JPH0492515A - Modified huffman decoding system - Google Patents

Abstract

PURPOSE:To reduce the quantity of omitted information by utilizing the normal information even to a line where an error is detected by performing the comparison of contents between the 1st and 2nd buffers if an error is detected in the contents of the 2nd buffer. CONSTITUTION:The subsequent bits are continuously stored until a 2nd buffer line termination code after the information on a single line is stored in a 1st buffer. Then the contents of the 1st and 2nd buffer are continuously compared with each other until an error is detected in the contents of the 2nd buffer. When the coincidence is secured between the contents of both buffers, the contents of the 1st buffer substitute for those of the 2nd buffer. If no coincidence of contents is obtained between both buffers, the line information is regenerated with the bits needed for detection of the error of the contents of the 2nd buffer. That is, the bits needed for occurrence of a bit error in a single line are effectively used. Thus the quantity of omitted information (number of omitted bits in a single line) is reduced.

Description

[Detailed Description of the Invention] The present invention relates to a modified Huffman decoding method,
More specifically, RunLength Mod Huffman (RunLength Mod
Huffman; RL-MH) decoding method. For example, it is applied to image compression/expansion methods.

The G3 facsimile uses MH (Modified Huffman) encoding to compress and transmit image information line by line. In reality, the number of consecutive white pixels and black pixels is counted in the order of white and black for each line, and this number is M
R L -M H encoding, in which the information is H encoded and transmitted, is used. In general, if an unencoded digital image causes an error during transmission, it will remain in that part, but if it is encoded, the impact will be greater, and therefore there will be no way to detect errors or deal with errors when they occur. It is being

Error detection is as follows: 1. Is the number of bits of the line decoded data equal to the specified number of bits? (A; 1728 bits, B; 2
048 bits) 2. Are the makeup codes consecutive?

3. Are you receiving data that is not in the code table?

4. Next EOL of makeup code (End o
fLine).

will be judged.

In addition, what to do when an error occurs is to change the bit string between the time EOL is detected and the next EOL is detected.
If 1 to 4 above apply, a process of replacing with the previous line is performed. Furthermore, if EOL is not detected for a predetermined period of time, the modem itself interrupts processing.

Therefore, even if there is a 1-bit error, 1
Even if a line is not reproduced and the position of the error bit is one line later, processing is performed to replace the previous line, resulting in many missing pieces of information.

The present invention was made in view of the above-mentioned circumstances.
The purpose of this is to provide a modified Huffman decoding method that attempts to reduce missing information by utilizing as much normal information as possible even for lines where errors have been detected.

Fifth aspect: In order to achieve the above object, the present invention provides (1) a decoding system for a run-length modified Huffman encoding system used for facsimile communication, which includes two line information storage means, an error detection means for each line, and the 2 line information comparison means, the line end code is detected,
After one line information is stored in the first buffer, subsequent bits are stored in the second buffer until a line termination code is detected, and if an error is detected in the contents of the second buffer, Compare the contents of the second buffer and the contents of the first buffer until the error is detected, and if the contents of both buffers are the same, substitute the contents of the first buffer for the second buffer, If they are not the same, the line information is reproduced from the contents of the second buffer using the bits up until the error is detected; When comparing the contents of the second buffer with the contents of the first buffer, if the number of bits until an error is detected in the second buffer is smaller than the predetermined number of bits, the contents of the second buffer are compared with the contents of the first buffer. (3) In (1) or (2) above, replacing the bits of the second buffer until the error is detected with the corresponding bits of the first buffer,
Calculating the sum of exclusive ORs, when the sum is less than a predetermined threshold, the content of the second buffer is replaced with the content of the first buffer, and when it is greater than the threshold, the content of the second buffer is used. (4) forming a line with the bits until an error is detected; (4) the above (1) and (2);
Or, in (3), when the number of bits until an error is detected in the second buffer is larger than the number of bits in the first buffer, the comparison is performed using the number of bits in the first buffer; , (5) (1), (2), (3) or (
4) is characterized in that when using the bits of the second buffer until an error is detected, the corresponding bits of the first buffer are substituted for the subsequent bits. Hereinafter, the present invention will be explained based on examples.

FIG. 1 is a block diagram for explaining an embodiment of the modified Huffman decoding method according to the present invention. In the figure, 1 is a code table extraction section, 2 is a second (B,) buffer section, and 3 is a judgment block. 4 is a comparison section, 5 is an interpolation section, 6 is a 1-line information section, 7
is the first (B1) buffer section.

First, if the input bit sequence is 1st order, M
The number of pixels is decoded according to a code table corresponding to white and black pixels using the H code table. For example, as shown in FIG. 2, "0111" means that there are two consecutive white pixels, and then "011" means that there are many consecutive black pixels. As above, EOL
828 until (End of l, jne) is detected
277 part 2 is filled with the number of bits corresponding to the number of black and white pixels. That is, here, when white is correct, II OII
, and when black is the prisoner, the corresponding number of ``'']-'' is stored in the buffer section 2 of B.

Next, the determination unit 3 determines whether or not the contents of the B2 buffer are correct. The determination conditions at this time are error detections 1 to 4 described in the prior art.

When it is correct, the contents of the 828277 part 2 are outputted as one line information through the route (■) in the figure, and the contents of the B, buffer part 7 are replaced with the contents of the 828277 part 2.

If the result of the determination is incorrect, a comparison with the B1 buffer section 7 is performed. As shown in Figure 3, 828277 part 2
The contents of are stored until EOL is detected, but at this time it is assumed that the n bits up to point A in the figure can be accurately subtracted from the code table. When the number of bits n is smaller than a predetermined threshold thn, the contents of the B1 buffer section 7 are output as the contents of the 828277 section 2. When n is larger than the threshold thn, the total amount of exclusive OR (EXOR) of B2/<n bits of the sofa section 2 and n bits of the B1 buffer section 7 is determined. In the example of FIG. 3, n=16 and m=3. This m is compared with the threshold T I-I m, and m〈TH
When m, the contents of 828277 section 2 are replaced with the contents of B1 buffer section 7, and when m≧THm, 82827 section 2 is replaced with the contents of B1 buffer section 7.
Use the contents of Part 7, Part 2. Note that here, 0 is used for the data after the n bit, or the data after the n bit of the B1 buffer unit 7 is used. In the example of FIG. 3, if the threshold value T Hm = 2, the contents of the 828277 section 2 are used up to n bits, and the contents of the B□ buffer section 7 are used thereafter, for example. This situation is shown in FIG. Furthermore, when n bits is larger than the number of bits in one line (1728 bits in case of A4), the number of bits in one line is targeted.

Processing - Conclusion As is clear from the above description, according to the present invention, when a bit error occurs in one line, by effectively using the focus until the bit error occurs, missing information (
(bit loss within one line) can be reduced. Further, by changing the processing according to the number of bits until a bit error occurs in one line, it is possible to reduce the number of missing bits.

[Brief explanation of drawings]

FIG. 1 is a block diagram for explaining an embodiment of the modified Huffman decoding method according to the present invention, and FIG.
A diagram showing the decoded signal, FIG. 3 is the second (B2)
FIG. 4 is a diagram showing the contents of the buffer section and the first (B) buffer section.
2) It is a diagram showing a case where the contents of the buffer section are used. DESCRIPTION OF SYMBOLS 1... Code table extraction part, 2... 2nd (B2) buffer part, 3... Judgment part, 4... Comparison part, 5... Interpolation part, 6... 1 back information Part 7... First (B□) buffer part.

Claims (1)

[Claims] 1. Comparison of two line information storage means, error detection means for each line, and the two line information in a decoding method of a run-length modified Huffman encoding method used for facsimile communication. means for storing subsequent bits in the second buffer until the end-of-line code is detected after the end-of-line code is detected and one line information is stored in the first buffer; If an error is detected in the contents of the second buffer, the second buffer until the error is detected.
Compare the contents of the buffer with the contents of the first buffer,
When the contents of both buffers are the same, the contents of the first buffer are substituted for the second buffer, and when they are not the same, the contents of the second buffer are used as line information with the bits up to when an error is detected. Modified Huffman decoding method characterized by reproduction. 2. When comparing the contents of the second buffer in which an error has been detected and the contents of the first buffer, the number of bits until an error is detected in the second buffer is smaller than a predetermined number of bits. The modified Huffman decoding system of claim 1, wherein the contents of the second buffer are sometimes replaced by the first buffer. 3. Calculate the sum of the exclusive ORs of the bits in the second buffer until an error is detected and the corresponding bits in the first buffer, and when this is smaller than a predetermined threshold, 3. A line according to claim 1 or 2, characterized in that the content is replaced with the content of the first buffer, and when the content is greater than the threshold value, a line is formed with the bits up to when an error in the second buffer is detected. Modified Huffman decoding method. 4. When the number of bits until an error is detected in the second buffer is greater than the number of bits in the first buffer, the comparison is performed using the number of bits in the first buffer. or the modified Huffman decoding method described in 3. 5. Claims 1 and 2 characterized in that when using the bits of the second buffer until an error is detected, the corresponding bits of the first buffer are substituted for subsequent bits.
, 3 or 4.