JPH01144779A - Circuit for substituting line before encoding error for modified huffman code - Google Patents

Abstract

PURPOSE:To eliminate a need of an encoding circuit and a decoding circuit to reduce the circuit scale and to shorten the processing time by checking only decoding error in the modified Huffman(MH) code. CONSTITUTION:The MH code whose decoding error should be checked is stored in an input buffer memory 1. First, one-line components of the MH code are decoded by a decoding circuit 2, and the decoding circuit 2 does not output an original image signal but outputs only run lengths to only add white and black run lengths at the time of decoding one-line components of the MH code. when EOT as the delimiter of one line is detected, the totalized run length is compared with the number of picture elements of one line preliminarily set for decoding error check, and decoding error is decided if they do not coincide with each other. When the MH code of decoding error is stored in a line memory 6, the MH code corresponding to the line correctly decoded just before is stored in a line memory 7. Thus, the preceding line substitution processing of decoding error is performed without returning to an original image.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a decoding error pre-line replacement circuit for facsimile signals, and in particular to a modified Huffman (MH) encoding system, which is one of the one-dimensional encoding systems for facsimile signals. The present invention relates to a circuit for replacing lines before decoding errors for facsimile signals encoded by.

Conventional Technology Regarding digital facsimile, various band compression methods such as -dimensional encoding and two-dimensional encoding have been proposed in order to reduce data spacing. As for the -dimensional encoding method, CCITT recommends the Modified Huffman encoding method as the standard encoding method for Group 3 (GJ) aircraft.

(2) In code decoding, decoding errors may occur due to processing during transmission. Normally, when a decoding error occurs, previous line replacement processing is performed.

The immediately preceding line that was correctly decoded is used in place of the line where the decoding error occurred.

Problems to be Solved by the Invention In facsimile-related devices, a process is performed in which a received enclosing code is checked only for decoding errors, the line in which the decoding error occurred is replaced with the previous line, and the line is sent again as the old code. There is something to do.

Conventionally, in order to perform the above processing, both a 6MH encoding circuit and a 4-bit decoding circuit are required, and the received encircling code is decoded and returned to the original image, and if there is no decoding error, it is encoded as is, and if there is a decoding error, it is encoded as is. The method is to discard that line, encode the original image data of the previous line, replace the previous line, and finally send it out again as a related code.

However, this method has disadvantages in that it requires both an encoding circuit and a decoding circuit, resulting in a large circuit size, and the processing is complicated and takes a long processing time.

The present invention has been made to eliminate the above-mentioned drawbacks inherent in the conventional technology, and therefore, the purpose of the present invention is to reduce the scale of one circuit, simplify control, and shorten processing time. The object of the present invention is to provide a novel line replacement circuit before decoding errors.

Means for Solving the Problems In order to achieve the above object, the modified Huffman code decoding error 9 previous line replacement circuit according to the present invention does not output the original signal as a result in decoding the MH code, but only the run length. A modified Huffman code decoding circuit that outputs and adds the run lengths, @/ that stores 7947 modified Huffman codes, a second line memory on one side, and a second line memory that stores 7947 modified Huffman codes, and a second line memory that stores 7947 modified Huffman codes.
a first selector for selecting an input to the first line memory; and a first selector for selecting an output from the first line memory to the output buffer memory.

Embodiment Next, a preferred embodiment of the present invention will be specifically explained with reference to the drawings.

FIG. 7 is a block diagram showing an embodiment of the present invention.

Referring to Figure 1, an input buffer memory 1 contains an output code for checking for decoding errors.

First, the decoding circuit KO decodes the 7947-minute encircling code, but when decoding the 4/7947-minute code, the decoding circuit KO outputs only the run length without outputting the original image signal.
Only the white and black run lengths are added. Compare the total run length added at the time when EOL, which is the delimiter of l line, is detected with the preset number of pixels of l line (e.g. /'/2g pixels/line) to check for decoding errors. If they match, it is determined that the decoding was successful, and if they do not match, it is determined that the decoding has been erroneous.

The decoding circuit 1 sequentially reads out the area codes from the input buffer memory l, but the extracted area codes are simultaneously stored in one of the line memory 6.7 (here, for example, line memory), l. If line decoding is completed and normal at point 9, -y 794 stored in in-memory 6
The 7/7 code is transferred to the output buffer memory 3. At the same time, the decoding circuit starts decoding the west code of the next line, and this deer code is simultaneously stored in the line memory leaf.

On the other hand, if it is determined that there is a decoding error when the decoding of the l line is completed, the next process is performed. Assume that a surrounding code that causes a decoding error is stored in the line memory 6. In this case, the line memory blank stores the old code for nine lines that was correctly decoded immediately before. Therefore, to perform pre-line substitution.

At the same time as sending out the second line code of the line memorandum to the output buffer memory 3 again, the decoding circuit starts decoding the second line of the next line, and the second code is simultaneously stored in the line memory B.

By the above operation, it is possible to perform previous line replacement processing for decoding errors without returning to the original image during decoding of 1Mki code.

As described in detail, according to the present invention, only decoding errors are checked in a 1MH code, and only the previous line of that line is replaced and output.

Since it is not necessary to have both an encoding circuit and a decoding circuit, the scale of one circuit becomes smaller, and control becomes simpler, resulting in the effect of shortening processing time.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention. /... human cover memory, co... 匪 code decoding circuit. 3... Output buffer memory, l, j... Selector,
6゜7...Line memory for enclosing code Patent applicant NEC Corporation

Claims (1)

[Claims] A modified Huffman code that checks for decoding errors in the modified Huffman code stored in the input buffer memory, performs previous line replacement on the decoded error line, and outputs the result as a modified Huffman code again to the output buffer memory. A modified Huffman code pre-decoding error line replacement circuit that outputs only run lengths without outputting the original signal as a signal result in decoding a modified Huffman code, and performs addition of the run lengths to check for decoding errors. A Huffman code decoding circuit, a line memory that stores the modified Huffman code for one line, a first line memory that stores the modified Huffman code of the line that is being decoded, and a first line memory that stores the modified Huffman code of the line that was correctly decoded immediately before. and a means for switching input/output between an input/output buffer and the first and second line memories according to the decoding result of the decoding circuit. Front line replacement circuit.