IMAGE CODER, IMAGE CODING METHOD, AND IMAGE CODING PROGRAM

摘要

PROBLEM TO BE SOLVED: To provide an image coder which can prevent the deterioration of an image while improving the compressibility of an image, an image coding method, and an image coding program. SOLUTION: For the image coder, a DCT transform unit 1 transforms the original image data by DCT transformation, and a preprocessing quantizer 2 and a preprocessing inverse quantizer 3 quantizes and inversely quantizes DCT coefficients discrete cosine transformed by standard quantization coefficients Q1 UV. A preprocessing analyzer 4 computes the difference between the DCT coefficient given from the DCT transform unit 1 and the DCT coefficient given from the preprocessing inverse quantizer 3, computes the difference between high frequency components and low frequency components, and gives the result to a comparator 5. The comparator 5 compares the given differential value with a preset specified values, and selects quantization DCT coefficients and gives them to a quantizer 6, according to the comparison result. The quantizer 6 performs quantization using fine quantization coefficients Q2 UV, and gives the result to a coder 7.