JPH0898042A - Color conversion device - Google Patents

Abstract

(57) [Summary] [Object] To provide a color conversion device capable of realizing a highly accurate color conversion device with relatively simple hardware. [Structure] FIG. 4 is a block diagram of a color conversion apparatus adopting the present invention. The CPU 407 of FIG. 4 causes the image forming apparatus to measure various conditions such as the process state of the image forming apparatus and the environment around the apparatus. ROM 409 based on the subsequently measured information
The ROM 40 is referred to for each vertex by referring to the information stored in
1 or the optimum one of the vertex output values of the ROM 408 is selected, and the selected vertex output value is loaded into the RAM 403. The output value at the output P is linearly interpolated by the interpolation processing unit 402 based on the loaded vertex output value.
Calculate and obtain.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color conversion device for performing color processing on an input color image signal and converting it into color image data corresponding to an output device.

[0002]

2. Description of the Related Art Conventionally, there has been known a color conversion device which performs color processing on an input color image signal and converts the color image signal into color image data corresponding to an output device. An image forming color image output value in an arbitrary three-dimensional input color space is obtained by interpolating a vertex output value for each output color set at a vertex in the input color space divided into three-dimensional figures, so-called As a color conversion device using the memory map method, for example, Japanese Patent Publication No. Sho 58-16180, Japanese Patent Laid-Open No.
The device described in -284364 etc. is known.

Further, in a color conversion apparatus using the memory map method, it is determined whether or not the vertex is included in the color reproduction area of the image forming apparatus, and the output value on the vertex is calculated inside or outside the color reproduction area. The applicant has filed an application for a parameter calculation method such as switching the method.

Furthermore, when color image data at a position exceeding the color reproduction range of the image forming apparatus is input, a position within the closest color reproduction range is calculated, and the color at that position is converted and output. There are many known methods related to color space compression, such as a method of reducing an image toward the center of gravity of a color reproduction area and outputting the image.

[0005]

The above-mentioned prior art has the following problems. In the conventional color conversion device that employs the memory map method, the vertex output to be set at the vertex in the input color space is calculated in advance, and the output value for the input image data is obtained by interpolation processing. Therefore, in order to cope with the process variation of the image forming apparatus which cannot be controlled, a conversion table corresponding to each situation, that is, a vertex output value group is required.

Therefore, it is necessary to have many conversion tables and many memories. In addition, it is necessary to have the information of the color area (white corresponds in an extreme example) that does not affect the process variation of the image forming apparatus as the vertex output value for each situation, and the data that is rarely used is stored. A lot of wasted memory is needed.

Further, when the input color space is compressed in the color reproduction space of the image forming apparatus by the memory map method, many conversion tables corresponding to the types of the plurality of compression means must be provided, Information on a color area, such as the center of the color reproduction area, which is not so much related to the color space compression must be held as a vertex output value for each compression means.

Next, considering the color conversion accuracy, it is possible to perform highly accurate color conversion by switching the calculation method of the output value on the vertex inside and outside the color reproduction range. However, when the number of divisions is small, there is a problem in the accuracy of color conversion in the vicinity of the outermost color reproduction of the image forming apparatus. That is, FIG. 1 shows a plane of a constant lightness region in the uniform color space L * a * b *.

In FIG. 1, among the vertices A, B, C, and D, only the vertex C is within the color reproduction range of the image forming apparatus, and the color space is compressed to achieve the vertex A of color reproduction. ，
If the output values of B and D are the output values of the outermost part of the color reproduction area,
Since the output value of the input P outside the color reproduction range is output as a color inside the color reproduction range, that is, a color closer to the color corresponding to the vertex C than the actual color, the color inside the color reproduction range is output sensibly. If you have a problem.

[0010]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and provides a color image output for an image forming apparatus corresponding to input color image data in an arbitrary three-dimensional input color space. In the color conversion apparatus, the three-dimensional input color is obtained by interpolating a value using the vertex output value for each output color set at the vertex when the three-dimensional input color space is divided into a plurality of solid figures. Storage means for storing at least two types of output values that can be set at predetermined vertices in space, and selection means for selecting one output value from the output values stored in the storage means The selection condition storage means for storing the selection condition is provided, and the selection means employs a configuration for selecting the output value based on the selection condition stored in the selection condition storage means.

In the color conversion apparatus, the selection condition stored in the selection condition storage means is the process information of the image forming apparatus. The storage means further comprises a vertex selecting means for selecting a vertex in a color area in which an output color largely changes due to a process variation among the vertices when the three-dimensional input color space is divided into three-dimensional figures. Adopts a configuration in which at least two types of output values that can be set to the vertices are stored only for the vertices selected by the apex selecting means, for each output color.

Further, a color image output value for an image forming apparatus corresponding to input color image data in an arbitrary three-dimensional input color space is set to a vertex when the three-dimensional input color space is divided into a plurality of three-dimensional figures. In a color conversion device that is obtained by interpolating using vertex output values for each output color that has been set, input color image data that includes at least two types of colors outside the color reproduction range of the image forming device A color space compression means for compressing within the reproduction range, a color space compression means selection means for selecting one color space compression means, and a vertex selection means for selecting a vertex of the vertices to be compressed by the color space compression means. A storage means for storing at least two types of output values corresponding to the color space compression means for each output color with respect to the vertices selected by the vertex selection means; Selection means for selecting one output value from the output values stored in, the selection means selecting an output value corresponding to the color space compression means selected by the color space compression means selection means. It was adopted.

[0013]

Since the present invention employs the above configuration, it is possible to store a plurality of output values that can be set at predetermined vertices in the three-dimensional input color space and select them according to predetermined conditions.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below with reference to the accompanying drawings. First, a color conversion method necessary for explaining the embodiment of the present invention will be described. As shown in FIG. 2, an XYZ space that is an arbitrary color space is divided into cubes that are three-dimensional figures of the same type.

When the value of the output value P at the input L *, a *, b * coordinates is obtained, the input L *, a *, b
* A cube including coordinates is selected, and linear interpolation is performed based on the output values (the output values are known values obtained by a predetermined method) on the eight vertexes of the selected cube.

When converting into color image data for image formation, the output P corresponds to Y signal, M signal and C signal for controlling ink in the case of a three color printer. An overall configuration diagram of a color conversion device that performs the above-described color conversion will be described with reference to FIG. The ROM 301 is a ROM that stores output values on the vertices of the input color space. The interpolation processing unit 302 uses the RO
RA loaded with vertex information stored in M301
M303, Y from the input image signal by referring to the RAM303
It includes a Y processing unit 304, an M processing unit 305, and a C processing unit 306, which respectively generate a signal, an M signal, and a C signal. Further, the CPU 307 controls the entire device.

Next, a first embodiment of the present invention will be described. FIG. 4 shows an overall configuration diagram of the color conversion apparatus of the first embodiment of the present invention. The ROM 401 and the ROM 408 store the output values on the vertices of the image forming apparatus in the input color space calculated in advance. The interpolation processing unit 402 is a ROM when executing
When the vertex information is loaded from the ROM 401 and the ROM 408, the RAM 403 is referenced, and the RAM 403 is referenced from the input image signal to generate the Y signal, the M signal, and the C signal, respectively.
Processing unit 404, M processing unit 405, C processing unit 40
It consists of 6 and.

The CPU 407 is a CP for controlling the entire system.
The ROM 409 is a U and the ROM 409 or the ROM 4 for each vertex when loading the vertex information into the RAM 403.
This is a ROM that stores process information, which is a selection condition for selecting either of the vertex output values of 08. RAM
Reference numeral 410 is a RAM for temporarily storing process information and the like from the image forming apparatus.

Next, the operation of the apparatus of this embodiment will be described. The CPU 407 of FIG. 4 first causes the image forming apparatus to measure various conditions such as the process state of the image forming apparatus and the environment around the apparatus. The measured information is loaded into the RAM 410, and the RAM 410 temporarily stores this information.

The CPU 407 refers to the information stored in the ROM 409, selects the optimum one of the vertex output values of the ROM 401 or ROM 408 for each vertex, and loads the selected vertex output value into the RAM 403.
The output value at the output P is calculated and obtained by linear interpolation in the interpolation processing unit 402 based on the loaded vertex output value.

Further, among all the vertices formed by partitioning the input color space into three-dimensional figures, the vertices in the color area where the output color largely changes due to the influence of process variation are selected in advance, and The vertex output value corresponding to only the vertex is R
It can also be stored in the OM 408.

In this case, the CPU 407 refers only to the vertices having output values in the ROM 408 and refers to the information in the ROM 409 to select the optimum vertex output value for each vertex from either the ROM 401 or the ROM 408 and to the RAM.
Load to 403, and for other vertices, RO
The vertex output value of M401 is loaded, and the output value at the output P is calculated by linear interpolation in the interpolation processing unit 402 based on the vertex output value to obtain the value.

Next, the second embodiment will be described. Figure 5
FIG. 7 shows the overall configuration of the second embodiment device according to the present invention.
In FIG. 5, ROM 501 and ROM 508 store the output values on the vertices of the image forming apparatus in the input color space calculated in advance corresponding to color space compression 1 and color space compression 2, respectively. The interpolation processing unit 502 uses the ROM 5 at the time of execution.
01, R when the vertex information is loaded from the ROM 508
AM processing unit 504, M processing unit 505, C processing unit 506, which generates a Y signal, an M signal, and a C signal by referring to the AM 503 and the RAM 503 from the input image signal.
Consists of.

The CPU 507 is a CP that controls the entire system.
ROM 509 is a ROM 501 or ROM 5 for each vertex when the vertex information is loaded into the RAM 503.
The ROM stores a color space compression method, which is a selection condition for selecting either of the vertex output values of 08. RA
M510 is a RAM for temporarily storing the code of the color space compression method selected by the user or the like.

Next, the operation of the apparatus of this embodiment will be described. The CPU 507 of FIG. 5 first displays a message prompting the user to input a desired color space compression method, and requests the user to input the desired color space compression method. Here, as an example, when the color space compression 1 is input with color image data at a position exceeding the color reproduction range of the image forming apparatus, a method for detecting and outputting the position within the closest color reproduction range, and the color space compression 2 is a method of reducing the input color image signal toward the center of gravity of the color reproduction range and outputting the image signal.

At this time, the user can select a desired color space compression method suitable for an image to be output, for each region of the input color space, for example, for each hue. The information selected by the user is loaded into the RAM 510 and the RAM 51
0 temporarily stores this information.

The CPU 507 refers to the information stored in the ROM 509, selects the optimum one of the vertex output values of the ROM 501 or ROM 508 for each vertex, and loads the selected vertex output value into the RAM 503.
The output value at the output P is calculated and obtained by linear interpolation in the interpolation processing unit 502 based on the loaded vertex output value.

In the ROM 508, among all the vertices formed by dividing the input color space into three-dimensional figures, only the vertex output values corresponding to the vertices having different values from the vertex output values of the ROM 501 are stored. CPU 507 is ROM5
The ROM 509 only has the output value at 08.
Information is loaded into the RAM 503 with reference to the information, and the vertex output values of the ROM 501 are loaded for the other vertices.

Next, a third embodiment will be described. Figure 6
FIG. 3 shows the overall configuration of the third embodiment device according to the present invention.
In FIG. 6, ROM 601 and ROM 608 store the output values on the vertices of the image forming apparatus in the input color space calculated in advance corresponding to color space compression 1 and color space compression 2, respectively. The interpolation processing unit 602 uses the ROM 6 at the time of execution.
01, R when the vertex information is loaded from the ROM 608
AM processing unit 604, M processing unit 605, C processing unit 606, which generates a Y signal, an M signal, and a C signal by referring to the AM 603 and the RAM 603 from the input image signal.
Consists of.

The CPU 607 is a CP that controls the entire system.
U is the ROM 609, and the ROM 609 is the ROM 601 or the ROM 6 for each vertex when loading the vertex information into the RAM 603.
The ROM stores the color information of the outermost contour of the color gamut of the image forming apparatus, which is the selection condition for selecting either of the vertex output values of 08. The RAM 610 is a RAM for temporarily storing the code of the color space compression method selected by the user or the like.

Next, the operation of the apparatus of this embodiment will be described. First, the CPU 607 of FIG. 6 stores the vertex information of the ROM 601 in the RAM 603 and the vertex information of the ROM 608 as RA.
Load to M610 respectively. Only when the input is at the boundary of the color gamut of the image forming apparatus, the input is included in the color gamut of the image forming apparatus by referring to the outermost information of the color gamut of the image forming apparatus in the ROM 609 for each input. Is determined.

When the input is within the color reproduction range, the RAM 60
3. When it is outside the color reproduction range, the output value at the output P is calculated by the linear interpolation in the interpolation processing unit 602 based on the vertex output value of the RAM 610.

Further, among all the vertices formed by dividing the input color space into three-dimensional figures, in the RAM 610, outside the color gamut of the image forming apparatus shown by dots in FIG. 7, and
It is also possible to store only the vertices in the color area near the outermost contour.

[0034]

As described above, according to the present invention, the color image output value for the image forming apparatus corresponding to the input color image data in an arbitrary three-dimensional input color space is stored in the three-dimensional input color space. In a color conversion device that is obtained by interpolating using vertex output values for each output color set at the vertices when divided into a plurality of three-dimensional figures, it is possible to set at a predetermined vertex in the three-dimensional input color space. Storage means for storing at least two types of possible output values for each output color, selection means for selecting one output value from the output values stored in the storage means, and selection condition storage means for storing selection conditions Since the selection means adopts a configuration for selecting the output value based on the selection condition stored in the selection condition storage means, it is possible to select the output value suitable for the situation for each vertex, which is a wasteful sum. Since the output values is eliminated, it is possible to cope with such a variety of process variations of the image forming apparatus with relatively little hardware.

Further, there is provided a vertex selecting means for selecting a vertex in a color area in which the output color largely changes due to the process variation, among the vertices when the three-dimensional input color space is divided into three-dimensional figures. In addition to the above effects, the storage means has a configuration in which at least two types of output values that can be set to the vertices are stored only for the vertices selected by the vertex selection means. Can be reduced, and the calculation time can be shortened.

Further, while compressing the input color space into the color reproduction space of the image forming apparatus, it is possible to accurately output the colors within the color reproduction area near the outermost contour of the color reproduction area. Furthermore, since at least two types of output values that can be set for the selected vertices are stored for each output color, the hardware can be further reduced.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of color conversion.

FIG. 2 is an explanatory diagram of color conversion.

FIG. 3 is an overall configuration diagram of a color conversion device.

FIG. 4 is an overall configuration diagram of a first embodiment device.

FIG. 5 is an overall configuration diagram of a second embodiment device.

FIG. 6 is an overall configuration diagram of a third embodiment device.

FIG. 7 is an explanatory diagram of a color reproduction area.

[Explanation of symbols]

 401, 408, 409 ROM 407 CPU 403, 410 RAM 404 Y processing unit 405 M processing unit 406 C processing unit 501, 508, 509 ROM 507 CPU 503, 510 RAM 504 Y processing unit 505 M processing unit 506 C processing unit 601, 608, 609 ROM 607 CPU 603, 610 RAM 604 Y processing unit 605 M processing unit 606 C processing unit

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication H04N 1/40 D

Claims (6)

[Claims] 1. A color image output value for an image forming apparatus corresponding to input color image data in an arbitrary three-dimensional input color space is set to a vertex when the three-dimensional input color space is divided into a plurality of three-dimensional figures. In a color conversion device that is obtained by performing interpolation using the set vertex output value for each output color, at least two types of output values that can be set at predetermined vertices in the three-dimensional input color space are provided for each output color. It has a storage means for storing, a selection means for selecting one output value from the output values stored in the storage means, and a selection condition storage means for storing a selection condition, and the selection means stores the selection condition storage. A color conversion device, characterized in that an output value is selected based on a selection condition stored in the means. 2. The color conversion device according to claim 1,
A color conversion device, wherein the selection condition stored in the selection condition storage means is process information of the image forming device. 3. The color conversion device according to claim 2,
Among the vertices when the three-dimensional input color space is divided into three-dimensional figures, there is provided a vertex selecting means for selecting a vertex in a color area in which the output color greatly changes due to the influence of the process change, and the storage means has the above-mentioned. A color conversion device characterized in that at least two types of output values that can be set for vertices are stored only for the vertices selected by the vertex selection means, for each output color. 4. The color conversion device according to claim 1, wherein:
The color conversion device, wherein the selection condition stored in the selection condition storage means is whether or not the input color image signal belongs to the inside of the color reproduction area of the image forming device. 5. The color conversion device according to claim 4,
Among the vertices when the three-dimensional input color space is divided into three-dimensional figures, there is a vertex selecting means for selecting a vertex that is outside the color reproduction range of the image forming apparatus and is in the color region near the outermost contour, and the storage means. The color conversion device stores at least two types of output values that can be set for the vertices only for the vertices selected by the vertex selecting means. 6. A color image output value for an image forming apparatus corresponding to input color image data in an arbitrary three-dimensional input color space is set to a vertex when the three-dimensional input color space is divided into a plurality of three-dimensional figures. In a color conversion device that is obtained by interpolating using vertex output values for each output color that has been set, input color image data that includes at least two types of colors outside the color reproduction range of the image forming device A color space compression means for compressing within the reproduction range, a color space compression means selection means for selecting one color space compression means, and a vertex selection means for selecting a vertex to be compressed by the color space compression means among the vertices. A storage unit for storing at least two types of output values corresponding to the color space compression unit for each output color with respect to the vertices selected by the vertex selection unit; Selection means for selecting one output value from the stored output values, the selection means selecting an output value corresponding to the color space compression means selected by the color space compression means selection means. Characteristic color conversion device.