JPH02170671A - System and device for encoding picture signal - Google Patents

Abstract

PURPOSE:To perform progressive encoding of high resolution from an initial stage by encoding bits corresponding to one or plural bit positions to be coded in each stage out of quantization bits constituting a quantization index and transmitting coded bits. CONSTITUTION:With respect to variable length encoding, an encoding part 4 codes all bits constituting a quantization index 103 to output a code 104 by the control of a control part 9 and stores it in a code storage part 5. When picture information is divided to plural stages to be transmitted, the position 107 of a bit to be transmitted in each stage is preliminarily stored. The control part 9 reads out one or plural bit positions 107 to be encoded in a first stage and controls the encoding part 4. The same processing as the first stage is performed in following stages. Consequently, when this code is decoded as it is, sequential picture decoding is carried out.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention provides an image signal encoding method and apparatus for shortening the transmission time of image signals or reducing storage capacity! Regarding.

[Conventional technology]

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. -Information non-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/decoding process. Although accompanied by quality deterioration,
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 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.

In addition, although the distribution of normal image signals differs greatly depending on the image, the distribution of this transformation coefficient often follows a certain model regardless of the image. Therefore, variable length codes designed based on this model By using
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 of the communication line is slow, the coarse image can be used as the first stage. can be displayed immediately. In this first step, since the entire image is displayed, although it is a coarse image, information about the entire image can be obtained more quickly than when a normal image is decoded line by line as finer images. Can be done. 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 is possible to distinguish the image before receiving all the information. Therefore, when it is desired to select only the necessary images from among 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 transform coefficients, first, among the orthogonal transform coefficients, only those in which power is concentrated are 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 is possible to transmit the information in a short amount of time. Also, since the information of the entire image is transmitted,
Although the image is rough, the entire image can be displayed.

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

In addition, in contrast to such a progressive encoding method, 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.

When such a method of quantizing orthogonal transform coefficients and variable length coding is used, there is a demand for realizing both progressive and sequential coding methods. For example, when an image is encoded and the codes are stored, and the stored codes are read out and used as needed, the sequential encoding method is sufficient. However, when transmitting image information accumulated in this manner, transmission using a progressive encoding method is required.

However, when attempting to realize a progressive or sequential encoding method using a method that quantizes orthogonal transform coefficients and encodes them with variable length, the configurations of the corresponding codes will be significantly different, so both codes are In order to use this encoding method, it is necessary to store codes corresponding to each encoding method separately, that is, two codes for one image, one for progressive and one for sequential. There is a problem in 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. On the other hand, when the transmission speed is very low, only a few orthogonal transform coefficients are encoded in the first stage, and only very rough information about the entire image is transmitted 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, making it impossible to realize encoding according to such a transmission rate.

In order to solve these problems, sequential codes are stored, and when using the sequential encoding method, images are decoded as they are, and when using progressive encoding, they are first decoded to orthogonal transform coefficients after quantization. There is a method in which a part of the code is encoded and transmitted in the first stage after decoding, and many codes are sequentially transmitted in stages.

In this method, an image is orthogonally transformed, orthogonal transform coefficients are quantized and variable-length encoded, and stored as sequential codes, and in the case of sequential encoding, the image is decoded as is. Furthermore, in the case of a progressive encoding method, the sequential code is first subjected to variable length decoding and then returned to the orthogonal transform coefficients after quantization. Then, in the first stage, the entire image is encoded and transmitted for the part where power is concentrated, and in subsequent stages, the remaining quantized orthogonal transform coefficients are encoded and transmitted, allowing for more precise decoding. You can get the image. Therefore, in the initial stage, only the orthogonal transform coefficients in the portion where power is concentrated are encoded and sent.

[Problem to be solved by the invention]

Using the above method, in the progressive encoding method,
Since the quantized orthogonal transform coefficients are encoded and transmitted starting from the part where the power is concentrated, only a part of the orthogonal transform coefficients can be sent in the initial stage. Therefore, since the image is decoded only from a part of the orthogonal transform coefficients, there is a problem that the resolution deteriorates and the reproduced image becomes blurred.

The present invention stores sequential codes and decodes them to the quantized orthogonal transform coefficients to generate progressive codes when transmitting image information, thereby efficiently storing image information. This is an image signal that can be stored as a digital image, and that can realize progressive encoding according to the transmission speed.Furthermore, by encoding and transmitting components related to all orthogonal transform coefficients from the initial stage, a high-resolution image can be restored. The purpose of this invention is to provide an encoding method and its device.

[Means to solve the problem]

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 to obtain a plurality of transform coefficients, and quantizes the transform coefficients to obtain each transform coefficient. Find the quantization index corresponding to the quantization index, store the code generated by variable-length encoding the quantization index, and store the bits that constitute the quantization index when transmitting the image information by dividing it into multiple stages. At least one bit position to be transmitted at each stage is given, the code is read out and the quantization index is decoded, and the at least one bit position of each quantization index is transmitted at each stage. A code is generated by variable-length coding of a portion corresponding to , and the code generated at each stage is transmitted for 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, and an orthogonal transformation unit that performs orthogonal transformation on each block to obtain a plurality of transformation coefficients. a quantization unit that quantizes the transform coefficients and outputs a quantization index corresponding to each transform coefficient; and a quantization unit that quantizes the transform coefficients and outputs a quantization index corresponding to each transform coefficient; When transmitting information by dividing it into multiple stages, the bits that constitute the quantization index that correspond to at least one bit position to be encoded in each stage are variable-length coded and a code is output. an encoding unit;
a code storage unit that stores codes output from the encoder; a code transmission unit that transmits the codes output from the encoder; and a quantization index that decodes the codes stored in the code storage unit. a decoding unit that outputs the quantization index; a bit position storage unit that stores the bit position to be transmitted among the bits forming the quantization index at each stage; The encoding unit is controlled to encode all bits constituting the index, and when the image information is divided into a plurality of stages and transmitted, the bits constituting the quantization index are encoded in each stage. and a control section that controls the encoding section so as to encode what corresponds to at least one bit position.

[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.

A common method for variable-length encoding this quantization index is to individually variable-length encode all quantization indexes in a block, but there are also other significant quantization indexes (non-zero quantization There is a method of variable-length encoding the position and size of the index) within the block, or first, scanning the quantization index within the block in a zigzag manner and grouping the consecutive O quantization indexes as a zero line. There are various methods, such as a method of variable length encoding the length.

When the image information accumulated in this way is divided into multiple stages in the form of progressive encoding and transmitted, one or more bits to be encoded at each stage among the bits that make up the quantization index. The position is determined in advance.However, instead of determining the bit position in advance in this way, it can also be determined in accordance with the statistics of the image and the transmission speed of image information.

Next, the stored code is read out and the quantization index is decoded. Then, among the bits constituting the quantization index, those corresponding to one or more bit positions determined in the first stage are subjected to variable length coding, and the code is transmitted. The first stage is completed by performing such code transmission for all blocks.

Similarly, among the bits that make up the quantization index,
What corresponds to one or more bit positions determined in the second stage is variable-length coded and the code is transmitted.

Such code transmission is performed for all blocks.

The same applies to the following stages.

On the decoding side, first, the code transmitted in the first stage is variable-length decoded, and is put into a portion corresponding to one or more bit positions constituting the quantization index determined in the first stage. Of the bits that make up the quantization index, a predetermined arbitrary value is placed in the part corresponding to the bit position that has not been sent yet to form the quantization index, and by inverse quantization and inverse orthogonal transformation. , display a grainy image.

Next, in the second stage, the code transmitted in the second stage is variable-length decoded and placed in a portion corresponding to one or more bit positions constituting the quantization index determined in the second stage. Of the bits that make up the quantization index, a predetermined arbitrary value is put into the part corresponding to the bit position that has not been sent yet to form the quantization index, and then inverse quantization and inverse orthogonal transformation are performed. Display the image by

Similarly, the third. By obtaining information on the fourth stage,
Sequentially decode and display finer images.

In this way, by encoding and transmitting the quantization bits that constitute the quantization index that correspond to one or more predetermined bit positions at each stage, 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, a total of 64 pixels, 8 pixels vertically and 8 pixels horizontally, of an 8-bit image signal per pixel, are read out as one block. 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.

Receiving the transform coefficients 102 calculated in this way, the quantization unit 3 performs quantization by dividing the transform coefficients 102 by a pre-given quantization step, and each transform coefficient 102
The quantization index 103 corresponding to 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.

The encoding unit 4 performs variable length encoding on these quantization indexes 103 to generate and output a code 104. In this variable length encoding, the encoding unit 4 encodes all bits constituting the quantization index 103 and outputs a code 104 under the control of the control unit 9. The code 104 thus output is stored in the code storage section.

FIG. 2 is an example of a method of dividing bit positions encoded in each stage when the quantization index 103 is divided into a plurality of stages and transmitted. When the quantization index 103 is composed of 8 bits as shown in FIG.
For example, the first stage encodes the upper two bits, and the second stage encodes the upper two bits.
At the stage, the next three highest bits are encoded, and at the third stage, the lowest three bits are encoded.

When transmitting image information by dividing it into a plurality of stages in this way, the bit position storage section 7 stores in advance the position 107 of the bit to be transmitted among the bits forming the quantization index in each stage. put. First, the code 104 stored in the code storage unit 5 is read out and decoded (the code 104 is decoded in the code storage unit 6 to decode the quantization index 106. This quantization index 106 is the same as the quantization index 103). They are the same.

Next, the control unit 9 controls the 1 to be encoded in the first stage.
One or more bit positions 107 are read out to control the encoding unit 4.

The encoding unit 4 encodes the quantization index 106 under the control of the control unit 9 and outputs a code 114.

The code 1111 generated by the encoder 4 is transmitted to the code transmitter 8
transmitted through. Then, the codes 114 of all blocks are transmitted and the first stage ends.

Then, in the second stage, the controller selects one or more bit positions 1 to be encoded in the second stage.
07 is read out from the bit position storage unit 7, the encoding unit 4 is controlled in the same way as in the first stage, and the code 114 is transmitted.

The code 1]4 generated by the encoding unit 4 in this manner is transmitted through the code transmission unit 8. Then, the codes 114 of all blocks are transmitted and the second stage ends.

The following stages also perform the same processing as the second stage,
After performing the final stage processing, the image information transmission processing ends.

Note that here, the decoding unit 6 has a quantization index 106.
It was decided that the decoding process would be performed only in the first stage, and the quantization index 106 stored in this memory would be used in the following stages.

Here, the code 104 stored in the code storage unit 5 is a code for all the quantization indexes 103, so it is a sequential code, and if this code is decoded as it is, it will be a sequential image code. Can be decrypted.

Furthermore, when transmitting image information, among the bits constituting the quantization index, those corresponding to the bit positions predetermined for each stage in the bit position storage unit 7 are encoded and transmitted. Therefore, on the decoding side, this is decoded up to the quantization index and placed in the part corresponding to the bit position. Progressive image transmission and decoding can be performed by entering predetermined arbitrary values into portions corresponding to bit positions that have not yet been transmitted and decoding the image.

Furthermore, by transmitting the code 104 stored in the code storage section 5 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.

In addition, by changing the number of bit positions stored in the bit position storage section 7, 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 can be freely controlled. Can be set to Therefore,
Even when targeting various transmission speeds and images, it is possible to realize a progressive encoding method corresponding to the various transmission speeds and images.

Furthermore, in the initial stage, the upper bits of the quantization index are encoded and transmitted. When transmitting a code, it takes time to transmit all the quantization indexes in a block and all the pits due to the transmission speed. Therefore,
If you try to send all the bits of the quantization index in a short time, you will only be able to send some of the quantization indexes within the block. However, if only the upper bits are sent, all quantization indices in the block can be sent in a short time. Therefore, when using this method, on the decoding side, the image is decoded from the upper bits of all quantization indexes in the block, so the gradation is somewhat degraded, but since the image can be decoded from all quantization indexes, the resolution can be improved. A good image can be restored.

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

In addition, in the above explanation, image signals are not particularly defined, but 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.

This interframe difference signal is described in the literature: "Television Bandwidth Compression Transmission by Motion Convenient Interframe Coding".
BandwidthCompression
rans+uission by Motion-
Compensated Interframe
IEEE Commun
cation Magazine) Magazine, 19
It is described in detail in the November 1982 issue, pages 24-30.

〔Effect of the invention〕

As described above, by using the image signal encoding method and device of the present invention, sequential codes can be stored and decoded to generate progressive codes when transmitting image information. can. Furthermore, since high-frequency components are sent from the initial stage, images with good resolution can be restored.

Therefore, image information can be stored efficiently,
Moreover, progressive encoding with good resolution corresponding to the transmission speed can be realized.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing an example of an encoding device that realizes the image signal encoding method of the present invention, and Figure 2 is a block diagram showing an example of an encoding device that implements the image signal encoding method of the present invention. Figure 2 shows encoding at each stage when the quantization index is divided into multiple stages and transmitted. FIG. 2 is an explanatory diagram showing an example of a method of dividing bit positions. 1...Block reading unit, 2...DCT conversion unit,
3... Quantization section, 4... Encoding section, 5... Code storage section, 6... Decoding section, 7... Bit position storage section,
8... Code transmission section, 9... Control section.

Claims (2)

[Claims] (1) Read out an image signal in blocks each consisting of a plurality of pixels, perform orthogonal transformation on each block to obtain a plurality of transform coefficients, and quantize the transform coefficients to obtain a quantization index corresponding to each transform coefficient. , the codes generated by variable-length coding the quantization index are stored, and when image information is divided into multiple stages and transmitted, the bits that make up the quantization index should be transmitted at each stage. Provide at least one bit position,
reading out the code and decoding the quantization index, and generating a code by variable length encoding a portion corresponding to the at least one bit position of each quantization index in each stage; An image signal encoding method characterized by transmitting a code generated in each block for all blocks. (2) A block readout section that reads out an image signal in units of blocks each consisting of a plurality of pixels; an orthogonal transformation section that performs orthogonal transformation on each block to obtain a plurality of transformation coefficients; and an orthogonal transformation section that quantizes the transformation coefficients to obtain each transformation coefficient. a quantization unit that outputs a quantization index corresponding to the quantization index; and when encoding and storing the image signal, variable length encoding is performed on all bits constituting the quantization index, and the image information is divided into a plurality of stages and transmitted. When doing so, an encoding section that performs variable length encoding on at least one bit position that should be encoded at each stage among the bits constituting the quantization index and outputs a code; a code storage unit that stores output codes; a code transmission unit that transmits the codes output from the encoder; and a decoder that decodes the codes stored in the code storage unit and outputs quantization indexes. a bit position storage unit that stores bit positions to be transmitted among the bits that make up the quantization index at each stage; and a bit position storage unit that stores all the bit positions that make up the quantization index when encoding and storing the image signal. The encoding unit is controlled to encode bits, and when the image information is divided into a plurality of stages and transmitted, at least one of the bits constituting the quantization index is to be encoded in each stage. An image signal encoding device comprising: a control unit that controls the encoding unit to encode a bit position corresponding to the bit position of the image signal.