ESTG - Comunicações em conferências e congressos internacionais
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- Classification-based early termination for coding tree structure decision in HEVCPublication . Correa, Guilherme; Assunção, Pedro; Cruz, Luis A. da Silva; Agostini, LucianoThe High Efficiency Video Coding (HEVC) standard provides improved compression rates in comparison to its predecessors at the cost of large increases in computational complexity. An important share of such increases is due to the introduction of flexible Coding Tree structures, which best configuration is decided through exhaustive tests in a Rate-Distortion Optimization (RDO) scheme. In this work, an early termination method for the decision of such structures was designed using classification trees obtained through Data Mining techniques. The classification trees were trained using intermediate encoding results from a training set of video sequences and implemented in the encoder to skip the full RDO-based decision. An average reduction of 37% in the HEVC encoder computational complexity was achieved when using the designed classification trees, with a negligible cost of only 0.28% in terms of Bjontegaard Delta-rate increase.
- Complexity control of HEVC through quadtree depth estimationPublication . Correa, Guilherme; Assunção, Pedro; Agostini, Luciano; Cruz, Luis A. da SilvaThe emerging HEVC standard introduces a number of tools which increase compression efficiency in comparison to its predecessors at the cost of greater computational complexity. This paper proposes a complexity control method for HEVC encoders based on dynamic adjustment of the newly proposed coding tree structures. The method improves a previous solution by adopting a strategy that takes into consideration both spatial and temporal correlation in order to decide the maximum coding tree depth allowed for each coding tree block. Complexity control capability is increased in comparison to a previous work, while compression losses are decreased by 70%. Experimental results show that the encoder computational complexity can be downscaled to 60% with an average bit rate increase around 1.3% and a PSNR decrease under 0.07 dB.
- Computational complexity control for HEVC based on coding tree spatio-temporal correlationPublication . Correa, Guilherme; Assunção, Pedro; Cruz, Luis A. da Silva; Agostini, LucianoThe High Efficiency Video Coding standard shows improved compression efficiency in comparison to previous standards at the cost of higher computational complexity. In this paper, a complexity control method for HEVC encoders based on the dynamic adjustment of the number of constrained coding treeblocks is proposed. The method limits the maximum tree depth used in the coding structures based on spatio-temporal correlation in order to decrease the number of evaluations performed in the Rate-Distortion Optimization process. Experimental results show that the proposed method is capable of maintaining the encoding time per frame under a pre-defined target, reaching computational complexity decreases of up to 50% at the cost of an average BD-PSNR loss of 0.26 dB in the worst case scenario.
- Constrained encoding structures for computational complexity scalability in HEVCPublication . Correa, Guilherme; Assunção, Pedro; Cruz, Luis A. da Silva; Agostini, LucianoThe High Efficiency Video Coding standard shows improved compression efficiency in comparison to previous standards at the cost of higher computational complexity. In this paper, a complexity scalability method for HEVC encoders based on the dynamic adjustment of the number of constrained coding treeblocks is proposed. The method limits the Prediction Unit shapes and the maximum tree depth used in each Coding Treeblock in order to decrease the number of evaluations performed in the Rate-Distortion Optimization process. The encoder is capable of trading off computational complexity and compression efficiency while still maintaining the encoding time per Group of Pictures (GOP) under a pre-defined target. The encoding complexity can be decreased in up to 60% when compared to the original encoder at the cost of small Bjontegaard Delta (BD)-rate increases.
- Dynamic tree-depth adjustment for low power HEVC encodersPublication . Correa, Guilherme; Assunção, Pedro; Cruz, Luis A. da Silva; Agostini, LucianoPower consumption is a major problem in multimedia-capable mobile devices, especially those equipped with the most advanced video codecs. The emerging HEVC standard introduces a set of features which significantly increase the encoder computational complexity and consequently the power consumption in comparison to its predecessor, H.264/AVC. This paper presents two complexity reduction methods that selectively constrain the coding tree depth to keep computational complexity below a pre-established limit. Experimental results show that the encoder complexity can be reduced to 60% of the original complexity, allowing the implementation of low power HEVC encoders with small or negligible loss in rate-distortion performance.
- Encoding time control system for HEVC based on Rate-Distortion-Complexity analysisPublication . Correa, Guilherme; Assunção, Pedro; Cruz, Luis A. da Silva; Agostini, LucianoThe improved compression efficiency of High Efficiency Video Coding (HEVC) comes with large increases in computational complexity, which has been lately dealt by researchers with complexity reduction and scaling methods. However, encoding time control at frame or Group of Pictures (GOP) level is still an open issue that must be investigated. In this work, a Rate-Distortion-Complexity analysis is performed upon a set of configurations that have been created based on findings and techniques of previous works. The proposed control system uses the best 27 configurations to adjust the encoding time per GOP and yields encoding time reductions of up to 84.5% with an average difference between target and encoding times of 4.1%. © 2015 IEEE.
- Four-step algorithm for early termination in HEVC inter-frame prediction based on decision treesPublication . Correa, Guilherme; Assunção, Pedro; Agostini, Luciano; Cruz, Luis A. da SilvaThe flexible encoding structures of High Efficiency Video Coding (HEVC) are the main responsible for the improvements of the standard in terms of compression efficiency in comparison to its predecessors. However, the flexibility provided by these structures is accompanied by high levels of computational complexity, since more options are considered in a Rate-Distortion (R-D) optimization scheme. In this paper, we propose a four-step early-termination method, which decides whether the inter mode decision should be halted without testing all possibilities. The method employs a set of decision trees, which are trained offline once, using information from unconstrained HEVC encoding runs. The resulting trees present a mode decision accuracy ranging from 97.6% to 99.4% with a negligible computational overhead. The method is capable of achieving an average computational complexity decrease of 49% at the cost of a very small Bjontegaard Delta (BD)-rate increase (0.58%).
- Motion compensated tree depth limitation for complexity control of HEVC encodingPublication . Correa, Guilherme; Assunção, Pedro; Agostini, Luciano; Cruz, Luis A. da SilvaThe recently introduced quadtree coding structures used in HEVC increase compression efficiency in comparison to previous standards at the cost of higher computational complexity levels. This paper proposes an evolution of a complexity control method for HEVC encoders based on the dynamic adjustment of these structures' maximum depth. The new method improves the previous solution by adopting a new control strategy and compensating the motion effect on a maximum tree depth map which is central to the complexity control strategy. The proposed method is capable of performing a more accurate complexity control than our previous strategy while still reducing compression efficiency losses in terms of image quality and bit rate.