Patent ID: 8411976

Claim:
An image compression apparatus, comprising: a line memory unit to hold pixel values for at least one immediately previous line in lines to be processed of an image to be compressed; a division unit to divide pixels of the line to be processed into 2 n -pixel blocks; a first estimation value calculation unit to extrapolation-estimate a 2 n-1 -th pixel and a 2 n -th pixel in the blocks divided by the division unit using, as reference values, values of pixels immediately above the 2 n-1 -th pixel and the 2 n -th pixel respectively, and to obtain an estimated value in processing for a first hierarchical level; a second estimation value calculation unit to interpolation-estimate certain pixels using, as reference values, pixel values of one immediately previous line in the line memory and estimated values obtained up to processing for an immediately previous hierarchical level, and to obtain an estimated value in processing for a second hierarchical level through processing for an n-th hierarchical level; and an estimation coding unit to obtain an estimation error from the estimated value obtained in the processes from the processing for the first hierarchical level to the processing for the n-th hierarchical level, to convert the estimation error into a quantization number, to convert the quantization number into a variable length code, and to obtain a compression code.