Atanas Boev

Towards compound stereo-video quality metric: a specific encoder-based framework

We suggest a compound full-reference stereo-video quality metric composed of two components: a monoscopic quality component and stereoscopic quality component. While the former assesses the trivial monoscopic perceived distortions caused by blur, noise, contrast change etc., the latter assesses the perceived degradation of binocular depth cues only. We use the structural similarity index as a measure for perceptual similarity and design a multiscale algorithm for obtaining a perceptual disparity map and a stereo-similarity map to be used in the suggested metric. We verify the performance of the metric with subjective tests on distorted stereo images and coded stereo-video sequences with a final aim to build a perceptually-aware feedback for a H.264 based stereo-video encoder

3D-DCT based perceptual quality assessment of stereo video

In this paper, we present a novel stereoscopic video quality assessment method based on 3D-DCT transform. In our approach, similar blocks from left and right views of stereoscopic video frames are found by block-matching, grouped into 3D stack and then analyzed by 3D-DCT. Comparison between reference and distorted images are made in terms of MSE calculated within the 3D-DCT domain and modified to reflect the contrast sensitive function and luminance masking. We validate our quality assessment method using test videos annotated with results from subjective tests. The results show that the proposed algorithm outperforms current popular metrics over a wide range of distortion levels.

Classification and simulation of stereoscopic artifacts in mobile 3DTV content

We identify, categorize and simulate artifacts which might occur during delivery stereoscopic video to mobile devices. We consider the stages of 3D video delivery dataflow: content creation, conversion to the desired format (multiview or source-plus-depth), coding/decoding, transmission, and visualization on 3D display. Human 3D vision works by assessing various depth cues - accommodation, binocular depth cues, pictorial cues and motion parallax. As a consequence any artifact which modifies these cues impairs the quality of a 3D scene. The perceptibility of each artifact can be estimated through subjective tests. The material for such tests needs to contain various artifacts with different amounts of impairment. We present a system for simulation of these artifacts. The artifacts are organized in groups with similar origins, and each group is simulated by a block in a simulation channel. The channel introduces the following groups of artifacts: sensor limitations, geometric distortions caused by camera optics, spatial and temporal misalignments between video channels, spatial and temporal artifacts caused by coding, transmission losses, and visualization artifacts. For the case of source-plus-depth representation, artifacts caused by format conversion are added as well.

Three-Dimensional Media for Mobile Devices

This paper aims at providing an overview of the core technologies enabling the delivery of 3-D Media to next-generation mobile devices. To succeed in the design of the corresponding system, a profound knowledge about the human visual system and the visual cues that form the perception of depth, combined with understanding of the user requirements for designing user experience for mobile 3-D media, are required. These aspects are addressed first and related with the critical parts of the generic system within a novel user-centered research framework. Next-generation mobile devices are characterized through their portable 3-D displays, as those are considered critical for enabling a genuine 3-D experience on mobiles. Quality of 3-D content is emphasized as the most important factor for the adoption of the new technology. Quality is characterized through the most typical, 3-D-specific visual artifacts on portable 3-D displays and through subjective tests addressing the acceptance and satisfaction of different 3-D video representation, coding, and transmission methods. An emphasis is put on 3-D video broadcast over digital video broadcasting-handheld (DVB-H) in order to illustrate the importance of the joint source-channel optimization of 3-D video for its efficient compression and robust transmission over error-prone channels. The comparative results obtained identify the best coding and transmission approaches and enlighten the interaction between video quality and depth perception along with the influence of the context of media use. Finally, the paper speculates on the role and place of 3-D multimedia mobile devices in the future internet continuum involving the users in cocreation and refining of rich 3-D media content.

Crosstalk Measurement Methodology for Auto-Stereoscopic Screens

Autostereoscopic displays utilizing slanted lenticular sheets produce specific artifacts. These artifacts affect the perception of a 3D scene, and are caused by a process which can be modeled as inter-channel crosstalk. We propose methodology for measuring such a crosstalk for arbitrary multiview 3D display. The measured data might be used for optimizing multiview image sets for a given display.

Relative importance of depth cues on portable autostereoscopic display

Depth of a three-dimensional scene is perceived using several different visual cues. The process of perceiving depth is delicate and vulnerable to artefacts. On autostereoscopic displays the aim is to enhance the sensation of reality of the experience by the added three-dimensionality without the need for aiding glasses. The factors that contribute to achieving a plausible 3D effect on autostereoscopic displays are numerous: for example stereoscopy combined with a supporting set of monocular cues: perspective lines, shadows, and textures. The goal of this study is two-fold. First, to gather knowledge on how different characteristics of a 3D scene impact the correct estimation of depth. Second, how the same characteristics impact on perceived quality. These were studied using subjective tests. The studied characteristics were chosen to be five different depth cues - three monocular and two binocular cues. The chosen monocular cues were shadows, texture and focal depth. For binocular cues, two different stereoscopic disparities were used: one optimal for a portable 3D display, and another designed for a HD resolution and later scaled down for a portable device making the disparity decrease. In addition, combination of all aforementioned cues was examined. All of the cues were also studied with three different compression levels (no compression, JPEG with quality factor of 50, and with quality factor of 90). A quantitative study using a portable autostereoscopic display in controlled laboratory environment was conducted. The results of this study indicate that the stereoscopic depth cues outperform the monocular depth cues in accuracy and speed of estimating depth in a 3D video. Interestingly enough, these results are not consistent with the ratings of perceived quality and acceptance. Furthermore, compressing images seems to have a significant effect on the accuracy and speed of depth estimation, and also on the perceived quality.

Comparative study of autostereoscopic displays for mobile devices

We perform comparative analysis of the visual quality of multiple 3D displays - seven portable ones, and a large 3D television set. We discuss two groups of parameters that influence the perceived quality of mobile 3D displays. The first group is related with the optical parameters of the displays, such as crosstalk or size of sweet spots. The second group includes content related parameters, such as objective and subjective comfort disparity range, suitable for a given display. We identify eight important parameters to be measured, and for each parameter we present the measurement methodology, and give comparative results for each display. Finally, we discuss the possibility of each display to visualize downscaled stereoscopic HD content with sufficient visual quality.

Simulator sickness — Five experiments using autostereoscopic mid-sized or small mobile screens

Visual comfort is one of the factors of 3D experience. The goal of this paper is to evaluate simulator sickness as a part of five different video quality evaluation studies. The experiments are conducted using three different dual-view autostereoscopic midsized and small mobile screens with varying constructed video quality levels, under different lengths of viewing, and with a total of 200 participants. The simulator sickness questionnaire (SSQ) was used in the data-collection in the pre- and postimmersion. The results showed only a small short term increase in the symptoms after exposure in four studies indicating a good applicability of these displays for short term video viewing.

Quantifying the importance of cyclopean view and binocular rivalry-related features for objective quality assessment of mobile 3D video

Abstract3D video is expected to provide an enhanced user experience by using the impression of depth to bring greater realism to the user. Quality assessment plays an important role in the design and optimization of 3D video processing systems. In this paper, a new 3D image quality model that is specifically tailored for mobile 3D video is proposed. The model adopts three quality components, called the cyclopean view, binocular rivalry, and the scene geometry, in which the quality must be quantified. The cyclopean view formation process is simulated and its quality is evaluated using the three proposed approaches. Binocular rivalry is quantified over the distorted stereo pairs, and the scene quality is quantified over the disparity map. Based on the model, the 3D image quality can then be assessed using state-of-the-art 2D quality measures selected appropriately through a machine learning approach. To make the metric simple, fast, and efficient, final selection of the quality features is accomplished by also considering the computational complexity and the CPU running time. The metric is compared with several currently available 2D and 3D metrics. Experimental results show that the compound metric gives a significantly high correlation with the mean opinion scores that were collected through large-scale subjective tests run on mobile 3D video content.

Visual-quality evaluation methodology for multiview displays

Abstract Multiview displays are characterized by a multitude of parameters, such as spatial resolution, brightness, 3D-crosstalk, and so forth, which individually and in combination influence the visual quality of 3D scenes. These parameters are specified by values precisely measured by optical means. However, it is difficult for an average consumer or content producer to compare the visual quality of two displays or to judge whether given 3D content is suitable for a certain display using only this set of parameter values. In this paper, we propose a quality-measurement methodology that aims to measure the visibility of structural distortions introduced by a multiview display by using a number of test signals with different frequency content and apparent depth. We use these measurements to derive what we call display passband for signals at different disparity levels. The passband determines the frequency components for which the intended signal is predominantly visible with respect to the distortion introduced by the display. Additionally, we propose a method to determine the approximate effective resolution of a display for signals with a given apparent depth. The result of the measurements can be used to compare the perceived visual quality of different multiview displays.