JPH07107310A - Picture signal processor - Google Patents

Abstract

PURPOSE:To suppress the deterioration of a picture quality due to unnecessary black generation in a hue changing area by controlling the generated amount of black signals included in a pixel under consideration based on the change of the hue of the pixel under consideration. CONSTITUTION:A hue change deciding part consists a hue detecting part and a change deciding part. The hue detecting part detects the hue of a picture signal outputted from an input pixel data buffer based on the C, M, and Y signals of the adjacent pixel areas in four up-and-down and right-and-left directions of the pixel under consideration. The change deciding part decides whether or not the pixel under consideration is a hue changing point based on the hue in the four directions adjacent to the pixel under consideration detected by the hue detecting part. A black generation processing part is controlled according to the decided result of the hue change deciding part. Then, the black signals in the same amounts as the minimum values of the C, M, and Y signals are generated in an area in which the hue is constant, and the generated amount of the black signals is suppressed in the area where the hue is changed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image signal processing apparatus for improving the quality of an output image in color image processing, and more particularly to a color copying machine and a color copying machine for reproducing a color image with four color materials. The present invention relates to an image signal processing device suitable for application to a printer or the like.

[0002]

2. Description of the Related Art In a conventional image processing apparatus such as a color copying machine or a color printer, when a color image is reproduced, it is represented by three color signals of cyan (C), magenta (M) and yellow (Y). When the output image is reproduced using these three color materials (ink, toner, etc.),
There is a case where a black signal is generated from these three color signals and an output image is reproduced with four colors to which a black (K) color material is added.

As a so-called black generation process (blackening process) for generating a black signal from three color signals of C, M and Y, generally, the minimum signal level among the color signals of C, M and Y is obtained. There is known a process for generating a black signal having a signal level equal to that of the color signal.

The advantage of using the black signal in addition to the three color signals of C, M, and Y when outputting a color image is that the reproducibility of the character edge is improved by processing the black character with a single black color. , The point that the color tone of the achromatic color in the output image is stable,
It is possible to increase the consumption of color materials such as toner used.

On the other hand, a drawback of reproducing an output image with four colors including black added to the reproduction of a color image is that color turbidity occurs in a highly saturated area in the image. The problem of color turbidity is a problem that occurs when a region of uniform color is spread over a certain area, and can be said to be a static problem that is not affected by changes in color in an image.

As a static problem which is not affected by the change in color in the image, that is, as a conventional technique for each pixel unit or a region having a constant area representing a uniform color, "L *
There is a technique reported in "Flexible UCR using a * b *" (1992 9th Color Engineering Conference). This black generation processing is characterized by suppressing the generation of color turbidity by reducing the generation amount of the black component with respect to a high-saturation pixel in which the ratio of the achromatic color component is small.

However, the deterioration of the image quality caused by the black generation process is affected by the change of the color in the image, and an unnecessary black signal is generated in the area where the color changes, thereby deteriorating the image quality of the output image. There was a dynamic problem that occurs.

The dynamic problem affected by the color change in the image will be described with reference to FIG. FIG. 5 is a one-dimensional illustration of a color image, where the horizontal axis represents the position and the vertical axis represents 3 for cyan (C), magenta (M), and yellow (Y).
It represents the density level of the color signal. FIG. 5A is an example showing an ideal state of hue change, where the red region R and the green region G are adjacent to each other, and the three color signals of the regions R and G are different on the left and right sides of the boundary. It takes two values.

However, in the boundary portion of the actual image data, the color of the boundary portion where the hue changes due to the influence of the characteristics of the scanner or the like at the time of inputting the image signal and the filter characteristic in the digital signal processing. The signal state changes smoothly as shown in FIG.

At this time, when the black signal K is generated by the conventional black generation processing, the black signal K having a convex portion at the boundary portion of the region where the hue changes is generated as shown in FIG. 5C. When this phenomenon is viewed in a two-dimensional image, there is a problem that a black fine line unnecessary for image reproduction is generated at the boundary portion where the hue changes, and the image quality deteriorates. .

Further, inside the image processing apparatus, the edge enhancement processing may be performed on the image signal in order to clearly reproduce the contour in the image, but the edge enhancement processing is performed on the black signal as shown in FIG. 5C. 5D, the black signal is emphasized as shown in FIG. 5D, and a pseudo contour is generated at the boundary between hues in the output image, resulting in a large deterioration in image quality.

[0012]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned dynamic problem affected by the change in color in an image.
An object of the present invention is to provide an image signal processing device that suppresses image quality deterioration due to unnecessary black generation in a hue change region without reducing the amount of black generation and the edge enhancement degree in a portion where a black signal is required.

[0013]

In order to solve the above-mentioned problems, the invention according to claim 1 is an image signal processing apparatus for processing an input color image signal, wherein the hue of the pixel of interest is extracted from the color image signal. And a control means for controlling the generation amount of the black signal included in the pixel of interest based on the detection result of the detection means.

According to a second aspect of the present invention, in the image signal processing apparatus for processing the input color image signal, the detecting means for detecting the change in the hue of the pixel of interest from the color image signal, and the detecting means. It is configured to have a control unit that controls the edge enhancement processing for the black signal included in the target pixel based on the detection result.

Further, in the invention according to claim 3, in the image signal processing device according to claim 1 or 2, the detecting means determines the hue of the neighborhood area of the pixel of interest, and the determination result of the hue of the neighborhood area is obtained. Based on this, the change in the hue of the pixel of interest is detected.

[0016]

According to the image processing apparatus of the present invention, an input color image signal is obtained, a change in hue is detected for each pixel data of the input image signal, and the change is included in the pixel of interest based on the detection result. The amount of black signals generated and the edge enhancement processing for the black signals are controlled. Whether or not the hue of the pixel of interest is the hue change point is detected by detecting the hue in each direction adjacent to the pixel of interest in the vicinity area of the pixel of interest and determining whether or not the hue in each direction is uniform. Decide For the hue change point, either or both of a process of reducing the generation amount of the black signal and a process of weakening the edge enhancement process for the black signal are performed to generate a black signal in a portion where the black signal is required. The generation of an unnecessary black signal is suppressed in the area where the color changes in the image without deteriorating the amount and the edge emphasis degree, and the deterioration of the image quality of the output image is prevented.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (Embodiment 1) An embodiment of the present invention will be described below with reference to the drawings. First Embodiment FIG. 1 is a block diagram of a first embodiment of the present invention, which realizes a process of suppressing a black generation amount at a hue change point. Reference numeral 1 is an input pixel data buffer, 2 is a hue change determination unit, and 3 is a black generation processing unit. The output of the black generation processing unit 3 is output by an image output device such as a printer (not shown).

The input pixel data buffer 1 has 8 bits (256 bits) for each pixel obtained by reading an original image and performing A / D conversion processing by a scanner using a CCD element or the like.
An 8-bit density signal obtained by performing Log conversion on a linear image signal of reflectance (gradation) is input and held.

The hue change determining section 2 detects the hue of adjacent pixel areas in four directions (up and down, left and right) of the target pixel in four directions (near four), and a change determination for determining a hue change from the hue detection result. It is composed of a section 22.

As shown in FIG. 1, the hue detecting section 21 detects the image signal output from the input pixel data buffer 1 based on the C, M and Y signals in the four neighboring areas of the pixel of interest. To detect the hue. In this hue detection unit, the average density value of the C, M, and Y signals of the area of 2 pixels located near 4 of the pixel of interest is obtained, and the one having the largest value is detected as the hue of that area. For example, if the density average value of C, M, and Y of the area of 2 pixels located above the target pixel is C>
When M> Y, the hue of the area located above the pixel of interest is detected as cyan (C).

In the hue detecting section, the average value of the densities in the neighborhood area of the pixel of interest is obtained to average and use the color information of the peripheral area of the pixel of interest. Even if a stable detection result is obtained, the color change in the image can be effectively determined.

Further, in the hue detecting section 21, the achromatic color area is determined from the color signal of the neighboring area in order to prevent an error in the hue determination which occurs when the target pixel is close to the achromatic color area such as the edge portion of the black character. To do. The determination of the achromatic region is performed by determining the difference between the maximum value and the minimum value of the C, M and Y signals in the neighboring region, m
Ax (C, M, Y) -min (C, M, Y) is calculated, and if this value is smaller than a preset threshold value T, the neighboring area is determined to be an achromatic area. As a result,
Each nearby area is classified into four areas of cyan, magenta, yellow, and achromatic color.

The change determination unit 22 determines whether the pixel of interest is a hue change point based on the hues in four directions adjacent to the pixel of interest detected by the hue detection unit 21. In this determination, it is determined that the pixel of interest is not the hue change point when all the hues in the four directions adjacent to the pixel of interest except the achromatic color are the same hue, and in other cases, the hue change point is determined. It is determined that

The black generation processing unit 3 is controlled by the determination result of the hue change determination unit 2 to perform an appropriate amount of undercolor removal processing on the pixel of interest to generate a black signal from the C, M and Y signals. . The conversion formula of the black generation processing in the black generation processing unit of the present invention is expressed as K = Amin (C, M, Y). A is a constant controlled by the determination result of the hue change determination unit 2, and is a color signal of the minimum signal level among the C, M, and Y color signals represented by min (C, M, Y). To obtain the black signal amount K.

When the pixel of interest is the hue change point, for example, black generation processing is performed with A = 0.6, and in other cases, black generation processing is performed with A = 1. According to this black generation process, the same amount as the minimum value of C, M, and Y is generated as a black signal in the region where the hue is constant, and the black generation process in which the generation of the black signal is suppressed is performed in the region where the hue changes. Is given.

The black signal output from the black generation processing unit 3 is
The output image is reproduced by inputting it to an image output unit (not shown) in the subsequent stage, obtaining the amount of the corresponding coloring material such as ink and toner.

(Second Embodiment) Next, a second embodiment of the present invention will be described. FIG. 6 is a block configuration diagram of a second embodiment of the present invention, and the same blocks as those in FIG. 1 are designated by the same reference numerals. Reference numeral 1 is an input pixel data buffer, 2 is a hue change determination unit, 3 is a black generation processing unit, and 4 is an edge enhancement filter processing unit.

In the second embodiment, the edge enhancement filter processing unit 4 controls the edge enhancement processing for the output of the black generation processing unit 3 based on the determination result of the hue change determination unit 2 similar to the first embodiment.

In the edge emphasis filter processing unit 4, for the normal pixel which is not the hue change point, the black component of the pixel of interest generated by the black generation processing unit 3 is filtered as shown in FIG. Edge enhancement processing is performed using a coefficient. When the hue change determination unit 2 determines that the pixel of interest is the hue change point, the edge enhancement processing is not performed on the black signal generated corresponding to the pixel of interest. Alternatively, the filter coefficient of the edge enhancement processing for the black signal generated corresponding to the target pixel is switched to the coefficient illustrated in FIG. 4, and the edge enhancement degree is controlled to be weaker than that of a normal pixel.

By the control of the edge enhancement filter processing unit, unnecessary edge enhancement processing for the black thin line in the hue change portion is suppressed, and an edge is applied to the edge portion of the black character on the white background which needs the edge enhancement processing. Appropriate edge enhancement processing can be performed, and a high-definition output image can be obtained.

In the embodiment of the present invention, the black generation processing by the three color signals of cyan (C), magenta (M) and yellow (Y) in the output system of the image signal has been described. Input system red (R), green (G),
It goes without saying that the present invention can be applied to the black generation processing using the blue (B) three-color signal.

Further, the condition for detecting a hue change in the present invention is not limited to the detection based on the continuous two pixels in the four neighborhoods of the target pixel shown in the embodiment, and the hue change in only one pixel in the four neighborhoods. It is also effective in a simplified configuration for detecting the color difference and a configuration for stabilizing the detection result by detecting the change in the hue by the density average value of the pixel regions of three or more pixels.

Further, since the image signal processing device according to the present invention performs the local area processing of the image data, it can detect the hue change point with high accuracy by using a buffer memory of about several lines, and a slight increase in hardware. Can be realized with.

[0034]

As described above, according to the invention described in claim 1, by detecting the hue change of the target pixel and controlling the black generation amount included in the target pixel based on the detection result, It is possible to reduce the image quality deterioration due to the occurrence of unnecessary black fine lines in the hue change portion of the image, and significantly improve the image quality of the output image.

According to the second aspect of the present invention, in order to detect the hue change of the pixel of interest and control the edge enhancement processing for the black component of the pixel of interest, it is unnecessary in the hue changing portion of the image. A high-definition image can be obtained as an output image without emphasizing the black thin line.

Further, according to the third aspect of the present invention, in order to determine the hue change of the target pixel based on the determination of the hue in the vicinity region of the target pixel, the local region processing based on the target pixel is performed. Since a highly accurate determination result is stably obtained, it is possible to suppress the scale of required hardware and improve the image quality of an output image.

[Brief description of drawings]

FIG. 1 is a block configuration diagram of a first embodiment of the present invention.

FIG. 2 is a block diagram of a second embodiment of the present invention.

FIG. 3 is an example of filter coefficients for edge degree enhancement.

FIG. 4 is an example of edge degree enhancement filter coefficients.

FIG. 5 is a diagram for explaining a problem of the conventional technique.

[Explanation of symbols]

 1 Input Image Data Buffer 2 Hue Change Judgment Section 21 Hue Detection Section 22 Change Judgment Section 3 Black Generation Processing Section 4 Edge Enhancement Filter Processing Section

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location 4226-5C H04N 1/46 Z

Claims (3)

[Claims] 1. An image signal processing apparatus for processing an input color image signal, wherein a detection unit for detecting a change in hue of a pixel of interest from the color image signal, and a pixel of interest based on a detection result of the detection unit are selected. An image signal processing device characterized by a control means for controlling the generation amount of a black signal included therein. 2. An image signal processing device for processing an input color image signal, wherein a detection unit for detecting a change in hue of the pixel of interest from the color image signal, and a pixel of interest based on a detection result by the detection unit are selected. An image signal processing device characterized by a control means for controlling an edge enhancement process for a black signal included therein. 3. The image signal processing device according to claim 1, wherein the detecting unit determines the hue of the area near the pixel of interest, and changes the hue of the pixel of interest based on the result of the hue determination of the area of interest. An image signal processing device, characterized in that