JP3287582B2 - Image transmission apparatus and image transmission method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image transmission apparatus and an image transmission method for transmitting image data after variable-length coding.

[0002]

2. Description of the Related Art In recent years, in the field of digital transmission of color images, high-efficiency encoding technology for information has been advanced, and high compression has been realized.

Accordingly, it is possible to transmit and receive a good image via a transmission line even at a low data rate. On the other hand, however, the influence of one word error on the transmission path on the image also increases. Therefore, it is necessary to take measures against a code error in the transmission line by using an error detection code, an error correction code, and the like.

In particular, when using a transmission line that is expected to deteriorate transmission quality, such as a magnetic recording medium or a communication satellite, it is necessary to pay special attention to measures against this code error.

FIG. 6 is a block diagram showing a schematic configuration of a conventional image transmitting / receiving system.

In FIG. 1, reference numeral 101 denotes a terminal to which an image signal is input. The image signal input from the terminal 101 is digitized by an analog-to-digital (A / D) converter 102. The digitized image signal is encoded by the high-efficiency encoding circuit 103, and its information amount (band) is compressed.

[0007] The image information compressed by the circuit 103 is supplied to an error correction coding circuit 104, where a parity check bit for correcting a code error is added (error correction coding is performed). Sent to

On the receiving side, the data sequence via the transmission line 105 is temporarily stored in a memory unit 106, and the memory unit 1
In the error correction unit 107 accessing 06, a code error is corrected using the above-described parity check bit.
Image information corrected for code errors is output from the memory unit 106 and input to the high-efficiency decoding circuit 108.
The circuit 108 performs a process opposite to that of the high-efficiency encoding circuit 103, that is, expands the information amount (band) to return to the original digital image signal. This digital image signal is converted into an analog signal by a digital-analog (hereinafter, referred to as D / A) converter 109 and output from a terminal 110 as an analog image signal.

In FIG. 6, the configuration of the high efficiency encoding circuit 103
That is, various methods have been proposed as image compression methods. As a typical color image coding method,
The so-called ADCT method has been proposed. The ADCT method is described in the Journal of the Institute of Television Engineers of Japan, Vol. 44, no.
2 (1990) Takahiro Saito et al., "Encoding method for still images", and 1982 Tomohiro Ochi et al. .

FIG. 7 is a block diagram schematically showing a configuration of a high-efficiency image coding circuit using the ADCT method.

In the figure, an image signal input to a terminal 111 is an 8-bit signal through an A / D converter 102 shown in FIG.
That is, it is assumed that the digital data string is converted into 256 gradations / colors. For the number of colors, RGB, YU
V, YP _b P _r, the three-color or four color YMCK or the like.

The input digital image signal is immediately subjected to a two-dimensional discrete cosine transform (hereinafter referred to as DCT) by a DCT converter 112 in units of (8 × 8) pixels.

The DCT-transformed (8.times.8) word data (hereinafter referred to as "transform coefficients") is quantized by a linear quantization circuit 113. The quantization step size differs for each transform coefficient. That is, the quantization step size for each transform coefficient is (8
× 8) is a value obtained by multiplying the quantization matrix element by 2 ^S by the multiplier 116.

The above-mentioned quantization matrix element is determined in consideration of the fact that the visual sensitivity to quantization noise differs for each (8 × 8) word conversion coefficient. Table 1 shows an example of this quantization matrix element.

[0015]

[Table 1]

On the other hand, the data of 2 ^S is supplied to the data generator 115.
Where S is 0 or a positive or negative integer;
Called scaling factor. With the value of S,
Image quality and data amount are controlled.

A DC component in each quantized transform coefficient, that is, a DC transform coefficient (hereinafter referred to as a DC component) in an (8 × 8) matrix is supplied to a one-dimensional predictive difference circuit 117, and the circuit The prediction error obtained in 117 is Huffman-coded by a Huffman coding circuit 118. Specifically, the quantized output of the prediction error is divided into groups, first, the identification number of the group to which the prediction error belongs is Huffman-coded, and subsequently, which value in the group is represented by an isometric code.

The conversion coefficients other than the DC component, that is, the AC conversion coefficients (hereinafter, referred to as AC components) are used for the zigzag scanning circuit 11.
9 and is zigzag scanned from a low frequency component to a high frequency component at a two-dimensional frequency as shown in FIG. From the circuit 119, the number of transform coefficients whose quantized outputs are not 0 (hereinafter referred to as significant coefficients) and the number of transform coefficients whose quantized outputs are 0 between the immediately preceding significant coefficients (hereinafter referred to as insignificant coefficients). (Run length) and the Huffman encoding circuit 120
Output to

The Huffman coding circuit 120 classifies the data into groups based on the value of the significant coefficient, performs Huffman coding by combining the group identification number and the run length, and then determines which value in the group is an equal length code. Expressed by

Outputs from the Huffman coding circuits 118 and 120 are multiplexed by a multiplexing circuit 121 and output from a terminal 122 as a coded output via a terminal error correction coding circuit 104 at a subsequent stage.
Supplied to

According to the high-efficiency coding as described above, even if the information amount is compressed to a fraction, no image deterioration is recognized at all, and extremely efficient compression can be performed.

[0022]

However, when the above-described compression with high compression efficiency, that is, information compression at a high compression ratio, is performed, the influence of one code error on an image becomes significant.

For example, when the above-described variable-length encoding is performed, subsequent decoding cannot be performed at all, and as a result, the image after the occurrence of the error may be disturbed, resulting in a very unsightly state.

In general, when such a high compression ratio is compressed, if an uncorrectable code error occurs in an important code serving as a key at the time of decoding, a reproduced image is broken. Would.

In particular, in recent years, this type of device has come to be used for a transmission line such as a communication satellite whose transmission quality is sometimes changed due to the weather and deteriorated. Measures for protecting data against occurrence of errors on transmission paths are required.

However, merely enhancing the error countermeasures results in unnecessarily increasing the code redundancy.
Even if highly efficient image compression is performed, its meaning will be lost.

An object of the present invention is to provide an image transmission apparatus and an image transmission method capable of minimizing image deterioration due to a code error on a transmission line.

[0028]

According to the present invention, there is provided an image transmitting apparatus, comprising: input means for inputting image data; and dividing the image data input by the input means into a plurality of coding blocks. Encoding means for performing variable-length encoding on a per-data basis basis, and generating a fixed-length transmission block by dividing the encoded data variable-length-encoded by the encoding means for each predetermined data amount and outputting the transmission block to a transmission path. Means, wherein the generating means divides an area for storing the encoded data in the transmission block into a plurality of hatches, and encodes a predetermined number of the encoded blocks in the hatch in a resync block unit. A fixed length boundary data for storing data and determining a hatch of a boundary of the encoded data between the resync blocks, and a data including the encoded data and the boundary data. A first error check code for performing an error check on the data and a second error check code for performing an error check on data including the boundary data and not including the encoded data. It is characterized by being arranged at a predetermined position in a block. In the image transmission method according to the present invention, an input step of inputting image data, the image data input in the input step are divided into a plurality of coding blocks, and variable-length coding is performed for each of the coding blocks. An encoding step, and a generating step of dividing the encoded data subjected to the variable length encoding in the encoding step into predetermined data amounts to generate a fixed-length transmission block and outputting the transmission block to a transmission path, In the generation step, an area for storing the encoded data in the transmission block is divided into a plurality of hatches, and the hatch stores encoded data in units of a resync block in which a predetermined number of the encoded blocks are collected. To perform error checking on fixed-length boundary data for determining a hatch at the boundary of encoded data between blocks, and data including the encoded data and the boundary data. Arranging a first error check code and a second error check code for performing an error check on the data including the boundary data and not including the encoded data at predetermined positions in the transmission block; Features.

[0029]

[0030]

[0031]

[0032]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, according to an embodiment in which the present invention is applied to a transmission apparatus for performing variable length coding of an image signal as described above,
This will be described in detail.

FIG. 2 is a block diagram showing a schematic configuration of an image transmission / reception system as one embodiment of the present invention. Hereinafter, description will be given with reference to FIG.

The analog image signal input from the input terminal 1 is digitized by the A / D converter 3 and subjected to variable-length compression encoding by the high-efficiency encoding circuit 5 as described with reference to FIG. A sync code is inserted at a predetermined position by the sync code adding circuit 7 into the compression-encoded data string.

Further, the transmission ID adding circuit 9 inserts additional information (transmission ID) related to the transmission of the present system, for example, a synchronous block number, into this data string.

Reference numeral 11 denotes a boundary information generating circuit which indicates a boundary of information (variable-length encoded code) of each area when one screen is divided into a plurality of areas as described later. It is. This boundary information is important information, and the error detection coding circuit 13 adds a check bit of the error detection code and inserts it into the data string. This error detection coding circuit 13 forms the second error detection or correction code of the present invention.

Numeral 15 denotes an error correction coding circuit which performs error and correction coding on the boundary information and the compressed and coded image data (generation code). Here, the error correction coding circuit 15 forms the first error detection or correction code of the present invention.

The parity check bit of the error correction code is inserted from the error correction coding circuit 15 at a predetermined position in the above-mentioned data sequence, and transmitted through the transmission line 17.

As the transmission line 17, transmission media such as terrestrial radio waves such as optical fibers, satellites, and microwaves and optical space can be assumed as the immediate transmission line, and tape-like tapes such as digital VTRs and DATs can be used as the storage transmission lines. And a recording medium such as a disk-shaped medium such as a floppy disk or a light disk, or a solid medium such as a semiconductor memory.

The transmission rate is determined by the information amount of the original image, the compression ratio and the required transmission time, and varies from several tens of kilobits / second to several tens of megabits / second.

The data sequence received on the receiving side via the transmission line 17 is supplied to the sync code detection circuit 19, and the above-mentioned sync code is separated and detected. The transmission ID detection circuit 21 detects the above-mentioned transmission ID, and detects the attribute of each sync block.

The boundary information detecting circuit 25 separates and detects the aforementioned boundary information. The memory 23 stores a data string according to the sync code and the transmission ID.

The error correction unit 27 accesses the memory 23 and the memory in the boundary information detection circuit 25, and corrects a code error in the compression-encoded image data and the boundary information. This correction is, of course, performed using the check bits added by the error correction coding circuit 15 described above.

The error detection unit 27 detects a code error in the boundary information after the error correction processing by using the check bit added by the error detection coding circuit 13 described above. As described above, in this embodiment, double correction and detection of errors are performed on the boundary information, so that the reliability of the boundary information restored on the medical examination side can be improved.

The boundary information detecting circuit 25 detects the boundary of each area obtained by dividing one screen on the compression-encoded data string, and supplies this information to the memory 23. The high-efficiency decoding circuit 31 takes in only the variable-length coded image data according to the boundary information, expands and decodes it, and supplies the digital image signal returned to the original information amount (band) to the D / A converter 33. . Thus, an analog image signal is output from the output terminal 35.

Here, in the decompression decoding of the variable length data in the high efficiency decoding circuit 31, if the boundary on the compressed data string of each divided area is erroneously detected, correct decoding processing is not performed, and However, in this embodiment, as described above, the boundary information can be corrected by the error correction code, and the error detection code can detect the error correction of the error correction code. The receiving side can reproduce accurate boundary information.

The details of the system according to this embodiment will be described below with reference to FIGS. 1, 3, 4, and 5.

FIG. 3 is a diagram schematically showing information for one screen of an image to be transmitted. One screen is composed of 1280 pixels horizontally and 10 pixels vertically.
Sampling is performed at 88 pixels, and each pixel is A / D with 8 bits.
Shall be converted. Here, the data capacity per screen is 1280 × 1088 × 8 = 11,141,120 bits. In this embodiment, it is assumed that moving image transmission is performed.
When 30 screens are transmitted per second for screen data, 1
The data capacity per second is 11,141,120 × 30 = 334,233,600
Bits / sec. Now, such moving image information is described in the ADC described above.
It is assumed that the data is compressed and coded to about 1/10 by the T method and transmitted.

Here, (eight horizontal pixels) × (eight vertical pixels) is represented by D
As a CT sub-block, 40 DCTs as shown in FIG.
One resync block is composed of sub-blocks.
When one screen is divided into areas in units of the resync block, a total of 544 (horizontal 4) × (vertical 136) per screen is obtained.
It is divided into a plurality of regions.

Here, the data capacity per resync block is 40 × 8 × 8 × 8 = 20,480 bits.

FIG. 1 shows a data transmission format in the system of the present embodiment, particularly, a format of an error correction block (ECC block). As shown in the figure, one symbol (8 bits) of CRCC (cyclic redundancy) is applied to the boundary information of two symbols.
Check code) is added.

Also, an example is shown in which a double Reed-Solomon code is used as an error correction code for the boundary information and the compression-encoded image information.

FIG. 1 shows the range of the code word of the error detection code by CRC and the range of the code word of the error correction code by the outer code of the double Reed-Solomon code. As is apparent from FIG. Is added to one symbol of the CRC check bit.

Also, the boundary check information of two symbols after error detection coding, the CRC check bit of one symbol and the image information of 128 symbols compressed and coded are compared with the outer code check bit (C2 Parity) is added by four symbols.

Further, regarding the image information CRC check bit and the boundary information, the inner code check bit (C1) of the double Reed-Solomon code for 128 symbols in the vertical direction in FIG.
Parity) is added by four symbols.

In this case, the error correction code can correct up to two symbols in each of the vertical and horizontal directions. Furthermore, with respect to the boundary information after the correction processing is performed by the error correction code, when the error is overlooked or erroneously corrected at the time of the correction processing of the previous error correction code, the error detection code is used. Since existing errors can be detected, it is possible to more accurately determine whether the boundary information reproduced on the receiving side is correct or incorrect, and with incorrect boundary information,
It is possible to prevent the later-described compression code from being decoded.

In the upper part of FIG. 1, one horizontal row, that is, 128 symbols of image information and 4 symbols of C2 parity, or
A transmission block (sync block) in which boundary information of two symbols described above, a sync code of two symbols, a transmission ID of two symbols, and a check bit of one symbol are added to 132 symbols of all C1 parities, )showed that. One ECC block is configured by combining 132 of these transmission blocks.

Therefore, for one screen of transmission image information,
If ten ECC blocks are allocated, a transmission capacity of 128 × 128 × 8 × 10 = 1,310,720 bits is provided for one screen. That is, it is understood that the data for one screen described above should be compressed to about 11%.

For a moving image in which 30 screens are transmitted per second, a transmission capacity of 1,310,720 × 30 = 39,321,600 bits / sec is given per second. The total transmission rate at this time is 138 × 132 × 8 × 10 × 30 = 43,718,40
0 bits / sec or more.

The sync code in FIG. 1 is for detecting the synchronization of the transmission block, and is a predetermined fixed pattern. The transmission ID is the number of a transmission block required for one image transmission, and has 16 bits, so that 2 ¹⁶ = approximately 65,000 transmission blocks can be expressed. In the case of this embodiment, since 132 × 10 = 1320 transmission blocks, 11 bits are sufficient.

FIG. 4 shows the relationship between the boundary information in this embodiment and the image information in FIG. The image information area of 128 symbols in FIG. 1 is divided into 8 symbols, that is, hatches (small rooms) every 64 bits.
16 bits of boundary information correspond to each of the 16 hatches. As shown in FIG. 4, the fifth from the left, 13
First, if the boundary of the resync block of the transmission target image exists, the bit “1” is set at the fifth and thirteenth from the left of the corresponding boundary information (otherwise, “0”). As a result, boundary information is created.

FIG. 5 is a diagram for explaining a method of transmitting image information subjected to compression variable length coding.

On the transmitting side of the highly efficient coded image information, first, a number (resync number) 2 indicating the first resync block is assigned to the first resync block.
Outputs a symbol (16 bits), and from the third symbol,
Outputs compressed image information.

More specifically, as described with reference to FIG. 7, first, (8)
× 8) After performing DCT transform in units of pixel sub-blocks, linear quantization of transform coefficients is performed. The quantization step size differs for each transform coefficient, and the quantization step size for each transform coefficient is 2 ^S times the 8 × 8 quantization matrix element that takes into account the difference in luminosity factor for quantization noise for each transform coefficient. Value.

Here, S is a scaling factor, which is 0 or a positive or negative integer. The image quality and the amount of generated data are controlled by the value of S to be about 1/10. After quantization, DC
The component is one-dimensionally predicted between adjacent subblocks as a difference value from 0 in the first DCT subblock, and the prediction error is Huffman-coded. Then, the quantized output of the prediction error is divided into groups, first, the identification number of the group to which the prediction error belongs is Huffman-coded, and subsequently, which value in the group is represented by an isometric code.

The AC component is encoded while zigzag scanning the quantized output from a low frequency component to a high frequency component.
That is, the significant coefficients are classified into groups according to their values, and the group identification number and the number of invalid coefficients sandwiched between the immediately preceding significant transform coefficients are used as a set to perform Huffman coding. Is represented by an isometric code. In the same operation, encoding is performed over 40 DCT sub-blocks, and the output variable-length code is grouped into symbols composed of 8 bits and output to the image information area of the transmission block. For a hatch including the last bit of the compressed information of one resync block, that is, 40 DCT sub-blocks, nothing is written to the remaining area of the hatch (boundary hatch), and A flag “1” is set in a bit of boundary information corresponding to the boundary hatch at this time.

Next, for the second resync block, a number (resync number) 2 indicating the second sync block from the beginning of the hatch next to the hatch used in the first resync block. Symbol (16 bits)
And outputs compressed image information from the third symbol.

The DC component is one-dimensionally predicted between adjacent sub-blocks as a difference value from 0 in the first DCT sub-block, and the prediction error is Huffman-coded. Then, the quantized output of the prediction error is divided into groups, first, the identification number of the group to which the prediction error belongs is Huffman-coded, and subsequently, which value in the group is represented by an isometric code.

The AC component is encoded while zigzag-scanning the quantized output from a low-frequency component to a high-frequency component, and the output variable-length code is grouped into 8-bit symbols, and the image information of the transmission block is obtained. Output to area. Then, for the hatch including the last bit of the compressed information of 40 DCT sub-blocks for one resync block, nothing is written in the remaining area of the hatch, and it is determined as an indefinite bit. The flag “1” is set in the bit of the boundary information corresponding to the boundary hatch of “1”.

In the same manner, processing is continued until the last resync block, and high-efficiency encoding of image data and creation of boundary information are performed.

On the decoding side, the sync code is first detected by the sync code detection circuit 19 of the data received from the transmission path 17 in FIG. 2, and the transmission ID (transmission block number) is detected by the transmission ID detection circuit 21. Is detected. The write timing of the memory 23 is controlled by the sync code, and the memory 23 stores the transmission data at an address according to the transmission block number. Here, the capacity of the memory 23 is set to be equal to or more than the information amount of transmission data for one screen.

As described above, the error correction unit 27 corrects the errors of the boundary information and the compressed image information, and the error detection unit 29 misses the error in the error correction code correction process and corrects the error. Even if there is a correction, an error existing in the boundary information is detected. Therefore, it is possible to accurately extract only correct boundary information, thereby preventing use of incorrect boundary information in the decoding process of the compression code.

When reading the first resync block stored in the memory 23, since the first two symbols of the first hatch are resync numbers, the high-efficiency decoding subsequent to the third symbol of the first hatch is performed. To the conversion circuit 31.
Then, when the last hatch of the first resync block is detected by the boundary information detected by the above-described boundary information detection circuit 25, the efficiency of the next hatch, that is, the third symbol of the first hatch of the second resync block, is increased. Decoding circuit 3
Feed to 1.

Thereafter, this operation is repeated for the third resync block and thereafter, so that the digital image information returned to the original information amount from the high-efficiency decoding circuit 31 is restored.

Now, suppose that the error occurrence rate of the transmission line temporarily becomes extremely high, the frequency of occurrence of code errors exceeds the capability of the error correction unit 27, error correction becomes impossible continuously, and Is assumed, and the boundary information is also broken.

In this case as well, in the above-described embodiment, when the quality of the transmission path is restored and the error occurrence rate falls within the error-correctable range, new boundary information is detected and the boundary flag is set. The resync number existing in the first two symbols of the hatch next to the hatch corresponding to the standing bit can be detected. That is, image information can be restored in a normal state from the resync block in which the resync number is detected.

That is, even if there is a temporary deterioration of the transmission path, a complete image can be reproduced quickly.

It should be noted that the present invention is not only applied to the coding apparatus of the system as in the above-described embodiment, but is also applied to an apparatus for performing variable length coding of a generally transmitted image signal in units of areas on a screen. The effect is great.

In this embodiment, a codeword is formed by adding a check bit of an error detection code to boundary information, and a check bit of an error correction code is added to the boundary information and the compressed image information generation code. Are added to form a code word. However, a similar effect can be obtained by forming a code word of an error correction code for any of them.

[0080]

As described above, according to the present invention, all the boundaries of the coded data between the resync blocks in the transmission block can be easily recognized, so that the decoding operation can be performed even if a code error occurs during transmission. It is possible to return to a unit, and it is possible to suppress image deterioration when a code error occurs. Further, since a double error check code is added to the boundary data in the transmission block to strongly protect the boundary data, image degradation at the time of occurrence of a code error can be suppressed as compared with the related art.

[Brief description of the drawings]

FIG. 1 is a diagram showing a data transmission format, particularly a format of an error correction block, in an image transmission / reception system as one embodiment of the present invention.

FIG. 2 is a block diagram showing a schematic configuration of an image transmission / reception system as one embodiment of the present invention.

FIG. 3 is a diagram schematically showing information for one screen of an image transmitted in the system of FIG. 2;

FIG. 4 is a diagram showing a relationship between boundary information and image information in the system of FIG. 2;

FIG. 5 is a diagram for explaining a method of transmitting image information subjected to variable-length encoding in the system of FIG. 2;

FIG. 6 is a block diagram illustrating a schematic configuration of a conventional image transmission / reception system.

FIG. 7 is a block diagram schematically showing a configuration of a high-efficiency encoding circuit for an image using the ADCT method.

FIG. 8 is a diagram showing a state of zigzag scanning in the zigzag scanning circuit of FIG. 7;

[Explanation of symbols]

 Reference Signs List 5 Variable length high efficiency coding circuit 11 Boundary information creation circuit 13 Error detection coding circuit 15 Error correction coding circuit 17 Transmission line

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N ^7/ 24-7/68 H04N 1/41-1/419 G06F 11/10 H04L 12/56

Claims (2)

(57) [Claims] An input unit for inputting image data, an encoding unit for dividing the image data input by the input unit into a plurality of encoded blocks, and performing variable length encoding for each of the encoded blocks; Generating means for dividing the coded data variable-length coded by the coding means for each predetermined data amount to generate a fixed-length transmission block and outputting the transmission block to a transmission path, wherein the generation means The area for storing the coded data in the block is divided into a plurality of hatches, and the coded data is stored in a unit of a resync block in which a predetermined number of the coded blocks are collected in the hatch, and the coded data between the resync blocks is stored. A first error check for performing an error check on data including fixed-length boundary data for determining a hatch at the boundary of the data and data including the encoded data and the boundary data Image transmission, wherein a code and a second error check code for performing an error check on data including the boundary data and not including the encoded data are arranged at predetermined positions in the transmission block. apparatus. 2. An input step of inputting image data, an encoding step of dividing the image data input in the input step into a plurality of encoded blocks, and performing variable length encoding for each of the encoded blocks. Generating a fixed-length transmission block by dividing the coded data subjected to variable-length coding in the encoding step for each predetermined data amount and outputting the transmission block to a transmission path. The area for storing the coded data in the block is divided into a plurality of hatches, and the coded data is stored in a unit of a resync block in which a predetermined number of the coded blocks are collected in the hatch, and the coded data between the resync blocks is stored. Fixed-length boundary data for determining the hatch of the boundary of the first, and a first error check code for performing an error check on data including the encoded data and the boundary data, A second method for performing an error check on data including the boundary data and not including the encoded data;
An image transmission method, wherein the error check code is arranged at a predetermined position in the transmission block.