Transform-Exempted Calculation of Sum of Absolute Hadamard Transformed Differences

Sum of absolute Hadamard transformed differences (SATD) is an important distortion metric applied in the latest video coding standard H.264/AVC, which is an alternative to the sum of absolute differences (SAD) to improve coding efficiency. However, the SATD requires more computation load due to the Hadamard transform involved. Inspired by a geometric interpretation of the simplest two-point SATD calculation, an efficient way to compute the SATD is proposed, which considers the joint effect of the Hadamard transform and the following SAD processing in the SATD calculation and thus enables the computation of SATD without performing the Hadamard transform separately. We further extend the two-point transform- exempted SATD (TE-SATD) computation scheme to four-point and 4 times 4 block SATD calculation. With the same coding performance, the proposed TE-SATD-based fast algorithms can save 38% and 17% operations in computing a 4 times 4 block SATD compared with the conventional SATD calculation and the fast Hadamard transform-based calculation, respectively.