Space-domain-based CTU layer rate control for HEVC

Aiming at the loss of rate-distortion performance in the high-efficiency video coding tree units (CTU) layer rate control scheme, this paper proposes an improved CTU-level rate control algorithm in the spatial domain. Specifically, in the CTU layer, the Scharr gradient detection operator and the Hadamard transform algorithm are used to detect the texture complexity area and the transform compression area, respectively. The scale coefficients are normalized and adaptively adjusted to construct a new adjustment factor for the gradient and sum of the absolute transformed difference of the image. In this way, the target bits of each CTU layer are reasonably adjusted and accurately allocated. Meanwhile, a more accurate model parameter update is realized in the coding structure of the CTU group. The experimental results show that compared with the dynamic adjustment control algorithm under configurations of low-delay P and B frames, the relative error of code rate of the optimized algorithm is both reduced by 0.012% compared with the dynamic adjustment control algorithm, while the rate-distortion performance is improved by 2.4% and 2.6%, respectively.