Sylvain Tourancheau

Adaptive depth filtering for HEVC 3D video coding

Consumer interest in 3D television (3DTV) is growing steadily, but current available 3D displays still need additional eye-wear and suffer from the limitation of a single stereo view pair. So it can be assumed that autostereoscopic multiview displays are the next step in 3D-at-home entertainment, since these displays can utilize the Multiview Video plus Depth (MVD) format to synthesize numerous viewing angles from only a small set of given input views. This motivates efficient MVD compression as an important keystone for commercial success of 3DTV. In this paper we concentrate on the compression of depth information in an MVD scenario. There have been several publications suggesting depth down- and upsampling to increase coding efficiency. We follow this path, using our recently introduced Edge Weighted Optimization Concept (EWOC) for depth upscaling. EWOC uses edge information from the video frame in the upscaling process and allows the use of sparse, non-uniformly distributed depth values. We exploit this fact to expand the depth down-/upsampling idea with an adaptive low-pass filter, reducing high energy parts in the original depth map prior to subsampling and compression. Objective results show the viability of our approach for depth map compression with up-to-date High-Efficiency Video Coding (HEVC). For the same Y-PSNR in synthesized views we achieve up to 18.5% bit rate decrease compared to full-scale depth and around 10% compared to competing depth down-/upsampling solutions. These results were confirmed by a subjective quality assessment, showing a statistical significant preference for 87.5% of the test cases.

Stereoscopic 3D video coding quality evaluation with 2D objective metrics

The 3D video quality is of highest importance for the adoption of a new technology from a user’s point of view. In this paper we evaluated the impact of coding artefacts on stereoscopic 3D video quality by making use of several existing full reference 2D objective metrics. We analyzed the performance of objective metrics by comparing to the results of subjective experiment. The results show that pixel based Visual Information Fidelity metrics fits subjective data the best. The 2D stereoscopic video quality seems to have dominant impact on the coding artefacts impaired stereoscopic videos.

Reproducibility of crosstalk measurements on active glasses 3D LCD displays based on temporal characterization

Crosstalk is one of the main display-related perceptual factors degrading image quality and causing visual discomfort on 3D-displays. It causes visual artifacts such as ghosting effects, blurring, and lack of color fidelity which are considerably annoying and can lead to difficulties to fuse stereoscopic images. On stereoscopic LCD with shutter-glasses, crosstalk is mainly due to dynamic temporal aspects: imprecise target luminance (highly dependent on the combination of left-view and right-view pixel color values in disparity regions) and synchronization issues between shutter-glasses and LCD. These different factors influence largely the reproducibility of crosstalk measurements across laboratories and need to be evaluated in several different locations involving similar and differing conditions. In this paper we propose a fast and reproducible measurement procedure for crosstalk based on high-frequency temporal measurements of both display and shutter responses. It permits to fully characterize crosstalk for any right/left color combination and at any spatial position on the screen. Such a reliable objective crosstalk measurement method at several spatial positions is considered a mandatory prerequisite for evaluating the perceptual influence of crosstalk in further subjective studies.

Crosstalk Measurements of Shutter Glasses 3D Displays

Crosstalk is probably one of the main perceptual factors contributing to perceived image quality and visual comfort. The Video Quality Experts Group (VQEG) within their 3D video quality project is ...

Psychophysical study of LCD motion-blur perception

Motion-blur is still an important issue on liquid crystal displays (LCD). In the last years, efforts have been done in the characterization and the measurement of this artifact. These methods permit to picture the blurred profile of a moving edge, according to the scrolling speed and to the gray-to-gray transition considered. However, other aspects should be taken in account in order to understand the way LCD motion-blur is perceived. In the last years, a couple of works have adressed the problem of LCD motion-blur perception, but only few speeds and transitions have been tested. In this paper, we have explored motion-blur perception over 20 gray-to-gray transitions and several scrolling speeds. Moreover, we have used three different displays, to explore the influence of the luminance range as well as the blur shape on the motion-blur perception. A blur matching experiment has been set up to obtain the relation between objective measurements and perception. In this experiment, observers must adjust a stationary test blur (simulated from measurements) until it matches their perception of the blur occuring on a moving edge. Result shows that the adjusted perceived blur is always lower than the objective measured blur. This effect is greater for low contrast edges than for high contrast edges. This could be related to the motion sharpening phenomenon.

Subjective evaluation of user experience in interactive 3D visualization in a medical context

New display technologies enable the usage of 3D-visualization in a medical context. Even though user performance seems to be enhanced with respect to 2D thanks to the addition of recreated depth cues, human factors, and more particularly visual comfort and visual fatigue can still be a bridle to the widespread use of these systems. This study aimed at evaluating and comparing two different 3D visualization systems (a market stereoscopic display, and a state-of-the-art multi-view display) in terms of quality of experience (QoE), in the context of interactive medical visualization. An adapted methodology was designed in order to subjectively evaluate the experience of users. 14 medical doctors and 15 medical students took part in the experiment. After solving different tasks using the 3D reconstruction of a phantom object, they were asked to judge their quality of the experience, according to specific features. They were also asked to give their opinion about the influence of 3D-systems on their work conditions. Results suggest that medical doctors are opened to 3D-visualization techniques and are confident concerning their beneficial influence on their work. However, visual comfort and visual fatigue are still an issue of 3D-displays. Results obtained with the multi-view display suggest that the use of continuous horizontal parallax might be the future response to these current limitations.

Evaluation of quality of experience in interactive 3D visualization: methodology and results

Human factors are of high importance in 3D visualization, but subjective evaluation of 3D displays is not easy because of a high variability among users. This study aimed to evaluate and compare two different 3D visualization systems (a market stereoscopic display, and a state-of-the-art multi-view display) in terms of user performance and quality of experience (QoE), in the context of interactive visualization. An adapted methodology has been designed in order to focus on 3D differences and to reduce the influence of all other factors. Thirty-six subjects took part in an experiment during which they were asked to judge the quality of their experience, according to specific features. Results showed that a scene understanding and precision was significantly better on the multi-view display. Concerning the quality of experience, visual comfort was judged significantly better on the multi-view display and visual fatigue was reported by 52% of the subjects on the stereoscopic display. This study has permitted to identify some factors influencing QoE such as prior experience and stereopsis threshold.

Image and Video Quality Assessment Using LCD: Comparisons with CRT Conditions

In this paper, the impact of display on quality assessment is addressed. Subjective quality assessment experiments have been performed on both LCD and CRT displays. Two sets of still images and two sets of moving pictures have been assessed using either an ACR or a SAMVIQ protocol. Altogether, eight experiments have been led. Results are presented and discussed, some differences are pointed out. Concerning moving pictures, these differences seem to be mainly due to LCD moving artefacts such as motion blur. LCD motion blur has been measured objectively and with psycho-physics experiments. A motion-blur metric based on the temporal characteristics of LCD can be defined. A prediction model have been then designed which predict the differences of perceived quality between CRT and LCD. This motion-blur-based model enables the estimation of perceived quality on LCD with respect to the perceived quality on CRT. Technical solutions to LCD motion blur can thus be evaluated on natural contents by this mean.

Impact of the Resolution on the Difference of Perceptual Video Quality Between CRT and LCD

The incoming of the high-definition new visual experience at home has boosted the new display technologies such as liquid crystal displays (LCD), plasma and projectors. These technologies enable the increase of the screen size necessary to sense a cinema-like experience. However, they introduce some new visual shortcomings not present with the mature CRT technology. In this paper, some subjective tests are described which highlight a difference of the perceptual video quality between CRT and LCD. Moreover, its observed that this loss of quality on LCD is more important with high resolution sequences than with standard resolution ones. This influence of the resolution is particularly explainable in the case of the LCD motion blur defect.

Influence of motion on contrast perception: supra-threshold spatio-velocity measurements

In this paper, a supra-threshold spatio-velocity CSF experiment is described. It consists in a contrast matching task with a methods of limits procedure. Results enable the determination of contrast perception functions which give, for given spatial and temporal frequencies, the perceived contrast of a moving stimulus. These contrast perception functions are then used to construct supra-threshold spatio-velocity CSF. As for supra-threshold CSF in spatial domain, it can be observed that CSF shape changes from band-pass behaviour at threshold to low-pass behaviour at supra-threshold, along spatial frequencies. However, supra-threshold CSFs have a band-pass behaviour along temporal frequency has threshold one. This means that if spatial variations can be neglected above the visibility threshold, temporal ones are still of primary importance.