Coding method for multilevel-gradated picture signal

Claim 1

In a coding method for a multilevel-gradated picture signal, comprising the steps of: segmenting a series of binary codes obtained by processing a multilevel-gradated original picture signal for binary representation, every predetermined number n of picture elements on each scanning line, so as to form blocks respectively capable of assuming values of "0" to "2 n -1"; and encoding the value of a change block having changed its value and its position on the scanning line so as to be reproduced on the reproducing side; the improvement characterized by said encoding step performed by the use of the following data: a 0 : address of a block, on a coding line, with which coding starts; a 1 : address of a change block which occurs after the block of the address a 0 on the coding line; b 1 : address of a change block which occurs on a coded reference line after a block of the position just above the block of the address a 0 ; b 2 : address of a change block which occurs immediately after the block of the address b 1 on the reference line; v 1 (x): value of a block at a position x on the reference line; v 2 (x): value of a block at a position x on the coding line, said encoding step coding the value V 2 (a 0 ) and the address a 1 by coding a relative address of (a 1 -b 1 ) in a Vertical Mode where v 1 (a 0 )=v 2 (a 0 ) and the relative address of (a 1 -b 1 ) is included in a predetermined range of values; said encoding step coding the value v 2 (a 0 ) and the address a 1 by coding a relative address of (a 1 -a 0 ) in a Horizontal Mode I where v 1 (a 0 )=v 2 (a 0 ) and the relative address of (a 1 -b 1 ) exceeds the predetermined range of values; and said encoding step coding the value (v 2 (a 0 ) and the address a 1 by coding the value v 2 (a 0 ) and the relative address of (a 1 -a 0 ) in a Horizontal Mode II where the value v 1 (a 0 ) is not equal to v 2 (a 0 ), said Vertical Mode, said Horizontal Mode I and said Horizontal Mode II being mutually differentiated from one another by said coding.