JP4056277B2 - Color reduction processing apparatus and color reduction processing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a color reduction processing apparatus and a color reduction processing method for converting each pixel color of a color reduction processing target image into an image having a smaller number of colors than an original image by replacing the color of each pixel with a color included in a predetermined color palette.
[0002]
[Prior art]
In recent years, images of digital data taken with a digital camera or the like are transferred to an image distribution server using a mobile phone or a personal computer, or an image distribution server in which an image distributor prepares various image data for distribution has been operated. An image distribution system that distributes images stored in these image distribution servers to mobile terminals such as mobile phones and personal digital assistants (PDAs) has been put into practical use.
[0003]
In this type of image distribution system, there are strong restrictions on the memory capacity and display capability of the mobile terminal, and the memory capacity and display capability differ depending on the type of mobile terminal, so when distributing images from the image distribution server to the mobile terminal According to the memory capacity and display capability of the distribution-destination portable terminal, processing is performed to reduce the data amount by reducing the number of images and the number of colors. For example, after performing image reduction processing (thinning processing) that reduces the number of pixels to a predetermined number of pixels such as 130 × 130 pixels and 90 × 90 pixels, the number of colors included in the image is further increased to 256 colors, 128 colors, 16 Color reduction processing for reducing the number of colors such as colors to a predetermined number is performed.
[0004]
Conventionally, as this kind of color reduction processing method, a fixed type limited color display method (fixed palette color reduction method) and an adaptive type limited color display method (free palette color reduction method) are known.
[0005]
The fixed limited color display method uses one color palette consisting of a predetermined number of representative colors that are uniformly selected from colors that can be reproduced by a display device, and uses the color palette for the color of each pixel of the color reduction target image. This is a color reduction processing method that replaces the closest color included. This method does not need to create a color palette for each color reduction target image, so it can perform color reduction processing at high speed, but there is a bias in the colors in the image, such as a face image or autumnal image. In some cases, only some of the colors included in the color palette are used, and the remaining colors are not used at all. For example, only 50 colors may be used even though a color palette composed of 256 representative colors is used. In such a case, the color image representation after the color reduction processing is of low quality.
[0006]
The adaptive limited color display method creates a color palette composed of a predetermined number of representative colors suitable for expressing the color reduction processing target image based on the color information of the color reduction processing target image. This is a color reduction processing method in which the color of a pixel is replaced with the closest color included in the color palette. This method needs to create a color palette for each color reduction target image, so the processing speed is slower than the fixed limited color display method, but it uses a color palette suitable for each color reduction target image. High-quality color image representation is possible.
[0007]
[Problems to be solved by the invention]
In the adaptive limited color display method described above, the appearance frequency of each color in the color reduction processing target image is obtained by statistical processing using a histogram or the like, and a predetermined number of colors are given priority for each color reduction processing target image. A color palette is created by selecting representative colors.
[0008]
For this reason, for example, in the case of an image in which a person appears small against a background of autumn leaves or a green field, the color included in the background rather than the color included in the person, even though the person is the main subject Therefore, a color palette including more colors included in the background than colors included in the person is created. When subtractive color processing is performed using this color palette, the background image is expressed smoothly in many colors, so the degree of image quality degradation is small. Since the color is expressed with a small number of colors, the degree of degradation of image quality increases. In particular, when a large color reduction process is performed, important colors such as a person's skin color are deleted from the color palette, and there is a possibility that the color may change greatly with respect to the original image. For example, in the case of an image in which a person appears small with autumn leaves in the background, the color of the person becomes reddish as a result of the color reduction processing.
[0009]
The present invention has been made in view of the above circumstances, and an object of the present invention is to prevent important colors in a color reduction target image from being deleted from a color palette when performing color reduction processing, and to minimize image quality degradation. An object of the present invention is to provide a color reduction processing apparatus and a color reduction processing method capable of performing color reduction processing while suppressing.
[0010]
[Means for Solving the Problems]
The color reduction processing apparatus of the present invention includes a color palette creation means for creating a color palette having a predetermined number of representative colors, and the color of each pixel of the color reduction processing target image using the color palette. Important to store color replacement processing means to be replaced, important color information designated in advance as additional information of the color reduction processing target image, and weighting information in which a weighting factor is set for each region in the color reduction processing target image and a color information storage means, said color palette creation means, based on the subtractive color processing object image color information and the important color information storage means critical color information stored in the weighting information, the important color A color pallet that preferentially includes is created.
[0012]
According to the color reduction processing method of the present invention, important color information storage for storing important color information designated in advance as additional information of a color reduction processing target image and weighting information in which a weighting coefficient is set for each region in the color reduction processing target image. a method, based on the important color information that the stored color information of the color reduction process target image and the weighting information, to create a color palette that includes the important colors preferentially as a color palette having a representative color of a predetermined number A color palette creating step; and a color replacement processing step of replacing the color of each pixel of the color reduction target image with any of the colors included in the color palette using the color palette.
[0013]
In the color reduction processing apparatus and the color reduction processing method of the present invention configured as described above, a predetermined number of priority colors including the important colors are preferentially based on the color information of the color reduction processing target image and the information on the designated important colors. A color palette composed of representative colors is created, and color replacement processing is performed to replace the color of each pixel of the color reduction processing target image with the color included in the created color palette. Therefore, when the color reduction process is performed, the important color of the color reduction target image is designated, so that the important color of the color reduction target image is easily deleted from the color palette based on the appearance frequency. Therefore, it is possible to prevent the important color from being largely changed due to the color reduction, and to perform the color reduction processing while suppressing the deterioration of the image quality as much as possible.
[0014]
Further, in the color reduction processing apparatus and the color reduction processing method of the present invention, for example, a weight coefficient corresponding to the importance for each area, such as dividing the color reduction target image into a plurality of areas and increasing the weight of the center of the image. And a color palette composed of a predetermined number of representative colors may be created so as to preferentially include colors included in a large weight area.
[0015]
In this way, a predetermined number of color palettes that preferentially include colors included in areas of higher importance during the color reduction process are created, so colors included in areas of high importance of the color reduction target image are displayed. Based on the appearance frequency, it can be easily deleted from the color palette, it can be left preferentially so that important colors do not change due to color reduction, and color reduction processing can be performed with minimal deterioration in image quality. It becomes possible.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing a configuration example of an image distribution system using a color reduction processing apparatus according to an embodiment of the present invention.
[0017]
An image distribution system 1 according to this embodiment includes a personal computer (distribution source terminal device, hereinafter referred to as a PC) 10, a mobile phone (distribution destination terminal device) 20 as a mobile terminal, and an image distribution server (image conversion distribution). Device) 30 is interconnected via a communication network such as the Internet, and an image of digital data such as an image taken by the digital camera 2 is transferred to the image distribution server 30 using the PC 10, and the image distribution server 30 The image stored in the mobile phone 20 is distributed to the mobile phone 20.
[0018]
The PC 10 is installed with an application program (hereinafter referred to as an image distribution application) for transferring the image to be distributed to the mobile phone 30 to the image distribution server 20 together with important color information designating the image. A user of the PC 10 such as an image distributor can distribute an image from a large number of images such as an image taken from the digital camera 2 to the PC 10 or an image created by using image processing software by using an image distribution application. Select the desired image and specify an important color for each selected image. At that time, one or more colors can be designated as important colors in each image for distribution. When an image to be distributed using an image distribution application is selected and an important color is designated and a transfer instruction is issued, the PC 10 sends the selected image and information on the designated important color to the image distribution server 20. Forward to. The designated important color information is transferred to the image distribution server 20 as additional information of the image to be distributed.
[0019]
The mobile phone 20 includes a communication unit 21 for communicating with other mobile phones and servers on the Internet via a base station (not shown), a display unit 22 for displaying characters and images, and various operators such as dial buttons. And a terminal information storage unit 24 that stores information such as the communication speed of the mobile phone 20 and the display capability (the number of pixels and the number of colors that can be expressed) of the display unit 22. . When the mobile phone 20 communicates with another mobile phone or a server on the Internet, the mobile phone 20 reads the terminal information from the terminal information storage unit 24 and notifies the communication destination.
[0020]
The image distribution server 30 includes a pre-distribution image storage unit 31 that stores an image (original image) received from the PC 10, a terminal information storage unit 32 that stores terminal information received from the mobile phone 30, and a pre-distribution image storage unit 31. A distribution image generation unit 33 that performs a pixel number reduction process and a color reduction process on the image read from the terminal information storage unit 32 based on the terminal information read from the terminal information storage unit 32, and then performs a compression process to generate a distribution image; And a transfer unit 34 that transfers the distribution image generated by the distribution image generation unit 33 to the mobile phone 20.
[0021]
As shown in FIG. 2, the distribution image generation unit 33 includes a pixel number reduction processing unit 41 that reduces the number of images, a color reduction processing unit 42 that performs color reduction, a compression processing unit 43 that performs reversible or irreversible data compression, And a data capacity determination unit 44 that determines whether the data capacity of the output image is equal to or less than a predetermined value.
[0022]
The pixel number reduction processing unit 41 reduces the number of pixels of the image (original image) read from the pre-delivery image storage unit 31 to a predetermined number of pixels such as 130 × 130 pixels and 90 × 90 pixels (decimation processing). I do. At that time, the number of pixels after reduction (target value) is determined according to the number of pixels included in the terminal information read from the terminal information storage unit 33.
[0023]
The color reduction processing unit 42 replaces the color of each pixel of the image (the color reduction target image) processed by the pixel number reduction processing unit 41 with the closest color among the colors included in the color palette created for each image. Thus, a color reduction process is performed to reduce the number of colors included in the image to a predetermined number of colors such as 256 colors, 128 colors, and 16 colors.
[0024]
The compression processing unit 43 performs compression processing on the image (color-reduced image) processed by the color reduction processing unit 42 using a known compression method such as GIF or PNG. The data capacity determination unit 44 determines whether the data capacity of the image after data compression is equal to or less than the data capacity that can be processed in the communication path to the distribution destination and the portable terminal at the distribution destination and can be transmitted and displayed. The compressed image is transferred to the mobile phone 20 via the transfer unit 34 after the data volume is determined by the data volume determination unit 44.
[0025]
Since the transferable data capacity varies depending on the type of mobile phone and the communication carrier company, there is a possibility that transfer may be impossible or reception may be rejected due to the excess data capacity. If the data capacity determination unit 44 determines that the data capacity is exceeded, the image data is again subjected to further color reduction processing in the color reduction processing unit 42 and recompressed in the compression processing unit 43.
[0026]
As shown in FIG. 3, the color reduction processing unit 42 includes an important color information storage unit (important color information storage unit) 51 that stores important color information, and a color palette creation unit (color palette creation unit) that performs color palette creation processing. ) 52 and a color replacement processing unit (color replacement processing means) 53 that performs color replacement of each pixel in the original image using a color palette.
[0027]
The important color information storage unit 51 stores important color information transmitted as additional information of an image distributed from the PC 10. The color palette creating unit 52 is designated by the user of the PC 10 based on the important color information read from the important color information storage unit 51 and the color information of the color reduction processing target image given from the pixel number reduction processing unit 41. Create a color palette that preferentially contains important colors.
[0028]
The color replacement processing unit 53 replaces the color of each pixel of the color reduction processing target image given from the pixel number reduction processing unit 41 with the closest color included in the color palette created by the color palette creation unit 52. Then, the color-reduction processing target image is converted into a color-reduced image composed of colors included in the color palette. The reduced color image is compressed by the compression processing unit 43 and then transferred to the mobile phone 20.
[0029]
FIG. 4 shows an operation procedure of the color palette creation unit 52. The color palette creation unit 52 first checks the color of each pixel constituting the color reduction processing target image given from the pixel number reduction processing unit 41, and performs each color in the color reduction processing target image by statistical processing using a histogram or the like. Is calculated (step S1). Next, important color information is read from the important color information storage unit 51 (step S2). Then, after selecting the important color as the representative color of the color palette (step S3), it is confirmed whether or not the representative color of the color palette is sufficient with only the important color (step S4), and if not enough (Yes in step S4). The remaining representative colors are selected with priority given to colors having a higher appearance frequency (step S5). In this way, for each color reduction processing target image, a color palette (free palette) composed of representative colors that always include the important colors designated by the distribution source and that preferentially include the colors that appear frequently (step S6). ).
[0030]
As described above, the color palette creation unit 52 includes a predetermined number of representative colors that preferentially include important colors based on the color information of the color-reduction processing target image and the designated important color information. Thus, it is possible to prevent the important color of the color reduction target image from being easily deleted from the color palette based on the appearance frequency.
[0031]
Then, the color palette created by the color palette creation unit 52 is used, and the color replacement processing unit 53 replaces the color of each pixel of the image to be reduced with the color included in the color palette, thereby missing important colors. It is possible to perform the color reduction process without doing so.
[0032]
Therefore, when the image to be distributed is, for example, an image in which a person appears small against a background of autumn leaves or a green field, the user of the PC 10 uses the image distribution application to identify the person in the image. By specifying the included colors (skin color, clothes color, etc.) as important colors, it is possible to prevent the colors included in the person in the image from being easily deleted from the color palette. Can be prevented as much as possible even after the color reduction process. In the case of an image in which a person is shown small with autumn leaves in the background, the color reduction processing results in a problem that the color of the person becomes reddish in the conventional color reduction processing method. Such a problem can be solved by the color reduction processing method of the present invention described above.
[0033]
The function of the color reduction processing unit 42 can be realized by installing and operating a program for executing the color reduction processing by a color reduction processing method according to the present invention on a general-purpose server computer. That is, a step of creating a color palette including a predetermined number of representative colors preferentially including the important color based on the color information of the color reduction processing target image and the designated important color information, and the color reduction processing target image A server computer having the function of the color reduction processing unit 42 can be realized by installing and executing a program including the step of replacing the color of each pixel with a color included in the color palette on the server computer.
[0034]
As shown in the operation flow of FIG. 4, this program examines the color of each pixel constituting the color reduction processing target image, and determines the appearance frequency of each color in the color reduction processing target image by statistical processing using a histogram or the like. And a step of determining whether or not the representative color of the color palette is sufficient only for the important color, and if not, the step of preferentially selecting a color having a higher appearance frequency as the remaining representative color. It is desirable.
[0035]
In the embodiment described above, the important color information designated by the distribution source user is transferred together with each image from the PC 10 to the image distribution server 20 as additional information for each image to be distributed. Instead of the additional information, it may be transferred as a separate file linked for each image.
[0036]
Further, the designated important color information may be transferred as information for each distribution source. In this case, the distribution source user has only to designate the color that he / she always wants to keep regardless of the image as the important color and send the information once to the image distribution server 20, thus saving the trouble of designating the important color for each image. be able to.
[0037]
Further, as shown in FIG. 5, the color reduction processing target image is divided into a plurality of areas (in this example, 5 × 5 areas), and a weighting coefficient corresponding to the importance is set for each area. The color palette creation unit 52 may create a color palette composed of a predetermined number of representative colors that preferentially include a large number of colors included in the color palette. That is, weighting information is set together with important color information as additional information of an image, and a color palette giving priority to the important color is created based on the information.
[0038]
In this way, a predetermined number of color palettes that preferentially include colors included in an area of higher importance (an area closer to the center of the image in the example of FIG. 5) are created. It is possible to prevent the color included in the area of high importance from being easily deleted from the color palette based only on the appearance frequency, and to perform the color reduction processing that suppresses the deterioration of the image quality as much as possible.
[0039]
Further, when the color-reduced image after compression processing by the compression processing unit 43 needs to be further subjected to color-reduction processing by the color-reduction processing unit 42, the color of each pixel of the color-reduced image is added to the color palette created by the color palette creation unit 52. When replacing with the included color, it is desirable to replace the color by increasing the weight of a color closer to the designated important color, that is, a color closer to the important color in the color space. By increasing the weight as the color is closer to the important color, it is possible to prevent the important color from being easily deleted by statistical processing using a histogram or the like.
[0040]
In the above embodiment, the example of the color reduction process using the color palette by the free palette color reduction method has been described. However, in the case of performing the color reduction process after the color reduction once as described above, the fixed palette color reduction method is used. Even in the color reduction processing using the color palette, when the number of colors in the color palette is reduced, the same effects can be obtained by applying the configuration and procedure of the above-described embodiment.
[0041]
As described above, according to the color reduction processing device and the color reduction processing method in the present embodiment, a color palette including a predetermined number of representative colors is created based on the color information of the color reduction processing target image, and the color reduction processing target image When performing color reduction processing to convert the color reduction target image to an image with fewer colors than the original image by replacing the color of each pixel with the color included in the color palette, specify the important color of the color reduction target image By doing so, it is possible to prevent the important color of the image to be reduced to be processed from being easily deleted from the color palette based on the appearance frequency, and it is possible to perform a color reduction process that suppresses degradation of image quality as much as possible. .
[0042]
【The invention's effect】
As described above, according to the present invention, it is possible to prevent the important color in the color reduction processing target image from being deleted from the color palette when performing the color reduction processing, and to perform the color reduction processing while suppressing deterioration in image quality as much as possible. It becomes possible.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration example of an image distribution system using a color reduction processing apparatus according to an embodiment of the present invention.
FIG. 2 is a block diagram illustrating a configuration example of a distribution image generation unit in the present embodiment.
FIG. 3 is a block diagram illustrating a configuration example of a color reduction processing unit in the present embodiment.
FIG. 4 is a flowchart showing an operation procedure of a color palette creating unit in the present embodiment.
FIG. 5 is a diagram illustrating an example of setting a weighting factor for each area of a color reduction processing target image in the present embodiment.
[Explanation of symbols]
1 image distribution system 2 digital camera 10 personal computer (PC) (distribution source terminal device)
20 Mobile phone (distribution destination terminal device)
30 Image distribution server (Image conversion distribution device)
22 Display Unit 24 Terminal Information Storage Unit 31 Pre-Distribution Image Storage Unit 32 Terminal Information Storage Unit 33 Distribution Image Generation Unit 34 Transfer Unit 41 Pixel Number Reduction Processing Unit 42 Color Reduction Processing Unit (Color Reduction Processing Device)
43 Compression Processing Unit 51 Important Color Information Storage Unit 52 Color Palette Creation Unit 53 Color Replacement Processing Unit

Claims (4)

Color palette creating means for creating a color palette having a predetermined number of representative colors;
Color replacement processing means for replacing the color of each pixel of the color reduction processing target image with any of the colors included in the color palette using the color palette;
Important color information storage means for storing important color information designated in advance as additional information of the color reduction processing target image and weighting information in which a weighting factor is set for each region in the color reduction processing target image ;
The color palette creation means, based on the important colors of the information stored and weighted information to the important color information storage means and the color information of the color reduction processing target image, the color palette containing the important colors preferentially A color-reduction processing apparatus characterized by creating. An important color information storage step for storing important color information designated in advance as additional information of the color reduction processing target image and weighting information in which a weighting coefficient is set for each region in the color reduction processing target image;
Creating a color palette that preferentially includes the important color as a color palette having a predetermined number of representative colors based on the color information of the color reduction processing target image, the stored important color information, and weighting information Steps,
And a color replacement processing step of replacing the color of each pixel of the color reduction processing target image with any of the colors included in the color palette using the color palette . The color palette creation means preferentially selects a color other than the important color included in the color palette, with priority given to a color with a high frequency of appearance of each pixel color in the color reduction processing target image. The color reduction processing apparatus according to 1 . The color palette creating step is characterized in that, with regard to colors other than the important color included in the color palette, a color having a high appearance frequency of each pixel color in the color reduction processing target image is preferentially selected. 2. The color reduction processing method according to 2 .

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