JPH05122514A - Color image processing method - Google Patents

Abstract

PURPOSE:To execute exact color reproduction making much of an important color according to a masking method by automatically setting the important color corresponding to an input color image. CONSTITUTION:Image data R, G and B signals expressing a first color component are read in an image processor by scanning a source image 1 with a color scanner 2 and converted to color coordinate system color image signals. Then, a color slip having the nearest average value of calculated color coordinate system color image signal data is selected out of color slip data stored in a ROM 4. A weight is set to w1 concerning the selected color slip, and the other color slip is set to a weight w2 smaller than the weight w1 so as to decide a masking parameter. By using this masking matrix, the image data R, G and B signals are converted to C, M and Y signals and outputted to a recorder 5 as color print signals.

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 more particularly, to a first color image data representing a first color component of an input color image, and a second color component of the first image data by a masking method. Color conversion to the second image data
The present invention relates to a color image processing method that can be used in a color image output device such as a color copying machine that outputs a color image based on the second image data.

[0002]

2. Description of the Related Art For example, in a color copying machine, an input color original image is not faithfully copied to all the colors on average, but color reproduction of a specific color is emphasized based on the original image. There are times when you want to obtain a color copy image that was copied to.

However, conventionally, R, G, B signals (first image data) read by scanning a color original image are read.
Is converted into Y, M, C signals (second image data) corresponding to the printing ink by the color masking method and supplied to the recording section. As the color masking method, the color components R, The G and B signals are converted into C, M and Y signals by the operation using the first-order masking equation shown in the equation 1 or the second-order masking equation in which the second-order component term and the cross term component are taken into consideration. Techniques for doing so are known.

[0004]

[Equation 1]

Therefore, in order to particularly improve the color reproduction of the specific color, many color chips of the specific color are selected when determining the parameters of the masking matrix, and the sum E of the squared errors shown in Equation 2 is obtained. The coefficient terms a _{00 to} a ₂₂ may be determined so as to be the minimum.

[0006]

[Equation 2]

Here, C _i , M _i , and Y _i represent color component values when the i-th color chart is recorded, and c _i , m _i , and y _i read the i-th color chart with a color scanner. The color component values calculated by substituting the R, G, and B values in the above equation 1 into the above are shown.

However, in general, the important color is different for each input image. Therefore, in the above method, it is necessary to select the color chart for each input image and determine the parameters of the masking matrix. It was difficult to set the important color to.

As a countermeasure for this, in 1989, Image Electronics Society of Japan, Vol. 18, No. 1, "Color Masking (I)", the color patches of the important colors are not increased to determine the parameters of the masking matrix. Squared error weight w for each vote
A method has been proposed in which _i is given and a weight for a squared error of an important color is set large. Equation 3 shows an equation representing the sum of squared errors by this method.

[0010]

[Equation 3]

By adopting this conventional method and selectively increasing the weight for the important color, the same effect as when the number of color chips of the important color is increased can be obtained.

[0012]

However, according to the above-mentioned conventional method, the user has to set the important colors and weights in advance, and it is difficult to make the setting accurately for each input image. ..

The present invention has been made in view of the above problems, and an image in which an important color is automatically set according to an input color image and color reproduction is performed by emphasizing the important color by a masking method. It provides a processing method.

[0014]

According to the present invention, first image data representing a first color component of an input color image is converted into second image data representing a second color component by a masking method. In a color image output device that performs conversion and outputs a color image based on the second image data, first, an important color of the input color image is obtained based on the first image data. Next, based on the important color, a color chart is selected from a plurality of color chart data stored in advance in the apparatus body. Further, the weight for the selected color chip is set to w _1, and, for the other of said color chart is set to the weight w ₁ is smaller than the weight w _2, determines a masking parameter. Then, the first image data is converted into second image data based on the masking parameter.

[0015]

According to the above construction, a plurality of color chips stored in advance in the main body of the apparatus based on the important color obtained from the first image data representing the first color component of the input color image. A color chart is selected from the data, and the masking parameter for color-converting the first image data into the second image data representing the second color component is determined in consideration of the selected color chart. The important color for the input color image is automatically selected, and accurate color reproduction with the important color being emphasized is performed.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings showing an embodiment thereof.

FIG. 1 is a schematic block diagram of a color copying machine to which the image processing method of the present invention is applied. In the figure,
The image of the original image 1 is read for each pixel by the color scanner 2, and the read R, G, B signals (first image data) are transferred to the image processing device 3. The image processing device 3 uses the ROM 4 for the input R, G, B signals.
A masking process or the like is performed as will be described later based on the 125 color chart data and the like written in advance. Then, the processed Y, M, C signals (second image data) are output to the recording device 5, and the recording device 5 outputs the Y, M, C signals.
An image is recorded on the recording paper based on the signal.

Next, the image processing method of the present invention will be described with reference to the flowchart of FIG.

First, the original image 1 is scanned by the color scanner 2 to read the R, G, B signals, which are the first image data representing the first color component of the input color image, into the image processing device 3 ( S1), the read R, G, B signals are color spaces L ^* , a ^* , defined by CIE (International Commission on Illumination)
It is converted into a b ^* color coordinate system color image signal (S2). In step S2, the R, G, B signals are set to L ^* ,
The conversion into a ^* and b ^* signals is because the color image signal of this color coordinate system accurately expresses the color difference perceived by humans in the color space, so image processing can be performed in this color space. This is because the processing is most suitable for the human sense.

Then, in the next step, the average value of the L ^* , a ^* , b ^* signal data in all pixels of the original image is calculated (S3), and the process proceeds to the next step S4. This step S
3, the L ^* , a ^* , b ^* signal data of the important color of the original image is obtained.

In step S4, the average value of the L ^* , a ^* , b ^* signal data calculated in step S3 is the R value.
Of the 125 color chart data stored in OM4,
Select the closest color chart and proceed to the next step. In addition, this 1
The 25 color chips are set so that the Y, M, and C colors of the color copying machine can be output in 0 to 127 gradations.
The output gradation of the signal is 0, 30, 60, 90, 1 respectively.
125 color chips output from a color copier by combining signals with 20 gradations are used. And the RO
In M4, C, M, and Y signal data for the 125 color charts and the color chart measured by a color difference meter were obtained.
Five pieces of L ^* , a ^* , b ^* signal data and 125 pieces of R, G, B signal data read by the scanner are stored.

In step S5, a masking matrix is determined as described later, and the masking matrix is used to convert the first image data R, G, B signals of the original image 1 into the second image data C, M, Y. It is converted into a signal (S6). Then, the C, M and Y signals are output to the recording device 5 as a color print signal (S7).

Next, the masking matrix determination processing in step S5 will be described.

[0024] First, L ^* calculated in the step S3, a ^*, b ^* values and, in 125 pieces of color chips data stored in advance in the ROM4 L ^*, a ^*, 2 of the b ^* value The multiplication error is calculated, and the color chart data that minimizes the error is selected.

For the selected color chart, the weight w _i = 30 in the equation 3 is set, and for the other 124 color charts, w _i = 1 is set, and C _i , M _i , Y of the equation 3 is set. 125 of C that the stored in the ROM in the _i, M, and Y signal data, also c _i, m _i, y _i to said 125 stored in ROM4 the R, G, and B signal data The number 1
C, M, Y signal data calculated by substituting into In the present embodiment, since the number of color chart data is 125, q = 125 in the equation (3).

Then, the coefficient terms a _{00 to} a ₂₂ are calculated so that the sum E of the squared errors of the equation 3 is minimized, and the masking matrix is determined. Note that all of these processes are performed by the image processing device 3, and the result is output to the recording device 5.

In this way, since the first image data R, G, B signals of the original image are converted into the second image data C, M, Y signals using the masking matrix determined in this way, it differs for each original image. Important colors can be faithfully reproduced.

In the above embodiment, the case where the average value of the L ^* , a ^* , b ^* signal data for one original image is calculated and the important color is selected from the average value has been described. It is also possible to accumulate the ^* , a ^* , and b ^* signal data and select the important color from the weighted average value. As a result, the masking matrix can be determined in consideration of the usage status of the device.

Although the weight w _{i of the} important color is set to 30,
Other values may be used as long as they are larger than the weight w _i other than the important color. Note that the weight reproducibility of the important color is improved by making the weight w _i of the important color larger than the weight w _i other than the important color.

The case where the present invention is applied to a color copying machine has been described above, but the present invention is also applicable to a color image output device such as a color printer and a color display device.

[0031]

As described above, according to the present invention, the important color of the input color image is obtained based on the first image data,
A color chart is selected from a plurality of color chart data stored in advance in the apparatus main body based on the important color, and the first image data is obtained by using a masking matrix determined in consideration of the selected color chart. Since the image data is converted into the second image data, it is possible to automatically select the important color for the input color image and perform accurate color reproduction with the important color being emphasized.

Further, the user does not need to set the important color in advance for each input image, and the operability can be improved.

[Brief description of drawings]

FIG. 1 is a schematic block diagram of a color copying machine to which an image processing method of the present invention is applied.

FIG. 2 is a flowchart of an image processing method in a color copying machine to which an embodiment of the present invention is applied.

[Explanation of symbols]

 1 Original image 2 Color scanner 3 Image processing device 4 ROM 5 Recording device

Claims (3)

[Claims] 1. A first image data representing a first color component of an input color image is color-converted into a second image data representing a second color component by a masking method, and the second image data representing the second color component is color-converted. In a color image output device for outputting a color image based on image data, a step of obtaining an important color of the input color image based on the first image data; selecting a color chart from a plurality of color chips data stored, the weight for the selected color chip is set to w _1, and setting the weight w ₁ is smaller than the weight w ₂ for the other of said color chart And determining a masking parameter, and converting the first image data into second image data based on the masking parameter. Over image processing method. 2. The color image processing method according to claim 1, wherein in the step of obtaining the important color of the input color image, the average value of the image data is obtained for one input color image. 3. The step of obtaining the important color of the input color image is to accumulate image data of the input color image used in the apparatus main body and obtain a weighted average value thereof. Color image processing method.