As 360° videos are gradually gaining popularity, various display devices have emerged for watching 360° videos, including both head-mounted displays (HMDs) and touchscreen displays. While several experiments have been conducted to examine the quality of experience (QoE) of watching 360° videos using HMDs, the QoE when using touchscreen displays has not been examined thoroughly. In this work, we conducted subjective evaluation experiments to examine the influence of an HMD and touchscreen display, including the influence of scaling when using the touchscreen display, on the QoE when watching 8K 360° videos encoded via high efficiency video coding (HEVC) at various bitrates. The results show that better QoE scores are obtained (1) when using the HMD than when using the touchscreen display without scaling and (2) when enabling scaling on the touchscreen display than when disabling scaling at lower bitrates. Moreover, we examined the relationship between the QoE and other factors, such as the video quality and sense of presence. Our analysis revealed that when watching 360° videos on the touchscreen display, the QoE is more strongly associated with the sense of presence than with the video quality, particularly when scaling is enabled.

In the quality evaluation of high dynamic range and wide color gamut (HDR/WCG) images, a number of works have concluded that native HDR metrics, such as HDR visual difference predictor (HDR-VDP), HDR video quality metric (HDR-VQM), or convolutional neural network (CNN)-based visibility metrics for HDR content, provide the best results. These metrics consider only the luminance component, but several color difference metrics have been specifically developed for, and validated with, HDR/WCG images. In this paper, we perform subjective evaluation experiments in a professional HDR/WCG production setting, under a real use case scenario. The results are quite relevant in that they show, firstly, that the performance of HDR metrics is worse than that of a classic, simple standard dynamic range (SDR) metric applied directly to the HDR content; and secondly, that the chrominance metrics specifically developed for HDR/WCG imaging have poor correlation with observer scores and are also outperformed by an SDR metric. Based on these findings, we show how a very simple framework for creating color HDR metrics, that uses only luminance SDR metrics, transfer functions, and classic color spaces, is able to consistently outperform, by a considerable margin, state-of-the-art HDR metrics on a varied set of HDR content, for both perceptual quantization (PQ) and Hybrid Log-Gamma (HLG) encoding, luminance and chroma distortions, and on different color spaces of common use.

In image quality assessments, the results of subjective evaluation experiments that use the double-stimulus impairment scale (DSIS) method are often expressed in terms of the mean opinion score (MOS), which is the average score of all subjects for each test condition. Some MOS values are used to derive image quality criteria, and it has been assumed that it is preferable to perform tests with non-expert subjects rather than with experts. In this study, we analyze the results of several subjective evaluation experiments using the DSIS method. Our first contribution is to discuss the statistical meaning of the MOS values, which has not been previously addressed in the literature. Second, our results show that, contrary to the established belief, there are advantages when performing subjective tests with experts, in that they allow experiments to be performed with fewer subjects, and to better determine the lower threshold of image quality.

Full-reference objective quality metrics for high dynamic range (HDR) images must be validated in terms of their consistency with subjective evaluation results, and previous studies have found a number of metrics that appear to correlate well with the preference of observers. However, those conclusions were based on experiments that do not correspond to the practical use of a current day HDR professional production scenario. In this work, we carry out subjective evaluation experiments for the popular HDR standards of perceptual quantization (PQ) and Hybrid Log-Gamma (HLG), with a state-of-the-art HDR reference monitor used in broadcasting and post-production, and where all the observers participating in the tests are video experts. We find that the ranking of HDR metrics is now substantially different from what was reported earlier, and also that a simple standard dynamic range (SDR) metric can be applied directly to PQ or HLG encoded signals providing excellent results that surpass those of HDR metrics.

This paper studies the video bit-rate required for 8K 119.88 Hz (120 Hz) high efficiency video coding (HEVC)/H.265 temporal scalable coding that can partially decode 59.94 Hz (60 Hz) video frames from compressed 120 Hz bit-streams. We compress 8K 120 Hz test sequences using software that emulates our developing HEVC/H.265 encoder and conduct two types of subjective evaluation experiments to investigate the appropriate bit-rate for both 8K 120 and 60 Hz videos for broadcasting purpose. From the results of the experiments, we conclude that the required video bit-rate for 8K 120 Hz temporal scalable coding is estimated to be between 85 and 110 Mbps, which is equivalent to the practical bit-rate for 8K 60 Hz videos, and the appropriate bitrate allocation for the 8K 60 Hz video in 8K 120 Hz temporal scalable video coding at 85 Mbps is presumed to be ~80 Mbps.

In this study, we verify a pair comparison method in which videos being evaluated can be repeated by the evaluators as many times as desired. We use the method to conduct a subjective evaluation of 8K 119.88 Hz (120 Hz) and 59.94 Hz (60 Hz) videos that were compressed using software that emulates an 8K 120 Hz encoder. The experimental results confirm that (1) this method can detect small differences between video qualities, (2) all video pairs must be evaluated because the order effect is not negligible, and (3) the appropriate number of repeats is between four and nine.

This paper describes a hardware implementation of HEVC (High Efficiency Video Coding) video encoder for exploring performance of HEVC in real-time applications. By optimizing hardware architecture and developing fast mode decision algorithms, our FPGA-based prototype can encode 1080p, 10-bit video at 60fps in real-time. Both objective and subjective evaluations clearly demonstrate that the developed HEVC encoder achieves significant coding gain relative to professional-use AVC/H.264 encoder available on the market. This paper also refers to the development of a real-time HEVC encoder for much higher resolution video such as SHV (Super Hi-Vision, 8K) using the HD encoder in parallel.

The present paper provides transform bases with improved normality and orthogonality properties based on the integer DCT of high-efficiency video coding (HEVC). The proposed transform bases improve the normality and orthogonality properties compared to the HEVC transform bases. Coding and re-encoding experiments were conducted using HEVC test model (HM) version 6.0 and the proposed method. The experiments were conducted under various bitrate ranges. Under the high-bit-rate condition, the proposed method exhibited coding gains compared to HM 6.0 without increasing the encoding/decoding time.