JP3412699B2 - Image forming device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for obtaining a high quality color recorded image with good color reproducibility. In a conventional color image forming apparatus, a red signal (hereinafter, an R signal), a green signal (hereinafter, a G signal), and a blue signal (hereinafter, a B signal) are used as color input signals. In order to print these color input signals in color, they are converted into at least three signals of a C signal, an M signal, and a Y signal, or four signals obtained by adding a black signal (hereinafter, a K signal) thereto. In color input / output conversion represented by conversion from RGB signals to CMYK signals in this color image forming apparatus, linear masking and UCR (Un
der Color Removal (under color removal) to convert RGB signals to CMYK signals, or three color input values (RGB) to four color outputs (CMYK) in advance
Is constructed, and the output data is referred to from the value of the input data using the table.
CMYK from RGB signal by table data reference method
It has been proposed to perform a conversion to a signal. FIG. 6 shows an example of R using linear masking and UCR.
FIG. 2 is a schematic diagram of a processing system that performs color conversion from a GB signal to a CMYK signal. In FIG. 6, reference numeral 51 denotes a density value conversion unit, which converts a data value in order to print on a sheet from a reflectance to a density value. A masking processing unit 52 converts each data value of RGB into a color component CMYK in a printing apparatus. 53 is UC
The R processing unit performs undercolor removal and black printing. When three RGB signals are input as inputs to the processing system, the RGB reflectance signal data transmitted as data from a scanner or a host computer is converted into data that can be expressed on paper by the density value converter 51. Is converted to RGB density signal data. In the linear masking processing unit 52,
The Dr, Dg, and Db signals of the RGB signals converted to the density values are converted into CMY signals by calculation. The CMY signal is reduced by the UCR unit 53 to remove the undercolor by reducing the signal level of the CMY signal, black-printed by adding the K signal, and changed to the CMYK signal. One pass of the processing system processes color data of one pixel. FIG. 7 is a schematic diagram of a table data reference system. Reference numeral 54 denotes a table reference unit which performs processing for extracting data from table data in order to output CMYK data corresponding to input RGB data. Yes,
Reference numeral 55 denotes a table data storage unit that stores table data. The table data reference unit 54 refers to the CMYK signal from the table data storage unit 55 and outputs the CMYK signal based on the values of the RGB signals input to the processing system. In this processing system, color data of one pixel is processed in one pass. As a method of creating table data in the table data reference method, first, a color recording signal value for a color input signal (for example, an RGB signal) is obtained by a simulation using linear masking and UCR.
(CMYK signal value) is obtained to form table data. In this method, an output corresponding to an input of the processing system in FIG. 7 is converted into table data. Further, the color input signal and the color display characteristics of the color image forming apparatus are determined based on a standard for some colors (color system).
And a method of constructing a table by performing a combination suitable for associating as a color (equal color) that can be approximated most closely in the association as one table data for all the color input signals. There is also. FIG. 8 uses a color printer or a color copy as an image forming apparatus, and uses a color reference color system as a color reference color system. [0007] In FIG. 8, reference numeral 56 denotes an RGB data color standardization processing unit which converts RGB data into L * a * b * data used as data in a color reference space. 57
Denotes a color image forming apparatus, and 58 denotes a color analysis processing unit that analyzes the color reproduction of the color image forming apparatus 57. Reference numeral 59 denotes a CMYK data color standardization processing unit which converts CMYK data into L * a * b * data. 60 is a color reference space replacement processing unit,
Two L * a * b * data from GB and CMYK are placed in the same color space for comparison. Reference numeral 61 denotes a minimum color difference detection unit which detects a combination of two L * a * b * data having the minimum color difference among the data compared in the color reference space replacement processing unit 60. 62 is a table data processing unit,
The result detected by the minimum color difference detection unit 61 is converted into table data. Here, the RGB input signal is converted into L * a * b * data by the RGB data color standardization processing unit 56. On the other hand, a color that can be expressed by the color analysis processing unit 58 is analyzed from various characteristics (color material, mechanical, electrical, etc.) of the color image forming apparatus 57, and one CMYK signal is converted into CMYK data color reference based on the result. The processing unit 59 sets the data as L * a * b * data. The two L * a * b * data are compared in the reference color space such as the L * a * b * color space in the color reference space replacement processing unit 60, and the minimum color difference detection unit 61 detects the minimum color difference. The data is detected, and the combination of the RGB signals and the CMYK signals of the most equal colors is written into the table as one table data via the table data processing unit 62 as the table data. [0008] In the above prior art, the method using the linear masking and the UCR shown in FIGS. 6 and 7 has a problem in terms of color reproduction accuracy, and the In the method of creating a table by linking the signal and the color reproduction characteristics of the color image forming apparatus using some color standards, the color reproduction table method using one color standard also requires the number of data on the input side and the output side to be mapped. Is not sufficient, there is a limit in color reproduction accuracy. The present invention solves the above-mentioned conventional problems. In the construction of a color conversion table, a color space for performing color approximation is divided into a plurality of color space regions, and a different color approximation is provided for each color space region. It is an object of the present invention to provide a color image forming apparatus having good color reproducibility by introducing the above method and performing input and output color matching. [0010] In order to achieve the above object, an image forming apparatus according to the present invention provides a single color or plural color data.
Color input signal having a cyan signal which is a color recording signal.
Signal, magenta signal, and yellow signal.
Conversion means for converting the color input signal by the conversion means.
Stores the conversion table used when converting to color recording signals
The combination storage means,
Is a color space in which lightness, hue, and saturation for color approximation can be recognized.
Color difference with smaller color difference than lightness difference
Priority conversion table and color difference with lightness difference smaller than chromaticity difference
And a brightness difference priority conversion table having
The conversion means clarifies a color input signal and a color recording signal.
When developed in a color space where the degree, hue, and saturation can be perceived,
Saturation of color input signal and color recording signal is less than specified value
In the case of, the saturation is determined using the chromaticity difference priority conversion table.
If the value is more than the specified value, use the brightness difference priority conversion table
The conversion is performed . According to the present invention, the color input signal (represented by an RGB signal) in which the lightness is accurately reproduced in a low-saturation color and the hue and the saturation in a high-saturation color are improved by the above configuration. And a color conversion table for performing input / output color conversion of color recording signals (CMYK signals) and color recording signals (CMYK signals). Can be provided. An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of an image forming apparatus according to an embodiment of the present invention. In FIG. 1, reference numeral 11 denotes an image forming apparatus, and 12 denotes a host computer which sends image data and the like to the image forming apparatus.
A data transmission cable 13 connects the image forming apparatus 11 and the host computer 12. Reference numeral 15 denotes a data analysis unit which converts the data sent from the host computer 12 into data that can be subjected to image processing, and passes the data to an image processing unit 16. The image processing unit 16 converts the data passed from the data analysis unit 15 so that the color is reproduced by a color recording signal (CMYK) used as a printing color in the image recording unit 17, and sends the data to the image recording unit. Reference numeral 17 denotes an image recording unit which performs color recording on paper according to the CMYK data sent from the image processing unit 16. Reference numeral 18 denotes an image output unit which outputs a color image formed in the image recording unit 17 through a process such as fixing. In the present embodiment, the color input signal is generated in the host computer 12, but there is no problem if this is a scanner that reads a color original or the like. Data sent from the host computer 12 is RGB
A signal, XYZ, L * a * b *, etc. can also be used. The data input to the image forming apparatus 11 is analyzed by the data analysis unit 15 to determine the type of data. In the image recording unit 17, when the image recording device is a laser drive type, a laser beam is emitted from the laser scan unit to the polygon mirror based on the data in the color image memory, and the laser beam reflected from the polygon mirror is emitted. Irradiation is performed on the photoconductor to form a latent image on the photoconductor. According to the latent image, four developing units, a cyan developing unit, a magenta developing unit, a yellow developing unit, and a black developing unit, deposit color toner and transfer an image on a single-color photoconductor, thereby superimposing the images. After the color toner is attached to the paper and fixed, the image output unit 18 outputs a color print. This image recording device uses an LED (light e
It can be replaced by a driving type or an inkjet method. FIG. 2 is a schematic diagram of an image processing section including a color conversion table constituted by an image forming apparatus according to an embodiment of the present invention. The analysis data from the data analysis unit 15 of the image forming apparatus 11 in FIG.
Is input to input data 20 of color image data such as RGB, XYZ, HSV, etc., and a color conversion table selecting unit 21 determines which table to select from the table data registered as a conversion table. decide. The HSV here is the hue (Hu) of the Munsell color space which is a color space based on the Munsell color chart published in 1905.
e), saturation (Saturation), and lightness (Value). When the table is determined by the color conversion table selecting unit 21, the table determined as the current table is defined by the color conversion table adopting unit 22, and the process proceeds to the color conversion process. RGB in the color conversion table adoption unit 22
→ CMYK indicates a table for converting RGB color image data into CMYK color image data. Before and after this conversion, the format of the data expressing the color is different, but if the input and output data is replaced with the same data format when configuring the color conversion table and approximated on the same coordinates and linked, this conversion will be performed. In, the data is stored in color and the data is transmitted. In the color conversion of the color conversion processing unit 23, the input data is color-converted using the selected current conversion table. The color-converted data is stored in C by the writing process 24 of the image memory.
Data is written to each of the MYK color image memories, and the data is held. The written color data is output by the color memory data output unit 25 to the image recording unit 18 for color recording. The color conversion table used in the color conversion table adopting section 22 shown in FIG. 2 is constructed by making a table as shown in the conceptual diagram of FIG. The data conversion processing unit A26 in FIG. 3 performs an RGB → L * a * b * conversion process on the input RGB signal to convert it into L * a * b * data. Here, in order to convert RGB into L * a * b *, first, by using (Equation 1) to (Equation 3), RGB is first used.
To XYZ. X = 0.6067R + 0.1736G + 0.2001B (2) Y = 0.2988R + 0.5868G + 0.1144B (3) Z = 0.0661G + 1.1150B From the XYZ, (4) ) To (Equation 6), L * a *
b * is obtained, and the conversion from RGB to L * a * b * is completed. [Equation 4] [Equation 5] [Equation 6] Here, Xn, Yn, and Zn are tristimulus values of the CIE standard color system on the perfect diffusion surface. On the other hand, based on various characteristics (color material, mechanical, electrical, etc.) of the color image forming apparatus (printing apparatus) 27, the color analysis processing section 28
Analyzes the color range that can be reproduced on paper by a color printing apparatus (reproducible colors and the number of colors, a method for reproduction, and the like). The color analysis processing unit 28 transfers the CMYK data that can be expressed in the color image forming apparatus 27 to the data conversion processing unit B29. In the data conversion processing unit B29, the color analysis processing unit
CMYK data passed from 28 is converted to CMYK → L * a * b
* Color space data is converted to L * a * b * data.
The L * a * b * data obtained by the data conversion processing of the data conversion processing unit A26 and the data conversion processing unit B29 is expanded into the L * a * b * color space by the expansion processing unit 30 for developing into the reference color space. Reference numeral 31 denotes a color space area division processing unit that divides the color space area of the developed L * a * b * data and changes the color approximation method appropriate for each of the divided areas. In the color space area division processing unit 31, L * a * b *
From the center of the color space A process of dividing the color space 33 into two color spaces is performed. 34 is a table data search decision processing unit,
The data combination of the CMYK output with respect to the B input is compared and searched to determine the combination of the table data. The table data search determination processing unit 34 uses the color difference derivation formulas with different weights in the two divided color spaces to minimize the input / output color difference according to the meaning of each divided color space. Find out the combination. (Equation 7) is L * a
From the center of the * b * color space [0026] Taking a single combination of color conversion table having a small color difference chromaticity difference from. In the color space using (Equation 8), since the lightness difference is weighted, [0028] Taking a single combination of color conversion table having a small color difference lightness difference from. The color gamut of a color recording apparatus is relatively widely distributed in the lightness direction in a low-saturation color space, and the color gamut is not extremely widely distributed in the lightness direction in a high-saturation color space. Therefore, in the present method, it can be said that the color difference is obtained based on the characteristics of the two divided color spaces, and an optimal combination of the color conversion tables is derived. (Equation 7) (Equation 8) The derived combination is adopted like the minimum color difference combination 35 to make one table data. Reference numeral 36 denotes a table data processing unit which registers, as table data, data adopted to be table data. Since this process is performed for all the color input data, the conversion to table data is repeated for another input value. [Ex. 5] Is present in the L * a * b * color space, the color difference ΔE at that time is from (Equation 9) to (Equation 11) to (Equation 12). Equation 9 [Mathematical formula-see original document] [Mathematical formula-see original document] [Mathematical formula-see original document] This ΔE is used to determine the color difference shown in FIG. The smaller the ΔE, the smaller the color difference and the closer the color. FIG. 5 is an image of the color conversion table. The table has three inputs, RGB,
If it is assumed that each side of the three-dimensional cube is an image 37 of a color conversion table, C
The small cube of the MYK table data 38 becomes the data of the color recording signal CMYK and becomes the actual value. In the embodiment of the present invention, such a cube is defined as XYZ → CMYK or H
It has several conversions, such as SV → CMYK, and changes the table according to the type of input data. As is apparent from the above embodiment, according to the present invention, lightness is accurately reproduced for low-saturation colors, and reproduction of hue and saturation is improved for high-saturation colors. As a whole, the preferred color reproduction of the user becomes possible, and there is an effect that an image forming apparatus corresponding to the color reproduction of the input of many color image input devices can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a configuration diagram of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a schematic diagram of an image processing unit according to an embodiment of the present invention. FIG. 3 is a conceptual diagram of creating a color conversion table. FIG. 4 is a conceptual diagram of a method for obtaining a color difference. FIG. 5 is an example of a conceptual diagram of a color conversion table. FIG. 6 is a schematic diagram of a conventional conversion processing system from RGB signals to CMYK signals. FIG. 7 is a schematic diagram of a conventional table data reference method. FIG. 8 is a conceptual diagram of creating a color conversion table of a conventional general color image forming apparatus. [Description of Signs] 11 ... Image Forming Apparatus, 12 ... Host Computer, 13 ...
Data transmission cable, 15 Data analysis unit, 16 Image processing unit, 17 Image recording unit, 18 Image output unit, 20 Input data, 21 Color conversion table selection unit, 22 Color conversion table adoption unit, 23 ... color conversion processing unit, 24 ... writing processing to image memory, 25 ... color memory data output unit, 26 ... data conversion processing unit A, 27, 57 ... color image forming apparatus, 28, 58 ... color analysis processing unit, 29 ... data conversion processing unit B, 30 ... expansion processing unit to reference color space, 31 ... color space area division processing unit, 32 ... color space with saturation within 20,
33: color space with saturation of 20 or more, 34: table data search decision processing unit, 35: combination of minimum color differences, 36: table data processing unit, 37: image of color conversion table, 38: CMYK table data, 51 ... Density value conversion unit, 52 ... Mask processing unit, 53 ... UCR processing unit
54: table reference unit, 55: table data storage unit,
56 ... RGB data color standardization processing unit, 59 ... CMYK data color standardization processing unit, 60 ... Color standard space replacement processing unit, 61
... Minimum color difference detection unit, 62 ... Table data conversion processing unit.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-108865 (JP, A) JP-A-4-156779 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04N 1/46-1/48 H04N 1/52 H04N 1/60

Claims (1)

(57) [Claims 1 Cyan signal is a color recording signal color input signal having a single color or multiple color data, magenta Shin
No., conversion means for converting at least three yellow signals, the color input signal to a color recording signal by said converting means converting
And a combination storage means for storing a conversion table used for performing the color conversion , wherein the combination storage means performs lightness, hue, and saturation for performing color approximation.
Color difference is smaller than lightness difference in color space
Chromaticity difference priority conversion table with chrominance
A lightness difference priority conversion table having a color difference with a small difference
The conversion means stores the color input signal and the color recording signal.
When developed in a color space where the degree, hue, and saturation can be perceived,
Saturation of color input signal and color recording signal is less than specified value
In the case of, the saturation is determined using the chromaticity difference priority conversion table.
If the value is more than the specified value, use the brightness difference priority conversion table
An image forming apparatus that performs conversion .