Operational distortion-quantization curve-based bit allocation for smooth video quality

Quality fluctuation has a major negative effect on subjective video quality. A desirable single-pass frame-level constant-distortion bit allocation scheme is proposed in the paper for smooth video quality throughout the video sequence. The average distortion of all previous coded frames is taken as the target distortion for the current frame. According to the linear rate control algorithm [Z. He, S.K. Mitra, A linear source model and a unified rate control algorithm for DCT video coding, IEEE Trans. Circuits Syst. Video Technol. 12 (2002) 970-982; Z. He, S.K. Mitra, Optimum bit allocation and accurate rate control for video coding via ρ domain source modeling, IEEE Trans. Circuits Syst. Video Technol. 12 (2002) 840-849], the distortion and rate are exponential and linear functions of the number of zero coefficients, respectively. Based on the distribution of the absolute DCT coefficients, an operational distortion-quantization stepsize (D-Q) relationship curve can be established quickly. With the target distortion and operational D-Q curve, we then derive the close-form formulas for estimating the number of zero coefficients and the slope θ in the linear rate model, as well as the bit budget for the current frame. Experimental results show that the proposed constant-distortion (but variable rate) bit allocation scheme provides much smoother video quality on all test video sequences than the constant bit allocation scheme that has been used in many standard video coding reference software.