Statistical Computation of Discrete Cosine Transform in Video Encoders

Computation reduction is important for the implementation of software video codecs. This paper describes a scheme for reducing the required computations in video encoders by skipping some of the Discrete Cosine Transform (DCT) and quantization calculations. We study the relationship between the Mean Absolute Error (MAE) of the motion compensated difference blocks and the distribution of DCT coefficients. The relationship between the quantized DCT coefficients and the quantization level is also investigated. Based on the MAE of the motion compensated difference block and the quantization level, three options for the DCT calculation can be chosen: calculating all 8x8 DCT coefficients, calculating the DC coefficient only, or skipping the whole DCT computation. Simulation results show that the Peak Signal-to-Noise Ratio (PSNR) degradation is negligible with significant computation reduction achieved.