Assessments of Subjective Video Quality on HEVC-Encoded 4K-UHD Video for Beyond-HDTV Broadcasting Services

In this paper, we present the experimental results with analysis for subjective quality assessment on 4K-ultra-high definition (UHD) video encoded by high efficiency video coding (HEVC) to investigate its feasibility for 4K-UHD TV broadcasting services. The subjective quality assessment on the HEVC-encoded (impaired) 4K-UHD video is conducted for the three target bitrates of 18, 23, and 36 Mb/s, the two color formats of YUV420 and YUV444, and the two viewing distances of 0.75 times the height of a display screen (H) and 1.5 H. The subjective quality assessment experiments on 4K-UHD test sequences show that the HEVC-encoded (impaired) YUV420 4K-UHD video even at the target bit of 18 Mb/s yields perceptual similar visual quality: 1) with MOS of 4.7 and 4.8 in 0.75 H and 1.5 H viewing distances, respectively, compared to the original YUV420 4K-UHD test video; and 2) with MOS of 4.8 in 1.5 H viewing distance, compared to the original YUV444 4K-UHD test video. This implies that the HEVC-encoded YUV420 4K-UHD video at the target bit rate of 18 Mb/s is perceptually good enough in the usage of legacy DTV broadcasting systems with single channel bandwidths of 6 MHz. It is also shown that the HEVC-encoded 4K-UHD test sequences mostly yield higher perceptual quality in the 420 YUV color format than in the YUV444 color format at the same target bitrates.