Coding method for increasing compressing efficiency of data in transmitting or storing picture signals

Claim 1

A coding method for compressing picture data in transmitting or storing picture signals involving: - a CPU (10) for controlling an overall system; - a ROM (20) for storing a coding table and an execution program for the CPU; - a RAM (30) for storing sub-blocks of DCT ac coefficients of the video data and outputting the stored ac coefficients to the CPU by a predetermined control; and - a zig-zag scanning section (40) for controlling the RAM so that ac coefficients stored in the RAM are zig-zag scanned under the control of the CPU and are outputted to the CPU; the method comprising: - a first step (A1) of initializing a run field, a count and a coefficient number; - a second step (A2) of reading ac coefficients stored in said RAM (30) by zig-zag scanning said sub-block and controlling said zig-zag scanning section (40); - a third step (A3) of shifting the run field by one bit toward the upper bits and inserting zero into the lowermost bit; - a fourth step (A4) of judging as to whether said read ac coefficient is zero or not; - a fifth step (A5) of increasing both said run field and said count by one only if it is found at the fourth step that said read ac coefficient is non-zero; - a sixth step (A6) of grouping, coding and outputting said read ac coefficient on the basis of a coding table stored in said ROM (20) only if it is found at the fourth step that said read ac coefficient is non-zero; - a seventh step (A7) of judging as to whether all of the ac coefficients for one sub-block are completely processed by checking the coefficient number; - an eighth step (A8) of increasing the coefficient number by one and returning to the second step if it is found at the seventh step that not all of the ac coefficients for one sub-block are completely processed; - a ninth step (A9) for outputting an EONZ code showing the completion of the coding of the non-zero coefficients if it is found at the seventh step that all of the ac coefficients for one sub-block are completely processed; and - a tenth step (A10) of coding the run field if it is found at the seventh step that all of the ac coefficients for one sub-block are completely processed, whereby in said tenth step of coding are included: first sub-steps (C1, C2) for removing from said run field the invalid upper bits, in order to leave only the valid lower bits, when said count is not zero; a second sub-step (C3) for outputting the uppermost bit of said run field; a third sub-step (C4) for checking as to whether the whole of said run field has been outputted up to the last '1' bit according to whether said count is 1; and fourth sub-steps (C5, C6) for decreasing said count by 1 and for shifting said run field by 1 bit toward the upper bits if it is found at the third sub-step that not the whole of said run field has been outputted, said second, third and fourth sub-steps being repeated only until the whole run field has been outputted up to the last '1' bit, as determined by said third step.