JP2004236157A - Image processing device, image processing method, and image processing program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve high-speed color determination/monochrome binary conversion without the need for a memory. <P>SOLUTION: The image processing device comprises a color space conversion section 101 that converts a color image into color space, a color area table 103 that includes a space coordinate as the center of color and a first distance r of space showing the range of a color area by each color, a color determination section 102 that calculates a second distance L between the space coordinates of the image data after color space conversion and a space coordinate of the color area table for each color by each pixel and that determines color, where the second distance L becomes minimum, as the color of a pixel when a color area whose second distance L becomes equal to or less than the first distance r (L≤r) exists, a conversion density value table 104 that includes density data after converting the color area corresponding to pixel color, and a conversion section 105 that converts an image into a monochrome image by each pixel based on the density data of the conversion density value table. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image processing apparatus, an image processing method, and an image processing program, and particularly to an image processing apparatus, an image processing method, and an image processing program for converting a color image into a monochrome image.
[0002]
[Prior art]
2. Description of the Related Art In an image processing apparatus such as a copying machine, a printer, a scanner, and a facsimile, it is sometimes required to convert a color image read or received from a document into a monochrome image.
[0003]
Conventionally, when a color image is converted into a monochrome binary image using only the luminance component of each pixel, for example, if two colors having similar luminance values such as red and blue are adjacent to each other, the binary As a result of the conversion into an image, the difference between the two color regions becomes unclear and information is lost. Further, a color having a high luminance value such as yellow may be regarded as white at the time of conversion, and information may be lost after the conversion. Furthermore, even if a color component or the like is used in addition to the luminance component, there are a plurality of colors that are expressed with the same density after the conversion, so that the above-described region may become unclear. I will.
[0004]
FIG. 3 shows an example of monochrome binary conversion. FIG. 3A shows an original image. If the original image is binarized by monochrome graying using, for example, a luminance component, an image as shown in FIG. 3B is obtained. It is difficult to distinguish black characters in a red rectangle from surrounding red characters, and a phenomenon occurs in which data for a yellow rectangle disappears.
[0005]
Various solutions have been proposed for this problem. For example, Patent Document 1 discloses that a plurality of colors included in a color image are determined, a density after conversion is determined for each pixel included in the color image based on color information, and the color is the color of each pixel in a layer. There is a description of converting the components to the determined concentrations (FIG. 3 and the like).
[0006]
Further, in FIG. 1 of Patent Document 2 and the like, FIG. 1 of Patent Document 3 and the like, FIG. 1 of Patent Document 4 and the like of FIG. There is a description of an image processing apparatus that determines a color area and gives a gradation difference in order to prevent sticking.
[0007]
[Patent Document 1]
JP 2001-352454 A
[Patent Document 2]
JP 2002-10090
[Patent Document 3]
JP-A-62-088071
[Patent Document 4]
JP-A-10-155085
[Patent Document 5]
JP-A-11-339034
[0008]
[Problems to be solved by the invention]
However, the techniques described in the above patent documents require a certain memory in the area determination processing, are expensive, and require a certain amount of time for the processing.
[0009]
[Means for Solving the Problems]
The image processing device according to the present invention, for each pixel of the color image, a color determination unit that determines the color of the pixel,
A conversion density value table including density data corresponding to the color of the pixel,
Conversion means for converting each pixel into a monochrome image based on the density data in the conversion density value table.
[0010]
Further, the image processing apparatus of the present invention, means for converting a color image to a color space,
A color area table including, for each color, a space coordinate serving as a center of the color and a first distance of a space representing a range of the color area;
A second distance between the spatial coordinates of the image data after color space conversion and the spatial coordinates of the color area table is obtained for each color for each pixel, and a color area where the second distance is equal to or less than the first distance A color determination unit that determines a color in which the second distance is the minimum when the pixel is present as a pixel color;
A conversion density value table including density data after conversion of a color area corresponding to the color of the pixel,
Conversion means for converting each pixel into a monochrome image based on the density data in the conversion density value table.
[0011]
An image processing method of the present invention is an image processing method for converting a color image into a monochrome image, wherein for each pixel of the color image, the color of the pixel is determined, and the converted density value includes density data corresponding to the color of the pixel. It is characterized in that a monochrome image is converted for each pixel using a table.
[0012]
Further, the image processing method of the present invention, the step of converting a color image to a color space,
Using a color area table including, for each color, space coordinates that are the center of the color and a first distance of the space that represents the range of the color area, the spatial coordinates of the image data after color space conversion and the color area table A second distance from the space coordinates is obtained for each color for each pixel, and when there is a color region in which the second distance is equal to or less than the first distance, a color in which the second distance is minimum is determined. Determining the color of the pixel;
Converting a monochrome image for each pixel based on the density data using a converted density value table including density data after conversion of a color area corresponding to the color of the pixel.
[0013]
The image processing program according to the present invention comprises: a color determination unit that determines a color of a pixel for each pixel of a color image; and a pixel determination unit for each pixel based on density data of a conversion density value table including density data corresponding to the color of the pixel. This is for causing a computer to function as a conversion means for converting the image into a monochrome image.
[0014]
Further, the image processing program according to the present invention includes means for converting a color image into a color space,
A second distance between a color area table provided for each color and a space coordinate serving as a center of the color and a first distance of a space representing a range of the color area, and a space coordinate of the image data after the color space conversion. Color determination means for each color for each pixel, and when there is a color region in which the second distance is equal to or less than the first distance, a color determining unit that determines a color in which the second distance is the minimum as a pixel color. ,
This is for causing a computer to function as conversion means for converting each pixel into a monochrome image based on density data in a conversion density value table including density data after conversion of a color area corresponding to the color of the pixel.
[0015]
The present invention performs a simple area determination that does not require a memory for the conversion of a color image into a monochrome binary image, and arbitrarily determines a specific color based on the determination result irrespective of the luminance value that the original document originally has. Is assigned to a specific density (multi-valued), a binarization process is performed on the entire image, and a monochrome binary image that can be distinguished for each color is generated.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0017]
First, the configuration of an embodiment of the image processing apparatus of the present invention will be described with reference to FIG.
[0018]
Referring to FIG. 1, an image processing apparatus according to the present embodiment includes an image input unit 100 that captures an image, a color space conversion unit 101 that performs color space conversion of an input image, and performs color determination on the converted color space. The conversion unit 106 includes a color determination conversion unit 106 that converts the converted monochrome gray data into binary data according to the result, and a binarization unit 107 that binarizes the converted monochrome gray data.
[0019]
The color determination conversion unit 106 performs a color determination, a color region table 103 having data of each color region used as a standard sample for the color determination, and a specific monochrome gray data according to the color determination result. The conversion unit 105 converts and outputs the converted density values. The converted density value table 104 stores the converted density values for each color area.
[0020]
(Description of operation)
Next, the operation of the image processing apparatus will be described.
[0021]
Digital color image data is input to the image input unit 100 from a still image input device such as a color image scanner or a digital camera, or from a memory or the like in which image data is stored.
[0022]
The input color image is converted into a color space (CIE1976 L * a * b * color) having a luminance component and a hue component such as L *, a *, b * or L, u, v from RGB in a color space conversion unit 101. Space, CIE 1976 L * u * v * color space) (CIE: Suppl. No. 2 to CIE Publ. No. 15, Colorimetry (E-1.3.1) 1971, (1976)) . Here, as for the color space after the color space conversion, the uniform color space such as L *, a *, and b * described above has less distortion and the accuracy of subsequent processing is high, but a color space such as YCbCr or Yuv is used. Even though a slight distortion occurs, there is almost no effect on the present embodiment, so it can be said that there is no problem.
[0023]
The color space conversion unit 101 also performs conventional monochrome gray data conversion at the same time. This conversion processing includes general conversion such as conversion of RGB G components into monochrome gray data, conversion of luminance components such as Lab space into monochrome gray data, and conversion by calculation of (αR + βG + γB) ÷ (α + β + γ). Monochrome gray conversion is performed. Target pixel data P _G after the target pixel data P and the monochrome gray conversion after the color space conversion is output to both the color judgment conversion unit 106.
[0024]
The color determination conversion unit 106 performs color determination and conversion into monochrome gray data. FIG. 2 is a flowchart showing the processing of the color determination conversion unit 106.
[0025]
Hereinafter, description will be made with reference to FIGS. The target pixel data P after the color space conversion is input to the color determination unit 102, and the color determination is performed. Here, the processes of steps S1 to S4 and S6 of FIG. 2 are performed.
[0026]
First, in step S1, an average value P _AVE of several pixels is calculated in the horizontal direction around the pixel to be converted. This is calculated for each pixel. The number of pixels to be averaged varies depending on the resolution of the input image, the image quality setting of the output image, and the like. In the case of an image of 600 dpi, about 2 to 5 are considered to be usable levels. This averaging makes it possible to reduce the color determination error between adjacent pixels as compared to a case where averaging is not performed. In addition, since this averaging is performed only in the horizontal direction, no extra memory is required when implemented by hardware.
[0027]
In step S2, the average value _{P AVE} calculated in step S1, the distance Len _i of each color region of the color region table 103 in (C_Table) is obtained. Here, i is an index of each color area in the color area table. The color area table 103, the spatial coordinate for the center of each color region _{(x i, y i, z} i) and the radius r _i of the space representing the range of the color region are prepared. Therefore distance Len _i is calculated as the distance between the spatial coordinates of the color of the pixel after averaging (x, y, z) and center coordinates of the color area _{(x i, y i, z} i). Here, the distance is usually determined by the Euclidean distance, but there is no major problem with the Pascal distance. When implemented in hardware, Pascal distance can be easily implemented. In this case, the value of the color area table 103 changes. Color space coordinates of the pixel after averaging (x, y, z) and center coordinates of the color area _{(x i, y i, z} i) the distance between, the determined Euclidean distance, _{{(x-x i} ) ² + (y−y _i ) ² + (z−z _i ) ^{2 １ ／ 1/2} , and when it is calculated by the Pascal distance, (x−x _i ) + (y−y _i ) + (z−z _i ) It becomes.
[0028]
To distance Len _i determined in step S3 in each color area to determine whether the target pixel data P _AVE is included in the color area. Here, as a threshold for determining makes the determination using the radius r _i which is set in the color area table 103, respectively. This is because an optimal threshold value is used for each color region because the range of the region differs for each color region. In the determination of step S3, when the color region to be Len _i ≦ r _i exists even one, then proceeds to step S4, if the Len _i ≦ r _i become the color region is not present Then, the process proceeds to step S6.
[0029]
Determining the minimum distance in step S4 Len _i ≦ _{r i} and became Len _i, and outputs it to the converter 105 and the color ID of the target pixel the index of the color area. In step S6, an identification value indicating that the color is not a conversion target color is output as a color ID. Here, when it is indicated that the color is not the color to be converted, it is not necessary to output the color ID, and in that case, the color is notified to the conversion unit 105 as a separate flag.
[0030]
The conversion of the conversion unit 105 to the final monochrome gray data P _M in place, step S5 in FIG. 2, the process of step S7 is performed.
[0031]
When the color determination unit 102 determines that the target pixel data P _AVE is a color of a specific color area, in step S5, a density value corresponding to the color ID is read from the conversion density value table 104 (D_Table). processing is performed to the monochrome gray data P _M of the target pixel density values. Here, the conversion density value table 104, the density value D _i after conversion corresponding color _region corresponding flag tflag _i to the color region selects whether to convert the density value D _i are prepared. That is, in the case of tflag _i = 1, monochrome gray data _{P M} after conversion _becomes P M = _{D i,} if the tflag _i = 0, is not performed replacing the density value of the color region, the color space conversion unit so that the converted monochrome gray data P _G at 101, is used. In other _words, the _P M = P _G. This can be used, for example, when specifying a color area for which density value conversion is not to be performed. Therefore, it is possible to switch between conversion and non-conversion for each color area.
[0032]
Not data of a specific color region in the color determination section 102, that is, when it is determined not to be data to be converted, as a monochrome gray data P _M of the pixel of interest in step S7, the converted monochrome color space conversion unit 101 gray data _{P G} is used.
[0033]
Target pixel is converted into monochrome gray data P _M is binarized by binarization unit 107. Here, as the binarization method, a general method such as simple binarization, dither, and error diffusion method is used.
[0034]
FIG. 3 shows an example of a processing result by the image processing apparatus of the present embodiment and a processing result of general monochrome binary conversion. FIG. 3B, which shows the result of a general monochrome binary conversion process on the original image shown in FIG. 3A, is indistinguishable between a black character and a red background. It has disappeared. On the other hand, in FIG. 3C showing the processing result of the present embodiment, by giving a density value smaller than that of FIG. 3B as the red density value, the character and the background can be distinguished. By giving a certain density value to yellow, a yellow background is output. No conversion is performed on the light blue region, and the image is output at the same density as that in FIG. 3B. That is, an area that does not require conversion can be output as it is. As a result, in the image of FIG. 3C, the monochrome image can be satisfactorily converted by replacing the original image information with appropriate density information without losing the information other than the color information.
[0035]
The above is an example of the operation of the image processing apparatus. The color space conversion unit 101 and the color determination conversion unit 106 have no correlation with adjacent pixels except for the calculation of the moving average in the horizontal direction, and can perform processing for each pixel. It is. Also, since the horizontal moving average is at a level of several pixels, the processing according to the present embodiment can be performed in a raster without a specific memory. Therefore, processing can be performed at high speed. Furthermore, by adding a line memory of several lines, it is possible to perform moving average in the vertical direction and improve the accuracy of color determination.
[0036]
The number of data in the color area table 103 can be freely configured by the resource capacity at the time of mounting and the final image quality level setting. However, about 16 or 24 colors, and at most about 32 colors are sufficient. I think that the. Further, in the present embodiment, a good result can be obtained for a document composed of a small number of colors, such as a business document, and therefore, by switching to a general monochrome binary conversion, a configuration similar to a photographic image can be obtained. By performing monochrome binary conversion without performing the processing according to the present embodiment, a suitable image can be used properly. In this case, if a photograph image or a business image is known in advance, and if a flag or the like indicating that is known, automatic discrimination is possible. Is required, which increases the cost.
[0037]
In the color determination of the present embodiment, when there is a certain target sample, a distance is calculated for each standard sample, and a pattern recognition technique that regards the target sample as a member of the standard sample having the minimum distance is applied. In the present embodiment, since the color judgment is performed for each pixel, the memory required for the area judgment, for example, one page of memory is not required until now. As a result, processing can be performed in raster, and high-speed processing can be performed.
[0038]
Further, since the target color is limited in the color area table, only the designated color can be converted. This is because it is not possible to express all the colors or all the colors in the page even if the density value is intentionally manipulated, so that the binary data cannot be used to make all the determinations. Is performed only for the color for which the color is required, the resources constituting the present invention can be reduced. For example, in the case of an office document such as a graph, since the number of colors is small, it is sufficient to be able to determine the basic color.
[0039]
Furthermore, a specified color can be represented by a specified density regardless of the luminance value that the original originally has. This is because the information of the color at the time of conversion into the monochrome binary is converted into information of the change in density, and there is no need to represent the change with the original luminance value. Therefore, the information is damaged by the method of specifying the color and the density. Without this, monochrome binary conversion is possible. In an extreme case, it is possible to output only the designated color or to erase only the designated color, and it is possible to perform conversion according to the user's preference.
[0040]
In the present embodiment, the digital image processing apparatus has been described, but the digital image processing can be realized by software. Further, the present embodiment can be applied to a monochrome facsimile equipped with a color scanner, a monochrome copy, and the like.
[0041]
FIG. 4 is a block diagram of a computer that functions as the respective units illustrated in FIG. 1 and executes a program for executing the flow illustrated in FIG. 2.
[0042]
Image information input from a scanner or the like is stored in a memory 123 such as a DRAM or a storage unit such as a disk device 124 such as an MO or a hard disk via the IO unit 120. The CPU 126 functions as each unit in FIG. 1 described above, and performs processing based on a program (here, the program is stored in the disk device 124) describing the flow in FIG. The keyboard 121 serves as an input unit for inputting data, and the CRT 122 serves as a display unit for displaying an image processed. Reference numeral 125 denotes a bus such as a data bus.
[0043]
【The invention's effect】
As described above, according to the present invention, it is possible to perform a process of intentionally replacing a color that is difficult to determine in general monochrome gray conversion with a certain density value. As a result, a good monochrome binary image can be obtained for business documents represented by a relatively small number of colors, such as presentation documents and graphs.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of an embodiment of an image processing apparatus according to the present invention.
FIG. 2 is a flowchart illustrating processing of a color determination conversion unit 106.
FIG. 3 is a diagram illustrating an example of a processing result by the image processing apparatus according to the embodiment and a processing result of general monochrome binary conversion.
4 is a block diagram of a computer that functions as each unit shown in FIG. 1 and executes a program for executing a flow as shown in FIG. 2;
[Explanation of symbols]
Reference Signs List 100 Image input unit 101 Color space conversion unit 102 Color judgment unit 103 Color area table 104 Conversion density value table 105 Conversion unit 106 Color judgment conversion unit 107 Binarization unit

Claims (8)

For each pixel of the color image, color determination means for determining the color of the pixel,
A conversion density value table including density data corresponding to the color of the pixel,
A conversion unit for converting each pixel into a monochrome image based on the density data of the conversion density value table. Means for converting a color image to a color space;
A color area table including, for each color, a space coordinate serving as a center of the color and a first distance of a space representing a range of the color area;
A second distance between the spatial coordinates of the image data after color space conversion and the spatial coordinates of the color area table is obtained for each color for each pixel, and a color area where the second distance is equal to or less than the first distance A color determination unit that determines a color in which the second distance is the minimum when the pixel is present as a pixel color;
A conversion density value table including density data after conversion of a color area corresponding to the color of the pixel,
A conversion unit for converting each pixel into a monochrome image based on the density data of the conversion density value table. 3. The image processing apparatus according to claim 2, wherein the image data after color space conversion is an average value of a plurality of pixels. 3. The image processing apparatus according to claim 2, wherein the converted density value table includes data indicating whether or not density conversion of a color area has been performed. In an image processing method for converting a color image into a monochrome image, for each pixel of the color image, the color of the pixel is determined, and a converted density value table including density data corresponding to the color of the pixel is used. An image processing method for converting a monochrome image. Converting a color image to a color space;
Using a color area table including, for each color, space coordinates that are the center of the color and a first distance of the space that represents the range of the color area, the spatial coordinates of the image data after color space conversion and the color area table A second distance from the space coordinates is obtained for each color for each pixel, and when there is a color region in which the second distance is equal to or less than the first distance, a color in which the second distance is minimum is determined. Determining the color of the pixel;
Converting a monochrome image for each pixel based on the density data using a converted density value table including density data after conversion of a color region corresponding to the color of the pixel. Color determination means for determining the color of each pixel of a color image; and conversion means for converting each pixel into a monochrome image based on density data in a conversion density value table having density data corresponding to the color of the pixel. As an image processing program for causing a computer to function. Means for converting a color image to a color space;
A second distance between a color area table provided for each color and a space coordinate serving as a center of the color and a first distance of a space representing a range of the color area, and a space coordinate of the image data after the color space conversion. Color determination means for each color for each pixel, and when there is a color region in which the second distance is equal to or less than the first distance, a color determining unit that determines a color in which the second distance is the minimum as a pixel color. ,
An image processing program for causing a computer to function as a conversion unit that converts a pixel into a monochrome image based on density data of a conversion density value table including density data after conversion of a color region corresponding to the color of the pixel; .

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