JPH05114867A - Orthogonal transformation and encoding device - Google Patents

Abstract

PURPOSE:To improve the picture quality of the whole screen by detecting a case wherein a brightness signal whose visual deterioration is inconspicuous is large and a case wherein the signal is small. CONSTITUTION:This orthogonal transformation and encoding device is equipped with an input terminal 10 where a block-divided image signal is inputted, an orthogonal transformer 11 which performs orthogonal transformation, a quantization control circuit 12 which outputs a control signal for quantization control with the amplitude value of the DC component of an orthogonal transformation coefficient outputted by the orthogonal transformer 11, an encoder 13 consisting of a rearranging means 20, a quantizer 21, a quantization selecting circuit 22, and an encoding circuit 23, and an output terminal 14 where the encoded signal output of the encoder 13 is outputted. Then the quantization control circuit 12 detects the case (close to pure white) wherein the brightness signal whose visual deterioration is inconspicuous is large and the case (close to deep dark) wherein the brightness signal is small from the DC component of the orthogonal transformation coefficient and controls the step width of the quantization by the quantization selecting circuit 22. Consequently, deterioration in the picture quality of the whole screen is reducible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an orthogonal transform coding apparatus used to increase the compression rate when a video signal is coded with high efficiency.

[0002]

2. Description of the Related Art Generally, since a video signal has a very large amount of information, a method of reducing the amount of information is used in recording or transmission so that deterioration of image quality is not visually noticeable by high efficiency coding. .. One of the methods is an orthogonal transform coding device that performs orthogonal transform coding.

FIG. 4 is a block diagram showing the configuration of this conventional orthogonal transform coding device. The operation will be described below with reference to FIG.

Reference numeral 1 is an input terminal, 2 is an orthogonal transformer, 3 is an encoder, and 4 is an output terminal. The encoder 3 is composed of a rearrangement unit 5, a quantizer 6, a quantization selection circuit 7 and an encoding circuit 8. First, a block of a predetermined size input from the input terminal 1 is orthogonally transformed by the orthogonal transformer 2,
It becomes a block consisting of orthogonal transform coefficients. Next, the rearrangement means 5 in the encoder 3 rearranges the coefficient sequence for encoding. The quantizer 6 in the encoder 3 quantizes the orthogonal transform coefficient with a certain step width.
The quantization selection circuit 7 selects a quantization coefficient having a step width suitable for containing the quantized data amount of the output of the quantizer 6 into a desired data amount. The encoding circuit 8 assigns a shorter code word to a code having a higher frequency of occurrence of an encoded code word, and outputs the coded data from the output terminal 4 as encoded data.

FIG. 5 (a) is an arrangement of the coefficients of the output A of the orthogonal transformer 2 for explaining the operation of the rearrangement means 5, and FIG. 5 (b) is the arrangement of the rearrangement means 5. The arrangement of the coefficients of the output B of the orthogonal transformer 2 for explaining the operation is shown. The coefficient array of FIG.
As a method of dimensional orthogonal transformation, the block is horizontal 4 pixels,
It has a block size of 4 pixels vertically. Therefore, in the signal A shown in FIG. 5 (A), 16 blocks of horizontal 4 coefficients and vertical 4 coefficients form one block. In the block shown in the figure, the frequency component represented by each coefficient corresponds to the lower horizontal band in the left side and the lower vertical band in the upper direction. Then, in the sorting means 5,
For encoding for the two-dimensional orthogonal transformation, (see FIG.
The coefficients of the signal B shown in (B)) and the two-dimensional frequency called the zigzag scan as shown are rearranged from low to high. This is because the low-frequency component including the DC component has a great influence on the visual sense, and the low-frequency component is treated as an important component.

Therefore, the step width (quantization coefficient) for quantizing the output of the quantization selector 7 is set to the lower range of the orthogonal transform coefficient so that the output of the quantizer 6 has a desired data amount. It should be increased in order.

[0007]

However, the above-mentioned conventional structure has the following problems.

In the above-mentioned conventional orthogonal transform coding apparatus, the amount of data to be coded is quantized so that the amount of data is within a predetermined amount with several blocks as one unit. Therefore, low-frequency components are protected as important information, and a sufficient amount of data is not allocated to blocks with a wide distribution of orthogonal transform coefficients from low to high frequencies or blocks with large amounts of data, which deteriorates image quality. Was there.

The present invention solves the above-mentioned problems of the prior art. The image quality of the entire screen is improved by increasing the compression rate of a block whose image quality deterioration is difficult to visually recognize and allocating the corresponding data amount to another block. It is an object of the present invention to provide an orthogonal transform coding device capable of improving the above.

[0010]

In order to achieve this object, an orthogonal transform coding apparatus according to the present invention is an orthogonal transform which inputs a signal blocked into a predetermined size and orthogonally transforms the input block. And a quantization control circuit that outputs a control signal that controls the compression rate in quantization by the amplitude value of the orthogonal transform coefficient of the output of the orthogonal transformer, and the output of the orthogonal transformer and the output of the quantization control circuit. It has a configuration of an encoder for performing quantization and coding so that a data amount of a predetermined size is obtained as an input.

[0011]

According to the present invention, the step width for quantizing the orthogonal transform coefficient of a block in which image quality deterioration is not noticeable visually when the block of the luminance signal is close to pure white or close to pure black can be controlled by the above-mentioned configuration. Therefore, it is possible to control the data amount while improving the image quality of the entire screen.

[0012]

1 is a block diagram showing the configuration of an orthogonal transform coding apparatus according to an embodiment of the present invention. (Fig. 1)
10 is an input terminal for inputting a blocked image signal, 11 is an orthogonal transformer for performing orthogonal transformation, and 12 is for quantization control by the amplitude value of the DC component of the orthogonal transformation coefficient of the output of the orthogonal transformer 11. Quantization control circuit for outputting control signal, 13 is an encoder comprising rearrangement means 20, quantizer 21, quantization selection circuit 22 and encoding circuit 23, 1
Reference numeral 4 denotes an output terminal for outputting a coded signal output from the encoder 13.

The operation of the above configuration (FIG. 2)
This will be described with reference to the distribution diagram of the amplitude value of the orthogonal transform coefficient in the block.

FIG. 2 (a) shows the distribution of the amplitude values of the orthogonal transform coefficients in the block input to the quantizer 21. As in the case of the conventional example, FIG. 4A shows a distribution in which the block size is 4 × 4 pixels and 16 orthogonal transform coefficients are used. However, the DC component is omitted.
Now, when the amplitude value of the DC component of the orthogonal transform coefficient of the output of the orthogonal transformer 11 is larger than a predetermined threshold value (close to pure white) or smaller than the predetermined threshold value (close to pure black).
think of. In such an image, the deterioration of image quality is visually inconspicuous. Therefore, in such a case, the quantizer 2
Quantize with a high compression rate of 1. An example at that time is (Fig. 2
It is the distribution shown in (b)). When the data shown in FIG. 2 (b) is decoded, the distribution shown in FIG. 2 (c) is obtained, and the low band part is reproduced, but the high band data is almost lost. In other words, this means that the amount of data required to encode this block is reduced.

On the other hand, when the DC component of the orthogonal transform coefficient is other than the above, quantization is performed without increasing the compression rate in the quantization 21. As a result, the distribution shown in FIG. 2D is obtained, and when this is decoded, the distribution shown in FIG. 2E is obtained. In (e), unlike the distribution in (c), the amount of data is large, but it is reproduced up to a high frequency range, and deterioration is reduced.

Further, the quantization control circuit 12 outputs the control signal with the amplitude value of the DC component in the case of the block of the luminance signal. When the input block is a color signal, the control signal for the block of the luminance signal at the same position on the screen is used. For example, when the sampling frequency of the chrominance signal is 1/2 of the sampling frequency of the luminance signal and the 4: 2: 0 signal is line-sequentially arranged in the vertical direction, the relationship between the luminance signal block and the chrominance signal block is As shown in (FIG. 3A), one block has a size of four luminance signal blocks. Therefore, if a plurality of blocks among the Y1, Y2, Y3, and Y4 blocks shown in (a) satisfy the condition, the color signal block is also quantized with a high compression rate. Further, FIG. 3B shows that the sampling frequency of the color signal is 1/4 of the sampling frequency of the luminance signal.
In the case of 4: 1: 1 signals, the same processing as in the case of (a) may be performed.

As described above, according to this embodiment,
The quantization selection circuit 22 detects the DC signal of the orthogonal transformation coefficient when the luminance signal in which the deterioration is not noticeable in the quantization control circuit 12 is large (close to pure white) and small (close to pure black) from the DC component of the orthogonal transform coefficient. It is possible to reduce the deterioration of the image quality of the entire screen by controlling the quantization step width in.

In the embodiment of the present invention, the block signal to be orthogonally transformed has a block size of 4 × 4 pixels, but it may have a block size of 8 × 8 pixels or 16 × 16 pixels. Furthermore, instead of the horizontal and vertical two-dimensional orthogonal transformation, a three-dimensional orthogonal transformation may be used.

Further, in the present embodiment, the case where the control signal in the block of the luminance signal is used as the block of the color signal has been described. There is an improvement effect.

[0020]

As described above, according to the present invention, it is possible to improve the image quality of the entire screen by detecting the cases where the luminance signal whose deterioration is visually inconspicuous is large and small and controlling the quantization coefficient. And its practical effect is very large.

[Brief description of drawings]

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

FIG. 2 is a distribution diagram of absolute values of orthogonal transform coefficients for explaining an embodiment of the present invention.

FIG. 3 is a conceptual diagram showing a relationship between blocks of a luminance signal and a chrominance signal in an embodiment of the present invention.

FIG. 4 is a block diagram showing a configuration of a conventional orthogonal transform encoding device.

FIG. 5 is a conceptual diagram showing an arrangement of coefficients of blocks for explaining the operation of a conventional orthogonal transform encoding device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Orthogonal transformer 12 Quantization control circuit 13 Encoder 20 Sorting means 21 Quantizer 22 Quantization selector 23 Encoding circuit

Claims (4)

[Claims] 1. An apparatus for orthogonally transforming and encoding a video signal, comprising: an orthogonal transformer for inputting a signal blocked into a predetermined size and orthogonally transforming the input block;
A quantization control circuit for outputting a control signal for controlling the compression rate in quantization by the amplitude value of the orthogonal transform coefficient of the output of the orthogonal transformer; and an output of the orthogonal transformer and an output of the quantization control circuit. An orthogonal transform coding device, comprising: a coder for quantizing and coding so as to obtain a data amount of a predetermined size as an input. 2. The quantization control circuit controls to perform quantization at a high compression rate when the amplitude value of the DC component of the orthogonal transform coefficient is larger than a predetermined value and smaller than the predetermined value. Orthogonal transform coding device. 3. The orthogonal transform coding apparatus according to claim 1, wherein the quantization control circuit outputs the control signal only when the input block is a luminance signal. 4. The orthogonal transform coding apparatus according to claim 1, wherein the quantized control signal outputs a control signal in a block of a luminance signal corresponding to the same image position when the input block is a color signal.