JP2006094039A - Image processor, processing method and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the deterioration of image quality much more than a conventional manner when generation copying is repetitively performed. <P>SOLUTION: A control unit 11 of an image forming apparatus 1 performs two-stage color conversion. Color limitation processing is performed as first color conversion processing with respect to image data which are inputted from an image reader 2, and subsequently, representative color conversion processing by which respective representative colors used for the color limitation processing are converted into colors corresponding to colors of sheets of paper to form an image is performed as the second color conversion processing. Then the image data where the color conversion is performed are outputted to the image forming apparatus 3. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a technique for suppressing image quality degradation in generation copying.

In offices, etc., generation copying is often performed. Here, generation copy refers to a document or graphic manuscript output from a printer or the like (hereinafter referred to as an “original manuscript”) by a copying machine or the like, and forms an image based on the obtained image data. And get a copy.
The copy obtained by the generation copy is slightly different from the original image due to the reading performance of the copier itself, such as changes over time and dynamic range of the light source and light receiving element of the copier, and MTF (Modulation Transfer Function) characteristics. As a result, a phenomenon in which the image quality gradually changes occurs. For example, when a copy is compared with the original document, the character outline is dulled in the character area, resulting in a so-called “character collapsed” state, or in the halftone area formed with halftone, the density is actually (In this case, the general phenomenon that the copy image does not accurately reflect the information of the original image is referred to as “degradation of image quality”. Define).

  In particular, when the background color of the original document is other than white, the deterioration of image quality appears more conspicuously. For example, if an original document printed on light yellow paper (hereinafter referred to as “colored paper” is a paper having a background color other than white) is read by a copying machine, A portion of the document where no image is formed is recognized as “light yellow” instead of “white”. Therefore, a copy of such an original document is output with the background area, which should be originally “white”, being “light yellow”. In addition, when the output image is compared with the original document, the color component of the colored paper is superimposed and recognized as a darker color than the actual one, and in particular, the original document has a hue similar to the color of the colored paper. In the area, the tendency to be recognized as a darker color than the actual color becomes remarkable. In such a copy, not only the image on the copy is different from the original image, but also the image area to be expressed in white cannot be expressed in white, or the color material is wasted. Various problems occur, such as consuming too much.

As a technique for solving such a problem, for example, there is a technique described in Patent Document 1. In this patent document 1, an image signal obtained by reading a document image is corrected according to the color of the surface of the paper, thereby forming an image that does not feel uncomfortable even if generation copying is repeated using colored paper. Is described.
However, when color correction is performed as in Patent Document 1, image quality deterioration caused by the color of the background of the original document can be suppressed to some extent, but image quality caused by the reading performance of the copying machine described above. Degradation cannot be prevented, and as a result, degradation of image quality when generation copying is repeated is at a level that cannot be ignored.

  In the generation copy, it is common to copy a manuscript having images formed on both sides. At this time, a so-called “show-through” phenomenon may occur in which an image formed on the back side of the read surface of the original document is reflected in a copy. Since the component corresponding to the show-through on the copy is naturally not included in the original image, it can be said that this show-through is also an element that deteriorates the image quality of the copy. It is impossible to remove such show-through.

JP-A-6-217117

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a technique capable of suppressing deterioration in image quality as compared with the related art when performing repeated generation copying.

In order to achieve the above object, the present invention provides image acquisition means for acquiring image data, and the color of each pixel included in the acquired image data in accordance with the background color of the image represented by the image data. First color conversion means for converting each of the determined plurality of representative colors, and each of the plurality of representative colors obtained by the conversion by the first color conversion means as the surface color of the recording material There is provided an image processing apparatus comprising: a second color conversion unit that converts to a color determined according to the above; and an output unit that outputs image data in which the color of each pixel is converted by the second color conversion unit.
According to this image processing apparatus, the first color conversion process, that is, the limited color process is performed on the image data, and then each of the representative colors used in the limited color process is obtained as the second color conversion process. By performing a two-step color conversion process that performs a representative color conversion process that converts the image to the color of the paper on which the image is to be formed, the background color of the colored paper or the show-through component is superimposed on the image data. It is possible to prevent the image quality from being deteriorated, and it is possible to suppress the deterioration of the image quality in the generation copy.

In a more preferred aspect of the image processing apparatus of the present invention, when the surface color of the recording material is white, a plurality of representative colors determined according to the background color of the image are images represented by the image data. Including a color in which at least part of the background color of the image is superimposed on a plurality of representative colors for reproducing the color of the color material used to form the color material, and depending on the surface color of the recording material The determined color includes a color obtained by removing the contribution of the background color from a plurality of representative colors determined according to the background color of the image.
Alternatively, in the image processing apparatus of the present invention, when the surface color of the recording material is other than white, a plurality of representative colors determined according to the background color of the image are used to form an image represented by the image data. The color determined according to the surface color of the recording material includes a color in which at least part of the background color of the image is superimposed on a plurality of representative colors for reproducing the color of the used color material. The contribution of the surface color of the recording material to the color of the color material on the recording material and the contribution of the background color are excluded from a plurality of representative colors determined according to the background color of the image. Including color.
By using such representative colors and colors, it is possible to more effectively suppress deterioration in image quality in the generation copy.

Further, as a more preferable aspect, the image processing apparatus of the present invention includes an image forming unit that forms an image on the recording material having the surface color based on the image data output by the output unit.
In this way, the image data output by the output means can be obtained as an image on the recording paper.

Further, as a more preferable aspect, the image processing apparatus of the present invention includes a background color specifying unit that specifies the background color based on the acquired image data, and the first conversion unit includes the background color specifying unit. The color of each pixel is converted into a plurality of representative colors corresponding to the background color specified by the means.
In this way, even when there are a plurality of types of background colors of the image data, the background color of the image data can be specified by the background color specifying means, so that it is possible to suppress deterioration in image quality in the generation copy. .

At this time, as a more preferable aspect, the background color specifying means specifies the color of the region having the maximum brightness in the image data as the background color.
Alternatively, the background color specifying means obtains a histogram relating to the lightness of each pixel of the image data, and specifies the color of the region showing the lightness that becomes a peak in the high lightness region of the histogram as the background color.
In this way, it is possible to specify the base color with high accuracy.

Further, the image processing apparatus of the present invention includes, as a more preferable aspect, a reference color storage unit that stores a plurality of reference colors, and the background color specifying unit selects a color of a region having the maximum brightness in the image data. This is detected and compared with the plurality of reference colors, and the reference color having the smallest color difference is specified as the background color.
Alternatively, the image processing apparatus of the present invention includes reference color storage means for storing a plurality of reference colors, and the background color specifying means obtains a histogram relating to the brightness of each pixel of the image data, and the high brightness area of the histogram The color of the region showing the lightness at the peak is detected and compared with the plurality of reference colors, and the reference color having the smallest color difference is specified as the background color.
In this way, the background color specifying means can specify the background color based on the reference color stored in advance, so that the background color can be specified more accurately and at high speed.

The image processing apparatus of the present invention further includes a background color input unit that receives an instruction for specifying the background color, and the first conversion unit corresponds to the background color specified by the instruction in the background color input unit. The aspect which converts the color of each said pixel into several representative colors may be sufficient.
In this way, since the user only needs to directly input the background color, the image processing apparatus does not need to perform processing for specifying the background color.

The image processing apparatus according to the present invention includes, as a more preferable aspect, a storage unit that stores a plurality of color tables indicating a plurality of representative colors determined for each background color for each background color, and the first color conversion unit. Is selected from among the plurality of color tables a color table determined for the background color of the image represented by the acquired image data, and is included in the image data using a plurality of representative colors indicated by the selected color table The color of each pixel is converted.
Alternatively, the image processing apparatus of the present invention includes a storage unit that stores a plurality of color tables indicating a plurality of representative colors determined for each background color for each background color, and the first color conversion unit includes the plurality of colors. A color table having a representative color that minimizes the color difference from the background color of the image represented by the acquired image data is selected from the table, and the image data is used by using a plurality of representative colors indicated by the color table. The color of each pixel included is converted.
In this way, since the first color conversion unit can convert the color of each pixel using an appropriate color table corresponding to the background color, it is possible to better suppress deterioration in image quality in the generation copy. It becomes possible.

Moreover, the image processing apparatus of the present invention includes, as a more preferable aspect, a surface color input unit that receives an instruction for specifying a surface color, and the second color conversion unit converts each of the plurality of representative colors into the The color is converted into a color corresponding to the surface color specified by the instruction in the surface color specifying means.
In this way, it is possible to output image data corresponding to various surface colors.

Further, the image processing apparatus according to the present invention, as a more preferable aspect, stores a plurality of color tables indicating a plurality of representative colors determined for each background color for each background color, and inputs the attribute of the image data. And an attribute input unit that accepts, the first color conversion unit selects any one color table from the plurality of color tables based on the attribute received by the attribute input unit, and the color table Are used to convert the color of each pixel included in the image data.
In this way, the first color conversion means can perform conversion according to the attribute of the image data.

In the image processing apparatus of the present invention, as a more preferable aspect, the image data acquired by the acquisition unit is image data obtained by reading a document on which an image is formed using a color material, The representative color includes the color of the color material used in the document or a nearby color.
In a more preferred aspect, the representative color includes at least one of cyan, magenta, yellow, black, red, green, blue, white, and white or its vicinity.
In this way, it is possible to perform a generation copy that faithfully reproduces the color of the document.

Further, according to the present invention, the image forming apparatus acquires an image data, and the color of each pixel included in the acquired image data is determined according to the background color of the image represented by the image data. A first color conversion step for converting each of the plurality of representative colors, and each of the plurality of representative colors obtained by the conversion in the first color conversion step according to the surface color of the recording material. It is also possible to provide an image processing method including a second color conversion step for converting to a predetermined color and an output step for outputting image data in which the color of each pixel is converted in the second color conversion step. It is.
Alternatively, the present invention provides a computer with an image acquisition function for acquiring image data, and a plurality of pixels in which the colors of each pixel included in the acquired image data are determined according to the background color of the image represented by the image data The first color conversion function for converting each of the representative colors and the plurality of representative colors obtained by the conversion by the first color conversion function are determined according to the surface color of the recording material. It is also possible to provide a program for realizing a second color conversion function for converting to a color and an output function for outputting image data in which the color of each pixel is converted by the second color conversion function. is there.

(1) Principle of Embodiment In one embodiment of the present invention, image quality degradation in a generation copy is suppressed by applying a so-called limited color technology. Here, the limited colorization means that the color of each pixel of image data formed with multiple colors (for example, about 16.77 million colors) is smaller in number (for example, 256 colors) than the original image data (hereinafter referred to as this). (Represented as “representative color”), whereby the number of gradations of the image data can be reduced and the data amount of the image data can be reduced.
In contrast to the number of representative colors used for general limited colors of about several hundred colors, in the present embodiment, the number of colors is much smaller than the number of typical representative colors, for example, about several to more than a dozen colors. It is desirable to use a representative color. Further, it is desirable that the representative colors include the color of the color material used for forming an image on the document and the paper color. Along with these reasons, the limited color processing in the present embodiment will be described below.

FIG. 1 is an enlarged view of a part of a document P ₁ . In the figure, the original P ₁ is a dot D _C formed by the color material of cyan (C) on the sheet of white (W), the dot D _M formed by the color material of magenta (M) Rules A plurality of them are arranged.
This document P ₁ is a document in which gradation expression is made by changing the area of halftone dots, and color shades are expressed by changing the halftone dot area ratio. That is, the gradation change in the original P ₁ is discontinuous when viewed microscopically.
As shown in the drawing, the color existing on the original P ₁ is paper color white, toner cyan, magenta, and blue (B) which is a subtractive color mixture of cyan and magenta. However, since these halftone dots are minute and have a size smaller than the human visual resolution, humans perceive them as “light blue” in which these colors are mixed (intermediate color mixture).

  In printing, in general, an original is represented by four types of color materials, cyan (C), magenta (M), yellow (Y), and black (K). The color gamut that can be reproduced in such a manuscript is 3 points indicating C, M, and Y on the chromaticity diagram and 3 indicating red (R), green (G), and blue (B) which are subtractive color mixture thereof. It is an area indicated by a hexagon connecting points. However, the only colors that actually exist on the original whose gradation is expressed by the halftone dots are the color of the color material, its subtractive color mixture, and the paper color, as described above. If it sees, it will be formed only by eight colors, C, M, Y, K, R, G, B, and W. That is, when the original is read by the image reading device, if the image reading device has a sufficient input resolution for reading halftone dots, the image data obtained by the image reading device is C, M, Y, K. , R, G, B, and W, the pixel is composed of only eight pixels.

  The inventor pays attention to this point, and as described above, C, M, Y, K, R, and G are applied to the image data of the original formed by the four color materials of C, M, Y, and K. , B, and W were tried for the limited color processing using eight representative colors. Then, it became clear that the output image obtained in this way can reproduce the original image on the original very faithfully. The principle will be briefly described below.

For example, assume that the color of a certain part on the original is black (density 100%). When this document is read by an image reading device such as a scanner, the pixels corresponding to the read portion are not actually detected due to the performance of the image reading device itself (such as changes over time of the light source and light receiving element and dynamic range) and other noises. A slightly different color is displayed, for example, gray having a density of 95%. However, when the above-described limited color processing is performed on this pixel, this pixel has the smallest color difference among the representative colors of C, M, Y, K, R, G, B, and W, that is, K ( The color information of the original document is restored.
Based on such a principle, the limited color processing corrects the error of the image data satisfactorily unless the error of the read image data causes a color difference that can be replaced with another representative color. The color information of the original image can be restored. For this reason, it is possible to suppress deterioration in image quality due to the reading performance of the copying machine, etc., by performing the limited color processing when performing the generation copy.

  In addition, the limited colorization process described above also enables removal of show-through. For example, when show-through occurs in a portion of image data that is originally white (density 0%), if the image formed on the back side is black, the show-through component is light gray (for example, density 5%). ). However, if a limited color process is applied to such a portion, it is replaced with white in the same manner as described above. In addition, since this is the same when show-through occurs in other color portions of the image data, the removal of the show-through by the limiting color processing forms not only the blank portion on the paper but also an image. It becomes effective even in the part which is.

Furthermore, by applying this limited color processing, it is possible to suppress deterioration in image quality when colored paper is used in generation copying.
Here, FIG. 2 is shown as an example. In the figure, a light yellow colored paper is used for the original P ₂ , and images G _C , G _M , and G _Y are formed on the colored paper with cyan, magenta, and yellow color materials, respectively. When this is read by an image reading device and image data is obtained, the area in which the image is formed in this image data is the color of the color material (cyan, magenta, yellow) of “light yellow” of colored paper. A color in which components are slightly superimposed is shown. Further, an area in which no image is formed in the image data, that is, an area that is originally “white” indicates “pale yellow”.

  The image data is first subjected to limited color processing using eight representative colors of C ′, M ′, Y ′, K ′, R ′, G ′, B ′, and W ′. Here, the representative colors of C ′, M ′, Y ′, and K ′ indicate colors when an image is formed on a pale yellow colored paper with cyan, magenta, yellow, and black color materials, respectively. . In other words, C ′, M ′, Y ′, and K ′ indicate colors that are slightly yellowish than the above-described representative colors of C, M, Y, and K, with a part of the background color superimposed. (In fact, the color change is small in a low-lightness color material such as black). The representative colors R ′, G ′, and B ′ indicate colors when an image is formed by mixing color materials of cyan, magenta, and yellow on colored paper. Here, the representative color of W ′ indicates the color of the background of the colored paper, that is, “light yellow”.

When this limited color processing is performed, the image data is composed of only pixels representing any one of C ′, M ′, Y ′, K ′, R ′, G ′, B ′, and W ′. It becomes. Next, for this image data, color conversion such as C ′ to C, M ′ to M, Y ′ to Y,..., W ′ to W, that is, simply put, representative colors Is replaced by subtracting the contribution of the background color from the image data (hereinafter referred to as “representative color conversion”). Then, the image data after the representative color conversion becomes an image as if the images G _C , G _M , and G _Y were formed on white paper, and only the contribution of the background color is removed from the original P _2. be able to.
If the image data obtained in this way is formed on white paper using color materials of C, M, Y, and K, an image from which the background color component of the original P ₂ is removed can be obtained. . In this way, even if generation copying is repeatedly performed on a colored paper document, it is possible to prevent the image quality from deteriorating due to the influence of the background color.

If such color conversion is performed, it is possible to satisfactorily suppress deterioration in image quality even when colored paper other than white paper is used as paper for forming an image. For this purpose, in the case of forming an image on chromatic colored paper, for example, pale yellow, the color used in the color conversion of the above C, M, Y, K, R, G, B, different from the W C _y, M _{y , Y y, K y, R} y, G y, B y, may be set to W _y. C _y, M _{y wherein, Y y, K y, R} y, G y, B y, W y is the aforementioned C, M, Y, K, R, G, B, pale yellow from each W Each color is obtained by subtracting the color component corresponding to the background color of the colored paper (however, K _y and W _y may be K _y = K and W _y = W, respectively). _{That, C y, M y, Y} y, K y, R y, G y, B y, W y is the image data formed by using these representative colors C, M, Y, color material K And image data formed using C, M, Y, K, R, G, B, and W representative colors when formed on pale yellow colored paper. Thus, the color is the same as that of the image formed on the white paper. In this way, even if the paper on which the image is formed in the generation copy is a colored paper, it is possible to prevent the color of the image from changing.

The principle of this embodiment is outlined as above. That is, in the present embodiment, the above-described limited color processing is performed as the first color conversion processing on the image data, and then each of the representative colors used in the limited color processing is processed as the second color conversion processing. Two-stage color conversion is performed in which representative color conversion processing is performed to convert the color to a color corresponding to the color of the paper on which the image is to be formed.
This is schematically shown in FIG. Referring to the drawing, first, each pixel of the obtained image data G ₁ by reading a document has a different color corresponding to the read result. When the limited color processing is performed on the image data G ₁ , each pixel becomes image data G ₂ in which eight representative colors 1 are replaced. Each of the representative colors 1 at this time is a color in which the contribution of the background color of the document is superimposed on the color of the color material. Subsequently Doing representative color conversion processing on the image data G _2, the color of each pixel of the image data G ₂ indicated by the representative color 1 is replaced, the image formed by the representative color 2 new 8-color the data G _3. Each of the representative colors 2 at this time is a contribution due to the background color of the document from each of the representative colors 1 used in the limiting color processing, and the background of the colored paper on which the image represented by the image data G ₃ is to be formed. This is the color minus the contribution due to the color. Therefore, when the image represented by the image data G ₃ is formed on the colored paper, each pixel of the image data G ₃ is superimposed on the colored paper's background color contribution on the colored paper, similar to the color of the color material. To show the color.

  In the present embodiment, by performing such processing, it is possible to very well suppress deterioration in image quality when performing generation copy. From here, the concrete structure which implement | achieves the effect | action mentioned above is demonstrated in detail, giving two embodiment used as an example of this invention.

In the following description, the RGB color space is used for the description using the color space. For example, colors indicating coordinates (0, 0, 0), (1, 0, 0), (0, 1, 0), (0, 0, 1), and (1, 1, 1) in this color space Are black, red, green, blue and white, respectively. Hereinafter, for the sake of convenience, these coordinate points are referred to as “RGB values”.
In the following embodiments, the color difference defined below is used as an index representing the difference between two different colors. That is, when the RGB values of _two colors C ₁ and C ₂ are represented by (R ₁ , G ₁ , B ₁ ) and (R ₂ , G ₂ , B ₂ ), respectively, these colors C ₁ and C 2 The color difference ΔE of ₂ is obtained by the following formula 1.
(Equation 1)
ΔE = {(R ₂ −R ₁ ) ² + (G ₂ −G ₁ ) ² + (B ₂ −B ₁ ) ² } ^1/2
That is, this color difference ΔE is equal to the distance between the coordinate points representing the colors C ₁ and C ₂ in the RGB color space.

(2) First Embodiment FIG. 4 is a block diagram showing a configuration of an image processing apparatus 1 according to an embodiment of the present invention. As shown in the figure, the image processing apparatus 1 according to the present embodiment includes a control unit 11, an HDD (Hard Disk Drive) 12, an input IF (Interface) 13, an output IF 14, and an operation unit 15. It is a computer equipped with. An image reading apparatus 2 and an image forming apparatus 3 are connected to the image processing apparatus 1.

  The control unit 11 includes a CPU (Central Processing Unit) 111, a ROM (Read Only Memory) 112, a RAM (Random Access Memory) 113, and the like, and performs various types of image processing to be described later on input image data. Execute the operation. At this time, the image data is temporarily stored in the RAM 113. The HDD 12 is a storage device, and is an image processing program PRG for executing image processing, representative color information R1 used in the limited color processing that is the first color conversion processing, and the second color conversion processing. It stores representative color information R2 used in certain representative color conversion and background color information BC which is data indicating the background color of the paper. The input IF 13 acquires image data from the image reading device 2, and the output IF 14 outputs the image data subjected to image processing by the image processing device 1 to the image forming device 3. The operation unit 15 is, for example, a touch panel type liquid crystal display, displays various screens, receives instructions from the user, and supplies the instructions to the control unit 11.

  In the present embodiment, the background color of the document read by the image reading device 2 and the color of the surface of the paper on which the image is formed by the image forming device 3 are both “white (w)” and “pale”. Three types, “yellow (y)” and “pink (p)”. In the following, in order to avoid confusion between these colors, the background color of the document read by the image reading device 2 is referred to as “background color”, and the paper (recording material) on which an image is formed by the image forming device 3 is used. The surface color is expressed as “surface color”.

Here, representative color information R1, R2, and background color information BC will be described.
FIG. 5 is a diagram schematically showing representative color information R1 in the present embodiment. As shown in the drawing, the representative color information R1 includes a plurality of color tables T _w1 , T _y1 , and T _p1 .
The color table T _w1 has eight representative colors of C _w1 , M _w1 , Y _w1 , K _w1 , R _w1 , G _w1 , B _w1 , W _w1 , and this color table T _w1 has a base color. FIG. 5 is a color table used when color-limiting processing is performed on image data obtained by reading a “white” document. FIG. Similarly, the color tables T _y1 and T _p1 are respectively C _y1 , M _y1 , Y _y1 , K _y1 , R _y1 , G _y1 , B _y1 , W _y1 and C _p1 , M _p1 , Y _p1 , K _p1 , R _p1, G _p1, B _p1, W has eight colors representative color of _p1, these color table T _y1, T _p1 is the background color, each reading a document of "pale yellow" and "pink" 3 is a color table used when performing limited color processing on image data obtained in this way.

FIG. 6 is a diagram schematically showing representative color information R2 in the present embodiment. As shown in the drawing, the representative color information R2 includes a plurality of color tables T _w2 , T _y2 , and T _p2 .
The color table T _w2 has eight representative colors of C _w2 , M _w2 , Y _w2 , K _w2 , R _w2 , G _w2 , B _w2 , W _w2 , and this color table T _w2 is a surface color. 4 is a color table used when the representative color conversion process is performed on the image data that has been subjected to the limited color process on the “white” paper. Similarly, the color tables T _y2 and T _p2 are C _y2 , M _y2 , Y _y2 , K _y2 , R _y2 , G _y2 , B _y2 , W _y2 and C _p2 , M _p2 , Y _p2 , K _p2 , respectively. _{R p2, G p2, B p2} , has eight colors of the representative color of the W _p2, these color table T _y2, T _p2 is on the sheet of surface color, each "pale yellow" and "pink" It is a color table used when a representative color conversion process is performed on image data on which a limited color process has been performed.

The background color information BC stores the background color data of the document used. That is, in the present embodiment, the RGB values of “white”, “light yellow”, and “pink”, which are background colors, are stored. In the following, the RGB values of “white”, “light yellow”, and “pink” are BC _w , BC _y , and BC _p , respectively. The background color information BC is used as a reference color for specifying the background color in the background color specifying process described later.
Each of the color table and background color data is stored as RGB values in the representative color information R1, R2 and background color information BC of the HDD 12.

Here, the image reading apparatus 2 and the image forming apparatus 3 will be described with reference to FIG. 4 again.
The image reading device 2 is a so-called scanner. The image reading device 2 includes a platen, a light source, an optical system, a light receiving element, and a signal processing unit (not shown), irradiates light on a document placed on the platen with a light source, and reflects the reflected light through the optical system. The light receiving element receives light and outputs an image signal. The signal processing unit performs various signal processing such as shading correction on the image signal, and supplies the image data obtained as a result to the image processing apparatus 1. .
The image forming apparatus 3 is an electrophotographic image forming apparatus such as a color printer or a color copying machine. The image forming apparatus 3 includes an image forming unit and a paper feeding unit (not shown). The image forming unit forms an image of toner (color material) corresponding to the image data output from the image processing apparatus 1 and supplies the image. An image is formed by fixing on the paper supplied from the paper section. In the image forming apparatus 3 of the present embodiment, sheets having three kinds of surface colors of “white”, “light yellow”, and “pink” are accommodated in the sheet feeding unit. A sheet of surface color designated by 1 is supplied.

In the present embodiment, the user can use the operation unit 15 to specify the surface color of the paper on which an image is formed by the image forming apparatus 3.
FIG. 7 is a diagram illustrating a screen displayed on the operation unit 15 when the user specifies a surface color in the present embodiment. As shown in the figure, the operation unit 15 displays four types of buttons BT11, BT12, BT13, and BT14. By pressing each button, the surface color of the paper used is “white”. , “Light yellow”, “pink”, and “automatic”. When the user designates the surface color of the sheet as “automatic” with the button BT14, the surface color of the same color as the background color of the document read by the image reading apparatus 2 is set.

  Next, image processing performed by the image processing apparatus 1 under the above-described configuration will be described. This process is a process realized by the control unit 11 of the image processing apparatus 1 executing the program PRG. Here, an example will be described in which a document whose background color is “light yellow” is read, and an image based on the image data as a result of the reading is formed on a sheet whose surface color is “pink”. That is, here, the user designates “pink” as the surface color of the output paper by pressing the button BT13 on the screen of the operation unit 15 shown in FIG. Information on the surface color designated by the user is temporarily stored in the RAM 113 of the control unit 11.

FIG. 8 is a flowchart showing image processing executed by the image processing apparatus 1 of the present embodiment. Explaining along the figure, first, the control unit 11 of the image processing apparatus 1 acquires the image data supplied from the image reading apparatus 2 via the input IF 13, and stores it in the RAM 113 (step S1). The acquired image data is analog data indicating a reading result by the image reading device 2 at this time.
The control unit 11 that has acquired the image data performs AD conversion on the acquired image data, and converts the analog image data into digital data (step S2). Subsequently, the control unit 11 performs gamma conversion to correct a deviation between the input / output characteristics (gamma characteristics) of the image forming apparatus 3 and the input / output characteristics of the image reading apparatus 2 (step S3).

Next, the control unit 11 performs a background color specifying process for specifying the color of the area corresponding to the background in the image data, that is, the background color (step S4). FIG. 9 is a flowchart showing the background color specifying process. Hereinafter, the background color specifying process will be described with reference to FIG.
In FIG. 9, the control unit 11 first acquires data relating to the brightness of each pixel included in the image data (step S41). As a method of acquiring data relating to the brightness of each pixel, for example, there is a method of calculating a weighted average value of RGB values of each pixel and comparing the brightness by the magnitude of the weighted average value. If it is desired to obtain the lightness difference more precisely, the RGB values are converted into tristimulus values in the XYZ color system, and the lightness is compared according to the magnitude of the Y value, or the CIELAB table that is a uniform color space. It is only necessary to convert to coordinate values represented by a color system and compare the lightness based on the metric lightness (L *) of the coordinate values.

Next, the control unit 11 compares the data relating to the brightness of each pixel acquired in step S41, identifies the pixel having the highest brightness from the data, and determines the RGB value of this pixel as a provisional background color (hereinafter referred to as the following color). “Temporary background color BC _t ”) (step S42). Subsequently, the control unit 11 refers to the background color information BC stored in HDD 12, it compares the temporary background color BC _t above background color BC _w, BC _y, and each BC _p (step S43). Thereafter the control unit 11, the base color BC _w, BC _y, the color difference between the temporary base color BC _t of BC _p identifies the background color with the minimum and the color and background color of the image data (step S44) . In the above example, since the background color is “light yellow”, the background color at this time is “BC _y ”.

When the background color is specified in this way, the control unit 11 next performs a color limiting process on the image data (step S5). FIG. 10 is a flowchart showing the limited color processing. The limited color processing will be described below with reference to FIG.
In FIG. 10, first, the control unit 11 refers to the background color specified in step S4 described above (step S51), and selects a color table corresponding to this background color from the representative color information R1 (step S52). . In the above example, since the ground color BC _y indicating "pale yellow" in step S44 is identified, wherein the color table color table T _y1 of "pale yellow" is selected.

Next, the control unit 11 calculates a color difference between each pixel of the image data (this pixel is referred to as “target pixel”) and each of the representative colors of the color table selected in step S52 (step S53). That is, to explain along the above-described example, the controller 11 determines the color difference between the pixel of interest and the representative colors C _y1 , M _y1 , Y _y1 , K _y1 , R _y1 , G _y1 , B _y1 , W _y1 of the color table T _y1. Are calculated and temporarily stored.
After calculating the color differences from all the representative colors, the control unit 11 compares these color differences and converts the color of the pixel of interest into a representative color that minimizes the color difference (step S54). For example, if the color of the pixel of interest is a color similar to black (for example, gray having a density of 95%), the color of the pixel of interest is converted to black (K _y1 ) at this time.
The control unit 11 performs such color conversion for all the pixels of the image data. That is, the control unit 11 repeats the processes of steps S53 and S54 described above until the above color conversion is performed on all the pixels of the image data (step S55; NO). When this color conversion is performed on all the pixels of the image data (step S55; YES), the control unit 11 ends the limited color processing, and the main image processing returns to the flowchart of FIG.

When the limited color processing in step S5 is completed, the control unit 11 subsequently performs representative color conversion processing on the image data (step S6). The representative color conversion process is a process of converting each of the representative colors obtained by the limited color to a representative color corresponding to the surface color of the paper to be output. That is, this is a process of converting each representative color of a certain color table stored in the representative color information R1 to each representative color of a certain color table stored in the representative color information R2, and in the case of the above example, since the surface color of the paper background color of the document is to be output is "pale yellow" is _{"pink", C y1, M y1, Y} y1, K y1, R y1, G y1 color table T _y1, respectively converting the representative color of B _y1, W _y1 in _{C p2, M p2, Y p2} , K p2, R p2, G p2, B p2, W p2 color table T _p2. As a result of this processing, the image data composed of the eight color pixels C _y1 , M _y1 , Y _y1 , K _y1 , R _y1 , G _y1 , B _y1 , W _{y1 has} the color of each pixel. It was converted, and _{C p2, M p2, Y p2} , K p2, R p2, G p2, B p2, W image data composed of eight colors of the pixels _p2.

  When the representative color conversion process in step S6 is completed, the control unit 11 subsequently converts the color space (step S7). In the present embodiment, conversion from the RGB color space used so far to the CMYK color space used in the image forming apparatus 3 is performed. Thereafter, the control unit 11 performs screen processing on the halftone area of the image data (step S8). When the screen process is completed, the control unit 11 outputs the image data to the image forming apparatus 3 via the output IF 14 (step S9). At this time, the image forming apparatus 3 selects a sheet having a surface color designated by the user (“light yellow” in the above example), and forms an image on the sheet based on the supplied image data.

  By performing such image processing, an image formed on a “pale yellow” document can be copied onto “pink” paper without degrading the image quality. Therefore, by using such an image processing apparatus 1, it is possible to perform generation copy in which deterioration of image quality is suppressed better than before.

(3) Second Embodiment Subsequently, an embodiment of the present invention that is different from the above-described first embodiment will be described. In the present embodiment, the user can specify the type of document to be generated and a suitable image can be formed according to the type of document. This is the first embodiment described above. This is a very different part. Therefore, a specific configuration and operation for realizing this function will be described here.
Note that this embodiment is substantially the same as the first embodiment described above except that it has a function of specifying the type of document. Therefore, in the description of the present embodiment, the same reference numerals are used for the same components as in the first embodiment, and the description thereof will be omitted as appropriate.

FIG. 11 is a block diagram showing the configuration of the image processing apparatus 1a of the present embodiment. As shown in the figure, the difference between the image processing apparatus 1a of the present embodiment and the image processing apparatus 1 of the first embodiment described above lies in the HDD 12a and the operation unit 15a.
The operation unit 15a is, for example, a touch panel type liquid crystal display, and displays various screens and receives instructions from the user. The operation unit 15a can display the screen shown in FIG. 7 and accept the designation of the surface color by the user, or can display the screen shown in FIG. 12 and accept the designation of the type of document by the user. It has become.

  In this embodiment, three types of “copy original”, “printer output original”, and “general original” can be designated as the type of original to be read, that is, the attribute of the original, and the image processing apparatus 1a. Has three types of image processing modes, “copy original mode”, “printer output original mode”, and “general original mode” corresponding to each original. Then, the image processing apparatus 1a performs image processing corresponding to each image processing mode. Buttons BT21, BT22, and BT23 in FIG. 12 are buttons for the user to input instructions indicating that the type of document is “copy original”, “printer output original”, and “general original”, respectively. Is pressed, “copy original mode”, “printer output original mode”, and “general original mode” are selected as image processing modes in the image processing apparatus 1a, respectively.

Here, the type of each document will be described.
The “copy original” is an original read by the image reading apparatus 2 and output by the image forming apparatus 3. That is, the copy original means an original that has been copied at least once.
The “printer output document” is a document output by the image forming apparatus 3 but is not read by the image reading apparatus 2 like a copy document. In other words, the printer color original means an original obtained by outputting an image supplied from a computer (not shown) connected to the image forming apparatus 3.
The “general document” is a document output by an image forming apparatus different from the image forming apparatus 3. That is, the general document is a document in which an image is formed and a color material used is unknown.

  That is, since the copy original and the printer output original are output by the image forming apparatus 3, it is possible to specify the color material used. Therefore, even if the limited color processing is performed only with the representative color corresponding to this color material (and subtractive color mixture of the color materials), the image can be restored with considerably high accuracy. On the other hand, in a general document, it is unclear what color material is used for output, and the limited colorization process is performed with a representative color based on the color material used in the image forming apparatus 3. Is not necessarily appropriate. Therefore, when the limited color processing is performed on a general document, the use of a representative color that does not depend on the color material used in the image forming apparatus 3 allows better limitation on various types of documents. Coloring processing can be performed. In this case, increasing the number of representative colors used for the color limiting process for a general document is also effective for suppressing deterioration in image quality as compared with the case of other documents.

Next, the contents stored in the HDD 12a will be described. The HDD 12a stores an image processing program PRGa and representative color information R1a, and this is a different part from the HDD 12 of the first embodiment.
FIG. 13 is a diagram schematically showing representative color information R1a in the present embodiment. As shown in the figure, the representative color information R1 includes _nine color tables _Tw1c , _Ty1c , _Tp1c , _Tw1p , _Ty1p , _Tp1p , _Tw1g , _Ty1g , and _Tp1g. Have
The color tables T _w1c , T _y1c , and T _p1c are color tables that are used when the “copy original mode” is set as the image processing mode. The color table T _w1c is used when the image processing mode is “copy original mode” and the background color is “white”. Similarly, the color tables T _y1c and T _p1c are used when the image processing mode is “copy original mode” and the background colors are “light yellow” and “pink”, respectively.
Similarly, the color tables T _w1p , T _y1p , T _p1p are color tables used when the “printer output original mode” is set as the image processing mode, and the color tables T _w1g , T _y1g , and T _p1g are This is a color table used when “general document mode” is set as the image processing mode. The representative colors of these nine types of color tables are different from each other (the same representative color may be included in part).

  The image processing program PRGa stores the image processing procedure shown by the flowchart of FIG. Comparing this figure with the flowchart (FIG. 8) showing the image processing in the first embodiment, only the limited color processing in step S5a is different. Therefore, the image processing executed by the image processing apparatus 1a in the present embodiment will be described mainly with respect to step S5a, and description of other steps will be omitted. For each step whose description is omitted, refer to the first embodiment as appropriate.

In step S5a, the limited color processing is performed using the representative color information R1a. That is, the control unit 11 selects a color table based on the background color specified in step S4 and the image processing mode specified by the user. For example, if the background color is “white” and the image processing mode is “copy original mode”, the control unit 11 selects the color table T _w1c and performs the limited color processing. If it is “pink” and the image processing mode is “general document mode”, the control unit 11 selects the color table T _p1g and performs the limited color processing.

  As described above, according to the image processing apparatus 1a of the present embodiment, a good generation copy can be performed on different types of documents. In other words, according to the image processing apparatus 1a, not only a document output from the image forming apparatus 3 and the color material used can be specified but also various documents whose color material used is unknown are used. However, it is possible to perform a generation copy in which deterioration of image quality is well suppressed.

(4) Modifications The implementation of the present invention is not limited to the above-described embodiments, and various modifications can be made. An example is shown below.
In the above-described embodiment, it has been described that the image processing apparatuses 1 and 1a perform the image processing shown in the flowcharts of FIGS. 8 and 12, but the embodiment of the present invention is not limited to such an aspect. For example, if the image data input to the image processing apparatus is digital data instead of analog data, the AD conversion in step S2 is naturally unnecessary. Further, the color space conversion in step S7 is not limited to the conversion to the CMYK color space. Thus, the image processing according to the present invention can be modified according to the embodiment.

In the above-described embodiment, it has been described that the limited color processing and the representative color conversion processing are performed using a color table. However, this color table is stored as a conversion formula for performing a predetermined numerical calculation, You may perform the above-mentioned process by performing this numerical calculation. For example, it can be easily understood by those skilled in the art that the representative color conversion processing of the above-described embodiment can be realized by matrix calculation using a matrix of 8 rows and 8 columns.
In the above-described embodiment, in order to facilitate the understanding of the present invention, the limited color processing and the representative color conversion processing have been described separately. However, these processing may be executed simultaneously by one conversion. Is possible.

In the above-described embodiment, it has been described that the background color specifying process of FIG. 9 is performed in order to specify the background color of the document. However, the method for specifying the background color is not limited to this. For example, in the base color identification process of FIG. 9 obtains a provisional background color BC _t In step S42, which identify the final ground color by comparing the background color stored in the background color information BC at step S43 had been, the temporary base color BC _t described above may be those directly specified as the base color. As for the method of obtaining the temporary base color BC _t, what its brightness of each pixel in the image data is maximized rather than a temporary base color BC _t, as shown in FIG. 15, A histogram relating to the lightness of each pixel of the image data is obtained, and the region having the lightness that becomes the peak in the high lightness region of this histogram, that is, the lightness with the highest appearance frequency in the image data is defined as the background region. May be a temporary ground color or a ground color. This is because, in image data obtained by reading an original, when the entire image area is color-separated and the appearance frequency of each color is obtained, the ratio of the background area where no image is formed is generally the highest. .
The image processing apparatus does not specify the background color in this way, but the image processing apparatus includes an interface for the user to input the background color, and the background color is specified by a user instruction. Good.
Alternatively, if the background color of the document read by the image reading device 2 is constant, such a background color specifying process may be omitted.

  In the second embodiment described above, the “copy original mode” and the “printer output mode” are described as image processing modes when an original is output by the image forming apparatus 3. However, if the document is output from an image forming apparatus using the same type of color material as that of the image forming apparatus 3, image processing is performed using these image processing modes, so that deterioration in image quality is well suppressed. It is possible.

  In the above-described embodiment, it has been described that the representative colors are eight colors. However, in the practice of the present invention, the representative colors are not limited to eight, and the number of colors can be increased or decreased. For example, by adding representative colors such as gray and brown in addition to the eight representative colors described above, it is possible to perform finer gradation expression, and the representative colors are C, M, Y, K. , W, there are certain effects even if there are only five colors. If the number of colors is extremely increased when increasing the representative color, not only will the time required for the limited color increase dramatically, but the show-through will become difficult to remove, rather. There is a concern that the image quality is degraded. Therefore, when determining the number of representative colors and selecting a representative color, it is necessary to select an appropriate color with an appropriate number of colors.

In the above-described embodiment, the background color of the document and the surface color of the paper are described as “white”, “light yellow”, and “pink”, but both the background color and the surface color are described. Of course, it is possible to use different colors or increase or decrease the number of colors.
Further, in the above-described embodiment, the mode in which the user specifies the surface color of the paper to be output has been described, but the surface color of the paper to be output may be constant. In such a case, it is naturally unnecessary to specify the surface color of the paper by the user.

In addition to the image processing apparatuses 1 and 1a that mainly perform image processing as described above, the present invention can of course be provided by an image forming apparatus having the functions of this image processing apparatus. Further, this image forming apparatus may have the function of the image reading apparatus 2 described above.
In the present invention, the image processing programs PRG and PRGa executed in the above-described embodiment are applied to various kinds of media such as a magnetic disk, a floppy (registered trademark) disk, a CD (Compact Disk), a DVD (Digital Versatile Disk), and a RAM. It is also possible to provide it in a state of being recorded on a recording medium.

  The image processing apparatus according to the present invention not only forms an image on a sheet by outputting to the image forming apparatus as in the above-described embodiment, but also displays image data on a display device such as a liquid crystal display. Alternatively, the image data may be stored in a storage device or a recording medium. In this way, paper color can be removed from image data such as documents created using colored paper, and deterioration of image quality such as show-through can be suppressed, so that high-quality image data is displayed or stored. It becomes possible. In such a case, color space conversion and screen processing may be omitted as appropriate.

  In the above-described embodiment, the color space is described as the RGB color space, but the present invention is not limited to such an aspect. For example, a uniform color space such as an L * a * b * color space or an L * u * v * color space may be used. Also, a color difference formula for obtaining a color difference can be appropriately selected according to these color spaces.

It is the figure which expanded and showed a part of a certain original document. It is the figure which showed a certain original document. It is a figure explaining the principle of this invention. 1 is a block diagram illustrating a configuration of an image processing apparatus according to an embodiment of the present invention. It is the figure which showed typically the representative color information which concerns on the same embodiment. It is the figure which showed typically the representative color information which concerns on the same embodiment. 6 is a diagram illustrating a screen displayed on an operation unit when a user specifies a surface color in the embodiment. FIG. 5 is a flowchart illustrating image processing executed by the image processing apparatus according to the embodiment. It is the flowchart which showed the base color specific process in the same embodiment. It is the flowchart which showed the limited colorization process in the same embodiment. It is the block diagram which showed the structure of the image processing apparatus of another embodiment of this invention. 6 is a diagram illustrating a screen displayed on an operation unit when a user specifies a document type in the embodiment. FIG. It is the figure which showed typically the representative color information which concerns on the same embodiment. 5 is a flowchart illustrating image processing executed by the image processing apparatus according to the embodiment. It is the figure which showed the histogram regarding the brightness of each pixel of image data.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image processing apparatus, 2 ... Image reading apparatus, 3 ... Image forming apparatus, 11 ... Control part, 111 ... CPU, 112 ... ROM, 113 ... RAM, 12 ... HDD, 13 ... Input IF, 14 ... Output IF.

Claims (18)

Image acquisition means for acquiring image data;
First color conversion means for converting the color of each pixel included in the acquired image data into any of a plurality of representative colors determined according to the background color of the image represented by the image data;
Second color conversion means for converting each of the plurality of representative colors obtained by the conversion by the first color conversion means into a color determined according to the surface color of the recording material;
An image processing apparatus comprising: output means for outputting image data obtained by converting the color of each pixel by the second color conversion means. When the surface color of the recording material is white,
The plurality of representative colors determined according to the background color of the image is different from the plurality of representative colors for reproducing the color of the color material used to form the image represented by the image data. Including a color on which at least part of the base color is superimposed,
The image processing according to claim 1, wherein the color determined according to the surface color of the recording material includes a color obtained by removing a contribution of the background color from a plurality of representative colors determined according to the background color of the image. apparatus. When the surface color of the recording material is other than white,
The plurality of representative colors determined according to the background color of the image is different from the plurality of representative colors for reproducing the color of the color material used to form the image represented by the image data. Including a color on which at least part of the base color is superimposed,
The color determined according to the surface color of the recording material is determined by the surface color of the recording material from the plurality of representative colors determined according to the background color of the image. The image processing apparatus according to claim 1, wherein the image processing apparatus includes colors excluding a contribution and a contribution of the background color. The image processing apparatus according to claim 1, further comprising: an image forming unit that forms an image on the recording material having the surface color based on the image data output by the output unit. A background color specifying means for specifying the background color based on the acquired image data;
The image processing apparatus according to claim 1, wherein the first conversion unit converts the color of each pixel into a plurality of representative colors corresponding to the background color specified by the background color specifying unit. The background color specifying means includes
The image processing apparatus according to claim 5, wherein a color of a region having the maximum brightness in the image data is specified as the background color. The background color specifying means includes
The image processing apparatus according to claim 5, wherein a histogram relating to the lightness of each pixel of the image data is obtained, and a color of a region showing lightness that becomes a peak in the high lightness region of the histogram is specified as the background color. A reference color storage means for storing a plurality of reference colors;
The background color specifying means detects a color of a region having the maximum brightness in the image data, compares the color with the plurality of reference colors, and specifies a reference color having a minimum color difference as the background color. Item 6. The image processing apparatus according to Item 5. A reference color storage means for storing a plurality of reference colors;
The background color specifying means obtains a histogram relating to the lightness of each pixel of the image data, detects a color of a region showing lightness that is a peak in the high lightness region of the histogram, and compares it with the plurality of reference colors. The image processing apparatus according to claim 5, wherein a reference color that minimizes the color difference is specified as the base color. A background color input means for receiving an instruction for specifying the background color;
The image processing apparatus according to claim 1, wherein the first conversion unit converts the color of each pixel into a plurality of representative colors corresponding to a background color specified by an instruction in the background color input unit. A storage means for storing a plurality of color tables indicating a plurality of representative colors determined for each background color for each background color,
The first color conversion unit selects a color table determined for a base color of an image represented by the acquired image data from the plurality of color tables, and selects a plurality of representative colors indicated by the selected color table. The image processing apparatus according to claim 1, wherein the color of each pixel included in the image data is converted. A storage means for storing a plurality of color tables indicating a plurality of representative colors determined for each background color for each background color,
The first color conversion unit selects a color table having a representative color that minimizes a color difference from a ground color of an image represented by the acquired image data from the plurality of color tables, and the color table The image processing apparatus according to claim 1, wherein the color of each pixel included in the image data is converted using a plurality of representative colors indicated by. A surface color input means for receiving an instruction for specifying the surface color;
The image processing apparatus according to claim 1, wherein the second color conversion unit converts each of the plurality of representative colors into a color corresponding to a surface color specified by an instruction from the surface color specifying unit. Storage means for storing a plurality of color tables indicating a plurality of representative colors determined for each background color for each background color;
Attribute input means for receiving input of attributes of the image data,
The first color conversion unit selects any one color table from the plurality of color tables based on an attribute received by the attribute input unit, and uses a plurality of representative colors indicated by the color table. The image processing apparatus according to claim 1, wherein the color of each pixel included in the image data is converted. The image data acquired by the acquisition means is image data obtained by reading a document on which an image is formed using a color material, and the color of the color material used in the document or a nearby color is The image processing apparatus according to claim 1, wherein the image processing apparatus is included in the representative color. The image forming apparatus according to claim 1, wherein the representative color includes at least one of cyan, magenta, yellow, black, red, green, blue, and white or a color in the vicinity thereof. The image forming apparatus
An image acquisition step for acquiring image data;
A first color conversion step of converting the color of each pixel included in the acquired image data into any of a plurality of representative colors determined according to the background color of the image represented by the image data;
A second color conversion step of converting each of the plurality of representative colors obtained by the conversion in the first color conversion step into a color determined according to the surface color of the recording material;
An image processing method comprising: an output step of outputting image data obtained by converting the color of each pixel in the second color conversion step. On the computer,
An image acquisition function for acquiring image data;
A first color conversion function for converting the color of each pixel included in the acquired image data into one of a plurality of representative colors determined according to the background color of the image represented by the image data;
A second color conversion function for converting each of the plurality of representative colors obtained by the conversion by the first color conversion function into a color determined according to the surface color of the recording material;
And an output function for outputting image data in which the color of each pixel is converted by the second color conversion function.

Images