Block merging for quadtree-based partitioning in HEVC

Abstract

Abstract-The joint development of the upcoming High Efficiency Video Coding (HEVC) standard by ITU-T Video Coding Experts Group and ISO/IEC Moving Picture Experts Group marks a new step in video compression capability. In technical terms, HEVC is a hybrid video-coding approach using quadtreebased block partitioning together with motion-compensated prediction. Even though a high degree of adaptability is achieved by quadtree-based block partitioning, this approach has certain intrinsic drawbacks, which may result in redundant sets of motion parameters being transmitted. Previous work has shown that those redundancies can effectively be removed by merging the leafs of a particular quadtree structure. Following this concept, a block merging algorithm for HEVC is now proposed. This algorithm generates a single motion parameter set for a whole region of contiguous motion-compensated blocks. In this paper, we describe the various components of the proposed block merging algorithm and, using experimental evidence, demonstrate their benefits in terms of coding efficiency.

HEVC Complexity and Implementation Analysis

“…HEVC introduces a so-called merge mode, which sets all motion parameters of an inter picture predicted block equal to the parameters of a merge candidate [6]. The merge mode and the motion vector prediction process optionally allow a picture to reuse motion vectors of prior pictures for motion vector coding, in essence similar to the H.264/AVC temporal direct mode.…”

Inter-Picture Prediction in HEVC

“…removing merge_flag, merge_index and skip_flag T r a f fi c 8:8 n/a n/a (2560 1600) PeopleOnStreet 6:5 n/a n/a Nebuta 1:5 n/a n/a SteamLocomotive 11:1 n/a n/a B [13] with the random access main, low delay B and P main coding configurations as described in [5]. The coding efficiency gains in terms of Bjøntegaard Delta (BD) rate [2], when enabling the merge and skip modes, are reported in [9] and [12] and also summarized in Table 5.2. Average bit rate savings between 6 % and 8 % are observed.…”

“…Also, the fact that a block can only be divided into exactly four child blocks will eventually lead to ineffective borders. To remedy these inherent drawbacks of the quad-tree structure, HEVC uses block merging which allows us to code motion parameters very cheaply (in terms of bit rate) in these ineffective border situations [9,12,23]. The algorithm was inspired by the work of [10], in which the authors show that rate-distortion optimized tree pruning for quadtree-based motion models can be substantially improved by introducing a subsequent leaf merging step.…”