JPH0797829B2 - Color image input / output device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a color image input / output device that inputs three primary color signals representing a color image, converts the signals into density signals, and outputs the density signals.

[Conventional technology]

Conventionally, as a compression method of a color image signal, there is a band compression method represented by the NTSC method of a color television.

This is a luminance signal (Y), color difference by linear conversion of an image signal read by a three-color color separation sensor of red (R), green (G), and blue (B) using the characteristics of the human eye. The signals are converted into three signals (I and Q) and the band of the color difference signals, I, and Q is limited.

However, in recent years, color image input / output devices such as an electrophotographic system and an inkjet system have been developed, but these hard copy devices use R, G, B3 primary color signals as density data, and further, R, G, B It is necessary to convert the signals into cyan (C), magenta (M), and yellow (Y) signals which have a complementary color relationship with.

Also, when compressing image data, it is more efficient to perform compression processing on the C, M, and Y signals that are the density data. Therefore, the Y, I, Q signals obtained by the band compression method used in the above-mentioned color television cannot be used in this case.

As a compression method for the C, M, and Y signals, for the magenta M signal, which is relatively sensitive to the resolution of the human eye,
Be sure to allocate enough bandwidth or bits,
There is a method to limit the band for the remaining cyan C and yellow Y signals, but as a general property of the image
The correlation between the C, M, and Y colors cannot be said to be small, and the compression efficiency is not good. In addition, the R, G, B3 primary color signals are converted into a uniform color space (L * a * b * etc.) corresponding to the density space, and a *, b
There is a method to limit the band of *, but from R, G, B to L
There is a drawback that the processing system becomes complicated because a means for conversion processing to *, a *, b * is required.

[Problems to be solved by the invention]

Therefore, an object of the present invention is to efficiently obtain the image information amount with respect to the density signals yellow (Y), magenta (M), and cyan (C) obtained from the input image signal and without complicating the processing system. It is possible to compress.

[Means for solving problems]

To achieve such an object, the present invention converts the three primary color signals into a density signal in a color image input / output device which inputs three primary color signals representing a color image, converts the signals into density signals and outputs the density signals. The conversion means, the first calculation means for performing a 3 × 3 matrix calculation for separating the density signal converted by the conversion means into the lightness information and the chromaticity information, and the first calculation means With respect to the lightness information and the chromaticity information, a compression unit that compresses the chromaticity information by increasing the compression rate of the chromaticity information as compared with the lightness information, and a decompression unit that decompresses the lightness information and the chromaticity information compressed by the compression unit. And a second calculation means for performing a 3 × 3 matrix calculation for re-converting the lightness information and chromaticity information output from the expansion means into the density signal.

[Operation] In the present invention, the density signal and the color difference signal are separated by performing the matrix operation on the density signal by the first calculating means, and the chromaticity is calculated with respect to the separated lightness information and chromaticity information. By compressing the information by making the compression rate higher than that of the lightness information, that is, by increasing the compression rate for the color difference signal and relatively lowering the compression rate for the density signal, the image quality is degraded. Minimize and achieve efficient compression.

〔Example〕

 Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment according to the present invention.

In the figure, 100 is an R, G, B sensor of three primary colors, 101 is an A / D converter, 102 is a logarithmic converter, 103 is a matrix calculator,
104 is a compression circuit, 105 is an image memory, 106 is a decoding / expansion circuit, 107 is a matrix calculator, and 108 is a masking processing circuit.

In FIG. 1, the three primary color signals R, G, B read by the RGB sensor 100 in the input image are sample-held and converted into digital data by the A / D converter 101. The R, G, B signals are logarithmically compressed by a logarithmic converter 102 and converted into density signals C, M, Y, and C, M by a matrix calculator 103.
It is converted into a signal value by the linear combination of M and Y and supplied to the compression circuit 104.

The compression circuit 104 efficiently compresses a signal input by a known method such as non-linear quantization or orthogonal transformation,
It is supplied to 105, written, and stored.

Next, in the case of outputting an image signal, the image data written in the image memory 105 is read out by the decoding circuit 106 to be decoded and expanded, and then the matrix calculator 107 performs the inverse conversion of the matrix calculator 103 described above. Run and C, M, Y again
Each color signal data of is generated and subjected to color correction processing such as masking processing and undercolor removal (UCR) inking in the masking processing circuit 108 to generate an ink color signal B _K corresponding to the minimum value of C, M and Y. , For example, by a color image output device such as a laser printer.

In the present invention, the matrix calculation is performed by the matrix calculators 103 and 107 to improve the efficiency of color signal compression processing and prevent deterioration of image data.

That is, as if converted to Y, I, Q signals in the color television NTSC system, by performing a matrix operation on C, M, Y density signals, the density signals and color difference signals are separated,
By increasing the compression rate only for the color difference signals and making the compression rate relatively low for the density signals, it is possible to minimize deterioration of image quality and realize efficient compression.

For example, as a matrix operation, , L, A, B are obtained as values close to the CIE uniform color space L *, a *, b *. Here, the value of each coefficient is obtained by the least square method.

Therefore, the compression rate can be suppressed for this L, and a high compression rate can be applied to the A and B color difference signals.

Here, the matrix calculator 107 may use the inverse transform of equation (1).

In this embodiment, the case where the compressed signal is written to the image memory at once is explained. In this example, the compressed signal is transmitted as it is, the compression-coded signal is combined on the receiving side, and C, M Therefore, it can be naturally applied to the transmission in the image communication in which the matrix calculation for converting into the Y signal is performed.

Further, the equation (1) is not uniquely determined, and a more optimal value can be selected in consideration of the characteristics of the input / output device and the human visual characteristics.

Further, in FIG. 1, the matrix operation circuit 107 and the masking circuit 108 are shown as separate units, but since they both operate on a 3 × 3 linear matrix,
It is possible to put them together.

〔The invention's effect〕

As described above, according to the present invention, the density signals yellow (Y), magenta (M), and cyan (C) obtained from the input image signal can be easily separated into the lightness information and the chromaticity information. It is possible to remove the redundancy among the Y, M, and C density signals, efficiently perform the compression process, and prevent the deterioration of the image quality.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment according to the present invention. 100 ... RGB sensor, 101 ... A / D converter, 102 ... Logarithmic converter, 103 ... Matrix calculator, 104 ... Compression circuit, 105 ... Image memory, 106 ... Decoding circuit, 107 ... Matrix calculator, 108 ... Masking processing circuit.

Claims (1)

[Claims] 1. A color image input / output device for inputting three primary color signals representing a color image, converting the signals into density signals and outputting the density signals, the conversion means converting the three primary color signals into density signals, and the conversion means. First calculation means for performing a 3 × 3 matrix calculation for separating the obtained density signal into lightness information and chromaticity information; and the lightness information and chromaticity information separated by the first calculation means. A compression unit that compresses the chromaticity information by increasing the compression rate of the chromaticity information in comparison with the lightness information; a decompression unit that decompresses the lightness information and the chromaticity information compressed by the compression unit; and a decompression unit that outputs the decompression unit. A color image input / output device, comprising: a second calculation means for performing a 3 × 3 matrix calculation for re-converting lightness information and chromaticity information into the density signal.