JPH0595539A - Orthogonal conversion encoder - Google Patents

Abstract

PURPOSE:To reduce the block noise for such a block by controlling the step width quantizing the orthogonal conversion coefficient of block of visually noticeable picture such as an edge part. CONSTITUTION:The orthogonal conversion encoder is provided with an orthogonal converter 11 orthogonally converting the inputted block, an edge detecting device 12 detecting whether or not an edge is in the inputted block, and an encoder 13 reducing the compression ratio of the block with edge when performing the bit compression so as to obtain the prescribed amount of data while taking the output of the orthogonal converter 11 and the output of the edge detecting device 12 as input. When the edge detecting device 12 detects an edge is in the block, the quantization coefficient of the output of a quantization selection circuit 22 is made small. For example, 1/4 quantization is replaced by 1/2 quantization. Thus, the orthogonal conversion coefficient with less error can be obtained, reducing the block noise.

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

In FIG. 6, 1 is an input terminal, 2 is an orthogonal transformer, 3 is an encoder, and 4 is an output terminal. Also,
The encoder 3 comprises 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 to become a block composed 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 occurrence frequency of the encoded code word and outputs the code word as output data from the output terminal 4 as encoded data.
Is output from.

FIG. 7 shows the arrangement of the coefficients of one block of the output A of the orthogonal transformer 2 and the output B of the rearrangement means 5 for explaining the operation of the rearrangement means 5.
In the coefficient arrangement in the figure, the orthogonal transformer 2 uses a two-dimensional orthogonal transformation method, and the block has a block size of 4 horizontal pixels and 4 vertical pixels. Therefore, in the signal A of (FIG. 7), one block is composed of 16 horizontal 4 coefficients and 4 vertical coefficients. 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 rearrangement means 5, for the coding for the two-dimensional orthogonal transformation, the coefficients of the signal B in FIG. Change. This is because a low-frequency component including a DC component has a great influence on vision, and a 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.

Considering the amount of data by encoding, a block with a large amount of data contains a large amplitude frequency component, a block with a small amount of data contains a small amplitude frequency component, and the orthogonal transform coefficient of There are various patterns, such as the distribution concentrated in the low range and the distribution spread from the low range to the high range. Nevertheless, since the optimum quantization performed in the encoder 3 of the conventional orthogonal transform encoding device is performed for each block unit, the same quantization selection operation can be performed for blocks of any pattern. However, the image quality of a block in which an orthogonal transform coefficient spreads, such as an edge portion, is deteriorated.

An object of the present invention is to solve the above-mentioned conventional problems, and an object thereof is to provide an orthogonal transform coding apparatus capable of improving the image quality of a block in which deterioration of the image quality is visually recognizable.

[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. , An edge detector that detects whether or not an edge exists in the input block, and the output of the orthogonal transformer and the output of the edge detector are input, and bit compression is performed to obtain a predetermined amount of data. It has a configuration with an encoder.

[0011]

According to the present invention, the step width for quantizing the orthogonal transform coefficient of a visually prominent block such as an edge portion can be controlled by the above-described structure, so that the amount of data can be controlled without degrading the image quality. Become.

[0012]

1 is a block diagram showing the configuration of an orthogonal transform coding device according to a first embodiment of the present invention. In 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 an edge detector that detects whether or not an edge exists in the input block, 13 is a rearrangement unit 20, a quantizer 21,
An encoder including a quantization selection circuit 22 and an encoding circuit 23, and 14 is an output terminal for outputting an encoded 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. Now, assuming that the quantization coefficient of the quantization selection circuit 22 is 4 and is quantized to 1/4 by the quantizer 21, its output has the distribution as shown in FIG. The distribution shown in FIG. As a result, the coefficient sequence of 6,
8, 13 and 15 are not decoded to the original amplitude value. This error becomes block noise.

In this embodiment, when the edge detector 12 determines that an edge exists in the block, the quantization coefficient of the output of the quantization selection circuit 22 is reduced. For example,
Where it is quantized by 1/4, it is quantized by 1/2. As a result, the distribution shown in FIG. 2D is obtained, and when decoded, the distribution shown in FIG. That is, (Fig. 2
An orthogonal transform coefficient with less error can be obtained from the distribution shown in (c), and block noise can be reduced.

The edge detecting method of the edge detector 12 is not particularly limited as long as it can be detected in the block.

As described above, according to this embodiment,
It is possible to reduce the image quality deterioration by detecting the edge portion where deterioration is visually noticeable in the edge detector 12 and controlling the quantization step width in the quantization selection circuit 22.

Next, an orthogonal transform coding apparatus according to the second embodiment of the present invention will be described. FIG. 3 is a block diagram showing the configuration of the orthogonal transform coding apparatus according to this embodiment. In FIG. 3, reference numeral 30 is an input terminal for inputting a blocked image signal, 31 is an orthogonal transformer for performing orthogonal transformation, and 32 is whether or not a predetermined distribution pattern is present in an output block of the orthogonal transformer 31. A pattern detector for detecting whether or not, 33 is an encoder including rearrangement means 40, a quantizer 41, a quantization selection circuit 42 and an encoding circuit 43, 3
Reference numeral 4 is an output terminal for outputting a coded signal output from the encoder 33.

In the above structure, the pattern detector 32
Detects a pattern in which the distribution pattern of the orthogonal transform coefficient of the output of the orthogonal transformer spreads from the low band to the high band. When the pattern is detected, the quantization coefficient of the output of the quantization selection circuit 42 is reduced to reduce the error due to the compression of the pattern, as in the first embodiment. That is, the detection pattern is protected. In the pattern in which the orthogonal transform coefficient spreads from the low band to the high band, the deterioration such as the edge is often a block that is visually noticeable.

Further, the pattern of the pattern detector 32
An example will be described using (FIG. 4) as a detection method.
In the distribution chart of the orthogonal transform coefficients shown in (FIG. 4),
It is divided into two regions, a low frequency band and a high frequency band, on the border of several numbers. That
The maximum value of each area is L _MAXAnd H_MAXAnd Previous
Two maximum values L_MAX, H_MAXHas a small absolute value due to its size
Divided into four classes of 0, 1, 2, and 3 from Sai
And the combination of selection methods shown in (Fig. 5) from that class.
It is determined whether or not the detection pattern is the matrix. (Figure
The circles shown in the matrix of 5) are the detection patterns.
In the example shown in the figure, the orthogonal transform coefficient is small overall.
Objects that spread from low to high frequencies are detected.
That is, objects concentrated in the low range are not detected. say
In other words, the orthogonal transform coefficients are concentrated in the low frequency range and the amplitude is large.
Quantize with a high compression rate for the threshold distribution pattern.
You can

The protection ratio of the pattern detected by this matrix, that is, the control of the quantization coefficient can be determined for each detected pattern.

As described above, according to this embodiment,
It is possible to reduce the deterioration of image quality by detecting a distribution pattern of orthogonal transform coefficients in which the deterioration is visually noticeable in the pattern detector 32 and controlling the quantization step width in the quantization selection circuit 42. Become.

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. Further, the case of three-dimensional orthogonal transformation may be used instead of the horizontal-vertical two-dimensional orthogonal transformation.

Further, as the method of the pattern detector 32 in the second embodiment, it is also possible to find the sum of the coefficients of the two regions of the low band and the high band and limit the detection pattern from the relationship.

[0025]

As described above, according to the present invention, it is possible to reduce the image quality deterioration by controlling the quantization coefficient by detecting the edge or the specific orthogonal transform coefficient distribution where deterioration is visually noticeable. The practical effect is very large.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an orthogonal transform coding apparatus according to a first embodiment of the present invention.

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

FIG. 3 is a block diagram showing a configuration of an orthogonal transform coding device according to a second embodiment of the present invention.

FIG. 4 is a distribution diagram of absolute values of orthogonal transform coefficients for explaining the operation of the pattern detector used in the second embodiment of the present invention.

FIG. 5 is a combination diagram of detection pattern selection methods for explaining the operation of the pattern detector used in the second embodiment of the present invention.

FIG. 6 is a block diagram showing a configuration of a conventional orthogonal transform encoding device.

FIG. 7 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]

 11 Orthogonal Transformer 12 Edge Detector 13 Encoder 20 Rearrangement Means 21 Quantizer 22 Quantization Selector 23 Encoding Circuit

Claims (6)

[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;
An edge detector for detecting whether or not an edge exists in the input block, and a bit for inputting the output of the orthogonal transformer and the output of the edge detector to obtain a data amount of a predetermined size. An orthogonal transform coding device including a coding encoder. 2. The orthogonal transform encoding device according to claim 1, wherein the encoder reduces the compression rate when an edge exists in a block to be encoded. 3. A device for orthogonally transforming and encoding a video signal, the orthogonal transforming device inputting a signal blocked into a predetermined size and orthogonally transforming the inputted block,
A pattern detector for detecting a predetermined distribution pattern with respect to the orthogonal transform coefficient of the output of the orthogonal transformer, and an output of the orthogonal transformer and an output of the pattern detector are input to obtain a data amount of a predetermined size. Transform coding apparatus having a coder for bit compression. 4. The orthogonal transform coding apparatus according to claim 3, wherein the encoder reduces the compression rate when the pattern detector detects a predetermined pattern in the block to be encoded. 5. The orthogonal transform coding apparatus according to claim 3, wherein the pattern detector detects a distribution pattern in which the orthogonal transform coefficient spreads from a low band to a high band. 6. The orthogonal transform coding apparatus according to claim 3, wherein the orthogonal transform coefficients are concentrated in a low frequency band and high efficiency coding with a high compression rate is performed on a distribution pattern having a large amplitude.