# Research on VVC Intra-Frame Bit Allocation Scheme Based on Significance Detection
## 2 Related Work
### Conventional Rate Control Algorithms  
Due to the critical nature of the rate control module in video coding standards, each standard recommends a distinct rate control model, such as TMN8 for H.263 [14], JVT-G012 for AVC [15], JCTVC-K0103 for HEVC, and JVET-K0390 for VVC [16]. From a mathematical modeling point of view, the bit rate control schemes can be classified into three types of models, namely, Q-domain models, \(\lambda\)-domain models, and \(\rho\)-domain models. The three models initially establish a correlation between bit rate and distortion; however, scholars have progressively transformed this correlation into one with the parameters of the proposed model, which subsequently dictate the quantization parameters. The Q-domain model explores the relationship between the code rate R and the distortion D in the QP domain and is the most widely used model for rate control. [PERSON] et al. [17] proposed a more accurate second-order Rate-Distortion (R-D) model based on Q-domain. In it, a sliding window is used to select the data, which can effectively reduce the impact of scene changes. Meanwhile, shape coding artifacts are eliminated using adaptive thresholding, which achieves accurate bit allocation with lower latency and limited buffer. This scheme has been adopted by the MPEG-4 standard. [PERSON] et al. [18] proposed a low-delay HEVC rate control scheme based on a temporal prediction structure. Firstly, a quadratic R-Q model is established and a method for determining the QP of the first frame is proposed. Then a frame-level bit allocation scheme is proposed, and finally, the CTU-level QP is predicted. In the 8 th meeting of JCT-VC, [PERSON] et al. [19] proposed a rate control algorithm based on the R-Q model, which captures the relationship between the target rate R and the QP value of a pixel, and then unifies the hierarchical relationship of the coding units in the rate control, which means that the model can be used for Group of Pictures (GOP), frame or CTU, and the algorithm is also adopted by the AVC coding standard. However, according to the research of JCTVC-I0426 [20], the slope \(\lambda\) of the R-D curve has a more important position in the determination of the bit rate. [PERSON] et al. [4] proposed the K0103 rate control proposal, which has been incorporated into the HEVC standard, and established the R-\(\lambda\) and \(\lambda\)-QP models to ascertain the quantization parameters of the coding unit in accordance with [PERSON]'s rate-distortion theory via the Lagrange multiplier \(\lambda\), which signifies the rate-distortion model's slope, as a link. [PERSON] et al. [21] proposed an intra-frame rate control scheme adapted to the R-\(\lambda\) model based on SATD, which provides better rate control at the intra-level and the slice level. In addition to this, [PERSON] et al. [22] proposed a frame-level bit allocation scheme in HEVC, which presents an improved R-D model to obtain higher accuracy with lower bit rate and mismatch rate by utilizing the information of the coded frames more fully. To achieve the most optimal R-D performance on a global scale, an optimal frame-level bit allocation formula and a GOP-level Lagrange multiplier are implemented. [PERSON] et al. [23] proposed a new R-D quadratic model using VTM-2.0 as a platform to model the distortion as a quadratic function of the logarithm of the bit rate and derive the R-D relationship from it. In addition, this new GOP-level and frame-level bit allocation schemes are proposed to implement the frame-level rate control algorithm for VVC. The study conducted by [PERSON] et al. [24] examined the impact of skip blocks on the estimation of rate-distortion parameters and the correlation between inter-frame quality.