Abstract
This paper proposes a novel method for early termination of a motion search. It first introduces an estimator of the sum of absolute difference (SAD) between the current block and a search point. After analyzing the SAD estimator, it proposes the SAD condition to decide whether the current search point is around a minimum point or not. The counter condition is used to evaluate the current search point as an early search termination cue. After the current search point is considered as a minimum point, the search is stopped immediately. The proposed algorithm can easily be combined with most existing fast motion estimation algorithms to further reduce computational cost. While previous thresholding techniques have focused on the correlation of SAD values between a current block and its neighboring blocks, the proposed algorithm studies its own characteristics to predict the threshold. Hence, the proposed termination scheme can complement the previous early search termination techniques by merging the termination methods together, in order to further reduce computational cost. Experimental results demonstrate that the proposed algorithm successfully reduces the computational cost by combining the previous early search termination techniques.
Highlights
Recent video coding standards, such as H.264 [1] and high efficiency video coding (HEVC) [2], significantly improve coding efficiency, compared to previous video coding standards
If the predicted distance between them is less than 0.5 pixel, the current search point is considered as the global minimum point, and the motion search was terminated early
3.2.1 Simulation environment In order to evaluate the performance of the proposed termination method on a video encoder, it was implemented on the H.264 reference software JM 18.5 [11] and combined with ‘Enhanced Predictive Zonal Search’ (SearchMode = 3), which is one of fast motion estimation algorithms
Summary
Fast motion estimation algorithms have been developed to reduce the heavy computational cost of the full search block matching algorithm, such as diamond search [3], MVFAST [4], PMVFAST [5], hexagon-based search [6], and hybrid unsymmetrical cross multihexagon-grid search [7]. Ismail [9] proposed a dynamic early stop search termination (DESST) by considering a SAD value of an initial search center (ISC) of a current block and the average SAD values of ISCs in all the previous coded blocks. These methods determine the threshold value from SAD values of blocks spatially and temporally adjacent to the current block. If the predicted distance between them is less than 0.5 pixel, the current search point is considered as the global minimum point, and the motion search was terminated early. This paper proposes the new early search termination for fast motion estimation by extending our previous work to a two-dimensional space.
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