Fractional motion estimation method with adaptive mode selection

A fractional motion estimation method with adaptive mode selection, comprising steps of:

• a) categorizing search modes of macroblocks into a single mode, a reduced mode, and a full mode;
• only 16×16 blocks are searched in the single mode, the searches for 16×16 blocks, 16×8 blocks, 8×16 blocks and 8×8 blocks can be done in the reduced mode, and searches for 16×16 blocks, 16×8 blocks, 8×16 blocks, 8×8 blocks, 8×4 blocks, 4×8 blocks, and 4×4 blocks can be done in the full mode, each of the blocks being composed of a plurality of integer pixels;
• in the 4×4 blocks as an example, there are 16 integer pixels;
• b) determining a search mode for a to-be-processed macroblock according to a predetermined condition;
• select the single mode if the best mode of the integer pixel motion estimation of the to-be-processed macroblock is 16×16 and the mode of its predetermined adjacent macroblock is 16×16;
• select the reduced mode if the best mode of the integer pixel motion estimation of the to-be-processed macroblock is not 16×16 and the mode of its predetermined adjacent macroblock is 16×16;
• or (3) select the reduced mode if the best mode of the integer pixel motion estimation of the to-be-processed macroblock is one of 16×16, 16×8, and 8×16 modes and the mode of its predetermined adjacent macroblock is one of 16×16, 16×8, and 8×16 modes;
• or select the full mode if the best mode of the integer pixel motion estimation of the to-be-processed macroblock and the mode of its predetermined adjacent macroblock are both different from the aforesaid three conditions;
• c) conducting a fractional motion estimation of a to-be-estimated pixel according to the search mode determined in the step b);
• the fractional motion estimation can be done by accessing a pixel located in a reference and corresponding to the to-be-estimated pixel, performing an interpolation computation of such two pixels to get a half pixel and a quarter pixel, calculating the SATD and the MV cost of each of the pixels (integer pixel, half pixel, and quarter pixel) within a predetermined search range corresponding to the to-be-estimated pixel, and comparing those pixels to get the location of the best pixel (integer pixel, half pixel, and quarter pixel) and the best macroblock type corresponding to the to-be-estimated pixel to further get the best MV of the to be-processed macroblock;
• and
• d) repeating the steps b) and c) for the next to-be-estimated pixel and its corresponding macroblock.