JP3247418B2 - Image processing 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 method, and more particularly to an image processing method suitable for a digital color copying machine or the like.

[0002]

2. Description of the Related Art Conventionally, C (cyan), M (magenta),
In a color copying machine that forms a full-color image using four-color toners of Y (yellow) and Bk (black), a theoretical signal obtained by calculation from an input light amount signal is converted into an actual toner color absorption characteristic. In order to convert the recording signal into a recording signal in consideration of the above, a masking operation is performed.

Although the actual absorption characteristic is linear, the calculation is performed by the following approximate expression (1) for the sake of convenience. That is,

[0004]

(Equation 1) Here, Bk0 = min (C0, M0, Y0).

[0005]

In the above conventional example,
Since the masking equation (1) is an approximate expression, the colors of the input and output may differ depending on the input image. A masking coefficient such that the colors match for all colors is a very difficult condition as long as it is a quadratic approximation.

The present invention has been made in view of the above-mentioned drawbacks of the conventional example, and has as its object to provide an image processing method for improving the reproducibility of more colors. In addition, the color
Pseudo-results in the output image
An object is to prevent occurrence of a similar contour.

[0007]

Means for Solving the Problems The above-mentioned problems are solved,
According to the image processing method of the present invention for achieving the object, color image data is input, and the color image data is determined to belong to any of a plurality of color regions including a white region and a black region, An image processing method for selecting a color processing condition according to the determination result, and performing color processing on the color image data using the selected color processing condition,
For an area of a color where the change of the color image data is almost constant, it is prohibited to select the color processing condition according to the determination result, and when the color image data changes discontinuously,
A color processing condition is selected according to the determination result.

[0008]

According to this configuration, the input color image data is converted into any of a plurality of color regions including a white region and a black region.
The color processing is performed according to the color processing conditions selected according to the result of the determination .
An image more faithful to the original can be obtained. Also,
In the configuration, the color image data is substantially constant.
If it is detected that the color area is
Switching of color processing conditions according to the results
If the data changes discontinuously, select one of the above color areas
The color processing condition is selected according to the result of the determination as to whether or not the color processing condition belongs to.
For this reason, the color processing condition changes due to a minute color difference.
This prevents a false contour that occurs due to this.

[0009]

Embodiments of the present invention will be described below in detail with reference to the drawings.

In the following embodiments, a color copying machine will be described as an example, but it goes without saying that the present invention can be applied to various other apparatuses. <First Embodiment> [Processing Flow] FIG. 1 is a block diagram showing a configuration of an image processing apparatus of a color copying machine according to a first embodiment of the present invention.

In the figure, 101 is a CCD, 102 is a light amount-density converter (indicated by "LOG" in the figure), 103 is a UCR
/ Masking circuit; 104, a hue determination circuit; 105, a hue signal; 106, a filtering unit; 107, a gamma correction unit for correcting printer characteristics.

Next, the operation of the above configuration will be described.

R, G, B3 input from the CCD 101
The color light quantity signal is converted into three color density signals C, M, and Y in a light quantity-density conversion unit 102. At the same time, R, G, B
Is input to a hue determination circuit 104, and a hue signal 105 indicating which space the input signal belongs to when the color space is divided into eight is output. Density signal C, M, Y, hue signal 1
05 enters the UCR / masking circuit 103 and the recording color 1
The image signals for the colors are calculated, and are filtered.
6. The signal is output to the printer unit through the γ correction unit 107.

FIG. 2 is a block diagram showing the configuration of the UCR / masking circuit 103 according to this embodiment. In the figure, 201 is a coefficient RAM, 202 is a minimum value detection circuit, 2
03 to 214 are multipliers, and 215 to 221 are adders. Reference numeral 222 denotes a product-sum operation unit.

Next, the operation of the above configuration will be described.

In a coefficient RAM 201, a UCR / HCR signal suitable for each recording color and hue signal is stored in advance by a CPU (not shown).
The masking coefficient has been written. The image signals C, M,
When the Y and hue signals 105 are input, the coefficient RAM 201
At the same time as the appropriate masking a _{1 to} a ₈ are read from the black signal Bk = min (C,
M, Y), masking second order terms CM, MY, CY, Bk ²
Is calculated. Thereafter, an output image signal is output by the product-sum operation of the equation (1).

[Hue Determination] FIG. 3 is a diagram for explaining the principle of an example of hue determination according to the present embodiment.

In FIG. 1, input signals R, G, and B standardized to 0 to 225 are represented in a three-dimensional space, and are divided into eight regions according to the magnitude of each signal. That is, Bk area 301: R <128, G <128, B <12
8 W area 302: R ≧ 128, G ≧ 128, B ≧ 12
8 C region 303: R ≧ 128, G <128, B <12
8 M area 304: R <128, G ≧ 128, B <12
8 Y area 305: R <128, G <128, B ≧ 12
8 R region 306: R <128, G ≧ 128, B ≧ 12
8 G area 307: R ≧ 128, G <128, B ≧ 12
8 B area 308: R ≧ 128, G ≧ 128, B <12
8 Since each of the above areas is represented by 3 bits, the MSB of each color signal is represented by bit2 = R, bit1 = G, bit0 = B
0: Bk, 1: Y, 2: M, 3: R, 4: C,
5: G, 6: B, 7: W.

As described above, the hue is divided for each area, the area in which the pixel is located is determined, and signal conversion is performed using a masking coefficient suitable for the area, thereby improving the approximation accuracy. Can be.

In other words, at the time of the masking operation, the color of the input image signal is classified into one of a plurality of predetermined hues, and the masking coefficient is switched on a pixel-by-pixel basis or on a region-by-region basis in accordance with the classification, whereby the color tone of the input image is improved. Has the effect of improving the reproducibility for more colors, ie, reproducing an image more faithful to the original.

Note that the method of determining the hue, the color space, and the like are shown by way of example, and are not limited thereto. <Second Embodiment> In the first embodiment, in the case of a document having a color near a transition of a hue signal, a masking coefficient is switched for each pixel by a minute level difference, and a pseudo contour is formed on an image. May occur.

In order to prevent this, a "substantially constant color region" is detected independently of the hue signal, and switching of the hue signal is prohibited in this region.

FIG. 4 is a block diagram showing a configuration of a color image processing apparatus of a color copying machine according to the second embodiment.

In the second embodiment, as shown in FIG.
A new area determining circuit 108 is provided. The area determining circuit 108 extracts a point where the color of the image changes discontinuously, and outputs an area switching signal 109. With this signal, the output signal from the hue determination circuit 104 is latched by the latch indicated by 116, and processing is performed with a constant masking coefficient until the next switching signal 109 is output.

In this way, it is possible to prevent the occurrence of a false contour in an image.

The present invention may be applied to a system composed of a plurality of devices or an apparatus composed of one device. Needless to say, the present invention can be applied to a case where the present invention is achieved by supplying a program to a system or an apparatus.

[0027]

As described above, according to the present invention, it is possible to execute appropriate color processing for the tint of an input image, and to obtain an image more faithful to a document. Ma
According to the present invention, the pseudo contour is changed by changing the color processing condition.
Is prevented from occurring in the output image.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an image processing apparatus of a color copying machine according to a first embodiment of the present invention.

FIG. 2 is a UCR / masking circuit 1 according to a first embodiment.
FIG. 3 is a block diagram showing a configuration of the third embodiment.

FIG. 3 is a diagram illustrating the principle of an example of hue determination according to the first embodiment.

FIG. 4 is a block diagram illustrating a configuration of an image processing apparatus of a color copying machine according to a second embodiment.

[Explanation of symbols]

 Reference Signs List 101 CCD 102 light intensity-density conversion unit 103 UCR / masking circuit 104 hue determination circuit 105 hue signal 106 filtering unit 107 gamma correction unit 108 area determination circuit 109 area switching signal 116 latch 201 coefficient RAM 202 minimum value detection circuit 203 to 214 multiplier 215 to 221 Adder 222 Product-sum operation unit

Claims (1)

(57) [Claims] 1. Color image data is input, and it is determined whether the color image data belongs to a plurality of color regions including a white region and a black region, and a color processing condition is selected according to the determination result. An image processing method for performing color processing on the color image data using the selected color processing conditions, wherein the determination result is obtained for an area of a color in which a change in the color image data is substantially constant. And selecting a color processing condition according to the judgment result when the color image data changes discontinuously.