Adaptive downsampling for high-definition video coding

Previous research has shown that downsampling prior to encoding and upsampling after decoding can improve the rate-distortion (R-D) performance compared with directly coding the original video using standard coding technologies, e.g., JPEG and H.264/AVC, especially at low bit rates. This paper proposes a practical algorithm to find the optimal downsampling ratio that balances the distortions caused by downsampling and coding, thus achieving the overall optimal R-D performance. Given the optimal sampling ratio, dedicated filters for down- and up-sampling are also designed. Simulations show this algorithm improves the R-D performance over a wide range of bit rates, e.g., from 1.0 dB at high bit rates to 2.5 dB at low bit rates.