JPH06268855A - Color image forming device - Google Patents

Abstract

PURPOSE:To improve the color reproducibility by combining a color input signal with only color recording signals of a hue within a limited range, selecting colors close to the input color and combining them and converting the result into a color recording signal (CMYK) so as to eliminate deviation in the hue. CONSTITUTION:L*a*b*(SIGMA*) data converted from RGB signals and CMYK signals from a color printer 26 analyzed by a color analysis section 27 at color space conversion sections 25, 28 are set to a SIGMA* color space 29, in which the hue is limited. Thus, a predetermined hue angle 32 including a SIGMA* value 31 depending on the RGB signals is set onto an a*b* plane and a color recording signal 34 is arranged in a SIGMA* color space area 33 in which the angle 32 is spread in the L* direction. A magnification section 35 magnifying a circumference of a color input signal in the area 33 expands the value 31 in the area 33 where the angle 32 is limited to obtain a SIGMA* value 36 with least color difference as table data 37. Thus, the input signal is converted into the CMYK signal by using the data 37 to eliminate color slurring thereby improving the color reproducibility.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus for forming a color recorded image having high quality and good color reproducibility.

[0002]

2. Description of the Related Art In a conventional color image forming apparatus, a red signal (R signal), a green signal (G signal), and a blue signal (B signal) are used as color input signals, and these color input signals are printed in color. Therefore, it is converted into at least three signals of a cyan signal (C signal), a magenta signal (M signal), and a yellow signal (Y signal), or four signals obtained by adding a black signal (K signal) thereto. C from RGB signals in this color image forming apparatus
In color input / output conversion represented by conversion to MYK signals, linear masking and UCR (Under Col) are used.
or Removal (under color removal) is used to convert RGB signals to CMYK signals, and a table for outputting ternary color input values (RGB signals) to four-value color output values (CMYK signals) in advance is provided. Configured
Using the table, refer to the value of the output data from the value of the input data, R by the table data reference method
Conversion from GB signals to CMYK signals has been proposed.

FIG. 7 is a schematic diagram of a processing system for performing color conversion from RGB signals to CMYK signals using linear masking and UCR. When an RGB signal is input as an input of the processing system, a density for expressing on a paper the RGB signal, which is the reflectance signal data sent as data from the scanner or the host computer in the reflectance-to-density conversion unit 1. The signal data is converted into Dr, Dg, and Db signals. In the linear masking processing unit 2, Dr, Dg, converted into density values,
The Db signal is converted into a cmy signal by calculation. This c
The UCR unit 3 reduces the level of the my signal to remove the undercolor of the my signal, adds the K signal, and converts the my signal into the CMYK signal. Color data for one pixel is processed in one pass through this processing system.

FIG. 8 is a schematic diagram of the table data reference system. Based on the values of the RGB signals input to the processing system, the table data reference unit 4 stores C data from the table data storage unit 5.
The MYK signal is referenced and the CMYK signal is output. Also in this processing system, color data of one pixel is processed by one pass.

As a method of creating table data in the table data reference method, first, a color recording signal value (CMYK signal value) for a color input signal (for example, RGB signal) is obtained by simulation using linear masking and UCR. There is a way to organize the table data. In this method, the output corresponding to the 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 linked by a reference (color system) relating to some color, and the color is approximated to the most similar color (color matching). There is also a method of forming a table by setting one table data as a combination suitable for addition and performing this for all color input signals.

In FIG. 9, a color printer or a color copier is used as a color image forming apparatus, and L ^* a ^* is used as a color system ^.
It is a conceptual diagram when a b ^* color space is used. R input
The GB signal is converted into L ^* a ^* b ^* data by the RGB → L ^* a ^* b ^* color space conversion unit 6. On the other hand, a color that can be expressed by the color analysis unit 8 is analyzed from various characteristics of the color printing device 7 (coloring material, mechanical, electrical, etc.), and one CMYK signal is used as a result, CMYK → L ^* a ^* b. ^*
The color space conversion unit 9 converts the data into L ^* a ^* b ^* data. These two L ^* a ^* b ^* data are placed in the L ^* a ^* b ^* color space 10, and the table data creation unit 11 checks the degree of closeness of the colors to combine the most equal color RGB signal and CMYK signal. Is written in the table 12 as one table data, and the RGB signal is converted into the CMYK signal by the table 12.

[0008]

In the above-mentioned conventional technique, the method using linear masking and UCR shown in FIGS. 7 and 8 has a problem in terms of color representation in terms of accuracy, and a color input signal and a color image are used. Even in the method of creating a table by connecting the color display characteristics of the forming device using some kind of color standard, there is room for consideration on how to use a scale of color approximation that connects input and output in the color standard when creating the table. .

Therefore, the present invention has been made to solve the above problems, and it is an object of the present invention to provide a color image forming apparatus having a small hue shift and good color reproducibility in consideration of human visual characteristics. To aim.

[0010]

SUMMARY OF THE INVENTION According to the present invention, in order to select an optimum combination for a color formed from a color input signal from among combinations of color recording signals having respective levels of respective colors, the characteristics of the color input signal are selected. From the hue determined by the above, only a color recording signal having a hue within a certain limit range is selected as a combination selection range, and a selecting means for selecting a color recording signal, and a hue, a luminance, and a saturation of the color input signal and the color recording signal can be recognized. The color space color system has a color difference determining means for determining the closeness of colors, and a selecting means and a color difference determining means for selecting a combination of data for color recording a color closest to a color formed from a color input signal. Means for selecting and storing the color input signal having a single color or a plurality of color data by using the storage means; Data signal is obtained by a color image forming apparatus and means for converting the at least three signal yellow signals.

[0011]

According to the present invention, with the above-described structure, a color input signal (C represented by an RGB signal) having a visually small hue shift can be obtained.
A color conversion table for a signal other than the MYK signal) and a color recording signal (CMYK signal) can be configured.

[0012]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of a color image forming apparatus according to an embodiment of the present invention. In the color image forming apparatus 13, the data analysis unit 16 analyzes the data 15 sent from the host computer 14, and the image processing unit 1
The color input signal data (RGB signal data, etc.) input at 7 is converted into color recording signal data (CMYK signal data) for printing on paper to develop a color image. The image recording section 18 forms a color recorded image by the color recording signal data and sends the color image to the image output section 19. In the present embodiment, the color input signal is generated by the host computer 14, but this may be a scanner that reads a color original or the like.

The data 15 may be RGB signals, XYZ, L ^* a ^* b ^*, or the like.
The data input to the color image forming apparatus 13 is analyzed by the data analysis unit 16 to determine which format the data is in, and then sent to the image processing unit 17 where color conversion is performed.
Each color is converted into a color image having four colors of CMYK with 256 gradations per pixel, and each color is stored in the color image memory. After the color conversion is completed, the data in the color image memory is output to the image recording unit 18.

In the image recording unit 18, when the image recording apparatus is a laser drive type, laser light is emitted from the laser scanning unit to the polygon mirror and reflected from the polygon mirror based on the data in the color image memory. A laser beam is applied to the photoconductor to form a latent image on the photoconductor. In accordance with the latent image, four developing devices, a cyan developing device, a magenta developing device, a yellow developing device, and a black developing device, adhere color toner, and the image on the photoconductor to which the color toner adheres is transferred to the intermediate transfer member. Then, the color toner is transferred from the intermediate transfer member onto the paper and then fixed, and the color printed paper is output from the image output unit 19. This image recording device is
It is also possible to replace it with an ED drive type or an inkjet type.

FIG. 2 is a schematic diagram of the image processing unit 17 including the color conversion table of the color image forming apparatus according to the embodiment of the present invention, and FIG. 3 is the image processing of the color image forming apparatus according to the embodiment of the present invention. It is a flowchart of a part.
First, referring to FIGS. 2 and 3, the color image forming apparatus 13
The data analysis unit 16 (see FIG. 1) analyzes the data type (step S1), and the analyzed data is sent to the image input unit 20 of the image processing unit 17 as RGB, XYZ, HVC signals (19).
The hue (Hue) and lightness (Value) of the Munsell color space, which is a color space based on the Munsell color chart announced in 2005.
e), chroma (Chroma) signals, etc., and sent as color image data, and a table for color conversion is selected by the table selection unit 21 according to the type of the color image data (step S2). Using the selected table, the color image data is color-converted by the color conversion unit 22 into CMYK signals (step S3) and output (step S4), and the color image memory 23 is divided into four colors of CMYK signals. Is written in (step S5). The color image memory 23 for which writing of data has been completed is rasterized for output to the image recording unit 18 and output from the data output unit 24 (step S6).

The color conversion table used in the CMYK color conversion unit 22 of FIG. 2 is constructed by tabulating the color conversion table as shown in the conceptual diagram of FIG.
The RGB signal is converted from the RGB → L ^* a ^* b ^* color space conversion unit 25.
Is converted into L ^* a ^* b ^* data by. Where R
In order to convert the GB signal into L ^* a ^* b ^* data, the RGB signal is first converted into XYZ data by the following equation.

X = 0.06067R + 0.1736G + 0.2001B Y = 0.988R + 0.5868G + 0.1144B Z = 0.0661G + 1.1150B From this XYZ data, L ^* a ^* b ^* data is obtained by the following equation, and RGB → L Complete the ^* a ^* b ^* conversion.

L ^* = 116 (Y / Yn) ¹ / 3−16 a ^* = 500 {(X / Xn) ¹ / 3− (Y / Yn) ^1/3 } b ^* = 200 {(Y / Yn) ¹ / 3- (Z / Zn) ^1/3 } Here, Xn, Yn, and Zn are tristimulus values of the CIE standard color system in the perfect diffusion diagram.

On the other hand, from the various characteristics (coloring material, mechanical, electrical, etc.) of the color printing device 26, a color that can be expressed by the color analyzing section 27 is analyzed, and one CMY is obtained from the analysis result.
The K signal is converted to L by the CMYK → L ^* a ^* b ^* color space conversion unit 28.
^{Use *} a ^* b ^* data. The two L ^* a ^* b ^* data from the RGB → L ^* a ^* b ^* color space conversion unit 25 and the CMYK → L ^* a ^* b ^* color space conversion unit 28 are converted into the L ^* a ^* b ^* color space 29. The L ^* a ^* b ^* value is 3 determined by the color input signal (RGB signal) in order to narrow down the hue 30.
A certain constant hue angle 32 including 1 is set on the a ^* b ^* plane, and the color recording signal 34 is arranged in the L ^* a ^* b ^* color space area 33 in which the hue angle 32 is constant and spreads in the L ^* direction. This L
^The enlargement unit 35 is an enlargement of the periphery of the color input signal in the ^* a ^* b ^* color space area 33, and the L ^* a ^* b ^* value 31 determined by the color input signal is L ^* with the hue angle 32 limited ^.
When developed in the a ^* b ^* color space area 33, the L ^* a ^* b ^* value 36 with the smallest color difference is adopted as one table data 37 and is converted into table data. Since this processing is performed for all color input data, it is repeated to make table data.

FIG. 5 is a conceptual diagram of a method for obtaining a color difference between two colors C1 (L ^* 1, a ^* 1, b).
^* 1) and C2 (L ^* 2, a ^* 2, b ^* 2) are L ^* a ^* b
^* If it exists in the color space, the color difference ΔE at that time is as follows.

ΔL ^* = L ^* 1-L ^* 2 Δa ^* = a ^* 1-a ^* 2 Δb ^* = b ^* 1-b ^* 2 ΔE = ΔL ^* + Δa ^* + Δb ^* L ^* a ^* b ^{* in} FIG. When obtaining the value 36, this ΔE
To use. The smaller this ΔE, the smaller the color difference and the closer the colors.

FIG. 6 is an image of the color conversion table used in the color conversion unit 22 of FIG. The table has three inputs corresponding to RGB signals, and assuming that each side is a side of a three-dimensional cube, it becomes as shown in FIG. 6, and a small cube 41 forming this cube is a CMYK color recording signal 34. It becomes data. In the embodiment of the present invention, such a cube is used as XYZ → CMYK or HV.
There are several conversions such as C → CMYK, and the table is changed according to the type of input data.

[0023]

As is apparent from the above description, according to the present invention, it is possible to accurately perform color reproduction without hue shift, and a color image corresponding to the color reproduction of the input of many color image input devices. A forming device can be provided.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a color image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic diagram of an image processing unit including a color conversion table of a color image forming apparatus according to an embodiment of the present invention.

FIG. 3 is a flowchart of an image processing unit of the color image forming apparatus according to the embodiment of the present invention.

FIG. 4 is a conceptual diagram of creating a color conversion table of a color image forming apparatus according to an embodiment of the present invention.

FIG. 5 is a conceptual diagram of how to determine a color difference between two colors in a color image forming apparatus according to an embodiment of the present invention.

FIG. 6 is an image diagram of a color conversion table used in the color conversion unit shown in FIG. 2 of the color image forming apparatus according to the embodiment of the present invention.

FIG. 7 shows C from RGB signals of a conventional color image forming apparatus.
Schematic of processing system for color conversion to MYK signals

FIG. 8 is a schematic diagram of a table data reference method of a conventional color image forming apparatus.

FIG. 9 shows L ^* as a color system of a conventional color image forming apparatus ^.
Conceptual diagram when using a ^* b ^* color space

[Explanation of symbols]

16 data analysis unit 17 image processing unit 18 image recording unit 19 image output unit 25 RGB → L ^* a ^* b ^* color space conversion unit 27 color analysis unit 28 CMYK → L ^* a ^* b ^* color space conversion unit 29 L ^* a ^* b ^* color space

Claims (1)

[Claims] 1. In order to select an optimum combination for a color formed from a color input signal having a single color or a plurality of color data from a combination of color recording signals consisting of a cyan signal, a magenta signal and a yellow signal, From the hue determined by the characteristics of the input signal, only a color recording signal having a hue within a certain limit range is selected as a combination selection range, and selecting means for selecting the color recording signal, and the color input signal and the color recording signal are hue, luminance, and saturation. In a color space of a color space that can be recognized by a color difference determination unit that determines the closeness of colors, and the data combination for color recording the color closest to the color formed from the color input signal is described above. Storage means for selecting and storing by the selection means and the color difference determination means, and means for converting a color input signal into a color recording signal using the storage means Color image forming apparatus characterized by comprising a.