Qpel

From Wikipedia, the free encyclopedia

Quarter pixel (often also called as q-pel or qpel) refers to a quarter of a standard pixel. It is an often-used term in video technology.

[edit] Operation

Advanced video encoding methods such as those based upon MPEG-4 specifications, such as XviD and DivX, use motion estimation algorithms to improve video compression. Typically either half or quarter pixel motion compensation is used, to describe movements between frames. Quarter pixel motion compensation has the advantage of delivering sharper images than default half pixel.

[edit] Implementations

Any gains in compressability from more precisely describing the intra-frame motion are typically offset by the increased bitstream overhead of running a higher level of description. Therefore, typically no net gain in overall compression is obtained by enabling QPEL. It is a qualitative feature.

[edit] Hardware compatibility

QPEL requires up to twice as much processing power to encode, and 30-60% more processing power to decode. For this reason, and to enable wider hardware compatibility, QPEL is disabled in the default DIVX encoding profiles.