Efficient Bit Allocation and CTU level Rate Control for HEVC Picture Coding Symposium, 2013, IEEE Junjun Si, Siwei Ma, Wen Gao Insitute of Digital Media, Peking University, Beijing, China 1

Overview  Introduction  Analysis and Proposed Bit Allocation Scheme  Proposed CTU Level Rate Control Scheme  Experimental Results  Conclusion 2

Overview  Introduction  Analysis and Proposed Bit Allocation Scheme  Proposed CTU Level Rate Control Scheme  Experimental Results  Conclusion 3

Introduction  The ultimate aim of video coding is to provide the best video quality at the receiver side, subject to the available channel bandwidth.  Given a bit budget, the best coding quality can be achieved by optimal bit allocation and accurate rate control schemes.  The schemes is to meet the bit allocation budget by setting an appropriate QP for each coding unit of the video.  In this paper, CTU level rate control algorithm along with an efficient bit allocation scheme is proposed to generate higher and smoother coding quality for HEVC encoder. 4

Introduction Step1Step2 5

6 Introduction [1] B. Li, H. Li, L. Li, and et al. “Rate Control by Rr-lambda Model for HEVC,” in Joint Collaborative Team on Video Coding (JCT-VC) 11 th Meeting, JCTVC-K0103, Shanghai, China, [2] Z. He, Y.K. Kim and S.K. Mitra, “Low Delay Rate Control for DCT Video Coding via ρ-domain Source Modeling,” IEEE Transactions on Circuits and Systems for Video Technology, vol.11, pp.928–940, [3] T. Chiang and Y. Q. Zhang, “A New Rate Control Scheme Using Quadratic Rate-Distortion Modeling” IEEE Transactions on Circuits System and Video Technology, vol.7, pp , Feb [4] L. Tian, Y. Sun, Y. Zhou, and et al., “Analysis of Quadratic R-D Model in H.264/AVC Video Coding,” 17th IEEE International Conference on Image Processing, pp , China, [5] Y. Zhou, Y. Sun, Z. Feng, and et al., “New Rate-Distortion Modeling and Efficient Rate Control for H. 264/AVC video coding,” Signal Processing: Image Communication, vol. 24, pp , 2009.

Introduction 7 1.ρ-domain model 2.Quadratic model After observing the relationship between Qstep and quantization, the equation is modified by [8] ρ is the percentage of zeros among the quantized transform coefficient.

Introduction 8 intra-picture complexity similar to MAD, may lead to the model error

Overview  Introduction  Analysis and Proposed Bit Allocation Scheme  Proposed CTU Level Rate Control Scheme  Experimental Results  Conclusion 9

Before Proposed Bit Allocation Scheme  Current HEVC bit allocation problem bits

Proposed Bit Allocation Scheme  Thus the computational complexity to generate the operational rate distortion curves, it cannot work well for practical video applications.  Three levels’ simple but efficient bit allocation scheme for HEVC is proposed, which are GOP, frame, CTU levels. 11

Proposed Bit Allocation Scheme – GOP level Proposed method  R : target bitrate  F : frame rate  N : GOP size HM

Proposed Bit Allocation Scheme – frame level  By Table1, taking low delay configuration as an example, frames in depth 0 are critical in the reference relationship.  Therefore, it’s reasonable to allocate more bits to these frames so that they can be coded as high quality. 13

Proposed Bit Allocation Scheme – frame level Proposed method HM

Proposed Bit Allocation Scheme – CTU level Proposed method HM  For basic unit :

Effectiveness of The Proposed Bit Allocation Scheme  The proposed bit allocation scheme is implemented on HM10.0.  Table2 below are the experimental result 16

Overview  Introduction  Analysis and Proposed Bit Allocation Scheme  Proposed CTU Level Rate Control Scheme  Experimental Results  Conclusion 17

Proposed CTU Level Rate Control Scheme  In authors’ previous work[1][2], they proposed a frame level rate control scheme. At CTU level the QP for each CTU is decided with a reaction factor based on the frame level QP.  Besides, a CTU level QP adjustment strategy is designed. The SATD value of each CTU in the frame is calculated and store for CTU level QP adjustment. 18 [1] J. Si, S. Ma, W. Gao, And M. Yang. ―Adaptive Rate Control For HEVC, ‖ ITU-T Sg16 Contribution, Jctvc- I0433, Geneva, Ch, Apr.-May 2012 [2] J. Si, S. Ma, X. Zhang, W. Gao, ―Adaptive Rate control for High Efficiency video Coding, ‖ in Proceedings of SPIE Conference on Visual Communications and Image Processing, VCIP, San Diego, USA, Nov.2012

19 CTU Level Rate Control

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CTU Level Rate Control – Compared with HM 10.0 Proposed method HM Different level may have different parameter Target bit-rate corresponding to different level

QP Adjustment Strategy 22

QP Adjustment Strategy– Compared with HM 10.0 Proposed method  CTU QP clipping HM 10.0  CTU QP clipping 23

QP Adjustment Strategy 24  The proposed QP adjustment scheme is implemented on HM10.0.  Table3 below are the experimental result

Overview  Introduction  Analysis and Proposed Bit Allocation Scheme  Proposed CTU Level Rate Control Scheme  Experimental Results  Conclusion 25

Experimental Design  Experiments are designed and implemented on HM10.0.  The R-D performance of proposed rate control scheme is compared with JCTVC-K0103 (Configuration is Table4 below). 26

Experimental Result – Rate Distortion Performance  The authors employ the JCTVC-K0103 rate control as anchor. 27

Experimental Result – Smoothness of the Coding Quality  Another advantage of the proposed rate control scheme is it helps to smooth the coding quality and reduce the quality fluctuation. 28

Overview  Introduction  Analysis and Proposed Bit Allocation Scheme  Proposed CTU Level Rate Control Scheme  Experimental Results  Conclusion 29

Conclusion  The proposed allocation method takes the hierarchical coding structure of HEVC into consideration.  For CTU level rate control, QP determination at CTU level is based on the frame level QP with feedback of the coding status of CTUs.  Besides, a CTU level QP adjustment strategy is proposed to improve the coding performance just like HM