Intra-Prediction Mode Decision for H.264 in Two Steps

Two fast mode decision methods for intra prediction in H.264 are proposed in this work to reduce the encoder complexity. The first method, the so-called two-level fast Intra4x4 mode decision, is based on the idea of reducing possible candidate directions of a 4x4 luma block in Intra4x4 mode decision. The second method enables an early selection of suitable 4x4 or 16x16 luma partitions of a given macroblock. The performance of the proposed algorithms are evaluated using the H.264 reference codec JM 10.1, which is compared with exhaustive RD mode decision of H.264 in metrics such as the encoding time, the average PSNR and the coding bit-rate for test sequences. It is observed that the proposed fast algorithms can save about 52% of encoding time resulting in a minor PSNR degradation of 0.03dB lower PSNR and a 2.5% higher bit rate.