Fast Intra Mode Decision Algorithm Using the Sum of Absolute Transformed Differences

This paper presents a fast intra mode decision algorithm using the sum of absolute transformed differences (SATD) in order to reduce the encoding time. Our algorithm consists of two main techniques: Early block-mode decision and candidate directional-mode selection. First, we use the early block-mode decision method, I4MB skip, to avoid unnecessary computation for I4MB. If all the 16 4x4sub-blocks in intra 16x16block (I16MB) have the minimum SATD in the same directional-mode, then we skip the I4MB prediction and choose the I16MB as the best block-mode for the current block. Besides, before performing the rate-distortion cost for all nine directional-modes of I4MB, which brings out the huge complexity, we reduce the number of the candidate directional-modes by comparing the SATD of each mode with the SATD of primary prediction mode (PPM). The PPM is obtained from the combination of the best mode of I16MB and the modes of neighboring blocks. Experimental results indicate that the proposed algorithm saved encoding time about 70% with negligible degradation.