Adaptive variable-length coding and decoding methods for image data

Abstract

An adaptive variable-length coding/decoding method performs an optimal variable-length coding and decoding depending on an intra mode/inter mode condition, quantization step size and a current zigzag scanning position, such that a plurality of variable-length coding tables having different patterns of a regular region and an escape region according to statistical characteristics of the run level data are set. One of the variable-length coding tables is selected according to mode, quantization step size and scanning position, and the orthogonal transform coefficients according to the selected variable-length coding table are variable-length-coded.

1. An adaptive variable-length coding method whereby quantized orthogonal transform coefficients are scanned in a zigzag pattern, are modified into run, level data and then are variable-length coded in a coding system for image data, said method comprising the steps of:
 setting a plurality of variable-length coding tables having different patterns of a regular region and an escape region according to statistical characteristics of said run, level data;    selecting one of said plurality of variable-length coding tables according to intra/inter mode information of the currently processed block, zigzag scanning position and quantization step size; and    variable-length coding the orthogonal transform coefficients according to said selected variable-length coding table, wherein said selecting step has the selecting range of a plurality of variable-length coding tables having different patterns of a regular region and an escape region according to said intra/inter mode information of the currently Processed block.    
     
     
       2. The adaptive variable-length coding method as claimed in  claim 1 , wherein said variable-length coding table is selected in accordance with said zigzag scanning position and quantization step size within the range determined by the corresponding mode. 
     
     
       3. The adaptive variable-length coding method as claimed in  claim 1 , wherein data of said escape region of said variable-length coding table selected in said variable-length-coding step is coded into data having variable run-length and level-length. 
     
     
       4. An adaptive variable-length decoding method for decoding the data coded by said adaptive variable-length coding method as claimed in  claim 1 , in a decoding system for image data, said decoding method comprises the steps of:
 setting a plurality of variable-length decoding tables having different patterns of a regular region and an escape region according to statistical characteristics of the run, level data;    inputting intra/inter mode information transmitted from said coding system;    inputting quantization step size transmitted from said coding system;    detecting position information while zigzag-scanning by accumulating run values of run, level data;    selecting one of said plurality of variable-length coding tables according to said intra/inter mode information, quantization step size and position information; and    variable-length decoding the data received according to said selected variable-length coding table.    
     
     
       5. The adaptive variable-length decoding method as claimed in  claim 4 , wherein said variable-length decoding table selecting step has the selection range of a plurality of variable-length coding tables having different patterns of a regular region and an escape region according to said intra/inter mode information of the currently processed block in said mode information inputting step. 
     
     
       6. The adaptive variable-length decoding method as claimed in  claim 5 , wherein said variable-length decoding table is selected in accordance with said zigzag scanning position and quantization step size within the range determined by the corresponding mode. 
     
     
       7. The adaptive variable-length decoding method as claimed in  claim 4 , wherein data of said escape region of said variable-length decoding table selected in said variable-length-decoding step is decoded into run, level data corresponding to variable run-length and level-length. 
     
     
       8. An adaptive variable- length decoding method for decoding image data encoded by an adaptive variable - length coding method, in which quantized orthogonal transform coefficients of the image data are scanned in a predetermined pattern and are encoded, the decoding method comprising:      receiving intra/inter mode information;        receiving the encoded quantized orthogonal transform coefficients;        detecting scanning position information of the encoded coefficients;        selecting one of a plurality of variable - length decoding tables according to the intra/inter mode information and the scanning position information, wherein the plurality of variable - length decoding tables comprise:      a table selectable for an alternating - current  ( AC )  component of an intra mode that is different from a table selectable for an inter mode, and        a table selectable for a direct - current  ( DC )  component of the intra mode; and          variable - length decoding the encoded quantized orthogonal transform coefficients according to the selected variable - length decoding table.      
     
     
       9. The adaptive variable- length decoding method of    claim 8   , wherein said variable - length decoding tables have different patterns of a regular region and an escape region.    
     
     
       10. The adaptive variable- length decoding method of    claim 9   , wherein data of said escape region of said variable - length decoding table selected in said variable - length - decoding step is decoded into data having variable or fixed run - length and level - length.