Amount-of-compressed data control method and image data compressing apparatus

摘要

An amount-of-compressed-data control method applicable to image data compression processing for compressing an amount of data is disclosed. The method includes the steps of: performing quantization by: dividing one digital image into multiple blocks each having n×n pixels; performing orthogonal transform on each block; and dividing n×n conversion coefficients resulting from the conversion by each threshold value of a quantization matrix including n×n threshold values each resulting from the multiplication of a predetermined coefficient S (where S is a positive real number); and variable-length encoding the quantized data. In this method, the value of the coefficient S allows the amount of compressed data to fit within a predetermined range of a target amount of data by performing the quantization and encoding by dividing the interval that the coefficient S can take on into multiple intervals and calculating the estimated value of the coefficient S based on the relationship between the amount of compressed image data and the coefficient S, which is defined for each of the divided intervals.