Publikationen


Suche nach „[Y.] [Rai]“ hat 3 Publikationen gefunden
Suchergebnis als PDF
    DigitalF: Angewandte Informatik

    Beitrag (Sammelband oder Tagungsband)

    Y. Rai, A. Aldahdooh, S. Ling, Marcus Barkowsky, P. Callet

    Effect of content features on short-term video quality in the visual periphery

    2016 IEEE 18th International Workshop on Multimedia Signal Processing (MMSP)

    2016

    Abstract anzeigen

    The area outside our central field of vision, also referred to as the visual periphery, captures most information in a visual scene, although much less sensitive than the central Fovea. Vision studies in the past have stated that there is reduced sensitivity of texture, color, motion and flicker (temporal harmonic) perception in this area, that bears an interesting application in the domain of quality perception. In this work, we particularly analyze the perceived subjective quality of videos containing H.264/AVC transmission impairments, incident at various degrees of retinal eccentricities of observers. We relate the perceived drop in quality, to five basic types of features that are important from a perceptive standpoint: texture, color, flicker, motion trajectory distortions and also the semantic importance of the underlying regions. We are able to observe that the perceived drop in quality across the visual periphery, is closely related to the Cortical Magnification fall-off characteristics of the V1 cortical region. Additionally, we see that while object importance and low frequency spatial distortions are important indicators of quality in the central foveal region, temporal flicker and color distortions are the most important determinants of quality in the periphery. We therefore conclude that, although users are more forgiving of distortions they viewed peripherally, they are nevertheless not totally blind towards it: the effects of flicker and color distortions being particularly important.

    DigitalF: Angewandte Informatik

    Beitrag (Sammelband oder Tagungsband)

    Y. Rai, Marcus Barkowsky, P. Le Callet

    Role of spatio-temporal distortions in the visual periphery in disrupting natural attention deployment

    Proceedings of SPIE Conference Human Vision and Electronic Imaging 2016 (HVEI 2016)

    2016

    DOI: 10.2352/ISSN.2470-1173.2016.16.HVEI-117

    Abstract anzeigen

    Human visual system based quality metrics and perceptually optimized video coders often use principles of foveation and saliency to weigh the distortion in certain regions more heavily or hide the artefacts in regions where they are less noticeable. These approaches however fail to consider the impact such a tuning produces on the non-salient surroundings usually incident on the para, peri and extra-peri foveal visual regions. Vision studies on the other hand, have highlighted the enhanced sensitivity of these peripheral visual regions towards spatio-temporal artefacts: more so in the supra-threshold region. Because such analysis has often been performed using controlled synthetic stimuli and forced fixation based experimental approaches, that assume perfect luminance adaptation, tracking and semantic comprehension of underlying content, a thorough understanding of the impact of peripheral disturbances in a natural viewing scenario is missing. The present work therefore uses a Gaze Contingent Display to study the impact of spatiotemporal distortions in the peri foveal and extraperi foveal regions in a free-viewing scenario, using natural scene stimuli. Using four state of the art gaze analysis-techniques to analyze the gaze data collected from 48 observers, spatio-temporally and semantically, confirms and extends our previous understanding of distortion perception in the periphery. Our observations indicate that non-flickering spatial distortions seem to have less of a disruptive effect in the visual periphery as compared to the temporally flickering artefacts and second, the threshold at which disruptions begin to occur is higher in the visual periphery as compared to that of the fovea, both of these effects being strongly scene dependent and prone to natural scene masking. The results highlight the need for sufficient consideration of the supra-threshold effects of peripheral distortions, in order to achieve an optimum perceptual experience.

    DigitalF: Angewandte Informatik

    Beitrag (Sammelband oder Tagungsband)

    Y. Rai, Marcus Barkowsky, P. Le Callet

    Does H.265 based peri and para-foveal quality flicker disrupt natural viewing patterns?

    2015 International Conference on Systems, Signals and Image Processing (IWSSIP)

    2015

    Abstract anzeigen

    Region of interest based coders and also those coders that extensively use the Intra coding mode tend to produce flickering artefacts due to the inherent quality fluctuations they produce in the non-salient or homogeneously textured intra coded regions of a scene respectively. These non-salient areas are in turn incident on the para, peri and extra-peri foveal retinal regions that are especially sensitive to temporal artefacts. To study the perceptual effects of such a quality based flicker in the retinal periphery, in this experiment gaze data was collected from 48 observers in a free viewing scenario using a regulated flicker stimulus. The video stimulus in the mentioned peripheral regions were flickered with a predetermined frequency and amplitude by adaptively combining the streams produced using a H.265 video coder, and presenting them in a Gaze Contingent Display(GCD) setup. Utilizing statistical gaze analysis techniques, we observe that, temporal quality flicker in the visual periphery plays a major role in disturbing the natural viewing patterns of an observer. Further, this effect was found to be maximum in the 7.5Hz temporal band thus showing that, encoders that affect temporal quality smoothness must aim to avoid such distraction effects.