Comparison of compression performance of 10-bit vs. 8-bit depth, under H.264 Hi422 profile

H.264 is one of the first video coding standard incorporating coding formats with a bit-depth of above 8 bits. This paper presents the results of compression comparison tests for the H.264 “High 422” profile, between 10-bit and 8-bit sample depths. The simulations were run on five 720p and 1080i high definition sequences. PSNR and SSIM metrics were used to evaluate the objective quality performance of both bit-depths, and with the aim of enabling a fair comparison, both metrics were computed with 10-bit precision, up-scaling the 8-bit decoded sequences to 10-bits. Some works have been published in this field based on the evaluation of commercial 10-bit H.264 implementations. In this work, we carry out a neutral evaluation of H.264 standard performance using the official H.264 Reference Software. Unlike the expected 10-bit coding gains, the results show unnoticeable differences between both sample depths in terms of objective quality, lower 0.1dB for PSNR and 0.002 for SSIM, with a 5% bit rate saving that can be achieved for the luminance component, especially for the 720p format, and negligible quality improvement for U and V chroma components.