A fast intra_4x4 mode selection method for H.264

H.264 main profile supports two intra modes at macroblock (MB) level: intra_4x4 and intra_16x16. There are nine possible spatial prediction directions per 4x4 block in intra_4x4 mode and four per 16x16 block in intra_16x16 mode. The prediction direction selection per MB in intra_4x4 can be very time-consuming, if all the nine possible prediction directions have to be checked per 4x4 block by a RD-based method. This paper proposes a method that can early detects those 4x4 blocks which select most probable mode (MPM) as the best mode. Once the encoder early detects the MPM as the best mode of one 4x4 block, the encoder can reduce nine RD computations to one and therefore save lots of computation. The saving in selecting a best prediction direction per 4x4 block depends on sequences and quantization parameters, for example, ranging from 16.80% to 60.19% for F1car sequence by using different measures. Simulation results demonstrated that the proposed method significantly reduce the processing time without performance degradation.