JPS6343473A - Modified huffman code decoding circuit - Google Patents

Abstract

PURPOSE:To eliminate a parallel serial converting circuit by providing the decoding circuit of MH (modified Huffman) code, a control data latching circuit that latches the output of the H code decoding circuit and a run length circuit that latches run length data. CONSTITUTION:First, a run length latching circuit 3 and a control data latching circuit 4 are initialized by a reset signal RS. Then, MH code (a) is read out from a buffer memory, and data for 1 byte are latched in an MH code latching circuit 1 and decoding is started. An MH code decoder circuit 2 outputs MH code data (a), white/black discrimination data (c), sequence data and bit position data (e). When the termination of MH code is detected, the MH code decoding circuit 2 outputs 1 code termination data (f). Succeeding MH code can be decoded by resetting only run length data (b), and in such a case, new control data are outputted.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention provides a decoding circuit for decoding a facsimile signal encoded by a modified Huffman encoding method, which is one of the one-dimensional encoding methods for facsimile signals. It is related to.

[Conventional technology]

Black and white binary facsimile signals generally have extremely high redundancy, so if this redundancy is reduced through appropriate signal processing and only the truly necessary signals are transmitted, the amount of data can be significantly reduced.

For this reason, various band compression methods have been devised for digital facsimile, one of which is the modified Huffman encoding method.

A modified Huffman code (hereinafter referred to as "MH code") is a Huffman code constructed based on the probability of occurrence of each run for black and white run lengths, and one run is composed of a make-up code and a terminating code. Encode in combination.

A code called EOL indicating a separation between scanning lines is inserted between codes for one scanning line.

When decoding an MH code, the code following EOL is set as a white code, and decoding is started from this code. When the code for one run of white or black is decoded, the next code is decoded by changing the white or black.

This process is sequentially repeated, and when EOL is detected, the decoding for one scanning line is completed.

MH code encoding and decoding are often processed by a microprogram, taking into account the execution of facsimile communication procedures.

In this case, the MH code to be decoded is stored in a buffer memory. The MHH encoder (decoder) sequentially reads MH codes from the buffer memory and decodes them. now,
For example, if the unit of data transfer between the buffer memory and the decoder is 8 bits, the decoder reads 8 bits of parallel data from the buffer memory, converts it from parallel to serial, and decodes it bit by bit. .

[Problems to be Solved by the Invention] The conventional decoder described above decodes the MH code bit by bit, so the parallel data read from the buffer memory must be converted from parallel to serial.
There is a problem in that a circuit for this is required, and the processing time increases accordingly.

[Means for solving problems]

In order to solve these problems, the present invention decodes a modified Huffman code encoded by a modified Huffman encoding method, which is one of the one-dimensional encoding methods for facsimile signals, and expressed as an n-bit parallel signal. In the decoding circuit for the purpose of The decoding circuit is provided with a data latch circuit and a run-length latch circuit that latches run-length data.

[Effect]

In the present invention, there is no need for a parallel-to-serial conversion circuit for converting an n-bit parallel signal from parallel to serial, and the n-bit parallel signal is decoded as it is.

〔Example〕

An embodiment of a modified Huffman code decoding circuit according to the present invention is shown in the figure. In the figure, 1 is an MHH code latch circuit for latching MH code a as an n-bit parallel signal, 2 is an MH code code decoding circuit for decoding the MH code, and 3 is a run-length latch circuit for latching run-length data b. Reference numeral 4 denotes a control data latch circuit that latches output control data from the MH code decoding circuit and the like.

Next, decoding of the MH code for one scanning line will be explained.

First, the run length latch circuit 3 and the control data latch circuit 4 are initialized by the reset signal R3. Thereafter, the MH code a is read from the buffer memory, 1 byte of data is latched into the MHH code latch circuit 1, and decoding is started. Note that the MH code latch circuit 1, the run length latch circuit 3, and the control data latch circuit 4 are connected to the clock C.
Synchronization is achieved by L.

The MH code decoding circuit 2 includes MH code data a, white/black data C for distinguishing whether a white code or a black code is being decoded, and sequence data (run length data b and make-up code/ data indicating the different termination code d) and bit position data (8
Data indicating the effective part of the bit's MH code a)e
is input, and control data such as run length b and decoding completion data f are output.

When detecting the end of one MH code in the MHH codes latched to 1, the MH code decoding circuit 2 notifies the 1 code decoding end data f, and also outputs its run length data b and make-up code/terminating code. d
and bit position data e indicating the remaining 8 bits of the MH code a. At this time, in order to continue decoding the <MH code, only the run length data b needs to be reset, and in this case new control data is output.

If the end of the MH code is not found in the MW code latched to 1, the decoding end data in the control data is not turned on, and 1-byte end data g is notified. In this case, the next data is read from the buffer memory and the MHH
The signal is latched into the number latch circuit 1. MHH decoding circuit 2
outputs control data etc. according to the newly latched data, so by performing the corresponding processing as described above and continuing this until EOL is detected,
Decoding of the MH code for one scanning line is completed.

〔Effect of the invention〕

As explained above, the present invention provides an MH code latch circuit for latching an n-bit parallel signal, an MH code decoding circuit for decoding a modified Huffman code, and an MH code decoding circuit for decoding a modified Huffman code.
By providing a control data latch circuit that latches output control data from the H-code decoding circuit and a run-length latch circuit that latches run-length data, the n-bit parallel signal read from the buffer memory is converted from parallel to serial. Since it is possible to decode various signals, it is possible to reduce the circuit scale by reducing the number of parallel-to-serial conversion circuits and to improve the signal processing speed.

[Brief explanation of the drawing]

The figure is a system diagram showing an embodiment of a modified Huffman code decoding circuit according to the present invention. 1... MHH code latch circuit, 2... MH code decode circuit 3... Run length latch circuit, 4... Control data latch circuit.

Claims (1)

[Claims] The n-bit parallel signal is latched in a decoding circuit for decoding a modified Huffman code encoded by the modified Huffman encoding method, which is one of the one-dimensional encoding methods for facsimile signals, and expressed as an n-bit parallel signal. an MH code latch circuit for decoding the modified Huffman code, a control data latch circuit for latching output control data from the MH code decoding circuit, and a run-length latch circuit for latching run-length data. A modified Huffman code decoding circuit, characterized in that it decodes the n-bit parallel signal as it is as a parallel signal.