Image coding method and apparatus therefor

An image coding apparatus comprising:

• a discrete cosine transform unit for performing a discrete cosine transform function on a sub-block as time-domain data so as to output a discrete cosine transform coefficient as frequency-domain data, wherein an input image signal is divided into sub-blocks composed of a predetermined number of unit blocks;
• a quantizing unit for quantizing said discrete cosine transform coefficient by a predetermined quantization step size determined in accordance with a scale factor;
• a variable-length coding unit for encoding the quantized coefficient into a variable-length code;
• a complexity calculating unit for producing a complexity signal in accordance with a pixel value of a sub-block of the input image signal;
• a complexity normalizing unit for normalizing the complexity signal for the sub-block, and outputting a complexity normalizing signal;
• a zero coefficient counting unit for counting zero coefficients of the sub-block which are the discrete cosine transform coefficients from the discrete cosine transform unit within a predetermined range;
• a zero coefficient normalizing unit for normalizing said zero coefficient of the sub-blocks;
• a weight calculating unit for producing a transient weight signal in accordance with said zero coefficient and a predetermined compression ratio;
• and
• a scale factor generator for summing said complexity normalizing signal, said zero coefficient normalizing value and said transient weight signal, to generate said scale factor, and supplying said scale factor to said quantizing unit.