JP2009033341A - Image processing device, image forming apparatus and image processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide toner saving in which hues do not change so much even in a multi-order color composed of a plurality of primary colors. <P>SOLUTION: An operation mode of this forming apparatus 100 has at least a toner saving mode that suppresses a consumption amount of toner and a normal mode that does not suppress the consumption amount of toner. An image processing part 110 converts color information corresponding to an image signal input from an image reading part 101 from color information in a certain color space into color information in another color space and outputs the converted color information. When color represented by color information is a primary color during converting the color information in toner saving mode, such conversion is configured to be performed so as to increase the suppression rate or suppression amount of the consumption amount of the toner. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a technique for suppressing consumption of an image forming material used when forming an image.

An image forming apparatus such as a page printer, a digital copying machine, or a facsimile apparatus has an operation mode called a toner save mode that saves toner (image forming material). For example, Patent Document 1 discloses a technique for performing toner save processing together with color conversion processing, and performing toner save processing by switching a gamma table used on the output device side in accordance with on / off switching of the toner save processing. Has been.
JP 2003-295701 A

Although the technique described in Patent Document 1 can reduce the amount of toner consumed, since the toner save rate is set for each primary color of CMYK and RGB, two types of primary colors are used. Secondary problems occur, such as a change in color with a secondary color consisting of or a color difference with a multi-color such as orange consisting of a plurality of primary colors.
An object of the present invention is to realize image formation in which the above-described secondary problems are unlikely to occur.

  The present invention converts an input unit to which an image signal is input and color information corresponding to the image signal input to the input unit from color information in one color space to color information in another color space. Converting means for outputting, and in the operation mode for suppressing consumption of the drawing material used to reproduce the color represented by the image signal, the converting means outputs the color represented by the image signal, When the primary color in the color space corresponding to the color of the image forming material is used, the consumption rate of the image forming material is suppressed as compared with the case where the color represented by the image signal is a multi-order color in the color space. An image processing apparatus is provided that performs conversion into color information that increases the amount of suppression.

  When the color represented by the image signal is the primary color, the converting means reduces the saturation of the color represented by the color information in the certain color space by reducing the saturation of the color represented by the color information. You may make it convert into the color information in a color space. In addition, when the color represented by the image signal is the primary color, the conversion unit increases the brightness of the color represented by the color information in the certain color space by increasing the brightness of the color represented by the color information. The color information in the color space may be converted.

  Further, the conversion means converts the color information corresponding to the value of the input image signal from the color information in the first color space to the color information in the second color space by a matrix operation method. The conversion may be performed according to the coefficients used for the matrix calculation. Further, the conversion means converts color information corresponding to the value of the input image signal from color information in the second color space to color information in the third color space by a look-up table method. The conversion may be performed in accordance with parameters described in the lookup table.

  Further, when the image forming material is composed of a plurality of chromatic color toners and a black toner, the ratio of reproducing the gray reproduced by overlapping the plurality of chromatic color toners with the black toner There may be provided means for increasing the operation mode in which the consumption of the shape material is suppressed and decreasing in the operation mode in which the consumption of the shape material is not suppressed.

  According to another aspect of the present invention, there is provided an image forming apparatus comprising: any one of the image processing apparatuses described above; and an image forming unit that forms an image on a recording medium based on the color information output by the conversion unit. There may be.

  Further, according to the present invention, when the color represented by the image data is a primary color in the color space corresponding to the color of the image forming material, the color represented by the image data is a multi-order color in the color space. An image forming method is characterized in that the image data is processed so that the suppression rate or the suppression amount of the consumption of the image forming material is larger than the case.

FIG. 1 is a diagram illustrating a configuration of an image forming apparatus 100 according to the present embodiment.
The image forming apparatus 100 includes an image reading unit 101, a first color conversion unit 102, a second color conversion unit 103, and an image forming unit 104. The first color conversion unit 102 and the second color conversion unit 103 constitute an image processing unit 110. The operation modes of the image forming apparatus 100 include at least a toner save mode that suppresses toner consumption, and a normal mode that does not suppress toner consumption. These operation modes are not shown in FIG. Is switched by the image processing unit 110 according to the operation. The image processing unit 110 functions as a unit that converts color information corresponding to an image signal input from the image reading unit 101 from color information in one color space to color information in another color space and outputs the color information. When color information is converted in the toner save mode, if the color represented by the color information is a primary color, the image processing unit 100 may increase the suppression rate or amount of toner consumption. Conversion has been made.

  The image reading unit 101 includes a platen glass (not shown), a CCD (Charge Coupled Device) image sensor, and the like. The image reading unit 101 irradiates light on a document placed on the platen glass and receives the reflected light by the CCD image sensor. R (red), G (green), and B (blue) image signals corresponding to the received light intensity are output. This image signal represents a color in an RGB color space specific to the performance and specifications of the image reading unit 101. This image signal is subjected to various correction processes such as an equivalent intermediate brightness correction using a one-dimensional tone correction LUT (Look Up Tabel) after shading correction and MTF correction by a pre-processing unit (not shown). Is input to the first color converter 102.

In the first color conversion unit 102, color information in which the R, G, and B gradation values of each pixel are represented by 8 bits is sequentially stored in a page memory (not shown) according to the input image signal. The The first color conversion unit 102 converts the RGB color information read from the page memory from the color information in the RGB color space (first color space) to the L ^* a ^* b ^* color space (second Color information in the color space) by a matrix calculation method. As described above, the RGB color information is unique to the image reading unit 101 as a device, but the color information in the color space of L ^* a ^* b ^* is color information independent of the device.

The coefficients used for the matrix calculation of the first color conversion unit 102 are the colorimetric values (values represented in the color space of L ^* a ^* b ^* ) of the patch image with uniform density, and the coefficients formed on the paper The patch image is prepared in advance on the basis of the correspondence with the result of actually reading the patch image by the image reading unit 101 (value expressed in the RGB color space). There are two types of coefficients, a coefficient used in the normal mode (that is, an operation mode when the toner save mode is not selected) and a coefficient used in the toner save mode. The coefficient used in the normal mode is a coefficient that matches the colorimetric value of the patch image with the read result of the patch image. On the other hand, the coefficient used in the toner save mode is a coefficient that has an effect of suppressing toner consumption, although the colorimetric value of the patch image does not completely match the read result of the patch image.

Here, FIG. 2 is a diagram showing a configuration of the matrix calculation circuit 102-1 for converting RGB color information into L ^* color information, and FIG. 3 shows RGB color information as a ^* color information. FIG. 4 is a diagram illustrating a configuration of a matrix arithmetic circuit 102-3 for converting RGB color information into b ^* color information. is there.
As shown in FIG. 2, the matrix operation circuit 102-1 for L ^* includes three multipliers 102-1a for squaring 8-bit R, G, and B gradation values, respectively, and a B gradation value. And G tone values, G tone values and R tone values, R tone values and B tone values, respectively, and three multipliers 102-1b and R, G, B tone value, and nine multipliers 102-1c for multiplying the coefficients a ₁₁ ~a ₁₉ for each of the multiplication result of the multiplication result of the multiplier 102-1a and multiplier 102-1b, multiplication of the multiplier 102-1c An adder 102-1d that adds all the results and a rounder 102-1e that rounds the addition result of the adder 102-1d and outputs the result as 8-bit color information L ^* are provided.

Matrix operation circuit 102-1 for L ^* as the coefficient a ₁₁ ~a _19, stores two kinds of things. One is coefficients a _{11 to} a ₁₉ used when the color represented by the RGB color information is the primary color in the YMCK color space. This coefficient is called a “primary color coefficient”. The other is a coefficient used when the color represented by the RGB color information is a multi-order color in the YMCK color space. This coefficient is referred to as a “multi-order color coefficient”. The “primary color” here is a color expressed by using Y (yellow), M (magenta), C (cyan), and K (black) toners alone, that is, yellow, magenta, cyan, black. Each of the colors itself. On the other hand, the multi-order color is a color expressed by using at least any two or more kinds of toners among Y, M, C, and K.

Next, as shown in FIG. 3, the a ^* matrix calculation circuit 102-2 includes three multipliers 102-2a that respectively square the 8-bit R, G, and B gradation values, Three multipliers 102-2b for multiplying the gradation value and the G gradation value, the G gradation value and the R gradation value, the R gradation value and the B gradation value, respectively, R, G, 9 multipliers 102-2c for multiplying the grayscale value of B, the multiplication result of the multiplier 102-2a and the multiplication result of the multiplier 102-2b by coefficients a _{21 to} a ₂₉ , and the multiplier 102 − An adder 102-2d that adds all the multiplication results of 2c and a rounder 102-2e that rounds the addition result of the adder 102-2d and outputs the result as 8-bit color information a ^* are provided. Similarly to the L ^* matrix calculation circuit 102-1, the matrix calculation circuit 102-2 for a ^* also uses the coefficients a _{21 to} a ₂₉ as the primary color in the color space in which the color represented by the RGB color information is YMCK. A coefficient used for a color (primary color coefficient) and a coefficient used for a multi-order color (multi-color coefficient) are stored.

Also, as shown in FIG. 4, the b ^* matrix operation circuit 102-3 includes three multipliers 102-3a each for squaring 8-bit R, G, and B gradation values, and Three multipliers 102-3b for multiplying the tone value and the G tone value, the G tone value and the R tone value, the R tone value and the B tone value, and R, G, B tone value, and nine multipliers 102-3c for multiplying the coefficients a ₃₁ ~a ₃₉ for each of the multiplication result of the multiplication result of the multiplier 102-3a and multiplier 102-3B, the multiplier 102-3c Are added, and an adder 102-3d for adding all the multiplication results is rounded, and a rounder 102-3e for rounding the addition result of the adder 102-3d and outputting it as 8-bit color information b ^* . Similar to the L ^* matrix calculation circuit 102-1, the b ^* matrix calculation circuit 102-3 uses the coefficients a _{31 to} a ₃₉ as the primary color in the color space where the color represented by the RGB color information is YMCK. A coefficient used for a color (primary color coefficient) and a coefficient used for a multi-order color (multi-color coefficient) are stored.

When the operations by the matrix operation circuits 102-1 to 102-3 in FIGS. 2 to 4 are summarized into a determinant, the equation (A) is obtained.

The value of the coefficient _{a 11 ~a 19, a 21 ~a} 29 and a ₃₁ ~a ₃₉ is a multinary color coefficient may be the same value as the coefficient used in the normal mode described above. Further, even if conversion is performed from RGB color information to YMCK color information, the coefficient may be a value that allows some toner reduction within a range in which the color hardly changes.

On the other hand, the coefficient _{a 11 ~a 19, a 21 ~a} 29 and a ₃₁ ~a ₃₉ coefficients for the primary color is characterized as follows.
First, the coefficient a ₁₁ ~a ₁₉ coefficients for the primary color, is larger than the multinary color coefficient a ₁₁ ~a _19. Next, the coefficients a _{21 to} a ₂₉ and the coefficients a _{31 to} a ₃₉ , which are the primary color coefficients, are smaller in value than the multi-color coefficients a _{21 to} a ₂₉ and the coefficients a _{31 to} a ₃₉ . Accordingly, when the color represented by the RGB color information is a primary color in the YMCK color space, the coefficients a _{11 to} a ₁₉ are larger, and the coefficients a _{21 to} a ₂₉ and the coefficients a _{31 to} a ₃₉ are smaller. From the equation (A), RGB color information is converted to color information of a ^* b ^* which is larger and smaller than L ^* . When L ^* is large in the primary color, that is, when the lightness is large, the toner concentration is low, that is, the amount of toner used for development is small, so the amount of toner can be reduced. In addition, if a ^* b ^* is small in the primary color, that is, the saturation is small, it means that the toner density is low, that is, the amount of toner used for development is small. Can do. In addition, even if the lightness is increased or the saturation is decreased in the primary color, the color does not change so much that the human eye does not seem to have changed so much. For example, even if the toner density of yellow is increased or decreased, it looks almost similar to the human eye. Thus, larger primary color coefficient a ₁₁ ~a _19, or by a smaller a ₂₁ ~a ₂₉ and the coefficient a ₃₁ ~a ₃₉ for primary colors, without changing the color, toner consumption It is possible to increase the amount suppression rate or amount.

As described above, the color information obtained by the conversion of the first color conversion unit 102 is input to the second color conversion unit 103. The second color conversion unit 103 converts the color information in the L ^* a ^* b ^* color space (second color space) into the color information in the YMCK color space (third color space), and performs a DLUT (Direct Conversion using a lookup table). This DLUT is a YMCK lattice with respect to discrete lattice points (parameters) of L ^* , a ^* , b ^* in a three-dimensional space represented by L ^* axis, a ^* axis, and b ^* axis orthogonal to each other. This is a structure in which points (parameters) are arranged. For example, in the case of a 9 × 9 × 9 DLUT, a total of 729 lattice points are stored, and in the case of a 17 × 17 × 17 DLUT, a total of 4913 lattice points are stored. Then, for L ^* a ^* b ^* between adjacent grid points, the value of YMCK is obtained by interpolation calculation.

  The grid points (parameters) described in the DLUT include the grid points (parameters) used in the normal mode and the grid points used in the toner save mode, like the coefficients in the first color conversion unit 102 described above. (Parameter). The grid points used in the normal mode are grid points that match the colorimetric value of the patch image with the read result of the patch image. On the other hand, grid points used in the toner save mode are grid points that have an effect of reducing the toner amount, although the colorimetric values of the patch image and the read result of the patch image do not completely match.

Here, FIG. 5 is a diagram for explaining the difference between the grid points used in the normal mode and the grid points used in the toner save mode. In the normal mode, the second color conversion unit 103 obtains a local area corresponding to the color information L ^* , a ^* , b ^* in the DLUT as illustrated on the left side in the drawing, and further illustrated on the right side in the drawing. Thus, the YMCK lattice point X1 is obtained by interpolation calculation in the local region. The arrow indicated by the dotted line indicates a case where the YMCK lattice point X1 is obtained by a complementary operation. On the other hand, in the toner save mode, the second color conversion unit 103 obtains a local area corresponding to the color information L ^* , a ^* , b ^* by the DLUT as in the normal mode, and further performs an interpolation operation in the local area. YMCK lattice points are obtained, but the values of the lattice points themselves are different from those in the normal mode. The YMCK lattice point X2 obtained at this time has lower saturation and greater brightness than the lattice point X1. Become. In FIG. 5, an arrow p extending from the lattice point X1 means a direction in which the saturation is low, and an arrow q extending from the arrow p means a direction in which the lightness is high. In this way, in the toner save mode, RGB color information is converted to color information of a ^* b ^* that is larger and smaller than L ^* .

The second color conversion unit 103 also has a UCR (Under Color Removal) function called “inking”. UCR is to replace a gray component expressed by superimposing three primary colors Y, M, and C, which are chromatic colors, with K. The replacement ratio of how much Y, M, and C of the gray component are replaced by K is large in the toner save mode and small in the normal mode. Considering the total toner amount of YMCK, as the replacement ratio by UCR increases, the amount of K, M, and C toners that exceed the amount of K toner can be reduced instead of increasing the amount of K toner. Therefore, the second color conversion unit 103 increases the replacement ratio of the gray component to K in the toner save mode as compared with the normal mode.
The YMCK color information obtained by the conversion of the second color conversion unit 103 is output to the image forming unit 104. The image forming unit 104 performs processing such as gradation correction and screen processing on the color information, and then forms a toner image on a recording medium such as paper.

  According to the embodiment described above, the color represented by the image signal in the color space corresponding to the color (Y, M, C, K) of the toner used by the image forming unit 104 by the conversion of the color information. In the case of a primary color, the color represented by the image signal is converted into color information such that the suppression rate or the suppression amount of the toner consumption is larger than when the color is a multi-order color in the color space. .

In the embodiment described above, the first color conversion unit 102, together with the use of the coefficients a ₁₁ ~a ₁₉ for primary colors is greater than the multinary color coefficient a ₁₁ ~a _19, multinary color coefficient a than ₂₁ ~a ₂₉ and the coefficient a ₃₁ ~a ₃₉ was by using the coefficient for the value is small primary color a ₂₁ ~a ₂₉ and the coefficient a ₃₁ ~a _39.
Not limited to this, the first color conversion unit 102 performs a matrix operation using the same coefficients a _{11 to} a ₁₉ , a _{21 to} a ₂₉ and coefficients a _{31 to} a ₃₉ for the primary color and the multi-order color, so that the primary color is changed. In this case, a predetermined constant is added to L ^* of the calculation result to increase the brightness, while a ^* and b ^* of the calculation result are added with a predetermined constant to lower the saturation. You may make it do.
Here, FIG. 6 is a diagram showing a configuration of a matrix operation circuit 102-4 for converting RGB color information into L ^* color information.
As shown in FIG. 6, the matrix operation circuit 102-4 for L ^* includes three multipliers 102-4a for squaring 8-bit R, G, and B gradation values, respectively, and a B gradation value. And G gradation values, G gradation values and R gradation values, R gradation values and B gradation values, respectively, and three multipliers 102-4b and R, G, B levels Nine multipliers 102-4c for multiplying coefficients a _{11 to} a ₁₉ by the multiplier, the multiplication result of the multiplier 102-4a, and the multiplication result of the multiplier 102-4b, and the multiplication of the multiplier 102-4c An adder 102-4d that adds all constants C1 (C1> 0) in addition to the result, and a rounder 102-4e that rounds the addition result of the adder 102-1d and outputs it as 8-bit color information L ^*. I have. Further, matrix calculation circuit, and b ^* a matrix operation circuit for for a ^*, instead of the constant C1 in FIG. 6, adds the coefficients a ₁₁ are constants from the multiplication result of _{~a 19 C2, C3 (C2 <} 0 , C3 <0).

When the operations by these matrix operation circuits are summarized into a determinant, the equation (B) is obtained.

In addition, the first color conversion unit 102 and the second color conversion unit 103 perform color conversion that increases the brightness and decreases the saturation, but only one of them, that is, the color conversion that increases the brightness. Alternatively, only color conversion that lowers the saturation may be used. Further, only one of the first color conversion unit 102 and the second color conversion unit 103 may perform color conversion for reducing the toner amount.
The image forming material used when forming an image is not limited to what is called “toner”, and any material can be used as long as it can form an image.

1 is a block diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. It is a figure which shows the structure of the matrix arithmetic circuit for converting the RGB color information into the L ^* color information. It is a figure which shows the structure of the matrix arithmetic circuit for converting the RGB color information into the color information of a ^* . It is a figure which shows the structure of the matrix arithmetic circuit for converting RGB color information into b ^* color information. It is a figure explaining the mechanism at the time of converting the color information of L ^* a ^* b ^{* into} the color information of YMCK. In a modification, it is a figure which shows the structure of the matrix calculating circuit for converting the RGB color information into the color information of L ^* .

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Image forming apparatus, 101 Image reading part, 102 1st color conversion part, 103 2nd color conversion part, 104 Image formation part

Claims (8)

An input means for inputting an image signal;
Conversion means for converting color information corresponding to the image signal input to the input means from color information in one color space to color information in another color space, and outputting the color information.
The converting means includes
In an operation mode that suppresses the consumption of the drawing material used to reproduce the color represented by the image signal,
When the color represented by the image signal is a primary color in a color space corresponding to the color of the image forming material, the color represented by the image signal is a multi-order color in the color space. An image processing apparatus that converts the color information into color information that increases a suppression rate or a suppression amount of consumption of the image forming material. When the color represented by the image signal is the primary color, the converting means reduces the color saturation of the color represented by the color information to the other color space. The image processing apparatus according to claim 1, wherein the color information is converted into color information. In the case where the color represented by the image signal is the primary color, the conversion means increases the brightness of the color represented by the color information by increasing the brightness of the color represented by the color information. The image processing apparatus according to claim 1, wherein the image processing apparatus is converted into color information. The conversion means converts the color information corresponding to the value of the input image signal from the color information in the first color space to the color information in the second color space by a matrix calculation method. The image processing apparatus according to claim 1, wherein the conversion is performed in accordance with a coefficient used for calculation. The conversion means converts color information corresponding to the value of the input image signal from color information in the second color space to color information in the third color space by a look-up table method. The image processing apparatus according to claim 1, wherein the conversion is performed in accordance with a parameter described in a lookup table. The drawing material comprises a plurality of chromatic toners and a black toner,
In the operation mode for suppressing the consumption of the drawing material, the ratio of reproducing the gray reproduced by superimposing the plurality of chromatic color toners with the black toner is increased, and the consumption of the drawing material is reduced. The image processing apparatus according to claim 1, further comprising a lowering unit in an operation mode that is not suppressed. The image processing apparatus according to any one of claims 1 to 6,
An image forming apparatus comprising: an image forming unit that forms an image on a recording medium based on the color information output by the conversion unit.   When the color represented by the image data is a primary color in a color space corresponding to the color of the drawing material, the color represented by the image data is more than the case where the color is a multi-order color in the color space. An image processing method, wherein the image data is processed so that a suppression rate or a suppression amount of the consumption of the drawing material is increased.

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