JPH02161874A - Picture signal coding system and device therefor - Google Patents

Abstract

PURPOSE:To realize a progressive coding system corresponding to the transmission speed by dividing plural quantization indexes included in a block into plural bands, transforming the quantization indexes included in the divided bands into the variable length codes for each band, and transmitting the produced codes over all blocks. CONSTITUTION:The quantization indexes included in a block are divided into plural bands based on a prescribed band dividing method. Each of these divided bands includes a quantization index 108. These indexes 108 included in the bands are successively transformed into the variable length codes via a coding part 6 and transmitted. At the decoding side a picture is decoded based on the index 108 included in the first band and a rough picture is displayed. The fine pictures are successively decoded with use of the second and third band information and displayed. Thus a progressive coding system is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an image signal encoding device and method for shortening the transmission time of image signals or reducing storage capacity.

(Prior Art) Data compression methods for multivalued images (for example, 8 bits per pixel, 256 levels) include information preservation type encoding and information non-preservation type encoding. Information-preserving encoding refers to encoding that does not include quantization in the encoding process, and although it is possible to reproduce an image that is exactly the same as the original image through encoding and decoding, it requires high compression. rate is not available. On the other hand, non-information preserving encoding refers to encoding that includes some kind of quantization processing during the encoding process, and the reproduced image contains quantization noise due to the encoding and decoding processing, resulting in deterioration of image quality. High compression ratio can be obtained.

In the case of non-information preserving encoding, quantization distortion (S/
It is evaluated based on the relationship between the S/N ratio (N ratio) and the data compression rate (information amount), and one method to achieve a good relationship between S/N ratio and information amount is to quantize the transform coefficients after orthogonal transformation and use variable length There is a method of encoding.

In this method, the power of the conversion coefficients is generally concentrated in some conversion coefficients, so a large amount of information is allocated to conversion coefficients with high power, and a small amount of information is not allocated to conversion coefficients with low power. By creating this bias in the amount of information, it becomes possible to significantly compress the amount of information.

Further, although the distribution of normal image signals varies greatly depending on the image, the distribution of the transformation coefficients often follows a certain model regardless of the image. Therefore, by using a variable length code designed based on this model,
It is possible to compress the amount of information independent of images.

Furthermore, there is a progressive encoding method as an encoding method for multivalued images. This progressive encoding method is a method in which, in the first step, rough information about the entire image is used to display a coarse image, and then finer information is used in stages to display a finer image. .

In this progressive encoding method, if the amount of rough information of the entire image used in the first stage is kept small, even if the information transmission speed in communication is slow, the coarse image will be used as the first stage. can be displayed quickly. In this first step, the entire image is displayed, albeit a coarse image, so it is possible to obtain information about the entire image more quickly than when a normal image is decoded line by line as finer images. can. Therefore,
Even when the transmission speed is slow, the burden on the user can be significantly reduced.

Furthermore, as the detailed information is received, the entire image gradually becomes finer, so it becomes possible to distinguish the image before receiving all the information. Therefore, when it is desired to search only the necessary images from a large number of images, the transmission of information can be stopped as soon as the determination is made, so that the efficiency of the search can be greatly improved.

Such a progressive encoding method can be easily realized by applying an encoding method using orthogonal transformation. That is, instead of transmitting all the orthogonal transforms, only those orthogonal transform coefficients in which power is concentrated are first encoded and transmitted for the entire image. Then, only the transmitted orthogonal transform coefficients are inversely transformed and the decoded image is displayed.

In this case, since only some orthogonal transform coefficients are transmitted, the amount of information is much smaller than when all orthogonal transform coefficients are transmitted. Therefore, even if the information transmission speed is slow, it can be transmitted at high speed. Furthermore, since information about the entire image is transmitted, the entire image can be displayed, although it is a rough image.

Then, by sequentially transmitting the remaining orthogonal transform coefficients, a more precise decoded image can be obtained.

In addition, in contrast to such a program/tsive encoding method, a method in which images are sequentially encoded and decoded row by row is called a sequential encoding method. In order to implement this method, it is sufficient to encode all orthogonal transform coefficients from the beginning.

(Problems to be Solved by the Invention) When using such a method of quantizing orthogonal transform coefficients and variable length encoding, there is a demand for realizing both progressive and sequential encoding methods. For example, if an image is encoded and the codes are stored, and the stored codes are read out and used as needed, the sequential coding method is sufficient. When transmitting accumulated image information, it is necessary to transmit it using a progressive encoding method.

However, when attempting to implement a progressive or sequential encoding method using a method in which orthogonal transform coefficients are quantized and variable-length encoded, the configurations of the corresponding codes differ greatly. Therefore, in order to use both encoding methods, codes corresponding to each encoding method must be stored separately. That is, two codes, one for progressive and one for sequential, are stored for one image, resulting in a problem that the capacity for storing image information is wasted.

There is also a demand for changing the progressive method depending on the transmission speed. For example, when the transmission speed is high to a certain extent, many orthogonal transform coefficients can be encoded from the first stage, and a lot of information can be transmitted. However, if the transmission speed is very low, only a few orthogonal transform coefficients should be encoded in the first stage to transmit only very rough information about the entire image with a small amount of information. However, in order to store the progressive code in advance with an accumulation of 1-, the number of orthogonal transform coefficients to be sent first must be fixed, and it is not possible to realize encoding according to such a transmission speed. .

The present invention enables image information to be efficiently accumulated by accumulating sequential codes and decoding them to generate progressive codes when transmitting image information. Our goal is to provide an image signal encoding method and device that can realize progressive encoding according to the transmission speed.

(Means for Solving the Problems) The image signal encoding method of the present invention reads out an image signal in blocks each consisting of a plurality of pixels, performs orthogonal transformation L2 on each block, and obtains a plurality of transform coefficients. , the above transform coefficients are quantized to obtain a quantization index corresponding to each transform coefficient, the codes generated by variable length coding the above quantization index are stored, and the above codes are used when transmitting image information. Read and decode the quantization index, divide the plurality of quantization indexes in the block into a plurality of bands, and code the quantization index included in the band for each band by variable length encoding. It is characterized in that it is transmitted after all blocks.

Further, the image signal encoding device of the present invention includes a block readout unit that reads out an image signal in units of blocks each consisting of a plurality of pixels, an orthogonal transformation unit that performs orthogonal transformation on each block to obtain a plurality of transform coefficients, and the a quantization unit that quantizes the transform coefficients and outputs a quantization index corresponding to each transform coefficient; and a band that stores a band division table for dividing the plurality of quantization indices in the block into a plurality of bands. a partitioning table storage section, an encoding position storage section that reads out the band division table and stores the position of a quantization index included in a band to be encoded, and a coding position storage section that corresponds to the position stored in the encoding position storage section. Only the above quantization index is variable length encoded 1-
an encoding unit that outputs a code, a code storage unit that stores the code output from the code storage unit, and a decoding unit that decodes the code stored in the code storage unit and outputs a quantization index. , a code transmission unit that transmits the code output from the encoding unit; and a code transmission unit that stores the position in the encoding position storage unit so that all bands are encoded when encoding and storing the image signal; Controls the process of encoding and accumulating codes, and when transmitting image information, stores the position in the encoding position storage unit so that only that band is variable length encoded for each band. and a control unit that controls a process of decoding the quantization index from the codes accumulated for all blocks, encoding and transmitting only the quantization index included in the band.

(effect) The image signal encoding method of the present invention will be explained.

First, image signals are read out in blocks each consisting of a plurality of pixels. As this block, a square block consisting of nXn pixels is often used.

Next, orthogonal transformation is performed on each block to obtain a plurality of transform coefficients. As this orthogonal transformation, any orthogonal transformation such as two-dimensional discrete cosine transformation or Hadamard transformation can be used. If a square block consisting of nXn pixels is used, the plurality of transform coefficients will also be nXn per block.

Then, quantization is performed by dividing each transform coefficient by a predetermined quantization step to obtain a quantization index corresponding to each transform coefficient. However, here we will quantize all transform coefficients with the same quantization step, but depending on the position of each transform coefficient within the block,
Different quantization steps can also be used.

The quantization index thus obtained is variable-length coded, and the generated codes are stored.

When transmitting the image information stored in this way in the form of progressive encoding, the stored code is first read out and the quantization index is decoded. Then, the plurality of quantization indices within the block are divided into a plurality of bands according to a predetermined band division method. Each band thus divided includes one or more quantization indices. Instead of predetermining the band division method in this way, it can also be determined in accordance with the image statistics and the transmission speed of image information.

Of the bands thus divided, only the quantization indexes included in the first band are variable-length coded for all blocks and transmitted. Next, the second band, the third
, and the quantization index included in each band is sequentially variable-length coded and transmitted.

On the decoding side, the image is first decoded based on the quantization index included in the first band, and a rough image is displayed. Then, by obtaining information on the second and third bands, finer images are sequentially decoded and displayed.

By encoding and transmitting each quantization index for each band in this way, progressive encoding can be realized.

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

FIG. 1 is a block diagram showing an example of an encoding device that implements the image signal encoding method of the present invention. Note that in the following description, a two-dimensional discrete cosine transform is used as the orthogonal transform, but it is also possible to use an orthogonal transform such as Hadamard transform.

As shown in FIG.
Image signals are read out in block units for CT conversion. For example, an image signal of 8 bits per pixel is read out as one block of 64 pixels in total, 8 pixels vertically and 8 pixels horizontally. Then, the DCT transform unit 2 performs two-dimensional discrete cosine transform on the read image signal 101 for one block, and calculates 8×8 transform coefficients 102.

Upon receiving the transform coefficients 102 calculated in this way, the quantizer 3 performs quantization by dividing the transform coefficients 102 by a pre-given quantization step, and each transform coefficient 10
A quantization index 103 corresponding to 2 is output. However, although all transform coefficients are quantized by the same quantization step here, different quantization steps may be used depending on the position of each transform coefficient 102 within the block.

FIGS. 2(a), (b), and (C) are explanatory diagrams showing a method of dividing a plurality of quantization indices in a block into a plurality of bands. As shown in FIG. 2(a), the band division table storage unit 4 stores information indicating the band in which the quantization index 103 is included, corresponding to the position of each quantization index 103 within the block. ing.

First, when storing the quantization index J-03 output from the quantization unit 3 as a code, the control unit 1
Control information indicating that all bands are to be encoded starting from 0 is sent to the encoding position storage section 5. The encoding position storage unit 5 that has received this control information stores the positions of all quantization indexes 103 within the block, regardless of the contents of the band division table entry/boundary section 4, as shown in FIG. 2(b). , position to be encoded]05 and i~. This, second position 105
, "'1" indicates the coefficient position to be encoded, +1
011 indicates an unencoded coefficient position.

Next, the encoding unit 6 extracts the position 105 of the quantization index 103 in the block to be encoded from the encoding position storage unit 5.
is read out, and the quantization unit 3 corresponds to this position 1.05.
The quantization index 103 outputted from the quantization index 103 is variable-length coded and a code 106 is output. However, in this case, the positions of all quantization indexes 103 in the block are specified as positions 105 to be encoded, so all quantization indexes 103 in the block must be variable-length encoded and output. become.

The code 106 thus output is stored in the code storage section 7.

When transmitting image information, first, the code 106 stored in the code storage section 7 is read out, and the decoding section 8 decodes the code 106 to decode the quantization index 108.

This quantization index 108 is the same as the quantization index 103.

Then, the control unit 10 sends control information indicating the fourteenth band as the band to be encoded in the block to the encoding position storage unit 5. The encoding position storage unit 5 that has received this control information reads out information indicating the bands from the band division table storage unit 4 (17), and as shown in FIG. The position of index 108 is stored as position 105 to be encoded.

Next, the encoding unit 6 extracts the position 105 of the quantization index 108 in the encoded schematized block from the encoding position storage unit 5.
out of the quantization indexes 108 output from the decoding unit 8, only the one indicated at position 105 is subjected to variable length encoding, and a code 116 is output.

The code 116 thus output is transmitted from the code transmitter 9.

After performing the processing from encoding to transmission of the quantization index 108 included in the first band for all blocks in the image, the control unit 10 converts the bands to be encoded in the block into the second band. Information indicating the band is sent to the encoding position storage section 5. Then, at L7, the quantization index 108 included in the second band is processed in the same way, and the code 116 is transmitted from the encoding/transmission unit 9.

Thereafter, each band is similarly encoded and transmitted in order,
The control unit 10 performs control to repeat the process until all bands in the block are encoded and transmitted.

Note that each time each band is encoded, the decoding unit 8 decodes the code 10G to obtain a quantization index of 10.
8 to be decoded. Instead, the decoding unit 8 is provided with a memory for the quantization index 108, and the first
It is also possible to perform this decoding process only when decoding the following bands, and use the quantization index 108 stored in this memory when encoding the following bands.

Here, the code 106 stored in the code storage unit 7 is a code for all the quantization indexes 103, so it is a sequential code, and if the code 1, : is decoded as it is, it will be a sequential code. Images can be decoded.

Furthermore, when transmitting image information, the quantization index 108 is encoded and transmitted for each band within the block, so progressive image transmission and decoding is possible by inversely transforming and decoding this. Can be executed.

Furthermore, by transmitting the code 106 stored in the code storage section 7 as it is, sequential image transmission and decoding can be performed.

In this way, both sequential and progressive modes can be realized simply by storing sequential codes.

Furthermore, by changing the band division table stored in the band division table storage unit 4, the total number of bands and the number of quantization indexes included in each band can be changed. With this, it is possible to freely set the amount of information to be transmitted at each stage when progressively transmitting image information and the manner in which the image becomes finer in stages. Therefore, even when various transmission speeds and images are targeted, it is possible to realize a progressive encoding method corresponding to the various transmission speeds and images.

In the above description, the block size is 8×8, but other sizes and shapes may be used.

In the above explanation, image signals are not particularly specified, but include multivalued black and white images, RGB color component images, luminance/color difference signals such as Y, (RY), (B-Y), etc. are all included in this image signal.

Similarly, the present invention can be applied to interframe difference signals in moving images such as television signals, and sufficient effects can be obtained. Regarding this interframe difference signal, please refer to the following reference: [Television Bandwidth Compression Transmission by Motion Interframe Coding (Television Bandwidth Compression Transmission
visionBandwidth Compressi
on Transmission by Motion
-compensated Interframe C
oding) J.I.E.E.
ion Magazine), November 1982 issue,
It is described in detail on pages 24-30.

(Effects of the Invention) As described above, by using the image signal encoding method and device of the present invention, sequential codes are accumulated and are decoded when transmitting image information to generate progressive signals. can generate codes for Therefore, image information can be stored efficiently, and progressive encoding can be realized according to the transmission speed.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of an encoding device that implements the image signal encoding method of the present invention, and FIGS. 2(a) and (b)
, (C) is an explanatory diagram showing a method of dividing a plurality of quantization indices in a block into a plurality of bands. In the figure, 1...Block reading unit, 2...DCT conversion unit,
3... Quantization section, 4... Band division table storage section, 580. Encoding position storage unit, 6... Encoding unit, 7.
... code storage section, 8. ...Decoding section, 9... Code transmission section, 10... Control section.

Claims (2)

[Claims] (1) Read the image signal in block units consisting of multiple pixels, perform orthogonal transformation on the block units to obtain multiple transform coefficients, and quantize the above transform coefficients to determine the quantization index corresponding to each transform coefficient. , store the codes generated by variable-length coding the above quantization index, read out the above code and decode the quantization index when transmitting image information, and decode the plurality of quantization indexes in the above block. An encoding method for an image signal in which the image signal is divided into a plurality of bands, and codes generated by variable-length encoding the quantization index included in each band for each band are transmitted for all blocks. (2) A block readout unit that reads out an image signal in blocks each consisting of a plurality of pixels; an orthogonal transformation unit that performs orthogonal transformation on each block to obtain a plurality of transform coefficients; and an orthogonal transform unit that performs orthogonal transformation on each block to obtain a plurality of transform coefficients, and quantizes the transform coefficients to obtain each transform coefficient. a quantization unit that outputs a quantization index corresponding to the block; a band division table storage unit that stores a band division table for dividing the plurality of quantization indices in the block into a plurality of bands; an encoding position storage unit that stores the position of a quantization index included in a band to be read and encoded; and a variable length encoding unit that encodes only the quantization index corresponding to the position stored in the encoding position storage unit. an encoding unit that outputs a code; a code storage unit that stores the code output from the encoding unit; and a decoding unit that decodes the code stored in the code storage unit and outputs a quantization index; a code transmission unit that transmits the code output from the encoding unit; and a code transmission unit that stores a position in the encoding position storage unit so that all bands are encoded when encoding and storing the image signal; Controls the process of encoding and accumulating codes, and when transmitting image information, stores the position in the encoding position storage unit so that only that band is variable-length encoded for each band, and then all An image signal encoding device comprising a control unit that controls a process of decoding a quantization index from the code accumulated for a block, encoding and transmitting only the quantization index included in the band. .