DESIGN OF IMAGE-ADAPTIVE QUANTIZATION TABLES FOR JPEG

The rate-distortion trade-off in the discrete cosine transform-based c oding scheme in ISO/JPEG is determined by the quantization table. To p ermit a different quality to be selected by a user, a common practice is to scale the standard quantization tables that have been empiricall y determined from psychovisual experiments. In this paper, an algorith m is presented to generate a quantization table that is optimized for a given image and for a given distortion. The computational complexity of this algorithm is reduced compared to other techniques. The optimi zed, image-adaptive quantization table typically yields an improvement of 15% to 20% in bit rate compared to the use of standard, scaled qua ntization tables. Once an optimized quantization table has been genera ted for a specific image, it can also be applied to other images with similar content with a small sacrifice in bit rate.