JPH02113775A - System and device for encoding image signal - Google Patents

Abstract

PURPOSE:To efficiently accumulate image information by accumulating a code for sequential, rearranging the sequence of the codes at the time of transmitting the image information and producing a code for progressive without decoding to a whole screen quantizing index. CONSTITUTION:An encoder is provided with a block reading part 1, an encoding part 100, a code string accumulating part 5, a code dividing part 6, a number counting part 7, a number storing part 8, a code deciding part 9 and a code transmission part 10. Here, the code for the sequential is accumulated, the sequence of the codes is rearranged at the time of transmitting the image information and thereby, the code for the progressive can be produced without executed the decoding. Thus, the image information can be efficiency accumulated.

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, 8b+t per pixel, 256 levels) include information preserving type encoding and information non-preserving type encoding. Information-preserving encoding refers to one that does not include quantization in the initial encoding process, and it is possible to reproduce an image that is exactly the same as the original image through the encoding Φ decoding process, but it is expensive. No compression ratio is 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 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/
One way to achieve a good relationship between the S/N ratio and the amount of information is to convert the transform coefficients after orthogonal transformation into a quantity Y. There is a method of J variable length 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 biasing the distribution of information, the amount of information can be significantly compressed by i+J.

Further, the distribution of normal image signals often differs greatly depending on the image, or 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 knob encoding method is a method that first displays a coarse image using rough information about the entire image in the first step, and then displays a more detailed image using detailed information step by step. .

In this progressive knob 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,
As a first step, a rough image can be displayed at high speed. In this first step, the entire image is displayed, although it is a coarse image, so information about the entire image can be obtained more quickly than when a normal image is transmitted and decoded at once as finer images. Can be done. Therefore, even when the transmission speed is slow, the psychological burden on the user regarding the waiting time until image display 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 search for only necessary images from a large number of images, the transmission of information can be stopped as soon as it is determined that the images are unnecessary, 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 transform. 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, the information can be transmitted in a short time. Furthermore, since information about the entire image is transmitted, the entire image can be displayed, albeit 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 progressive encoding method, a normal method for encoding and decoding a high-definition image at once is called a sequential code 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 encoding them with variable length, it is desirable to realize both the progressive force method and the sequential method with one device. It is only natural that there will be demands. For example, in the case where an image is encoded and the codes are stored, and the stored codes are read out and used as needed, the digital encoding method is sufficient. However, when transmitting image information accumulated in this manner using a low-speed line, transmission using a progressive encoding method becomes effective.

However, when trying to implement a progressive or sonic encoding method using a method of quantizing orthogonal transform coefficients and variable-length coding, the corresponding code configurations 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 7-quenoyal, 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, if the transmission speed is relatively high, a large number of orthogonal transform coefficients can be encoded from the first stage to transmit a large amount of information. However, if the transmission speed is very low, only a few orthogonal transform coefficients should be encoded in the first stage, and only very rough information about the entire image should be transmitted with a small amount of information. However, in order to store progressive codes in advance, the number of orthogonal transform coefficients to be sent first must be fixed.
Encoding according to such a transmission rate cannot be realized.

As a method to solve the above problems, only sequential codes are stored, and when transmitting image information, first decode part of this to obtain orthogonal transform coefficients.
There is an encoding method that realizes efficient accumulation of image information and progressive encoding corresponding to the transmission speed by encoding this to generate a progressive code. For details of this method, please refer to Tsuneaki Miura, Fushiko Iwata, Keiji Nemoto,
Paper by Takao Omachi, "Study of still image C0DEC that enables /-kenyar/progressive display", 1988
IEICE Autumn National Conference Proceedings, Volume D-
1, page D-1-72 (Reference 1). However, in this method, the accumulated codes are first decoded into quantization indexes for the entire screen and then encoded and transmitted again, which increases the hardware scale and takes time to process. be.

The present invention stores codes for /- sequential, rearranges the order of the codes when transmitting image information, and converts codes for progressive without decoding to a quantization index for the entire screen. 1. To provide an image signal encoding method and its device that can efficiently accumulate image information by generating an image signal, and also realize progressive encoding according to the transmission speed through on-board processing. shall be.

(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 encoding processing on a block-by-block basis, and encodes and generates a The codes to be transmitted are stored as a code string, and when image information is divided into multiple stages and transmitted, the number of codes to be transmitted per block is given at each stage. Read the column and split it into individual codes,
- It is characterized in that for each of the above blocks, codes that have not been transmitted in the previous stages are transmitted until the above number is reached or the codes of that block are exhausted.

Further, the image signal encoding device of the present invention includes: a = 10-block readout unit that reads out an image signal in units of blocks each consisting of a plurality of pixels; A code string storage unit that stores codes output from the encoding unit as a code string, and stores the number of codes to be transmitted per block in each stage when image information is divided into multiple stages and transmitted. a number storage unit, a code division unit that reads the code string from the code string storage unit and divides it into individual codes, and calculates the number of codes output from the code division unit for each block. a number calculation unit that outputs a value indicating the order within the block corresponding to each code, and a value indicating the number read from the number storage unit and the order of the codes read from the number calculation unit for each of the blocks; Based on this, it is determined whether each code output from the code dividing unit has been transmitted in the previous stage, and then the number of codes that have not yet been transmitted that should be transmitted in that stage is determined. The present invention is characterized in that it is comprised of a code determination unit that determines a code to be transmitted as a code to be transmitted, and a code transmission unit that transmits a code based on the determination result of the code determination unit at each stage.

(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 I'l x I' 1 pixel is often used.

Next, code conversion processing is performed for each block. As an example of this encoding process, cases in which orthogonal transformation, encoding, and variable length encoding are implemented will be described in detail.

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

Then, each transform coefficient is quantized using a quantization step given in advance, and a quantization index corresponding to each transform coefficient is determined. However, although all transform coefficients are quantized in 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 variable-length encoded, and the generated code is stored as a code string. 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 indexes). There is a method of variable-length coding of the position and size of the quantization index) within the block, and a method of zero-run scanning of the quantization index of consecutive O by scanning the quantization index within the block in a zigzag manner as shown in Figure 2. Close it up - put it all together,
There are various methods, such as a method of variable length encoding the length and the size of the quantization index other than O.

An example of these methods is, for example, a paper by Mutsumi Ota and Toshio Furuga, ``Comparison of various types of unequal length coding in motion-compensated frames and non-bridled coding systems,'' a lecture paper at the 1985 National Conference of the Telecommunications Division of the Institute of Electronics and Communication Engineers. Collection, Volume 1.1-2
06 pages (Reference 2), Yukitoshi Tsuboi, Teiji Okamoto, “Comparative Study of Various Entropy Coding Systems in Color Still Image Coding,” Image Coding Symposium, 2nd/Nponum Materials, pp. 71-72 (Reference 3) ).

When transmitting the 1-hour image information accumulated in this way by dividing it into multiple stages in the form of prodare and knob encoding,
First, the number of codes per block to be transmitted at each stage is determined in advance. Here, as an example of the number of codes, it is possible to use the number when each code assigned to the length of each zero run and the size of an arbitrary quantization index is counted as -1. However, instead of predetermining the number in advance, it may be determined based on the image statistics and image information transmission speed.

Next, the stored code string is read out and divided into individual codes. At this time, instead of decoding the code string and returning it to a quantization index and then dividing it into individual codes, the code string is divided as it is.

Therefore, there is no need to obtain a quantization index, and there is no need to generate individual codes by variable-length encoding the m-child inodenox again. However, since variable length encoding is performed, the length of each code is different. For this reason, it is necessary to find the breaks in each code. And the first
The number of codes per block determined as a stage is transmitted. Transmission of such codes is carried out by all professionals 1. Then, the first stage is completed. In the second stage, a predetermined number of codes per block are transmitted for all blocks from among the codes that were not transmitted in the first stage for each block. The same applies to the following stages.

By the way, when a variable length encoding method of quantization index is used, the number of codes for each block generally does not match. For example, is the number of quantization indexes in each block the same?If the length of Celloran is used, the number of quantization indexes indicated by one code is different for each code. If encoded, the number of codes for each block will be different.

Therefore, depending on the block, the transmission of all the codes of the block may end before the predetermined number of codes are transmitted at that stage. In such a case, processing for that block ends when transmission of all codes for that block is completed. As a result, only fewer codes than the predetermined number of codes are transmitted for that block, but the decoding side also knows that the transmission of codes for that block has ended when all i+ indexes of that block have been decoded. Since this information can be understood, the decryption process can be executed correctly.

Further, no code is transmitted for a block for which all codes have been transmitted in a stage before that stage. Even in such a case, since the decoding side knows that all the codes of the block were transmitted in the previous stage, the decoding process can be executed correctly.

On the decoding side, first, the image is decoded based on the quantization index decoded from the code transmitted in the first stage, and a rough image is displayed.

Then, by obtaining information from the second and third stages, finer images are sequentially decoded and displayed.

In this way, progressive encoding can be realized by transmitting a predetermined number of codes per block at each stage.

(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.

In addition, in the following description, a case where the encoding processing section is composed of orthogonal transformation, quantization, and variable length encoding will be described as an example. Furthermore, although a two-dimensional discrete cosine transform is used as the orthogonal transform, it is also possible to use an orthogonal transform such as Hadamard transform.

As shown in FIG.
An image signal is read out to a block location where CT conversion is to be performed. For example, an image signal of 8 bits per pixel is divided into 8 pixels vertically and 8 pixels horizontally.
A total of 64 pixels are read out as one block. The read image signal for one block is processed by an encoding section 1 consisting of a DCT transformation section 2, a quantization section 3, and a variable length encoding section 4.
00 is input. 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
Quantization integer corresponding to .

103 is output. However, here, all transform coefficients may be quantized with the same quantization step=18, or different quantization steps may be used depending on the position of each transform coefficient 102 within the block.

FIG. 2 shows an example of the order in which the variable length encoder 4 reads out the quantization indexes 103 within a block. The variable length encoding unit 4 performs variable length encoding on these quantization indexes 103 to generate and output a code string 104. The variable length encoding method of this quantization index 103 is shown in Reference 2 and Reference 3.

In this variable length encoding, the variable length encoding unit 4 encodes all the quantization indexes 103 of each block and outputs a code string 104. Code string 1 thus output
04 is stored in the code string storage section 5.

When transmitting image information by dividing it into multiple stages,
The number storage unit 8 stores in advance the number N, (,: stage number) of codes per block to be transmitted at each stage. First, the code string 104 stored in the code string storage section 5 is read by one digit, and the code string 104 is divided by the code dividing section 6, and a code 105 is output.

At this time, the code division unit 6 does not decode the code string 104 and return it to the quantization index 103 and then divide it into codes 105, but divides the code string 104 as it is. Therefore, in the code division section 6, the quantization index 10
There is no need to calculate 3, and there is no need to variable-length code the quantization index 103 again to generate the code 105.

Here, as an example of division processing, the code division unit 6 performs variable length decoding of the code string 104 to detect breaks in codes. Furthermore, if zero run is used, the sum of its length (number of zero quantization indexes) and the number of significant quantization indexes, or if zero run is not used, the number of quantization indices is determined in advance. A method can be used to check the last code of each block by comparing it with the number of quantization indexes in the block. At the same time, the code division section 6 outputs the control signal C every time it outputs one code 105. However, when the last code of each block is output, instead of the control signal C, a value Cend indicating that it is the last code of the block is output.

Then, the number calculation unit 7 that receives this control signal C calculates the number of codes 105 output from the code division unit 6 for each block, and calculates a value M indicating the order within the block corresponding to each code. Output. Here, the number calculation unit 7 sets 1 as a value M indicating the order corresponding to the first code of the block.
Each time the control signal C is received, the value of M is incremented by 1 and output. Therefore, if the number of codes in each block is M, (, niblock number), M is from 1 to M,
Takes continuous values up to. Then, the number calculation unit 7 calculates the control signals C, , fid corresponding to the last code of each block.
When the receiver receives the block, it finishes outputting the value M corresponding to the sign of the block.

Next, the code determination unit 9 reads the number N of codes corresponding to the first stage from the number storage unit 8, and reads it out from the number calculation unit 7.
A value M indicating the order within the block of each code output from
Compare with. Of the codes 105 output from the code dividing section 6, ■≦M≦N.

It is determined that N8 codes such that N8 codes are to be transmitted in the first stage.

Then, the code transmission unit 10 receives the determination signal 109 indicating the determination result of the code determination unit 9, and transmits only the code 110 determined to be transmitted in the first stage out of the codes 105 output from the code division unit 6. Select and transmit. The above processing is performed for all blocks, and the first stage is completed.

By the way, when a variable length encoding method of quantization index is used, the number M of codes in each block is generally different. Therefore, depending on the block, the number N1 of codes determined in the first stage may not exist, that is, M may be smaller than N1. In such a case, the number of codes output from the code dividing section 6 is only M1, and M
Since J is smaller than N, all NMJ codes are determined by the code determination unit 9 as codes to be transmitted. Therefore, all M codes are transmitted from the code transmitter 10. In this way, code determination and transmission can be performed correctly even for blocks smaller than MJ or N1.

Next, in the second stage, similarly to the first stage, the code string 104 is read out from the code string storage section 5, divided into codes 105 by the code division section 6, and output. Then, the code determination unit 9 obtains the number N of codes corresponding to the first stage and the number N2 of codes corresponding to the second stage from the number storage unit 8.
is read out and compared with a value M indicating the order of each code within the block output from the number calculation unit 7. Here, among the codes 105 output from the code dividing section 6, 1≦M≦N
The N0 codes that are 1 are codes that have already been transmitted in the first stage. Furthermore, since N2 codes are transmitted in the second stage, N2 codes satisfying Nl<M≦(N,+N2) are determined to be the codes to be transmitted in the second stage.

Next, the code transmission unit 10 receives the determination signal 109 indicating the determination result of the code determination unit 9, and selects and transmits only the code 110 determined to be transmitted in the second stage from among the codes 105. . The following process is performed for all blocks, and the second stage is completed.

Here, for a block where there are no (1'J r + N2) codes, that is, smaller than M or (Nl + N2), if M, ≦N1, then all the codes in the block have already been It is determined that the data has been transmitted in the first stage, and nothing is transmitted in the second stage. If Nl<MJ<(Nl+N2), it is first determined that N1 codes out of M3 codes have been transmitted in the first stage. Here, the number of codes output from the code division unit 6 is only M, and since M is smaller than (Nl + N2), MJ
The number of codes that have not been transmitted in the first stage is less than N2, so the remaining codes in the block, that is, from (N, +1) to M, are all transmitted in the second stage. It is determined that the code should be transmitted and is transmitted. In this way, code determination and transmission can be performed correctly even for blocks where Mr is smaller than (Nt + N2).

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, it is assumed that the code string 104 is read out from the code string storage section 5 at each stage.

Instead, the code division unit 6 is provided with a memory for code 105, and this code division process is performed only in the first stage.
In the following stages, the code 105 stored in this memory
You can also use

Furthermore, since the code string 104 stored in the code string storage unit 5 is obtained by encoding all the quantization indexes 103, it is a sequential code string, and if this code string is decoded as is, Sequential image decoding can be performed.

When transmitting image information, since the code 110 is transmitted at each stage, progressive image transmission and decoding can be performed by inversely transforming and decoding this code.

Furthermore, by transmitting the code string 104 stored in the code string storage section 5 as it is, it is possible to transmit and decode a random image.

In this way, only by accumulating sequential codes, it is possible to realize both /-gen noyal and progressive.

Furthermore, by changing the number stored in the number storage section 8, 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 targeting various transmission speeds and images,
A progressive encoding method corresponding to this can be realized.

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

In addition, we have shown examples using orthogonal transformation, quantization, and variable-length coding as examples of the encoding unit, and we have also shown examples of various types of coding, such as using predictive coding and variable-length coding, vector quantization, etc. Encoding methods are available.

Furthermore, it is also within the scope of this patent to use equal-length encoding instead of L'lT variable-length encoding, and in this case, the processing of the code division unit can be performed more easily than in the case of variable-length encoding. Become.

In addition, in the following explanation, although not specified as image signals, multivalued black and white images, RGB color component images, luminance φ color difference of Y, (R-Y) (B-Y), etc. All signals 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 inter-frame difference signal, please refer to “Telev
isionBandwidth Compressio
ntransmission by Motionc
on+pensated lr+terframe C
oding” (IEEE Communication
Magazine, November 1982 issue, 24-3
Page 0; Document 4) describes this in detail.

(Effects of the Invention) As described above, by using the encoding method for image No. 471 of the present invention and its device, sequential codes are stored, and this code is used when transmitting image information. By rearranging the order of , progressive codes can be generated without decoding. Therefore, it is possible to efficiently store image information, and also to efficiently store progressive encoding according to the transmission speed, and to perform progressive encoding according to the transmission speed with simple processing. realizable.

[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. 2 is an explanatory diagram showing an example of the order in which quantization indexes within a block are read. In the figure,

Claims (2)

[Claims] (1) Read out an image signal in block units consisting of a plurality of pixels, perform encoding processing in the block units, and store the code generated by the encoding as a code string,
When image information is divided into multiple stages and transmitted, the number of codes to be transmitted per block is given in each stage, and in each stage, the code string is read out and divided into individual codes, and the code string is read out and divided into individual codes. An image signal encoding method in which codes that have not been transmitted in previous stages are transmitted for each block until the above number is reached or the codes for that block are exhausted. (2) A block readout section that reads out an image signal in blocks each consisting of a plurality of pixels, an encoding section that performs encoding processing on each block, and a code that accumulates the code output from the encoding section as a code string. a column storage unit; a number storage unit that stores the number of codes to be transmitted per block in each stage when image information is divided into a plurality of stages and transmitted; and a code string is read from the code string storage unit. a code division unit that divides each code into individual codes, and a number that calculates the number of codes output from the code division unit for each block and outputs a value indicating the order within the block corresponding to each code. a calculating section, and each code outputted from the code dividing section is calculated based on the number read from the number storage section for each block and the value indicating the order of the codes read from the number calculating section. a code determination unit that determines, after determining whether or not the code has been transmitted at the stage, a code that is within the number of codes that should be transmitted at that stage among the codes that have not yet been transmitted, as a code that should be transmitted; An image signal encoding device comprising a code transmission section that transmits a code based on a determination result of a determination section.