Redundancy reduction coding method of multi-tone picture signal and apparatus therefor

A redundancy reduction coding apparatus of multi-tone picture signals, each of multi-tone picture signals indicating a corresponding tone of each of many picture elements resolved from a picture, comprising

• picture signal extracting means for delaying the picture signals of said picture elements already scanned and transmitted by a predetermined time period, so that a predetermined combination of picture elements is selected as reference picture elements from said picture elements already scanned and transmitted,
• a predetermined one of said reference picture elements being handled as a base reference picture element,
• first evaluating means for evaluating a plurality of first tone level differences between the tone level of said base reference picture element and each of the tone levels of said reference picture elements other than said base reference picture element,
• second evaluating means for evaluating a second tone level difference between a tone level of an objective picture element now to be transmitted and the tone level of said base reference picture element,
• region identifying means for identifying whether said plurality of first tone level differences and said second tone level difference are included in a predetermined region and applying an identifying signal,
• means for applying a first enabling signal in response to an identifying signal from said region identifying means indicating that said plurality of first tone level differences and said second tone level difference are all included in said predetermined region and for applying a second enabling signal in response to an identifying signal from said region identifying means indicating that said plurality of first tone level differences and/or said second tone level difference are not included in said predetermined region,
• code table means in which variable length codes are assigned by predicting an order in which the second tone level difference appears for each of a plurality of picture states represented by a combination of said plurality of first tone level differences, a shorter length of the code being assigned to the higher rank of said predicted orders,
• said code table means being enabled in response to said first enable signal and being responsive to said plurality of first tone level differences and said second tone level difference to apply said variable length code corresponding to said second tone level difference, and
• coding means responsive to said second enabling signal for coding the tone level of said objective picture element.