| 摘要 |
PURPOSE:To raise the efficiency of compressing of picture data by sequentially adding converted data in blocks, comparing a frequency at the time when the added value reaches a specified value with a threshold frequency and sampling the converted data according to the compared result. CONSTITUTION:Halftone picture data is orthogonally converted in terms of two dimensions in an orthogonal transform circuit 11 and the converted data (y) is arranged in vertical and horizontal directions in order of the sequence of conversion function in the respective blocks. Next, a bit distribution decision part 20 connected to a coding circuit 12 sequentially adds the absolute value of the data (y) from a high frequency component side to a low frequency component side and obtains the converted data y0 when the added value reaches the specified value, then compares the corresponding frequency F0 with the threshold frequency F'. When F0 is higher than F', the area on the low frequency side is set as a zone sampling area and when F0 is lower than F', the area nearer to the low frequency side than to a circular arc centering the data (y) and passing through the data Y0 is set as the zone sampling area. And the code length of a specified bit is assigned to each data (y) of the respective areas and information Q expressing the bit distribution is transmitted to the circuit 12 to encode the data (y). |
