Interpolation Free Subpixel Accuracy Motion Estimation

Abstract

Subpixel motion estimation plays an important role in compression efficiency within modern video codecs such as MPEG2, MPEG4, and H.264. Subpixel motion estimation is implemented within these standards using interpolated values at 1/2 or 1/4 pixel accuracy. Such interpolation gives a good reduction in residual energy for each predicted macroblock and, therefore, improves compression. However, this leads to a significant increase in computational complexity at the encoder. This is especially true for H.264 where the cost of an exhaustive set of macroblock segmentations need to be estimated in order to obtain an optimal mode for prediction. This paper presents a novel interpolation-free scheme for subpixel motion estimation using the result of the full pixel sum of absolute difference distribution of each motion compensated block applied to an H.264 encoder. This system produces reduced complexity motion estimation with a controllable tradeoff between compression performance and encoder speed. These methods facilitate the generation of a real time software H.264 encoder