Abstract
Motion-compensated prediction is used in video coding standards like High Efficiency Video Coding (HEVC) as one key element of data compression. Commonly, a purely translational motion model is employed. In order to also cover non-translational motion types like rotation or scaling (zoom), e. g. contained in aerial video sequences such as captured from unmanned aerial vehicles (UAV), an affine motion model can be applied. In this work, a model for affine motion-compensated prediction in video coding is derived. Using the rate-distortion theory and the displacement estimation error caused by inaccurate affine motion parameter estimation, the minimum required bit rate for encoding the prediction error is determined. In this model, the affine transformation parameters are assumed to be affected by statistically independent estimation errors, which all follow a zero-mean Gaussian distributed probability density function (pdf). The joint pdf of the estimation errors is derived and transformed into the pdfof the location-dependent displacement estimation error in the image. The latter is related to the minimum required bit rate for encoding the prediction error. Similar to the derivations of the fully affine motion model, a four-parameter simplified affine model is investigated. Both models are of particular interest since they are considered for the upcoming video coding standard Versatile Video Coding (VVC) succeeding HEVC. Both models provide valuable information about the minimum bit rate for encoding the prediction error as a function of affine estimation accuracies.
Highlights
M ODERN hybrid video coding standards like Advanced Video Coding (AVC) [1], or High Efficiency Video Coding (HEVC) [2] provide very good video compression capabilities for daily life applications like Digital Video Broadcasting (DVB) [3]
They reduce the redundancy contained in a video sequence by a combination of motion-compensated prediction (MCP), transform coding with quantization, both typically realized in a differential pulse-code modulation (DPCM) loop, and entropy coding [3]
For a potential quantization of the nontranslational affine parameters for encoding purposes this fact should be taken into account
Summary
M ODERN hybrid video coding standards like Advanced Video Coding (AVC) [1], or High Efficiency Video Coding (HEVC) [2] provide very good video compression capabilities for daily life applications like Digital Video Broadcasting (DVB) [3]. They reduce the redundancy contained in a video sequence by a combination of motion-compensated prediction (MCP), transform coding with quantization, both typically realized in a differential pulse-code modulation (DPCM) loop, and entropy coding [3]. The motion information, the quantized transform coefficients as well as additional signaling data needed for video decoding G. video dimensions, frame rate, block partitioning, etc.) are entropy encoded, e. For the first frame of a video sequence, which is intrinsically new, or blocks, for which no appropriate candidate for motion-compensated prediction is found, intra-frame coding or just intra coding can be applied as an alternative. A ratedistortion optimization (RDO) is used to test several encoding possibilities with different block sizes, partitioning as well as coding modes and the one which provides the best bit rate with respect to the introduced distortion is selected for final coding
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