JP2833290B2 - Orthogonal transform coding device - Google Patents

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 for increasing a compression ratio when a video signal is coded with high efficiency.

[0002]

2. Description of the Related Art In general, 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 image quality deterioration 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 apparatus. 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 includes a rearranging 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 coefficient arrangement is rearranged for encoding by the rearrangement means 5 in the encoder 3. The quantizer 6 in the encoder 3 quantizes the orthogonal transform coefficients with a certain step width. The quantization selection circuit 7 selects a quantization coefficient having a step width suitable for storing 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
Output from

FIG. 7 shows an arrangement of 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 shown in the figure, it is assumed that the orthogonal transformer 2 uses a two-dimensional orthogonal transformation technique, and that 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 constituted by 16 coefficients of 4 horizontal coefficients and 4 vertical coefficients. In the block shown in the figure, the frequency component represented by each coefficient corresponds to a low frequency band in the horizontal direction toward the left, and corresponds to a low frequency band in the vertical direction toward the top. Then, in the rearranging means 5, in order to encode the two-dimensional orthogonal transform, the coefficient of the signal B shown in FIG. 7 and the arrangement of the low- to high-frequency two-dimensionally called zigzag scan as shown in FIG. Change. This is because a low-frequency component including a DC component has a greater effect on vision, and a low-frequency component is treated as a more important component.

Therefore, the step width (quantization coefficient) for the quantization of the output of the quantization selector 7 is set to the lower band of the orthogonal transform coefficient so that the output of the quantizer 6 has a desired data amount. It is good to increase in order from the beginning.

[0007]

However, the above-described conventional configuration has the following problems.

Considering the amount of data by encoding, a block having a large amount of data includes a frequency component having a large amplitude, a block having a small amount of data includes a frequency component having a small amplitude, and the orthogonal transform coefficient There are various patterns, such as those whose distribution is concentrated in the low range and those which spread from the low range to the high range. Nevertheless, since the optimal quantization performed in the encoder 3 of the conventional orthogonal transform coding apparatus is performed for each block, the quantization selection operation is similarly performed for any pattern block. This is performed to degrade the image quality of a block in which the orthogonal transform coefficient such as an edge spreads.

An object of the present invention is to solve the above-mentioned conventional problems, and an object of the present invention is to provide an orthogonal transform coding device capable of improving the image quality of a block whose image quality deterioration is easily visually recognized.

[0010]

In order to achieve the above object, an orthogonal transform coding apparatus according to the present invention is provided with an orthogonal transform for inputting a signal divided into a predetermined size and orthogonally transforming the input block. Transformer and the orthogonal transformer for the output of the orthogonal transformer
Divide the number into at least two regions and respond to the coefficients in each region.
A predetermined distribution pattern determined from the relationship between
Pattern detector, the output of the orthogonal transformer and the pattern
It has a configuration with an encoder that receives the output of the output unit as an input and performs bit compression so as to have a predetermined amount of data.

[0011]

According to the present invention, with the above-described structure, a block that is visually conspicuous such as an edge portion is detected from orthogonal transform coefficients.
Since it is possible to control the step width for extracting and quantizing the orthogonal transform coefficients of the block, the data amount can be controlled without deteriorating the image quality.

[0012]

EXAMPLES (Fig. 1) is a block diagram showing a construction of a prior art become orthogonal transform coding apparatus of the present invention, hereinafter, the
A description will be given of a first embodiment. In FIG. 1, reference numeral 10 denotes an input terminal for inputting a blocked image signal; 11, an orthogonal transformer for performing orthogonal transformation; 12, an edge detector for detecting whether an edge exists in the input block; Is an encoder comprising a rearrangement means 20, a quantizer 21, 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.

In the above configuration, the operation is shown in FIG.
This will be described with reference to the distribution diagram of the amplitude values of the orthogonal transform coefficients in the block (1).

FIG. 2A 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 quantized to 1/4 by the quantizer 21, the output has a distribution as shown in FIG. The distribution is as shown in FIG. As a result, 6,
8, 13 and 15 are not decoded to their original amplitude values. This error becomes block noise.

In this embodiment, when the edge detector 12 determines that an edge exists in a block, the quantization coefficient of the output of the quantization selection circuit 22 is reduced. For example,
The place where quantization is performed by と こ ろ is quantized by ２. As a result, the distribution becomes as shown in FIG. 2D, and when decoded, the distribution becomes as shown in FIG. That is, (FIG. 2
An orthogonal transform coefficient having less error than the distribution shown in (c) can be obtained, and block noise can be reduced.

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

As described above, according to this embodiment,
The image quality deterioration can be reduced by detecting an edge portion where deterioration is easily noticeable by the edge detector 12 and controlling the quantization step width by the quantization selection circuit 22.

Next, an orthogonal transform coding apparatus according to a second embodiment of the present invention will be described. In the present embodiment, the first
Compared to the embodiment of the present invention (prior art),
Detect lock from orthogonal transform coefficient of output of orthogonal transformer
Differs in that FIG. 3 is a block diagram showing a configuration of the orthogonal transform coding apparatus according to the present embodiment. In FIG. 3, reference numeral 30 denotes an input terminal for inputting a blocked image signal, reference numeral 31 denotes an orthogonal transformer for performing orthogonal transformation, and reference numeral 32 denotes whether or not a predetermined pattern exists in a block of the output of the orthogonal transformer 31. 33 is an encoder comprising a rearrangement means 40, a quantizer 41, a quantization selection circuit 42 and an encoding circuit 43, and 34 outputs an encoded signal of the output of the encoder 33. Output terminal.

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

The pattern of the pattern detector 32
An example will be described using FIG. 4 as a detection method.
In the distribution diagram of the orthogonal transform coefficients shown in FIG.
It is divided into two regions, a low frequency region and a high frequency region, based on the number arrangement. Soshi
And the maximum value of each area is L _MAXAnd H_MAXAnd Previous
The two maximum values L_MAX, H_MAXIs the size and the absolute value is small
Divided into 4 classes of 0, 1, 2, and 3
And the combination of the selection methods shown in Fig. 5
It is determined whether or not it is a detection pattern in the matrix of (1). (Figure
The circles shown in the matrix of 5) are the detection patterns.
Therefore, the example shown in FIG.
Objects that extend from low to high frequencies are detected.
However, those that are concentrated in low frequencies are not detected. say
In other words, the orthogonal transform coefficients are concentrated in the low band and the amplitude is large.
High compression ratio quantization should be performed for threshold distribution patterns.
Can be.

The protection ratio of the pattern detected by the 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 image quality deterioration by detecting the distribution pattern of the orthogonal transformation coefficient in which the deterioration is easily noticeable in the pattern detector 32 and controlling the quantization step width by 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 may have a block size of 8 × 8 pixels or 16 × 16 pixels. Further, a three-dimensional orthogonal transform may be used instead of the horizontal-vertical two-dimensional orthogonal transform.

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

[0025]

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

[Brief description of the drawings]

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

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

FIG. 3 is a block diagram illustrating a configuration of an orthogonal transform encoding 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 an operation of a pattern detector used in a second embodiment of the present invention.

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

FIG. 6 is a block diagram illustrating a configuration of a conventional orthogonal transform coding apparatus.

FIG. 7 is a conceptual diagram showing a sequence of block coefficients for explaining the operation of a conventional orthogonal transform coding apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Orthogonal transformer 12 Edge detector 13 Encoder 20 Rearrangement means 21 Quantizer 22 Quantization selector 23 Encoding circuit

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-105579 (JP, A) JP-A-3-26081 (JP, A) JP-A 2-222386 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) H04N 7/24-7/68 H04N 1/41-1/419

Claims (4)

(57) [Claims] 1. An apparatus for orthogonally transforming and encoding a video signal, comprising: an orthogonal transformer for inputting a signal divided into a predetermined size and orthogonally transforming the input block;
At least two orthogonal transform coefficients of the output of the orthogonal transformer
Area, and determined from the relationship between the values according to the coefficients in each area.
A pattern detector that detects a predetermined distribution pattern to be determined, and an encoder that receives the output of the orthogonal transformer and the output of the pattern detector as inputs and performs bit compression to a data amount of a predetermined size. Orthogonal transform coding device provided. 2. The orthogonal transform encoding apparatus according to claim 1, wherein the encoder reduces a compression ratio when a block to be encoded is detected as a predetermined pattern by a pattern detector. . 3. The pattern detector according to claim 1 , wherein said pattern detector responds to a coefficient in each area.
The claim 1 orthogonal transform coefficient from the relationship between the Flip value is characterized by detecting a distribution pattern spreading from low frequency to a higher frequency
Is the orthogonal transform coding apparatus according to 2. 4. A pattern detector according to claim 1 , wherein said pattern detector responds to a coefficient in each area.
When the orthogonal transform coefficients are concentrated in the low frequency band and are detected as a distribution pattern having a large amplitude based on the relationship between
2. The orthogonal transform encoder according to claim 1 , wherein the transformer performs high-efficiency encoding at a high compression rate on the block .