BLOCK ENCODING SYSTEM FOR MULTI-VALUED IMAGE

摘要

PURPOSE:To restore an edge part with small gradation difference as reducing the encoding amount of noise by setting a threshold corresponding to the spatial distribution of gradation values in a block when obtaining a representative gradation value by comparing the difference between the maximum gradation value and the minimum gradation value in the block with the threshold. CONSTITUTION:The intermediate value arithmetic part 4 of a spatial distribution measurement part 20 calculates the intermediate value between the maximum gradation value and the minimum gradation value in a block. A binarization part 5 compares multi-valued image data Xij with the intermediate value and binarizes the data Xij. A binary data storing part 6 accumulates the binary data lambdaij in quantity equal to one block, and a variation times counting part 7 reads the data lambdaij sequentially in the horizontal direction and the vertical direction and counts respective variation times R1, R2 in order to measure the spatical distribution in one block. A threshold selection part 8 compares the calculation results R1 and R2 with a prescribed threshold S, in case the variation times in both directions are larger than the threshold S, the part 8 makes a threshold T1 for representative gradation number decision larger in order to increase the occurrence probability of single gradation quantization. In case the variation times in either direction is less than the threshold S, the threshold T1 is made less in order also to increase the occurrence probability of double gradation quantization.