METHOD AND APPARATUS FOR CODING AND DECODING DIGITAL IMAGE DATA USING IMAGE QUANTIZATION MODIFICATION

An image coding method and apparatus for transforming and quantizing an image to produce transformed and quantized coefficients. The coefficients are coded and a complexity index value is obtained from the input image to calculate local characteristic values used to modify the quantization scale. In this manner, rate control is obtained on the basis of the local characteristics of the image, whereby the quality of the coded image and the precision of the rate control is improved.