JPH059986B2 - - Google Patents

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 it is possible to reproduce an image that is exactly the same as the original image through the encoding and decoding processes.
High compression ratio cannot be obtained. 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 and deterioration of image quality due to the encoding/decoding process. However, a high compression ratio can be obtained.

In the case of non-information preserving encoding, it is generally evaluated based on the relationship between quantization distortion (S/N ratio) and data compression rate (information amount), but it is important to have a good relationship between S/N ratio and information amount. One method for realizing this is a method in which transform coefficients after orthogonal transform are quantized and variable length coded.

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 only a small amount of information is allocated to conversion coefficients with low power. By providing a 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 conversion 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 the image.

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, the first
By reducing the amount of rough information about the entire image used in each step, even if the information transmission speed in communication is slow, a rough image can be displayed at high speed as the first step. In this first step, the entire image is displayed, although it is 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 if 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.

This kind of progressive encoding method uses an encoding method using orthogonal transformation to
It can be easily achieved. 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 progressive encoding methods, a normal method of sequentially encoding and decoding images 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 such a method of quantizing orthogonal transform coefficients and variable length coding is used, there arises a demand for realizing both progressive and sequential coding methods. For example, in a case where an image is encoded and the codes are stored, and the stored codes are read out and used as needed, a sequential encoding method is sufficient. However, when transmitting image information accumulated in this manner, transmission using a progressive encoding method is required.

However, when trying to implement a progressive or sequential encoding method using a method of quantizing orthogonal transform coefficients and variable-length encoding, the configurations of the corresponding codes will 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 signals 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 progressive codes in advance, it is necessary to fix the number of orthogonal transform coefficients to be sent first, and it is not possible to realize coding according to such a transmission rate.

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. It is possible to realize progressive encoding according to the transmission speed. An object of the present invention is to provide a method and apparatus for encoding an image signal.

(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 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 above quantization index is variable length encoded, the generated code is stored, and the above code is read out when transmitting image information. decode the quantization index using
The plurality of quantization indexes in the block are divided into a plurality of bands, and the quantization indexes included in the band are subjected to variable length coding for each band, and codes generated are transmitted for all blocks. do.

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 of the blocks 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;
A band division table storage unit that stores a band division table for dividing a plurality of quantization indexes in the block into a plurality of bands, and a band division table storage unit that stores a band division table for dividing a plurality of quantization indexes in the block into a plurality of bands, and a position of a quantization index included in a band to be encoded by reading out the band division table. an encoding position storage section for storing the above-mentioned position; an encoding section for variable-length encoding only the above-mentioned quantization index corresponding to the above-mentioned position stored in the above-mentioned encoding position storage section and outputting a code; a decoding unit that decodes the code stored in the code storage unit that stores the output code and outputs a quantization index; a code transmission unit that transmits the code output from the encoding unit; and the image signal. Controls the process of encoding and accumulating codes of the image signal whose position is stored in the encoding position storage unit so that all bands are encoded when encoding and storing the image information, and when transmitting the image information, For each band, the position is stored in the encoding position storage section so that only that band is variable-length coded, and then the quantization index is decoded from the code stored for all blocks to encode the band. and a control unit that controls processing for encoding and transmitting only the quantization index included in the quantization index.

(Operation) 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. This block is n×n
A square block consisting of pixels is often used.

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

Then, quantization is performed by dividing each transform coefficient by a quantization index given in advance to obtain a quantization index corresponding to each transform coefficient. 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 within the block.

The quantization index thus obtained is subjected to variable length coding, and the generated codes are stored.

When transmitting image information stored in this manner 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 index included in the first band is variable-length coded for all blocks and transmitted. Next, the quantization indexes included in the second band, third band, and each band are 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) Hereinafter, an example of the present invention will be described 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. 1, a block readout section 1 reads out image signals in units of blocks that undergo DCT transformation. 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 converts the 8×8 transform coefficients 1
Calculate 02.

Receiving the conversion coefficient 102 calculated in this way,
The quantization unit 3 performs quantization by dividing the transform coefficients 102 by a predetermined quantization step, and outputs a quantization index 103 corresponding to each transform coefficient 102. 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. 2a, 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. 2a, 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. .

First, when encoding and storing the quantization index 103 output from the quantization section 3, control information indicating that all bands are to be encoded is sent from the control section 10 to the encoding position storage section 5. It will be done. Encoding position storage unit 5 receiving this control information
As shown in FIG. 2b, the positions of all quantization indices 103 within the block are stored as positions 105 to be encoded, regardless of the contents of the band division table storage section 4. Here, at position 105, “1” indicates the coefficient position to be encoded, and “0”
indicates the coefficient position that is not encoded.

Next, the encoding unit 6 retrieves the quantization index 10 in the block to be encoded from the encoding position storage unit 5.
3 is read out, and the quantization index 103 output from the quantization section 3 corresponding to this position 105 is variable-length coded and a code 106 is output. However, in this case, since the positions of all the quantization indexes 103 in the block are designated as the positions 105 to be encoded, all the quantization indexes 103 in the block are variable-length coded and output.

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 10
8 is the same as the quantization index 103.

Then, the control section 10 sends control information indicating the first band as the band to be encoded in the block to the encoding position storage section 5. The encoding position storage unit 5 that has received this control information reads information indicating bands from the band division table storage unit 4, and as shown in FIG. 2c, the position of the quantization index 108 that includes the first band Position 1 to encode
Store as 05.

Next, the encoding unit 6 retrieves the quantization index 10 in the block to be encoded from the encoding position storage unit 5.
Position 105 of 8 is read out, and position 1 of the quantization index 108 output from the decoder 8
Only the code indicated by 05 is variable-length coded 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 1
0 is the second band to be encoded within the block.
information indicating the band is sent to the encoding position storage section 5. Then, the quantization index 108 included in the second band is similarly processed and the code 116 is transmitted from the code transmitter 9.

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

Here, it is assumed that the decoding unit 8 performs decoding processing of the code 106 and decodes the quantization index 108 every time each band is encoded. Instead, the decoding unit 8 receives the quantization index 108.
It is also possible to perform this decoding process only when decoding the first band, 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
Since this is a code for all the quantization indexes 103, it is a sequential code, and if this code is decoded as it is, sequential image decoding can be executed.

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

Furthermore, the code 106 stored in the code storage unit 7
If the images are transmitted as they are, sequential image transmission and decoding can also 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 indices 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 explanation, the block size is 8×8.
However, other sizes and shapes may be used.

In addition, in the above explanation, although there is no specific specification as an image signal, multivalued black and white images, RGB
Each color component image of Y, (RY), (B-Y)
All luminance and color difference signals such as , etc. are 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".
Transmission by motioncompensated
Interframe Coding)” IE Communication Magazine (IEEE
Communication Magazine), November 1982 issue,
Details are given on pages 24-30.

(Effects of the Invention) As described above, by using the image signal encoding method and apparatus of the present invention, sequential codes are stored and 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 FIG. It is an explanatory diagram showing a method. In the figure, 1...block reading unit, 2...
DCT conversion unit, 3... Quantization unit, 4... Band division table storage unit, 5... Encoding position storage unit, 6... Encoding unit, 7... Code storage unit, 8... Decoding unit, 9... Code transmission unit, 10...Control unit.

Claims (1)

[Scope of Claims] 1. An image signal is read out in units of blocks consisting of a plurality of pixels, orthogonal transformation is performed on the blocks to obtain a plurality of transform coefficients, and the transform coefficients are quantized to obtain a quantum signal corresponding to each transform coefficient. The code generated by variable-length encoding the quantization index is stored, and when transmitting image information, the code is read out and the quantization index is decoded. A method for encoding an image signal, in which a quantization index is divided into a plurality of bands, and codes generated by variable-length encoding the quantization index included in the band for each band are transmitted for all blocks. 2. A block readout unit that reads out an image signal in units of blocks consisting of a plurality of pixels, an orthogonal transformation unit that performs orthogonal transformation on the block units to obtain a plurality of transformation coefficients, and a quantization unit that quantizes the transformation coefficients to correspond to each transformation coefficient. a quantization unit that outputs a quantization index to be processed; 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; and a band division table storage unit that reads out the band division table. A coding position storage unit that stores the position of a quantization index included in a band to be coded; and a code is generated by variable length coding only the quantization index corresponding to the position stored in the coding position storage unit. a code storage unit that stores the code output from the code storage unit; 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, and encodes the image signal. When transmitting image information, the position is stored in the encoding position storage section so that only that band is variable-length encoded for each band, and then all blocks are stored. an image signal encoding device comprising: a control section for controlling a process of decoding a quantization index from the code stored in the video signal and encoding and transmitting only the quantization index included in the band;