JP6740853B2 - Color conversion device and program - Google Patents

Description

The present invention relates to a color conversion device and a program.

There is known a technique of setting a negative number to an output value of color conversion in order to suppress fogging in a highlight region of an image (for example, Patent Document 1).

JP, 2003-153017, A

If a negative number is set for the output value of color conversion, it is difficult to speed up the processing by software. For speeding up, a method of changing an output value set with a negative number to 0 is conceivable, but this method causes more fogging than a case where the output value is a negative number.
An object of the present invention is to achieve both suppression of fog in the highlight area and speeding up of software processing.

The invention according to claim 1 has a table in which a grid point in a color space of the first color system is associated with an output value of the second color system, and the second value corresponding to the input value of the first color system is provided. If a negative number of output values of the second color system is associated with the plurality of grid points that interpolate the output value of the color system, the output value is changed to 0 and When a number of output values of the second color system are associated with each other, reduction means for reducing the output value according to a predetermined rule, and the second color system after reduction by the reduction means There is provided a color conversion device comprising: an output unit that outputs an output value corresponding to an input value of the first color system by interpolation using the output value.
The invention according to claim 2 is the color conversion device according to claim 1, wherein the reducing unit interpolates an output value of the second color system with respect to an input value of the first color system. The positive output value of the second color system is reduced according to the number of 0 or negative output values of the second color system associated with the point.
According to a third aspect of the present invention, in the color conversion apparatus according to the first aspect, the reduction unit interpolates a plurality of input values of the first color system and output values of the second color system. For each of the grid points of, the value of the output value is reduced according to the value of the output value of the second color system associated with the grid point.
According to a fourth aspect of the invention, the computer has a table in which the output values of the second color system are associated with the grid points in the color space of the first color system, and for the input values of the first color system. If a negative number of output values of the second color system is associated with the plurality of grid points that interpolate the output value of the second color system, the output value is changed to 0 and , A positive number is associated with the output value of the second color system, reduction means for reducing the output value according to a predetermined rule, and the second table after reduction by the reduction means. A program is provided for causing the output unit to output an output value corresponding to the input value of the first color system by interpolation using the output value of the color system.

According to the inventions of claims 1 and 4, it is possible to achieve both suppression of fog in the highlight area and high-speed software processing.
According to the invention of claim 2, the reduction amount of the positive output value can be adjusted according to the number of output values of 0 or negative number. The reduction amount of the output value can be adjusted according to the value of the value.

FIG. 1 is a diagram showing a configuration of a copying machine 10. FIG. 3 is a diagram showing a hardware configuration of a color conversion device 40. The figure which shows the color space of L*a*b* color system. The figure which shows eight unit cubes which share one grid point. The figure which shows the functional block which concerns on a color conversion process. The flowchart which shows the procedure of the color conversion process which concerns on the 2nd color conversion part 22. 6 is a flowchart showing the procedure of color conversion processing.

<First Embodiment>
An example of a mode for carrying out the present invention will be described. This embodiment is an example in which the present invention is applied to a copying machine.

FIG. 1 is a diagram showing the configuration of the copying machine 10. The copying machine 10 includes a reading unit 12, an A/D conversion unit 14, a correction unit 16, a first color conversion unit 18, an image processing unit 20, a second color conversion unit 22, a gradation correction unit 24, and an image forming unit 26. Prepare

The reading unit 12 reads a document and generates image data representing an image of the document. The reading unit 12 includes a plurality of CCDs (Charge-Coupled Devices) and outputs signals for each color component of R (Red), G (Green), and B (Blue). The A/D conversion unit 14 converts the output signal of the reading unit 12 into digital image data. The correction unit 16 performs shading correction and the like on this image data.

The first color conversion unit 18 performs color conversion on the image data supplied from the correction unit 16. Specifically, the first color conversion unit 18 converts the RGB color system image data into the L*a*b* color system based on preset data indicating the characteristics of the CCD sensor of the reading unit 12. Convert to image data.
The RGB color system is an example of the first color system that depends on the device, and other color systems may be used. The L*a*b* color system is an example of the second color system that does not depend on the device, and other color systems may be used.

The image processing unit 20 performs image processing on the image data after the color conversion by the first color conversion unit 18. Specifically, the image processing unit 20 performs an enlarging/reducing process according to a print instruction on the image data of the L*a*b* color system supplied from the first color converting unit 18, and an MTF (Modulation). Transfer Function) Sharpening processing such as correction, various image processing such as background removal processing to remove background components according to the type of original (straw paper, recycled paper, colored paper, etc.) are supplied to the second color conversion unit 22. To do.

The second color conversion unit 22 converts the image data of the L*a*b* color system supplied from the image processing unit 20 into image data of the YMCK color system and supplies the image data to the gradation correction unit 24. The second color conversion unit 22 includes a DLUT (Direct Lookup Table). This DLUT is a combination of L*, a*, b*, and each color of Y, M, C, K for outputting the color represented by this combination using Y, M, C, K color materials. It is a three-dimensional LUT that shows the correspondence relationship with the combination of component density values. The function of the second color conversion unit 22 is realized by the color conversion device 40 described later.

The gradation correction unit 24 performs gradation correction on the density values of Y, M, C, and K for each pixel of the image data supplied from the second color conversion unit 22 to obtain density values Y′, M′, and C. The image data is converted into “, K” and the converted image data is supplied to the image forming unit 26. The gradation correction unit 24 has density values Y′, M, C, and K and gradation-corrected density values Y′ for forming an image of a density corresponding to these density values in the image forming unit 26. It is provided with an LUT showing a correspondence relationship with M′, C′, and K′. This LUT is preset based on the output characteristics of the image forming unit 26 obtained by forming a test image in the image forming unit 26.

The image forming unit 26 forms an image based on the image data supplied from the gradation correction unit 24 on a recording medium using Y, M, C, and K color materials. As an example, the image forming unit 26 includes an image forming unit for each of Y, M, C, and K colors. The image forming unit includes a photoconductor, a writing unit that writes an electrostatic latent image on the photoconductor based on image data, a developing unit that develops the written electrostatic latent image using toner, and a developed toner. And a transfer unit that transfers an image onto a recording medium.

FIG. 2 is a diagram showing a hardware configuration of the color conversion device 40. The color conversion device 40 includes a control unit 42, a storage unit 44, and a communication unit 46. The control unit 42 includes an arithmetic device such as a CPU (Central Processing Unit) and a storage device such as a ROM (Read Only Memory) or a RAM (Random Access Memory). The ROM stores firmware that describes a procedure for activating hardware and an OS (Operating System). The RAM stores data when the CPU executes the calculation. The storage unit 44 includes a hard disk storage device, a semiconductor memory, etc., and stores an OS, application programs, and the like. The communication unit 46 is a communication I/F (Interface) between the color conversion device 40 and the outside. The color conversion device 40 is installed with software describing a procedure of color conversion processing. The function of the second color conversion unit 22 described above is realized by the control unit 42 executing this software.

FIG. 3 is a diagram showing a color space of the L*a*b* color system. For example, L*, a*, and b* in the L*a*b* color system are all represented by 8-bit data, and can take 256 gradation values from 0 to 255. Each coordinate axis is divided into 16 regions of 16 gradations, and a virtual unit cube whose length of one side corresponds to 16 gradations is formed. The vertices of each unit cube are defined as grid points in this color space.

The L*a*b* color system image data supplied from the image processing unit 20 is data indicating the values of L*, a*, and b* for each pixel. The upper 4 bits of L*, a*, b* specify the unit cube containing the combination of L*, a*, b*, and the lower 4 bits of this combination of L*, a*, b*. The position within the unit cube is identified.

The DLUT provided in the second color conversion unit 22 uses a combination of L*, a*, and b* at each grid point and a color represented by this combination using Y, M, C, and K color materials. 3 is a three-dimensional LUT showing a correspondence relationship with a combination of density values of Y, M, C, and K color components for output. When the combination of L*, a*, and b* input to the DLUT corresponds to any of the grid points, the output values of Y, M, C, and K corresponding to the grid point are output. If there is no grid point corresponding to the combination of L*, a*, b* input to the DLUT, Y is obtained by interpolation from a plurality of grid points close to this combination of L*, a*, b*. , M, C, K output values are obtained.

FIG. 4 is a diagram showing eight unit cubes sharing one lattice point. When there is no grid point corresponding to the combination of L*, a*, b* input to the DLUT, the grid point P0 closest to this combination of L*, a*, b* is specified. Six grid points P1 to P6 are specified as the grid points adjacent to the grid point P0. Y, M, C and K corresponding to the combination of L*, a* and b* input to the DLUT are obtained by interpolation of the grid point P0 and one or more grid points of the grid points P1 to P6. Desired. Since a known method is used as the interpolation method, the description thereof will be omitted.

FIG. 5 is a diagram showing functional blocks related to color conversion processing. The reducing unit 401 has a table in which the grid points in the color space of the first color system are associated with the output values of the second color system, and the second color system with respect to the input values of the first color system. If a negative number of the output values of the second color system is associated with the plurality of grid points that interpolate the output value of, the output value is changed to 0 and a positive number of When the output values of the second color system are associated, the output values are reduced according to a predetermined rule. The output unit 402 outputs the output value corresponding to the input value of the first color system by interpolation using the output value of the second color system after the reduction by the reduction unit 401. Specifically, it is as follows.

FIG. 6 is a flowchart showing the procedure of the color conversion process performed by the second color conversion unit 22. This color conversion process is realized by the control unit 42 of the color conversion device 40 executing software. For each pixel in the image data of the L*a*b* color system supplied from the image processing unit 20, the process according to the flowchart shown in the drawing is executed for each of the Y, M, C, and K color components. In the following description, an example of outputting the Y component is shown, but similar processing is performed for each of the M, C, and K components.

<Step A01>
The control unit 42 acquires the values of L*, a*, and b*. Specifically, the L*, a*, and b* values of one pixel are acquired from the image data of the L*a*b* color system supplied from the image processing unit 20.

<Step A02>
The control unit 42 identifies the lattice point P0 closest to the combination of L*, a*, and b*.

<Step A03>
The control unit 42 identifies six grid points P1 to P6 near the grid point P0.

<Step A04>
The control unit 42 determines whether the output value Y of the grid point P0 is a positive value. When the output value Y is a positive value (step A04: YES), the control unit 42 ends the process. When the output value Y is not a positive value (step A04: NO), the process of the control unit 42 proceeds to step A05.

<Step A05>
The control unit 42 changes the output value Y of the grid point P0 to 0.

<Step A06>
The control unit 42 counts the number of 0 or negative output values Y for the six grid points P1 to P6 near the grid point P0. If 0 or the number of negative output values Y is 0 (step A06: number=0), the process of the control unit 42 proceeds to step A10. When the number of 0 or negative output values Y is 1, 2, 3, 4, 5, 6, (step A06: number=1, 2, 3, 4, 5, 6), the processing of the control unit 42 is Proceed to steps A11, A12, A13, A14, A15, A16, respectively.

<Step A10>
The control unit 42 does not recalculate the output value Y.

<Step A11>
The control unit 42 multiplies the output value Y by 5/6. As a result, the output value Y is reduced by about 17%. However, the negative output value Y is changed to 0.

<Step A12>
The control unit 42 multiplies the output value Y by 4/6. As a result, the output value Y is reduced by about 34%. However, the negative output value Y is changed to 0.

<Step A13>
The control unit 42 multiplies the output value Y by 3/6. As a result, the output value Y is reduced by about 50%. However, the negative output value Y is changed to 0.

<Step A14>
The control unit 42 multiplies the output value Y by 2/6. As a result, the output value Y is reduced by about 67%. However, the negative output value Y is changed to 0.

<Step A15>
The control unit 42 multiplies the output value Y by 1/6. As a result, the output value Y is reduced by about 83%. However, the negative output value Y is changed to 0.

<Step A16>
The control unit 42 changes the output value Y to 0.
In other words, the process of steps A11 to A16 is a process of multiplying the output value Y by (6-n)/6 (n is 0 or the number of negative output values Y). The above is the procedure of the color conversion process.

Next, a specific example according to the above procedure will be described. For the L*, a*, and b* acquired in step A01, it is assumed that the following grid point P0 is specified in step A02 and the following grid points P1 to P6 are specified in step A03. Here, they are described in the order of (L*, a*, b*:Y). Further, in order to facilitate understanding, L*, a*, and b* are values of 10 gradation intervals (16 gradation intervals in FIG. 3).
P0 (90, -10, 0:-5)
P1 (80, -10, 0:10)
P2 (90, -20, 0: 5)
P3 (90, -10, 10: 5)
P4 (90, -10, -10: 5)
P5 (90, 0, 0:-5)
P6 (100, -10, 0:0)

Since the output value Y of the grid point P0 is not a positive number (step A04: NO), the output value Y of the grid point P0 is changed to 0 (step A05). Next, when the number of 0 or negative output values Y is counted for the grid points P1 to P6, it is 2 (step A06: number=2), so the output value Y is multiplied by 4/6 (step A12). .. The negative output value Y is changed to 0 (lattice point P5). As a result, the output value of each grid point is set as follows. In this example, the output value Y was rounded to the first decimal place.
P0 (90, -10, 0:0)
P1 (80, -10, 0: 6.7)
P2 (90, -20, 0: 3.3)
P3 (90, -10, 10: 3.3)
P4 (90, -10, -10: 3.3)
P5 (90, 0, 0:0)
P6 (100, -10, 0:0)

According to this embodiment, since the negative output value is changed to 0, the processing speed is increased. Further, since the positive output value is reduced, the background fog is suppressed. Therefore, according to the present embodiment, both high processing speed and suppression of background fog are achieved.

<Second Embodiment>
FIG. 7 is a flowchart showing the procedure of color conversion processing. The color conversion process according to the second embodiment has a procedure different from that of the color conversion process according to the first embodiment. In the following description, an example of outputting the Y component is shown, but similar processing is performed for each of the M, C, and K components.

<Step B01>
The control unit 42 acquires the values of L*, a*, and b*. Specifically, the L*, a*, and b* values of one pixel are acquired from the image data of the L*a*b* color system supplied from the image processing unit 20.

<Step B02>
The control unit 42 identifies the lattice point P0 closest to the combination of L*, a*, and b*.

<Step B03>
The control unit 42 identifies six grid points P1 to P6 near the grid point P0.

<Step B04>
The control unit 42 determines whether the output value Y of the grid point P0 is a positive value. When the output value Y is a positive value (step B04: YES), the control unit 42 ends the process. If the output value Y is not a positive value (step B04: NO), the process of the control unit 42 proceeds to step B05.

<Step B05>
The control unit 42 obtains the output value Y by the following equation.
Y=T×(T/(T+|S|)) Formula (1)
However,
S: output value Y of grid point P0,
T: output value Y of grid points P1 to P6
When both S and T are 0 or a negative number, the output value Y is changed to 0.

<Step B06>
The control unit 42 changes the output value Y of the grid point P0 to 0.

Next, a specific example according to the above procedure will be described. For the L*, a*, and b* acquired in step B01, it is assumed that the following grid point P0 is specified in step B02 and the following grid points P1 to P6 are specified in step B03.
P0 (90, -10, 0:-5)
P1 (80, -10, 0:10)
P2 (90, -20, 0: 5)
P3 (90, -10, 10: 5)
P4 (90, -10, -10: 5)
P5 (90, 0, 0:-5)
P6 (100, -10, 0:0)

Since the output value Y of the grid point P0 is not a positive number (step B04: NO), the output value Y is obtained by the equation (1) (step B05), and the output value Y of the grid point P0 is changed to 0 ( Step B06). As a result, the output value of each grid point is set as follows. In this example, the output value Y was rounded to the first decimal place.
P0 (90, -10, 0:0)
P1 (80, -10, 0:6.7)
P2 (90, -20, 0:2.5)
P3 (90, -10, 10:2.5)
P4 (90, -10, -10:2.5)
P5 (90, 0, 0:0)
P6 (100, -10, 0:0)

According to the present embodiment, the greater the absolute value of the negative output value of the grid point used for interpolation, the greater the reduction amount of the output value.

The above embodiment may be modified as follows.
<Modification 1>
In the embodiment, the example in which the color conversion device 40 realizes the color conversion process related to the second color conversion unit 22 by software has been described. However, the first color conversion unit 18, the image processing unit 20, the gradation correction unit 24, and the like are provided. The color conversion device 40 may have a configuration in which a part or all of the processing is implemented by software. Further, the function of the color conversion device 40 may be provided in a control device that controls the entire copying machine 10.

<Modification 2>
In the above embodiment, an example in which the present invention is applied to a copying machine is shown. However, the present invention is applied to an image forming apparatus that forms an image based on PDL (Page Description Language) data or bitmap data acquired from the outside. May be.

DESCRIPTION OF SYMBOLS 10... Copier, 12... Reading unit, 14... A/D conversion unit, 16... Correction unit, 18... First color conversion unit, 20... Image processing unit, 22... Second color conversion unit, 24... Gradation correction Unit, 26... Image forming unit, 40... Color conversion device, 42... Control unit, 44... Storage unit, 46... Communication unit

Claims (4)

There is a table in which the output values of the second color system are associated with the grid points in the color space of the first color system, and the output values of the second color system are interpolated with respect to the input values of the first color system. When a negative number of output values of the second color system is associated with the plurality of grid points, the output value is changed to 0 and a positive number of the second color system is used. When the output value of is associated with a reduction means for reducing the output value according to a predetermined rule,
An output unit that outputs an output value corresponding to the input value of the first color system by interpolation using the output value of the second color system after reduction by the reduction unit. The reduction unit may be a 0 or a negative number of the second color system associated with the plurality of grid points for interpolating the output value of the second color system with respect to the input value of the first color system. The color conversion device according to claim 1, wherein a positive number of output values of the second color system is reduced according to the number of output values. The reducing unit, for each of the plurality of grid points that interpolates the output value of the second color system with respect to the input value of the input first color system, the second unit associated with the grid point. The color conversion device according to claim 1, wherein the value of the output value is reduced according to the value of the output value of the color system. Computer,
There is a table in which the output values of the second color system are associated with the grid points in the color space of the first color system, and the output values of the second color system are interpolated with respect to the input values of the first color system. When a negative number of output values of the second color system is associated with the plurality of grid points, the output value is changed to 0 and a positive number of the second color system is used. When the output value of is associated with a reduction means for reducing the output value according to a predetermined rule,
A program for functioning as an output unit that outputs an output value corresponding to an input value of the first color system by interpolation using the output value of the second color system after reduction by the reduction unit.

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