Toward optimal real-time transcoding using requantization in the DCT domain

Real-time multimedia applications often require efficient bit-rate reduction. This is mainly done by requantization, usually in the DCT domain. This work introduces theoretical rate-distortion analysis that allows for straightforward selection of the quantization step needed to achieve a given bit-rate. The analysis is based on the Laplace-like distribution of DCT coefficients in the transform domain and on the structure of the quantizers commonly used in image coding. We show that the proposed transcoding design achieves efficient compression at relatively low distortion, while keeping the computational complexity very low, allowing for real-time implementation.