JPH04236571A - Color picture reproduction system - Google Patents

Abstract

PURPOSE:To reproduce a white/black original with high picture quality without coloring. CONSTITUTION:A picture input section 1 reads an original by a scanner and color separates the signal of the original into an RGB signal. The RGB signal is smoothed by a smoothing processing section 2 and the smoothed signal is converted into a hue signal and a saturation signal by a conversion section 3. The RGB signal not subjected to smoothing processing is converted into a lightness signal by a conversion section 4. The hue, saturation and lightness signals are inversely converted by an rgb signal by a conversion section 5 and a color correction section 6 applies linear masking system to the inversely converted rgb signal to convert the signal into a YMC signal. An halftone processing section 7 uses an error diffusion method to binarize the YMC signal and a picture whose halftone is expressed is printed out by a printer 8.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image reproduction method for reproducing black and white images with high image quality using a color copier.

0002

2. Description of the Related Art Conventionally, an original is read by an image scanner, color-separated into R (red), G (green), and B (blue) signals, and the R, G, and B signals are smoothed and then Y A well-known color image reproduction method is to perform color conversion into (yellow), M (magenta), C (cyan), and Bk (black) and reproduce and output them in halftones using a dither method or the like. Since this type of image reproduction method smoothes the R, G, and B signals, halftone originals can be reproduced without causing moiré, and even if the original is a black-and-white image original, it can be reproduced without causing moiré. , because it is smoothed, it can be reproduced in achromatic colors.

[0003] However, there are drawbacks in that the resolution of the image decreases (the image becomes blurry) due to the effect of smoothing, and the reproduced image quality deteriorates.

0004

[Problem to be solved by the invention] As a method to solve this problem, convert R, G, B signals to Y, M, C, Bk,
There is a method of performing halftone processing using the error diffusion method, which is superior to the systematic dither method in terms of gradation and resolution. According to this method, it is possible to reproduce images with high resolution and almost no moiré.

However, in the case of a black and white halftone image, R, G,
Since the color balance of B is disrupted, the method described above has the problem that the black and white image original is reproduced in a slightly colored state, and the reproduced image quality deteriorates.

An object of the present invention is to provide a color image reproduction method that reproduces a black and white original with high image quality without coloring it.

[0007]

[Means for Solving the Problems] In order to achieve the above object, the present invention performs image processing on input R (red), G (green), and B (blue) signals, and processes Y (yellow) and M (magenta) signals. ),C
In a method for color reproduction using three colors (cyan) or four colors including Bk (black), the method includes means for smoothing the R, G, and B signals, and converting the smoothed signals into a hue signal and a saturation signal. a first converting means for converting, a second converting means for converting the R, G, B signals into brightness signals, and a third converting means for inversely converting the output signals of the first and second converting means. It is characterized by including.

[0008]

[Operation] The image input section reads an input document using an image scanner and separates the input document into R, G, and B signals. This R, G, B
The signal is smoothed in a smoothing processing section, and the smoothed signal is converted into a hue signal and a saturation signal in a first conversion section. The R, G, and B signals that are not subjected to smoothing processing are converted into brightness signals by a second conversion section. These hue, saturation, and brightness signals are inversely converted into r, g, and b signals in a third converter, and the inversely converted r,
The color correction unit converts the g and b signals into Y, M and C signals using a linear masking method. In the halftone processing section,
The Y, M, and C signals are binarized using the error diffusion method, and an image expressing halftones is output by the printer.

[0009] As a result, high resolution image quality can be obtained because the brightness signal is reproduced without smoothing, and since the hue signal and saturation signal are smoothed, black and white halftone originals can be reproduced with Y
, M, and C can be reproduced without coloring.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram of a color image reproduction method according to the present invention. 1 is an image input unit that reads a document with an image scanner, etc.; 2 is a color-separated R, G,
The smoothing processing unit 3 smoothes the B signals, respectively, and the R,
A first conversion unit that converts the G, B signals into a hue signal and a saturation signal; 4 a second conversion unit that converts the R, G, B signals into a brightness signal; and 5 a hue signal and a saturation signal. , brightness signals r, g
, a third conversion unit that inversely converts the signals into b signals; 6 is a color correction unit;
7 is a halftone processing section, and 8 is an image output section such as a printer.

To explain the operation of the present invention, the image input section 1
reads the input document with an image scanner and sets the pixels to R.
, G, and B signals. These R, G, and B signals are smoothed in a smoothing processing section 2. As this smoothing filter, a general filter having a large weight in the center, as shown in FIG. 2, for example, is used. A first converter 3 converts the smoothed signal into a hue signal and a saturation signal. As described above, in the present invention, since the hue signal and the saturation signal are smoothed, even if a black and white halftone dot image is reproduced in Y, M, and C, it will not be colored. In other words, it is reproduced in achromatic colors (note that the technology for converting R, G, and B signals into hue, saturation, and brightness signals can be found in, for example, the 1st Color Engineering Conference, 1984 or Toshiba Review Vol. 40, No. 8, 1
985 etc.).

On the other hand, the R, G, and B signals that are not smoothed are converted into brightness signals in the second conversion section 4 (this conversion method is also described in the above-mentioned document). In the present invention, since the brightness signal that retains the information on the contour is not smoothed, the resolution does not decrease. Then, these hue, saturation, and brightness signals are converted into r, g,
b signal (see the above-mentioned document for the method of inverse conversion).

The color corrector 6 converts the inversely transformed r, g, and b signals into Y, M, and C signals by, for example, a linear masking method in order to remove the turbidity components of the color separation filter. This color correction is performed, for example, according to the following equation. Y=a11×r+a12×g+a13×bM=a21×
r+a22×g+a23×bC=a31×r+a32×
g+a33×b (a11 to a33 are constants determined by experiment).

Next, the halftone processing section 7 binarizes the Y, M, and C signals by, for example, an error diffusion method, and the printer 8 outputs an image expressing the halftones. In addition,
Regarding the error diffusion method, please refer to the Proceedings of the Institute of Image Electronics Engineers Research Group 90-
01-02, PP7-12 (Selective Enhancement Error Diffusion Method).

[0015]

[Effects of the Invention] As explained above, according to the present invention, R, G, and B signals are converted into hue, saturation, and brightness signals, and the brightness signals are reproduced without smoothing, resulting in high resolution. Furthermore, since the hue signal and saturation signal are smoothed, even if a monochrome halftone original is reproduced in Y, M, and C, it can be reproduced in achromatic colors without being colored.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a color image reproduction method according to the present invention.

FIG. 2 is a diagram showing a smoothing filter.

[Explanation of symbols]

1 Image input section 2 Smoothing processing section 3 First conversion section 4 that converts R, G, B signals into hue signals and saturation signals Second conversion section 5 that converts R, G, B signals into brightness signals Third conversion unit 6 that inversely converts the hue signal, saturation signal, and brightness signal into r, g, and b signals Color correction unit 7 Halftone processing unit 8 Image output unit

Claims (1)

[Claims] [Claim 1] Image processing is performed on input R (red), G (green), and B (blue) signals, and Y (yellow), M (magenta), and C
In a method for color reproduction using three colors (cyan) or four colors including Bk (black), the method includes means for smoothing the R, G, and B signals, and converting the smoothed signals into a hue signal and a saturation signal. a first converting means for converting, a second converting means for converting the R, G, B signals into brightness signals, and a third converting means for inversely converting the output signals of the first and second converting means. A color image reproduction method characterized by comprising: