JPH07107298A - Method and device for encoding picture signal - Google Patents

Abstract

PURPOSE:To extend the runlength of a zero coefficient by successively scanning the quantization coefficient located at the same position on the screen on each band component and sending it to a variable length encoding circuit. CONSTITUTION:A picture signal S1 to be inputted is divided into plural bands by a wavelet conversion circuit 1. A quantization coefficient S4 is obtained for a divided coefficient S2 of each band component through a macro block conversion circuit 2 and a quantization device 3. A scan pass conversion circuit 4 successively scans the quantization coefficient S4 located at the same position on the screen between band components and sends it to a variable length encoding circuit 5. Thus, when the quantization coefficient S4 being the prescribed band is 0, the coefficient S4 located at the same position on the screen in another band shall be also zero. Thus, the coefficient S4 at the same position is being scanned in succession and the length of the run length of the zero coefficient can be extended, resulting in improving the encoding efficiency.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image signal encoding method and an image signal encoding apparatus, and when transmitting or recording or reproducing an image signal, for example, a remote transmission of an image by a transmission medium having a limited transmission capacity. The present invention can be applied to recording and reproducing on a tape recorder, a disc recorder, or the like.

[0002]

2. Description of the Related Art Conventionally, when image coding is carried out by a division coding method into band components such as subband coding or wavelet coding, after performing quantization corresponding to each component, , Are sequentially read in accordance with a constant scan path, and variable length coding is performed by combining, for example, a Huffman code and a run length code of zero coefficient, and a variable length coded quantized coefficient is obtained.

FIG. 10 shows an image signal coding apparatus for wavelet-converting an input image signal to decompose it into macroblocks and then quantizing them to obtain variable-length coding coefficients. In this image signal encoding apparatus, the input image signal S1 is input to the wavelet conversion circuit 1 and converted into a coefficient S2. The coefficient S2 is input to the macroblock conversion circuit 2,
The coefficients are rearranged in the order of macroblocks to obtain the coefficient S3.

The coefficient S3 is input to the quantizer 3 and quantized into a coefficient S4. The coefficient S4 is input to the scan path conversion circuit 4 and rearranged according to a constant scan path to become a coefficient S5. The coefficient S5 is input to the variable-length coding circuit 5, variable-length coded, and output as a variable-length coding quantized coefficient S6.

FIG. 12 shows the circuit configuration of the scan path conversion circuit 4 for a 4 × 4 image block as shown in FIG. 11, for example. The quantized 16 images of the 4 × 4 image block are input to the skimp path conversion circuit 4 as the coefficient S4 in the alphabetic order. The coefficient S4 is temporarily stored in the scan path conversion RAM 10 using the output Q1 generated by the counter 11 as a write address, and is sequentially output as the coefficient S5 according to the read address Q2 generated by the address decoder ROM12.

In this case, the order of the scan paths in the scan path conversion circuit 4 is determined by the memory map of the address decoder ROM 12. In variable-length coding in which a Huffman code and a zero-coefficient run length code are combined, the longer the zero-coefficient run length is, the higher the coding efficiency is.

Here, in subband coding and wavelet coding, the coefficients in each band have a spatial correlation within the band, and thus the skim path is taken for each band. . That is, FIG. 13 shows the scan of the 4 × 4 image block after the wavelet transform by the Haar basis is performed on the input image signal and further the quantization is performed, and the contents of the address decoder ROM 12 corresponding to this scan path are shown. Figure 14 shows a memory map
Shown in.

When the image block is 8 × 8, the counter 11 of the scan path conversion circuit 4 is set to 0 to 63, and the conventional scan order in the scan path conversion circuit 4 is shown in FIG. In this figure, scan in the order of numbers.
FIG. 16 shows a memory map including the contents of the address decoder ROM 12 at this time.

[0009]

By the way, in the component division coding method such as the above-mentioned subband coding or wavelet coding, it is necessary to take a scan path for each band component as in the prior art. There is a problem that it is not possible to obtain sufficient efficiency because the information of the position that it has is not fully utilized.

The present invention has been made in consideration of the above points, and an image signal coding method and an image signal code which can significantly improve the variable length coding efficiency when variable length coding the quantized coefficient. It is intended to propose a digitalization device.

[0011]

In order to solve such a problem, in the present invention, the input image signal S1 is divided into a plurality of bands, and the coefficient S2 of each divided band component is quantized. In the image signal coding method of variable-length coding the quantized coefficient S4 obtained in each row, the quantized coefficient S4 at the same position on the screen is sequentially scanned between the band components to the variable-length coding circuit 5. I tried to send it out.

Further, in the present invention, the input image signal S1 is divided into a plurality of bands, and the coefficient S2 of each divided band component is quantized to obtain a quantized coefficient S4 of variable length. In the image coding apparatus for coding, coefficient scanning means 4 for sequentially scanning the quantized coefficient S4 at the same position on the screen between each band component and sending it to the variable length coding circuit 5 is provided. .

[0013]

The quantized coefficient S4 at the same position on the screen is sequentially scanned between the respective band components and sent to the variable length coding circuit 5. The quantization coefficient S4, which is actually a predetermined band, is 0
In the case of, the coefficient S4 at the same position on the screen in another band is also likely to be 0. Therefore, the coefficient S4 at the same position
By continuously scanning, the length of the run length of zero coefficient can be extended, and thus the coding efficiency of variable length coding can be significantly improved.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings.

In this embodiment, first, the shape of 16 bases obtained by carrying out a wavelet transform by Haar basis on a 4 × 4 image block and the band of each base are shown. Shown in 1. Here, each coefficient is named for each band as shown in FIG. From FIG. 3, the coefficient d (1,1), the coefficient e (1,1), and the coefficient f (1,1)
It can be seen that is a coefficient with respect to the base at the same position on the screen.

Here, these three coefficients d (1, 1), e
When any one of (1,1) and f (1,1) is small, it is often the case that the upper left part of the block on the original image has little information about the fine frequency component in the first place. The values of the two coefficients are also often small. Therefore, by connecting these and scanning, the length of the run length of zero coefficient can be extended.

Coefficients d (2,1), e (2,1), f
The same applies to (2, 1) and the like. Therefore, in this embodiment, these points are connected and scanning is performed in the order shown in FIG. 4, for example. In order to realize this scan order with a circuit, the data of FIG. 2 is stored in the scan path conversion RAM 10 described above with reference to FIG. 12, as shown in FIG.
The contents of No. 2 are set as shown in FIG.

When the correlation between the coefficients in the block when the image block is 8 × 8 is actually obtained, it becomes as shown in FIG. Here, after performing wavelet transformation by Haar basis for an image, the coefficient is changed to 1 when the coefficient exceeds a certain value and 0 when the coefficient is less than a certain value, and then the correlation between the coefficients is obtained. ing. From this figure, the coefficient d (1,1)
And f (1,1), and coefficients e (1,1) and f (1 ,,)
The correlation of 1) is the band including the coefficient d (1,1) or the coefficient f.
It can be seen that it is higher than the correlation between the coefficients in the band including (1, 1).

In order to realize a scanning sequence of the form in which these are connected by a circuit, the counter 11 described above with reference to FIG. 12 is used.
0 to 63, and the contents of the address decoder ROM 12 are as shown in FIG. The scan order in this scan path conversion circuit is shown in FIG. In this figure, scan is performed in numerical order.

According to the above configuration, the quantization coefficients at the same position on the screen between the respective band components are sequentially scanned and sent to the variable length coding circuit, so that the run length of zero coefficient can be obtained. Since the length can be extended, the position information possessed by each band component data can be utilized, and the coding efficiency of variable length coding can be significantly improved.

In the above-described embodiment, as the scan path order conversion, writing is performed in the order of the memory when writing, and addressing is performed when reading.
On the contrary, even when addressing is performed at the time of writing and is sequentially read at the time of reading, the same effect as that of the above-described embodiment can be realized.

Further, in the above-mentioned embodiment, the block which is a processing unit of each of the transformation, the quantization, the skip path and the variable length coding may be not only 4 × 4 or 8 × 8 but also a smaller or larger size. Further, the block size may be adaptively changed according to the case, and further, one screen may be processed as it is without being divided into blocks.

[0023]

As described above, according to the present invention, the quantized coefficients at the same position on the screen are sequentially scanned and sent to the variable length coding circuit between the band components. An image signal coding method capable of extending the run length of the coefficient, thereby utilizing the position information held by each band component data, and significantly improving the coding efficiency of variable length coding Also, the image signal encoding device can be realized.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a basis of a two-dimensional wavelet transform based on a Haar basis.

FIG. 2 is a schematic diagram showing naming for two-dimensional wavelet transform coefficients.

FIG. 3 is a schematic diagram showing a base shape corresponding to each coefficient.

FIG. 4 is a schematic diagram showing a scan path of an embodiment of an image signal encoding method and an image signal encoding apparatus according to the present invention.

FIG. 5 is a schematic diagram showing contents written in a RAM for scanning path conversion to realize scanning path according to an embodiment.

FIG. 6 is a schematic diagram showing contents of an address decoder ROM for realizing a scan path according to an embodiment.

FIG. 7 is a schematic diagram showing a correlation between coefficients in an 8 × 8 block in an image.

FIG. 8 is an address decoder ROM for an 8 × 8 image.
It is an approximate line figure showing the contents of.

FIG. 9 is a schematic diagram showing a scan path according to an embodiment for an 8 × 8 image.

FIG. 10 is a block diagram showing an image signal encoding device using wavelet transform.

FIG. 11 is a block diagram showing a scan path conversion circuit in the image signal encoding device.

FIG. 12 is a schematic diagram showing an input order of a 4 × 4 image block.

FIG. 13 is a schematic diagram showing a conventional scan path after wavelet conversion for a 4 × 4 image.

14 is a schematic diagram showing the contents of an address decoder ROM that realizes the conventional scan path of FIG.

FIG. 15 is a schematic diagram showing a conventional scan path after wavelet conversion for an 8 × 8 image.

16 is a schematic diagram showing the contents of an address decoder ROM that realizes the conventional scan path of FIG.

[Explanation of symbols]

1 ... Wavelet conversion circuit, 2 ... Macroblock conversion circuit, 3 ... Quantizer, 4 ... Skip path conversion circuit, 5 ... Variable length coding circuit, 10 ... Skip path conversion RAM, 11 ... Counter, 12 ... Address decoder ROM.

Claims (4)

[Claims] 1. An image signal coding method in which an input image signal is divided into a plurality of bands, and the coefficient of each divided band component is quantized to obtain a quantized coefficient by variable length coding. In the method, the image signal encoding method is characterized in that the quantized coefficients at the same position on the screen are sequentially scanned between the respective band components and transmitted to the variable length encoding circuit. 2. The image signal coding method according to claim 1, wherein within each of the band components, the quantized coefficients are sequentially scanned in the correlation direction. 3. An image signal coding for dividing an input image signal into a plurality of bands, and performing variable length coding on a quantized coefficient obtained by quantizing the coefficient of each divided band component. The image signal coding apparatus according to claim 1, further comprising coefficient scanning means for sequentially scanning the quantized coefficients at the same position on the screen between the respective band components and sending the quantized coefficients to a variable length coding circuit. . 4. The image signal coding apparatus according to claim 3, wherein the coefficient scanning means sequentially scans the quantized coefficients in the respective band components in the correlation direction.