A hardware-oriented concurrent TZ search algorithm for High-Efficiency Video Coding

Abstract

High-Efficiency Video Coding (HEVC) is the latest video coding standard, in which the compression performance is double that of its predecessor, the H.264/AVC standard, while the video quality remains unchanged. In HEVC, the test zone (TZ) search algorithm is widely used for integer motion estimation because it effectively searches the good-quality motion vector with a relatively small amount of computation. However, the complex computation structure of the TZ search algorithm makes it difficult to implement it in the hardware. This paper proposes a new integer motion estimation algorithm which is designed for hardware execution by modifying the conventional TZ search to allow parallel motion estimations of all prediction unit (PU) partitions. The algorithm consists of the three phases of zonal, raster, and refinement searches. At the beginning of each phase, the algorithm obtains the search points required by the original TZ search for all PU partitions in a coding unit (CU). Then, all redundant search points are removed prior to the estimation of the motion costs, and the best search points are then selected for all PUs. Compared to the conventional TZ search algorithm, experimental results show that the proposed algorithm significantly decreases the Bjøntegaard Delta bitrate (BD-BR) by 0.84%, and it also reduces the computational complexity by 54.54%.

Relying on a Rate Constraint to Reduce Motion Estimation Complexity

“…Although TZS brings ME complexity down when compared to FS, the number of searched points is still considered too large for real-time applications [4] [10]. In addition, the iterative nature of its search steps prevents efficient parallel implementations [9]. The "Octagonal-Axis Raster" search, proposed by [11], exemplifies how a smaller number of search points can reduce ME complexity with a negligible increase in Bjøntegaard Delta Bitrate (BD-Rate).…”

“…Many different fast ME algorithms attempt to reduce this cost by limiting the Integer Motion Estimation (IME) search region to as few points as possible [5], but while this strategy does improve performance, the search becomes sub-optimal and may get trapped in a local minimum [6]. The Test Zone Search (TZS) algorithm, adopted as the default IME method in both of the reference software implementations of HEVC [7] and VVC [8], mitigates this problem by combining a variant of Diamond Search with the semi-exhaustive Raster Search [9].…”