multi-valued image corresponding to the connected component of black pixels is replaced with the obtained background color (S65). As a result, the corresponding part of the multi-valued image is an image in which characters have disappeared.

  (5) The processes (3) and (4) described above are performed for all connected components (S66).

6). Image Encoding The image encoding means 27 encodes a multi-value image without characters and a reduced color image constituting the characters to compress the size (S7). Of these, multi-valued images without characters are highly irreversibly compressed by JPEG or the like, assuming that there is no important information already. If the resolution is reduced and then compressed, the size is further reduced. The reduced color image is reversibly compressed. In the case of a binary image, PNG compression or the like, such as PNG compression or MMR compression, may be used in the case of a quaternary or 16-valued image.

7. Summary File Generation The summary file creation means 28 combines the compressed images into one file (FIG. 3 (g), S8). If the files are formatted so that they can be displayed in a superimposed manner, the visibility of the character portion does not deteriorate, and the background can be reproduced to a certain degree and a color image with a small file size can be obtained.

  In addition, in the case of an encoded image file, if only the character part is desired, it is sufficient to obtain and use only the subtractive color image. If only the background is desired, only the characterless image may be used. The size has greatly decreased. In this case, the summary file creation means is not necessary.

  In this embodiment, a character is targeted as a specific attribute, but another attribute such as a ruled line or a line drawing may be used as a target, or these may be used together.

  Another embodiment of the present invention will be described with reference to FIGS. The same parts as those shown in the above embodiment are indicated by the same reference numerals, and the description thereof is also omitted.

  In the above-described embodiment, a character area is extracted and a character image is generated as a subtractive color image. However, even if a mark composed of a single color is not a character, it is better to binarize the image quality and compression rate. Therefore, in the present embodiment, “areas that can be regarded as a single color” are used as the specific attributes instead of “characters”.

  FIG. 10 is a schematic flowchart showing an outline of the processing of the present embodiment, and FIG. 12 is a functional block diagram. 2 and 4 shown in the above-described embodiment, but the portion for obtaining a monochromatic area instead of a character is different (S3 '). Further, the part where the specific attribute pixel specifying unit 24 refers to the multi-value image of the multi-value image acquiring unit 21 is also different.

  Here, how to obtain a single color area (specific attribute pixel) will be described with reference to a schematic flowchart shown in FIG. FIG. 13 is a functional block diagram showing an example of the configuration of the specific attribute pixel specifying means 24 in more detail.

First, the connected component extracting unit 31 extracts a connected component of black pixels from the binary image. (S71). Then, the color information acquisition unit 32 acquires the color information of the multivalued image at the position corresponding to the black pixel of the connected component, and obtains the variation in the color information (S72). The variance may be calculated by using the variance calculation means 33 to calculate the variance of each color component. If E () represents the average and the color components are r, g, b, the variance V is
V = E (r ² ) − {E (r)} ² + E (g ² ) − {E (g)} ² + E (b ² ) − {E (b)} ²
It can be calculated with The magnitude of this value represents variation.

  Therefore, the magnitude of this variation is examined (S73). If the magnitude of the variance is larger than a preset value, it may be determined that the variance is large. Those having large variations are erased from the binary image by the white pixel replacement means 25 (S74). Since this is a binary image, the corresponding pixel is replaced with a white pixel. And the process of step S72-S74 is performed with respect to all the connected components (S75).

  With the above processing, the processing of steps S4 'and S5' is completed.

  According to the method of the present embodiment, regardless of whether it is a character or not, a monochrome region is assigned to a reduced color image, so that both image quality and compression efficiency are improved.

It is a block diagram which shows the electrical connection of the image processing apparatus which shows one embodiment of this invention. It is a schematic flowchart which shows the outline | summary of a process. It is a conceptual diagram of a process. It is a functional block diagram of an image processing apparatus. It is a schematic flowchart which shows the example of a color reduction image creation process. It is a schematic flowchart which shows an example of a representative color calculation process. It is a schematic flowchart which shows the other example of a representative color calculation process. It is a schematic flowchart which shows the representative color allocation process etc. with a specific attribute. It is a schematic flowchart which shows the process example which fills a character part with a background color. It is a schematic flowchart which shows the outline | summary of the process of another embodiment of this invention. It is a schematic flowchart which shows the example of a part of the process. It is a functional block diagram of an image processing apparatus. It is a functional block diagram which shows the structural example of a specific attribute pixel specific means.

Explanation of symbols

21 Multi-value image acquisition means 22 Binary image acquisition means 23 Specific attribute pixel elimination multi-value image generation means 24 Specific attribute pixel specification means 25 White pixel replacement means 26 Specific attribute pixel image generation means 27 Image encoding means 31 Connected component extraction means 32 color information acquisition means

Claims (6)

Multi-value image acquisition means for acquiring a multi-value image as a processing target image;
Binary image acquisition means for acquiring a binary image generated based on the processing target image;
Specific attribute pixel specifying means for specifying a pixel having a specific attribute from the processing target image or the binary image ;
White pixel replacement means for replacing pixels having no specific attribute with white pixels in the binary image;
Specific attribute pixel image generation means for generating one or a plurality of images composed only of pixel portions having the specific attribute corresponding to black pixel portions remaining without being replaced with white pixels by the white pixel replacement means; ,
Specific attribute pixel erasure multi-value image generation means for generating a multi-value image in which pixels having the specific attribute corresponding to the black pixel portion remaining without being replaced with white pixels by the white pixel replacement means are filled with a background color When,
Image encoding means for encoding each of the plurality of images generated by these image generation means;
With
The specific attribute pixel image generation means includes
Means for obtaining a pixel value in a corresponding multi-valued image of a pixel on the binary image having the specific attribute;
Means for calculating a representative color from the acquired pixel values;
Means for assigning a pixel value having the specific attribute to any of the calculated representative colors;
Means for generating a single image or a plurality of images having only the calculated representative color as a constituent pixel color according to a result of assigning the pixel value;
With
The means for calculating the representative color is:
Means for creating a histogram of pixel values;
Means for selecting a representative color candidate having a higher priority from the higher frequency of the histogram;
Means for determining whether the representative color candidate is an achromatic color;
Achromatic determined to be high priority achromatic first representative color candidates of a predetermined number greater than the achromatic a representative color candidates than by the determining means, and excluding means from the representative color candidates,
Means for selecting, as representative colors, a second predetermined number of representative color candidates that remain without being excluded by the excluding means ;
An image processing apparatus comprising: Multi-value image acquisition means for acquiring a multi-value image as a processing target image;
Binary image acquisition means for acquiring a binary image generated based on the processing target image;
Specific attribute pixel specifying means for specifying a pixel having a specific attribute from the processing target image or the binary image ;
White pixel replacement means for replacing pixels having no specific attribute with white pixels in the binary image;
Specific attribute pixel image generation means for generating one or a plurality of images composed only of pixel portions having the specific attribute corresponding to black pixel portions remaining without being replaced with white pixels by the white pixel replacement means; ,
Specific attribute pixel erasure multi-value image generation means for generating a multi-value image in which pixels having the specific attribute corresponding to the black pixel portion remaining without being replaced with white pixels by the white pixel replacement means are filled with a background color When,
Image encoding means for encoding each of the plurality of images generated by these image generation means;
With
The specific attribute pixel image generation means includes
Means for obtaining a pixel value in a corresponding multi-valued image of a pixel on the binary image having the specific attribute;
Means for calculating a representative color from the acquired pixel values;
Means for assigning a pixel value having the specific attribute to any of the calculated representative colors;
Means for generating a single image or a plurality of images having only the calculated representative color as a constituent pixel color according to a result of assigning the pixel value;
With
The means for calculating the representative color is:
Means for creating a histogram of pixel values;
Means for selecting a representative color candidate having a higher priority from the higher frequency of the histogram;
Leaving from the high priority representative color candidate to the first predetermined number in the order, the other representative color candidate and excluded means from the representative color candidates,
Means for determining whether the representative color candidate is an achromatic color;
Achromatic determined to be high priority achromatic a second representative color candidates of a predetermined number greater than the achromatic a representative color candidates than by the determining means, and excluding means from the representative color candidates,
Means for calculating the degree of color difference between representative color candidates;
Means for excluding the one with the lowest priority from the representative color candidates having the smallest color difference, from the representative color candidates;
Means for repeating the exclusion from the representative color candidates from the calculation of the color difference between the representative color candidates until the number of representative color candidates reaches a third predetermined number, and selecting the remaining representative color candidates as representative colors;
An image processing apparatus comprising: A means for assigning a pixel value having the specific attribute to any of the calculated representative colors,
Means for obtaining an average value of pixel values having the specific attribute ;
A distance between the average value of the pixel values having the specific attribute obtained by the means for obtaining the average value and the representative color calculated by the means for calculating the representative color is obtained, and the representative color is selected from the representative colors. A means of selecting the closest representative color;
With
Assigning a pixel value having the specific attribute to the representative color selected by the selecting means;
The image processing apparatus according to claim 1 or 2 . A means for assigning a pixel value having the specific attribute to any of the calculated representative colors,
Means for obtaining a mode value of pixel values having the specific attribute ;
Means for obtaining the distance between the mode value obtained by the means for obtaining the mode value and the representative color calculated by the means for calculating the representative color, and selecting the nearest representative color from the representative colors When,
With
Assigning a pixel value having the specific attribute to the representative color selected by the selecting means;
The image processing apparatus according to claim 1 or 2 . A means for assigning a pixel value having the specific attribute to any of the calculated representative colors,
Means for obtaining a mode value of pixel values having the specific attribute ;
Means for performing a correction to replace the mode value with a black color by a subtraction process using a predetermined correction value when the mode value obtained by the unit for obtaining the mode value is an achromatic color;
Means for obtaining the distance between the mode value corrected by the means for performing correction and the representative color calculated by the means for calculating the representative color, and selecting the nearest representative color from the representative colors;
With
Assigning a pixel value having the specific attribute to the representative color selected by the selecting means;
The image processing apparatus according to claim 1 or 2 . A means for assigning a pixel value having the specific attribute to any of the calculated representative colors,
Means for obtaining a mode value of pixel values having the specific attribute ;
Means for correcting the mode value obtained by the unit for obtaining the mode value by a multiplication process using a predetermined correction value to replace the mode value with a darker color;
Means for obtaining the distance between the mode value corrected by the means for performing correction and the representative color calculated by the means for calculating the representative color, and selecting the nearest representative color from the representative colors;
With
Assigning a pixel value having the specific attribute to the representative color selected by the selecting means;
The image processing apparatus according to claim 1 or 2 .

Images