JP3184232B2 - Image processing apparatus and method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus and method for performing color correction on input image information according to illumination light conditions input together with image information from an external device.

[0002]

2. Description of the Related Art In a conventional color printing apparatus, colorimetric color reproduction is generally used for color reproduction of an input color image to the printing apparatus. Colorimetric color reproduction refers to a case where the chromaticity of the colors of the original image and the reproduced image are equal and their relative luminances are also equal. In this case, since the spectral reflectances of those images are different, the images have the same condition. In this color reproduction method, it is sufficient that the colorimetric values X, Y, and Z (tristimulus values of object colors) obtained by colorimetry using a spectrophotometer or the like are equal between the original image and the reproduced image. This is an effective method under certain observation conditions.

[0003] The following describes what these observation conditions are. In color perception, as shown in FIG. 10, a light beam from a light source is incident on an object color, and the reflected light is incident on the human eye to produce color perception. This process will be described with reference to FIG. (A) is the spectral distribution S (λ) of the light source, (b) is the spectral reflectance distribution p (λ) of the object, and (c) is the distribution S of the reflected light.
(Λ) indicates p (λ).

The radiant energy shown in FIG. 11 (c) enters the human eye. The human eye has color matching functions x (λ), y (λ), z (λ) (FIG. 11 (d)). The incident light S (λ) p (λ) is x (λ),
Weighted by y (λ) and z (λ), and three-color separation is performed as shown in FIG. The integrated value is called a color stimulus value of the object color for the observer. When these are expressed by equations, the following equation (1)
become that way.

[0005]

(Equation 1)

Here, the integration range is a wavelength of 380 nm in the visible range.
From 780 nm. Further, the coefficient K in the equation (1) is a standardization coefficient shown in the equation (2).

[0007]

(Equation 2)

That is, the colorimetric values X, Y, and Z described above are expressed by the following equation (1).
Is calculated. As can be seen from equation (1), colorimetric color reproduction requires that colorimetric values X, Y, and Z under the same light source be matched. Therefore, the observation condition is that the original image and the reproduced image are observed under the same illumination.

[0009]

Since a reference illumination light source for color reproduction by a printing apparatus is uniquely determined,
When the print result is viewed under illumination other than the reference illumination light source, the color appearance may be significantly different.

An object of the present invention is to solve the above-mentioned problem, and an object of the present invention is to easily set a color correction suitable for an observation condition of an output image. Another object is to realize good color reproduction under the observation conditions of an output image.

[0011]

The present invention has the following configuration as one means for achieving the above object. An image processing method according to the present invention is an image processing method for performing color correction on image information input from an external device, and includes image light from the external device, and illumination light for observing the output image. Is input from the color correction conditions for performing the colorimetric color reproduction process corresponding to each of the plurality of pieces of illumination light information held in the memory, and the color corresponding to the information indicating the input illumination light is obtained. Selecting a correction condition, and performing color correction for realizing colorimetric color reproduction corresponding to illumination light when observing the output image on the input image information based on the selected color correction condition. And

An image processing apparatus according to the present invention is an image processing apparatus that performs color correction on image information input from an external device, and is used for observing image information and an output image from the external device. Input means for inputting information indicating the illumination light, and color correction conditions for performing a colorimetric color reproduction process corresponding to each of the plurality of pieces of illumination light information held in the memory. Selecting means for selecting a color correction condition in accordance with the information to be shown, and performing colorimetric color reproduction corresponding to illumination light when observing the output image on the input image information based on the selected color correction condition. The image processing apparatus is characterized by including a correction unit for performing color correction to be realized and a forming unit for forming a visible image on a recording medium based on the color-corrected image information.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a block diagram showing a circuit configuration of a printing apparatus according to one embodiment of the present invention. The printing apparatus according to the present embodiment includes a host computer 1 and a printing apparatus main body 2.

The host computer 1 sends print data, print commands, and the like to the printing apparatus main body 2 and causes the printing apparatus main body 2 to perform a printing process. The printing apparatus main body 2 includes a CPU 26a, a ROM,
26b and a microprocessor system including a RAM 26c. That is, the printing apparatus main body 2 is an interface 2 for exchanging data with the host computer 1.
1. A color reproduction processing selection table 22-1 used to select a color reproduction processing according to the reference illumination light is provided, and information such as an LUT (lookup table) for color reproduction processing is stored. A color information storage unit 22, a color reproduction processing unit 23 that actually performs color reproduction processing, and an operation panel 2 that can be used to set various parameters for controlling printing
4. Data bus 25, control unit 2 for controlling the entire device
6. A command analysis unit 27 for analyzing print data and print commands from the host computer 1, a pattern development unit 28 for developing color data such as characters and figures into memories for each of C, M, Y, and K colors; An output section 29 is provided for forming a permanent visible image of color data on paper by, for example, a color laser beam printer. Control unit 26
Includes a CPU 26a operated by a program,
ROM 26 which stores a program for operating 26a
b, a RAM 26c used as a work area of the program in the ROM 26b.

FIG. 2 shows an example of colorimetric color reproduction processing for performing processing so that color original image data becomes equal to the output result of the printing apparatus. Specifically, the original image, which is the luminance data of R, G, and B, is required to be output to the printing apparatus by C, M, and C.
An example of color reproduction processing for converting into Y and K density data is shown. In process 1, a density conversion process is performed in which R, G, and B values that are luminance information are subjected to LOG conversion and converted into C, M, and Y that are density information. In process 2, C,
Under color removal processing for extracting the value of K (Black) from the values of M and Y is performed. In process 3, masking processing is performed on the unnecessary absorption characteristics of the C, M, and Y toners or inks so as to perform appropriate color reproduction. In process 4, γ conversion processing for adjusting contrast and brightness according to the image is performed.

The above processing is performed in the color reproduction processing section 23 shown in FIG. FIG. 3 shows an example of a print command used when selecting a reference light for performing colorimetric color reproduction and outputting a color image by a printing apparatus. As shown in the figure, the reference illumination light selection command is the identification No. of the corresponding command. And an illumination light selection parameter. Here, the standard lights A, B and C are 19
In 1931, CIE (International Commission on Illumination) established D55, D65, D
75 is a standard light source for colorimetry determined by the CIE in 1964. As for a fluorescent lamp, an incandescent lamp, and an OHP light source, a commonly used light source is selected and assigned, or a light source having an average spectral distribution characteristic of a generally used light source is virtually assigned. It is also possible.

FIG. 4 shows a color reproduction processing selection table for selecting the color reproduction processing for each reference illumination light source described with reference to FIG. This table stores pointers to algorithms for performing optimal color reproduction processing for each reference illumination light source. Here, the optimal color reproduction processing refers to processing in which the color appearance of the input color image to the printing apparatus matches the color appearance of the output color image of the printing apparatus based on the colorimetric color reproduction processing method.

FIG. 5 shows the appearance of the operation panel 24 of FIG. As shown in the figure, the switch is composed of an LCD display unit and a switch. The switch on the right end is used to select a reference illumination light, select a color reproduction processing algorithm for each reference illumination light, and perform color printing. FIG. 6 shows an example of a print command used when a character is colored and output.
As shown in FIG.
o. , Print position, and data of the character to be printed. , R
It is composed of immediate values of GB luminance data.

FIGS. 7 and 8 are flowcharts for explaining the printing process of the present embodiment. In FIG. 7, the reference illumination light selection command (FIG. 3) and the color print command (FIG. 6) sent from the host computer 1 are processed.
The operation up to output of the color-printed characters is shown. In step S11, a reference illumination light selection command, a color print command, and pattern information including character information (character size and the like) transmitted from the host computer 1 are read, and the process proceeds to step S12 to analyze the command. In step S13, the illumination light selection parameter is extracted from the reference illumination light selection command, and the process proceeds to step S14, where a pointer is set at the head of the color reproduction process selection table, and the process proceeds to step S15.

In step S15, information corresponding to the extracted illumination light selection parameter (here, a pointer to the color reproduction algorithm, ie, when the parameter value is 3, the color reproduction algorithm for the standard light D65 is selected. ) Is extracted from the color reproduction processing selection table. In step S16, the R, G, and B luminance data read from the character color designation command are read by the color reproduction processing unit 23 in accordance with the selected color reproduction algorithm.
The data is converted into Y and K density data, and the flow advances to step S17.
In step S17, dot development is performed in the pattern development unit 28 based on the above-described density data of C, M, Y, and K and necessary character information, and the flow advances to step S18. In step S18, a permanent visible image of characters is formed on a sheet or the like based on the data developed in step S17, the sheet is discharged, and the process ends.

As described above, it is possible to analyze the reference illumination light command from the host computer 1, select a color reproduction processing algorithm corresponding to the reference illumination light, and perform color printing of characters based on the algorithm. . FIG. 9 shows that the color information immediately after step S16 is Y = 100%, M = 50%,
The print result of the character A when C = 25% and K = 0% is shown.

Since the printer of the output unit 29 of this embodiment uses a binary printer, the desired density is expressed by the dot density. FIG. 8 shows the operation of selecting the reference illumination light from the operation panel 24 of FIG. 1, processing the color print command (FIG. 6) transmitted from the host computer 1 and the like, and outputting the character color print. Have been.

In step S21, a reference illumination light selection mode is selected from a switch on the operation panel 24, and the flow advances to step S22. In step S22, the reference illumination light is selected on the panel, the reference illumination light selection parameter (FIG. 3) is read, and the flow advances to step S23. In step S23, a color print command (FIG. 6) and pattern information including character information (character size and the like) transmitted from the host computer 1 are read, and the flow advances to step S24 to analyze the command.

In step S25, a pointer is set at the head of the color reproduction processing selection table, and the flow advances to step S26. In step S26, information (here, a pointer to the color reproduction processing algorithm) corresponding to the illumination light selection parameter read from the operation of the operation panel 24 is extracted from the color reproduction processing selection table. Step S27
The processing from S29 to S29 is exactly the same as the processing from S16 to S18 in FIG.

Here also, the color information immediately after step S27 is Y
= 100%, M = 50%, C = 25%, K = 0%, the character "A" is printed as shown in FIG. As described above, the reference illumination light is selected from the operation panel 24,
It is possible to select a color reproduction processing algorithm corresponding to the reference illumination light and print characters based on the selected algorithm.

In the above-described embodiment, an example of color reproduction processing when RGB luminance data is input has been described. However, data formats of other color systems, such as L * a * b * and L * u * v
Even when data such as * and YIQ is input, only the method of color reproduction processing is changed, and the present invention is applicable. In the above-described embodiment, only the printing of characters has been described. However, the present invention can also be applied to color printing of figures, raster images, and the like.

Further, in the above-described embodiment, the reference illumination light is raised only for the one shown in FIG. 3, but it is needless to say that the present invention is not limited to these. The printer of the output device may be a color laser beam printer, a color dot printer, a color ink jet printer, a color thermal transfer printer, a bubble jet printer, or the like. The printer is not limited to a binary output printer, but may be a multi-value output printer.

The present invention may be applied to a system including a plurality of devices, may be applied to an apparatus including a single device, or may be applied to a system or an apparatus for supplying a program. It is needless to say that the present invention can be applied to the case where it is achieved.

[0029]

As described above, according to the present invention,
Since the color correction condition of the image information is selected based on the information indicating the illumination light when observing the output image input from the external device, the color correction suitable for the observation condition can be easily set. Furthermore, since the color correction conditions corresponding to each of the plurality of pieces of illumination light information are stored in the memory in advance, colorimetric color reproduction can be realized, and good color reproduction can be realized under observation conditions. .

[Brief description of the drawings]

FIG. 1 is a block diagram showing a circuit configuration of a printing apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating an example of colorimetric color reproduction processing for performing processing so that color original image data is equal to an output result of a printing apparatus.

FIG. 3 is a diagram illustrating an example of a print command used when an illumination light serving as a reference for performing colorimetric color reproduction is selected and a color image is output by a printing apparatus.

FIG. 4 is a diagram showing a color reproduction process selection table for selecting a color reproduction process for each reference illumination light source described in FIG.

FIG. 5 is a diagram showing an appearance of an operation panel 24 of FIG.

FIG. 6 is a diagram illustrating an example of a print command used when a character is colored and output.

FIG. 7 is a flowchart illustrating a printing process according to the present exemplary embodiment.

FIG. 8 is a flowchart illustrating a printing process according to the present exemplary embodiment.

FIG. 9 is a diagram illustrating an example of a character print result.

FIG. 10 is a diagram illustrating general human perception.

FIG. 11 is a diagram for explaining the principle of general color tristimulus value calculation.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Host computer 2 Printer main body 21 Interface 22 Color reproduction processing information storage part 23 Color reproduction processing part 24 Operation panel 25 Data bus 26 Control part 27 Command analysis part 28 Pattern development part 29 Output part

Claims (2)

(57) [Claims] 1. An image processing method for performing color correction on the image information inputted from an external device, image information from the external device, and information indicating the illumination light when observing the output image And input each of the multiple illumination light information stored in the memory.
Color correction conditions to perform the corresponding colorimetric color reproduction process
The color correction conditions according to the information indicating the input illumination light.
Based on the selected color correction condition, the input image information is added to the measurement corresponding to the illumination light when observing the output image.
An image processing method characterized by performing color correction for realizing chromatic color reproduction . 2. An image processing apparatus for performing color correction on image information input from an external device, comprising: image information from the external device; and information indicating illumination light when observing the output image. Input means for inputting, and each of a plurality of illumination light information held in the memory.
Color correction conditions to perform the corresponding colorimetric color reproduction process
The color correction conditions according to the information indicating the input illumination light.
Based on the selection means for selecting and the selected color correction conditions, based on the input image information, the measurement corresponding to the illumination light when observing the output image is performed.
An image processing apparatus, comprising: a correction unit for performing color correction for realizing color reproduction, and a forming unit for forming a visible image on a recording medium based on color-corrected image information.