JPS6264168A - Color picture encoder - Google Patents

Abstract

PURPOSE:To efficiently encode a color picture by quantizing the predicted error of a luminance signal with P-bits by using a predictive encoder and quantizing the predicted error of a color difference signal with Q-bits wherein Q is smaller than P. CONSTITUTION:A selector 12 selects the luminance signal Y and either one of the two color difference signals C1 and C2 by means of a selection signal Z outputted from a controller 11. A subtracter 13 subtracts a predicted value X from the selected picture signal S, and outputs a predicted error signal D=S-X to a quantizer 14. The predicted value X is generated by a predictor 15 based on a predictive reference picture element and a quantized error signal E, etc. A quantizer 14 has plural quantization characteristics, and selects one of said characteristics by means of the election signal Z, quantizes the signal D based on the selected quantization characteristic, and outputs the result as a quantized error signal E. The quantizer 14 that has plural quantization characteristics can easily be generated by using a memory dedicated to writing.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a color image encoding device used in an image transmission device for transmitting color images such as color still images and color photographs.

Conventional technology Color images are transmitted using the NTSC system and PAL system, which separate the luminance signal and two color difference signals. There is a known method of allocating a narrow band by taking advantage of this fact. Even when transmitting such a color image as a dental image, highly efficient encoding can be performed by separating it into a luminance signal and two color difference signals and encoding each separately using an encoder suitable for each. This is shown in ``Color Image Signal Coding System'' of Japanese Patent Application Laid-Open No. 48-8422.

Problems to be Solved by the Invention However, the method shown in the prior art uses separate encoders for the luminance and color difference signals, which poses a problem in that the scale of the encoding device increases.

SUMMARY OF THE INVENTION In view of the above-mentioned drawbacks of the prior art, it is an object of the present invention to provide a color image encoding device that has a simple configuration and is capable of efficiently encoding color images.

Means for Solving the Problems In order to achieve the above-mentioned object, the present invention provides a method for predicting a color image separated into a luminance signal and a color difference signal, and when quantizing and encoding the prediction error, the quantization characteristics of the prediction error are A single predictive encoder is provided which can be made variable.

The present invention uses the predictive encoder described above to efficiently encode color images by quantizing the prediction error of the luminance signal with P bits and quantizing the prediction error of the color difference signal with Q bits smaller than P. can do.

Example An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is a block diagram of a system using the present invention.

The red signal R1 green signal G1 blue signal B of the color image scanned by a color image reading device 21 such as a color camera or a color scanner is digitized by a luminance and color difference separation device 22 into a luminance signal Y and two color difference signals Ct and 02. After separation, it is stored, read out and encoded by the color image encoding device 28. The luminance/color difference separator separates luminance signals Y and 2 from the digitized R and G%B signals according to the following formula.
Two color difference signals C1 and C2 are generated.

FIG. 1 shows the configuration of a color image encoding device according to an embodiment of the present invention, that is, the configuration of figure 23 shown in FIG.

Hereinafter, in this embodiment, as shown in FIG. 3, Y, CI, C2
The signals are sent to the luminance/color difference separation device 22 in this order in units of scanning lines.
The case of reading and encoding from the following will be explained.

First, the selector 12 outputs a selection signal 2 output from the controller 11.
to select one of the Y, CI, and C2 signals. The selected image signal S is subtracted from the predicted value X by the subtracter 18, and a predicted error signal D (D=S−X) is output to the quantizer 14.

The predicted value X is generated by the predictor 15. An example of the predictor 15 is shown below.

However, R1, R2, and R3 are predictive reference pixels, and E is a quantization error signal. Further, the arrangement of predicted reference pixels is shown in FIG.

Now, the quantizer 14 has a plurality of quantization characteristics, selects one quantization characteristic using the selection signal Z, and quantizes the prediction error signal according to the selected quantization characteristic, thereby reducing the quantization error. Outputs signal E. The prediction error signal of the luminance signal is quantized with 4 bits (15 levels), and the two color difference signals CI,
The table shows an example in which the prediction error of C2 is quantized in 3 bits (7 levels).

A quantizer with multiple quantization characteristics can be easily implemented using a write-only memory.

The operation of the controller 11 will be described below. The controller 11 outputs a selection signal 2 for selecting the luminance signal Y at the start of image encoding, and starts encoding the luminance signal Y. The controller 11 counts the number of encoded pixels, and calculates the luminance signal for a predetermined l scanning line (for example, when digitized at 4 times the color subcarrier, the number of luminance signal pixels in the effective screen is 76).
After counting 8 pixels), the selection signal Z is changed, and the color difference signal CI is selected and encoded. Regarding the color difference signal, the number of pixels for l scanning lines determined in the same manner is counted, and after counting, the selection signal Z is changed to select and encode the color difference signal C2.

In this way, as shown in FIG. 3, the luminance signal Y1 and the color difference signals CI and C2 are sequentially encoded in units of scanning lines.

Finally, the code output unit 16 converts the quantization error signal E into 2
Convert to decimal code and output. When converting the quantization error signal E into a binary code, the code word is different between the luminance signal Y and the color difference signals CI and C2 depending on the selection signal Z. For example, when the quantization error in the table is encoded with a fixed length code, the quantization error of the luminance signal is encoded with 4 bits, and the quantization error of the color difference signal is encoded with 3 bits.

In the description of this embodiment, the color difference signals CI and C2 have the same quantization characteristics, but it is also possible to use different quantization characteristics. Further, the code output device can also use a variable length code.

Effects of the Invention As described above, the present invention provides a luminance signal Y and two color difference signals C.
When encoding a color image separated into I and C2, a predictive encoder that can make the quantization characteristic of prediction error variable is used, and the luminance signal Y is P (P) (P is an integer), and the color difference signal C11C2 is smaller than P by using human visual characteristics.
By encoding with 1 and Q2 pips) (Q1 and Q2 are integers), an efficient color image encoding device with a single predictive encoder can be realized at a low cost and with little deterioration in image quality.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a color image encoding device according to an embodiment of the present invention, Fig. 2 is a block diagram of a color image encoding system using the present invention, and Fig. 3 shows the order of encoding. FIG. 4 is a conceptual diagram showing an example of a predictive reference pixel arrangement of a predictive encoder. 11...Controller, 12...Selector, 13...
- Subtractor, 14... Quantizer, 15... Predictor, 16... Code output device.

Claims (1)

[Claims] When separating a color image into a luminance signal and two color difference signals and predictively encoding each, the luminance signal is converted into P bits (however,
P is an integer), and the two color difference signals are Q1 and Q2 bits smaller than P (however, Q1 and Q2 are integers), and the color image encoding device quantizes and encodes the prediction error.