JPH07274024A - Method and device for processing color picture - Google Patents

Abstract

PURPOSE:To perform flexible color transformation by a simple operation. CONSTITUTION:The color transformation characteristic of a display 1 and the color transformation characteristic of a color printer 14 defined by using standard color space are stored in a memory 16 beforehand. Then, at the point of time when it is decided to output pictures displayed at the display 1 from the color printer 14, when that effect is inputted to a CPU 15, the CPU 15 reads the color transformation characteristic of the display 1 and the color transformation characteristic of the color printer 14 from the memory and generates a transformation matrix for which the two color transformation characteristics are synthesized. The coefficient of the matrix is set to a matrix transformation circuit 12 and input RGB signals from the display 1 are transformed to R'G'B' signals to be output signals to the color printer 14.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image processing method and apparatus thereof, and more particularly, to the same color reproduction between devices having different color reproduction characteristics, such as color image input device, display device and output device. The present invention relates to a color image processing method and apparatus for obtaining characteristics.

[0002]

2. Description of the Related Art When a conventional color image displayed on, for example, a CRT color monitor is to be output by an ink jet color printer, the image on the color monitor indicates the emission brightness of each of the phosphors of RGB three colors. While the color is reproduced by changing the additive color mixture, the image on the color printer reproduces the color by the subtractive color mixture which changes the ink density of the four YMCK colors. Therefore, it has been customary that the color reproduction characteristics of the two differ greatly.

In order to solve such a problem, the color reproduction characteristic of the monitor and the color reproduction characteristic of the printer are measured in advance, and the same color characteristic is obtained by compensating for the color difference between the two. Many attempts have been proposed.

As an example of such an attempt, there is a method as shown in FIG. In FIG. 8, 71 is a first conversion function for converting the first color signal displayed on the monitor into a standard color signal, and 72 is data representing the color reproduction characteristic of the monitor measured in advance. The coefficient of the first conversion function is determined based on this data. Here, the standard color space signal 73 is the XYZ color system defined in 1931 by the CIE (International Commission on Illumination). Also, 74 is X
A second conversion function for converting the standard color space signal 73 expressed in the YZ color system into a second color signal for printer output, and 75 is data representing the color reproduction characteristic of the printer. The second conversion function 74 is determined based on this data.

That is, the concept shown in FIG. 8 is XY.
2 through the standard color space signal expressed in the Z color system
It is intended to convert an image on a monitor into an image on a printer having the same color characteristic by one conversion function.

[0006]

However, in the above-mentioned conventional example, the color signal conversion is executed twice by the two conversion functions, which has a drawback that the processing time becomes long. Therefore, it is conceivable that a function that combines these two functions is created in advance and the conversion is executed by that, but the characteristics of the device to be used may change, or conversion to another device with different output characteristics may be performed. When it is desired to output the result, the compositing function must be created each time, resulting in a problem that the image processing procedure becomes complicated.

Further, when the XYZ color system is used as the standard color space, there is a drawback that a quantization error during conversion becomes large and an image signal is deteriorated.

An object of the present invention is to solve the problems of the above-mentioned conventional examples individually or all, and to provide a color image processing method and apparatus capable of performing color conversion flexibly by a simple procedure. And

[0009]

In order to achieve the above object, the color image processing method of the present invention comprises the following steps. That is, the first conversion relationship for converting the color image signal from the first color image processing device so as to be expressed by the color component in the predetermined common color space, and the second conversion of the color component signal in the predetermined common color space into the second And a second conversion relationship for converting the color image signal to the color processing device, and outputting the color image signal output from the first color image processing device from the second color image processing device. Is generated, a conversion relationship based on the first conversion relationship and the second conversion relationship is generated in association with the instruction, and the first color image processing is performed based on the generated conversion relationship. A color image processing method is provided, in which a color image signal from the device is converted and output to the second color image processing device.

According to another aspect of the present invention, a first setting for setting a first conversion relationship for converting a color image signal from the first color image processing device so as to be expressed by a color component in a predetermined common color space. Means, second setting means for setting a second conversion relationship for converting a color component signal in the predetermined common color space into a color image signal for a second color processing device, and the first and second conversions. Storage means for storing information indicating the relationship; instruction means for instructing to output the color image signal output from the first color image processing device from the second color image processing device; and the instructing means. The first conversion relationship and the second conversion relationship are triggered by an instruction.
A first conversion relationship is newly generated as a third conversion relationship between the color image signals of the first color image processing device and the second color image processing device based on the conversion relationship of
Based on the generating means and the third conversion relationship, the first
A color image processing device for converting a color image signal from the color image processing device to output the second color image signal.

Further, according to the embodiment of the present invention, in order to prevent image deterioration due to quantization error, a predetermined common color space is used, and a vertex of a triangle circumscribing a spectrum locus in the CIE1931-xy chromaticity diagram is used as an original stimulus. Use the color space defined by having.

[0012]

According to the present invention having the above-described structure, the first color image processing device and the first color image processing device are triggered by an instruction to output the color image signal output from the first color image processing device from the second color image processing device. A new color image signal conversion relationship between the two color image processing apparatuses is newly created, and the first color image processing apparatus converts the color image signal according to the new conversion relationship and outputs the second color image signal. Works like.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

[First Embodiment] FIG. 1 is a block diagram showing the arrangement of an image processing system as a typical embodiment of the present invention. This system includes a display 1, a color conversion device 2, and an electrophotographic color printer 14, and outputs an image displayed on a CRT monitor 10 of the display 1 to the color printer 14 via the color conversion device 2.
In FIG. 1, 10 is a CRT color monitor and 11 is a CR
A color image signal (RGB
Signal), a frame memory 12 for storing color signals, a matrix conversion circuit 12 for performing color signal conversion, and a converted R ′.
Frame memory for storing G'B 'signal, 15 is CP
U and 16 are memories that store a plurality of color signal conversion functions or conversion coefficients for color signal conversion. Although not particularly shown, it goes without saying that the CPU 15 controls a ROM storing a control program and the like and a RAM used as a work area to execute the processing.

The matrix conversion circuit 12 is RGB
A signal is input and converted into an R′G′B ′ signal by the following equation.

[0016] Here, the conversion coefficient a _ij (i, j = 1,3) is determined by the procedure described later.

The frame memory 13 transmits the R'G'B 'signal obtained by the matrix conversion circuit 12 to the color printer 14 and outputs a visualized image. Also, CP
U15 reads out a plurality of color signal conversion functions or conversion coefficients written in the memory 16, inputs them to the matrix conversion circuit 12, and controls execution of signal conversion.

It should be noted that the CPU 15 is capable of externally designating a color characteristic and a visualization display command (display 1 here).
There is provided an instruction unit (not shown) capable of inputting (outputting the image displayed on the color printer 14 to the color printer 14). The instruction unit may be a keyboard or 10 keys, but it can also read a large amount of color characteristic information (for example, conversion coefficients corresponding to many devices) and floppy information so that instructions and commands can be collectively input at one time. It may be configured so that a floppy disk drive can be mounted.

When the color characteristics of a plurality of types of displays or color printers expected to be used in the memory 16 are stored in advance as a color signal conversion function or conversion coefficient, the color characteristics of those devices are specified by specific numbers. The color characteristics can be designated by uniquely associating with a symbol, a character string, or the like, and selectively inputting the specific number, symbol, or character string from the instruction unit. This method is used to specify color characteristics in the following description.

FIG. 2 is a block diagram showing the detailed arrangement of the color printer 14. When the R'G'B 'signal is input from the frame memory 13 to the color printer 14, the logarithmic conversion circuit 21 outputs the R'G'B' signal to Y.
Convert to MC signal. This YMC signal is passed through a black signal extraction circuit 22, a masking circuit 23, a UCR circuit 24, and a gamma conversion circuit 25, and YMC subjected to known color correction processing.
It becomes a K signal. This signal is pulse width modulated (PWM) by the light emission pulse width modulation circuit 26 for each color component,
Finally, it becomes a pulse signal for emitting laser light for forming an image on the electrophotographic photosensitive member. This pulse signal is
It is sent to the printer engine unit 27 and drives a semiconductor laser (not shown) to emit laser light. This laser light is controlled by a polygon mirror rotating at high speed so as to scan a photosensitive drum (not shown), and a latent image is formed on the photosensitive drum. This latent image is developed with Y, M, C, and K four-color toners to form a visualized image, which is transferred to print paper.
It is fixed. After that, the color printer 14 ejects the print paper to the outside of the apparatus.

Next, the conversion coefficient a _ij using the apparatus having the above configuration
The method of determining and the operation of the CPU 15 associated therewith will be described with reference to the flowchart shown in FIG. 3 and the chromaticity diagram shown in FIG.

First, in step S31, a color signal (RGB signal) characteristic on the display 1 side that is input data of the color conversion device 2 is selected and input to the CPU 15. Hereinafter, the color signal on the display 1 side is referred to as a first color signal. this is,
This is equivalent to designating the color reproduction characteristic of the CRT monitor 10 used by the user, but can be entered, for example, by the manufacturer name or the device type name. Succeedingly, in a step S32, the color printer 14 serving as output data of the color conversion device 2 is outputted.
CPU 15 by selecting the color signal (R'G'B ') characteristic on the side
To enter. Hereinafter, the color signal on the color printer 14 side is referred to as a second color signal. This is the designation of the color reproduction characteristic of the color printer 14, but the printer manufacturer name and model name can also be input.

When the above procedure is completed, the process proceeds to step S33, and the user further sends a visualization display command to CP.
Input in U15.

Next, the processing proceeds to step S34 triggered by this visualization display command, and the CPU 15 converts the first color signal on the input side from the memory 16 into a standard color space signal in accordance with the input color characteristic information. Of the standard color space signal is called in step S35, and then the second conversion function for converting the standard color space signal into the second color signal of the output side is called. If the corresponding conversion function does not exist in the memory 16 in steps S34 and S35, the process returns to step S31 or S32 as an error.

The first and second conversion functions are 3 × 3 matrix conversions similar to the equation (1), but the conversion coefficient is determined in advance by the monitor color characteristics, the printer color characteristics, and the standard color space definition. And the value is stored in the memory 16.

In the present embodiment, the standard color space is 41, in the CIE1931-xy chromaticity diagram as shown in FIG.
A color space having the three primary colors 42 and 43 as primary stimuli is defined. There are two main reasons for this. Since the triangle formed by 41, 42 and 43 contains the spectral locus 44, it can handle all the color signals to be executed. Since the triangles 41, 42, and 43 circumscribe the spectrum locus, it is possible to suppress the occurrence of a quantization error in which the ratio of the number of quantization bits assigned to a color that does not exist is small.

The color signal on the standard color space is L,
If M and N are written and the conversion function is obtained in consideration of the color reproduction characteristics of typical monitors and printers, the values will be as follows, for example.・ First conversion function ・ Second conversion function If the conversion coefficients of the equations (2) to (3) are written in the memory 16 in advance, the CPU 15 reads them and the process further proceeds to step S36.

In step S36, the following equation (2) is obtained.
And equation (3) are combined to generate a new matrix that associates R′G′B ′ with RGB. That is, the following matrix calculation is executed to obtain the conversion coefficient of a new 3 × 3 matrix. The conversion coefficient represented by the equation (4) is the input side color signal (RG
This is a function for directly converting B) into the output side color signal (R'G'B '). Then, in step S37, the CPU 15 sets the obtained coefficient (a _ij ) of the equation (4) in the matrix conversion circuit 12. Further, in step S38, the CPU 15 reads the input color image from the frame memory 11, and finally in step S39, the color conversion process is executed based on the set coefficient (a _ij ).

As described above, in the present embodiment, the color characteristics of the image input device (display in this case) and the image output device (printer in this case) connected to the system are defined in a common standard color signal space, and each is defined. The conversion function is defined so that the input image signal from the device and the output signal to each device can be expressed by the linear conversion from the standard color signal space. Then, when the input / output device is determined, a conversion matrix for directly connecting the image input device and the image output device is generated using the conversion function from / to each input / output device.

Therefore, according to this embodiment, after the color characteristics of each input / output device of the system for inputting and outputting color image data are determined, the input / output device is directly connected by a simple instruction input to the CPU. The conversion matrices can be combined and color conversion can be performed using the combined conversion matrix.

[Second Embodiment] In the first embodiment, since the first and second conversion functions are 3 × 3 matrix conversions, a composite function can be easily obtained by the product of two matrices. Actually, in many cases, it is necessary to perform more complicated calculation. Therefore, in this embodiment, R is more easily
A case where a three-dimensional lookup table is used instead of the matrix conversion circuit to convert the GB signal into the R′G′B ′ signal will be described.

FIG. 5 is a block diagram showing the arrangement of the image processing system according to this embodiment. However, in FIG.
The same reference numerals are given to the same elements as the apparatus constituent elements shown in FIG. Therefore, here, only the characteristic elements of this embodiment and the operation thereof will be described, and the description of the common parts will be omitted. The difference from the system shown in FIG. 1 is that the color signal conversion circuit is a three-dimensional lookup table conversion circuit 51.

FIG. 6 is a block diagram showing the configuration of the three-dimensional lookup table conversion circuit 51. According to this configuration, the input RGB signal is divided into the upper bit data 61 and the lower bit data 62, only the output signal for the upper bit is stored in the table memory 63, and the output value 64 for the upper bit data is interpolated by the interpolation circuit 65. To the output signal 66 by linearly interpolating the output value 64 using the lower bit data 62. Although only R'is shown as the output signal 66 in FIG. 6, G'B 'is obtained by similar processing.
Needless to say to output.

In this way, the RGB signal is converted into R'G '.
By converting the B ′ signal, not only the matrix conversion but also an arbitrary conversion function is used, the table memory 6
Signal conversion can be performed by rewriting the contents of 3.

[0035] Here, the first color signals R inputs as the first transformation function, G, B and the standard color space signals L, M, functional relationship of three-dimensional and _{N F L, F M, F} N Is defined as follows.

L = F _L (R, G, B) M = F _M (R, G, B) (5) N = F _N (R, G, B) Further, as a second conversion function, standard Color space signals L, M, N
And the second color signals R ′, G ′, B ′ of the output are also defined as three-dimensional functions H _R , H _G , H _B.

R ′ = H _R (L, M, N) G ′ = H _G (L, M, N) (6) B ′ = H _B (L, M, B) Formula (5) to Formula The expression (6) corresponds to the expressions (2) to (3) of the first embodiment.

The CPU 15 operates according to the flow chart shown in FIG. 3 as in the first embodiment. In step S36, a composite function of equations (5) and (6) is generated, and in step S37 the result is set to 3 Write to the table memory 63 of the dimensional lookup table conversion circuit.

In the table memory 63, output values for all combinations of upper bits of each input RGB signal,
That is, the value of the output signal value R′G′B ′ for all RGB input signals whose lower bit data is “0” must be written. Therefore, the CPU 15 sequentially generates such RGB signal values, obtains L, M, and N by the equation (5) for each of them, and calculates the L, M, and N from the equation (6).
To obtain R'G'B 'and write the obtained value in the table memory 63.

When the writing process is completed for all such combinations, the first step is performed in steps S38 to S39.
Processing similar to that in the embodiment is executed.

Therefore, according to this embodiment, since the color conversion is performed using the look-up table, even if the color characteristic of the input / output device has a complicated conversion relationship with the standard color space, a complicated calculation is performed. Color conversion can be performed without performing. This also has the advantage that higher speed color conversion can be performed.

Although the two embodiments have been described as the processing between the color display and the color printer, the present invention is not limited to this. For example, when outputting an image separated by a flatbed scanner to a color printer, or when outputting the same color separated image obtained from the flatbed scanner on a CRT monitor, various image input devices and image outputs The same can be applied to the device.

Further, according to the present invention, when the color image data inputted from the image input device is visualized and the image is printed out, the image is not actually outputted. For example, the output result is predicted and reproduced on the monitor. It can also be applied to a system having a preview function such as a function (called a preview).

In the case of such a preview system, the following three color signal characteristics, namely, the input device (scanner,
It is necessary to define the color characteristics of a monitor, etc., the color characteristics of a device (printer, etc.) that outputs a visualized image, and the color characteristics of a device (monitor) that displays a preview image. If these (first to third conversion functions) are defined for the standard color space, conversion coefficients of the respective color characteristics for the standard color space are used to preview the input color image signal as shown in FIG. Can be converted into a color image signal.

That is, the color image signal to the output device (printer or the like) is converted into the image signal in the standard color space by using the fourth conversion function, and this is converted into the preview image display device by using the fifth conversion function. Convert to color image signal to (monitor). Therefore, in the system shown in FIGS. 1 and 5, the CPU 15 inputs the color characteristics of the three devices and synthesizes a new function from the three conversion functions (first to third conversion functions) shown in FIG. If a preview image display device is connected, the preview of the visualized image can be easily obtained.

Although the color conversion in the above embodiment is performed by the circuit or the look-up table, it is needless to say that the present invention is not limited to this and can be executed by software.

The present invention may be applied to a system composed of a plurality of devices or an apparatus composed of one device. Further, it goes without saying that the present invention can be applied to the case where it is achieved by supplying a program to a system or an apparatus. Further, the instruction to output the color image signal output from the first color image processing apparatus in the present invention from the second color image processing apparatus may be a manual instruction or an instruction automatically generated from the apparatus. But good. Furthermore, the new conversion relationship described above may be generated immediately in response to the instruction, or the new conversion relationship may be generated after a predetermined time has elapsed.

[0048]

As described above, according to the present invention, in connection with the instruction to output the color image signal output from the first color image processing device from the second color image processing device, A color image signal conversion relationship between the color image processing device and the second color image processing device is newly created, the color image signal is converted from the first color image processing device according to the new conversion relationship, and the second Since the color image signal is output, it is possible to construct a system capable of flexibly absorbing a difference in color reproducibility between different devices with a simple instruction.

There is also an advantage that a more flexible system can be constructed because it is not necessary to predefine the conversion relationship between the first color image processing device and the second color image processing device.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an image processing system according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a detailed configuration of a color printer 14.

FIG. 3 is a flowchart showing a color conversion process.

FIG. 4 is a CIE1931-xy chromaticity diagram.

FIG. 5 is a block diagram showing a configuration of an image processing system according to a second embodiment.

FIG. 6 is a block diagram showing a configuration of a three-dimensional lookup table conversion circuit 51.

FIG. 7 is a diagram showing a relationship of color conversion in the preview system.

FIG. 8 is a diagram showing a procedure of color conversion according to a conventional example.

[Explanation of symbols]

 1 Display 2 Color Conversion Device 10 Color CRT Monitor 11 Frame Memory (RGB) 12 Matrix Conversion Circuit 13 Frame Memory (R'G'B ') 14 Color Printer 15 CPU 16 Memory 51 Three-dimensional Look Up Table (LUT) Conversion Circuit 63 Table memory 65 Interpolation circuit

Continuation of front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display location H04N 1/46 G06F 15/66 310 H04N 1/46 Z

Claims (8)

[Claims] 1. A first conversion relationship for converting a color image signal from a first color image processing device so as to be expressed by a color component in a predetermined common color space, and a color component signal in the predetermined common color space. Is set to a second conversion relationship for converting a color image signal to a second color processing device, and a color image signal output from the first color image processing device is output from the second color image processing device. Instructing to output, generate a conversion relation based on the first conversion relation and the second conversion relation in association with the instruction, and generate the conversion relation based on the generated conversion relation. A color image processing method comprising converting a color image signal from a color image processing device and outputting the converted color image signal to the second color image processing device. 2. A first setting means for setting a first conversion relationship for converting a color image signal from a first color image processing device so as to be expressed by a color component in a predetermined common color space, and the predetermined setting means. Second setting means for setting a second conversion relationship for converting a color component signal in a common color space into a color image signal for a second color processing device; and information representing the first and second conversion relationships. Storage means, instruction means for instructing to output the color image signal output from the first color image processing apparatus from the second color image processing apparatus, and with the instruction by the instruction means as a trigger, Based on the first conversion relationship and the second conversion relationship, the conversion relationship between the color image signals of the first color image processing device and the second color image processing device is newly set as a third conversion relationship. A first generation unit that generates the color image signal and a conversion unit that converts the color image signal from the first color image processing device based on the third conversion relationship to output the second color image signal. Characteristic color image processing device. 3. The predetermined common color space is CIE193.
The color image processing apparatus according to claim 2, wherein the color image processing apparatus is a color space defined by having, as an original stimulus, a vertex of a triangle circumscribing a spectrum locus in the 1-xy chromaticity diagram. 4. The color image processing apparatus according to claim 2, wherein each of the first, second, and third conversion relationships is a conversion function represented by a matrix. 5. The color image processing apparatus according to claim 2, wherein the first, second, and third conversion relationships are each represented by a look-up table. 6. The color image processing apparatus according to claim 2, wherein the first color image processing apparatus includes a scanner and a display, and the second color image processing apparatus includes a printer and a display. 7. A fourth conversion relationship for converting a color image signal output to a third color image processing device so as to be expressed by a color component in the predetermined common color space.
Setting means, based on the fourth conversion relationship and the first conversion relationship,
A fifth generation unit that newly generates a conversion relationship between the color image signals of the first color image processing device and the third color image processing device as a fifth conversion relationship; Based on the first color image processing device, further includes output means for converting the color image signal from the first color image processing device and outputting the converted image signal to the third color image processing device; 3. The color image processing apparatus according to claim 2, wherein the color image signal from the image processing apparatus is displayed on the third color image processing apparatus in advance before being output from the second color image processing apparatus. 8. The color image processing apparatus according to claim 7, wherein the third color image processing device is a color monitor.