Jerkiness

Abstract: Over the past few years there has been an increasing interest in real time video services over packet networks. When considering quality, it is essential to quantify user perception of the received sequence. Severe motion discontinuities are one of the most common degradations in video streaming. The end-user perceives a jerky motion when the discontinuities are uniformly distributed over time and an instantaneous fluidity break is perceived when the motion loss is isolated or irregularly distributed. Bit rate adaptation techniques, transmission errors in the packet networks or restitution strategy could be the origin of this perceived jerkiness. In this paper we present a psychovisual experiment performed to quantify the effect of sporadically dropped pictures on the overall perceived quality. First, the perceptual detection thresholds of generated temporal discontinuities were measured. Then, the quality function was estimated in relation to a single frame dropping for different durations. Finally, a set of tests was performed to quantify the effect of several impairments distributed over time. We have found that the detection thresholds are content, duration and motion dependent. The assessment results show how quality is impaired by a single burst of dropped frames in a 10 sec sequence. The effect of several bursts of discarded frames, irregularly distributed over the time is also discussed.

Abstract: The widespread diffusion of hand-held devices with video recording capabilities requires the adoption of reliable digital Stabilization methods to enjoy the acquired sequences without disturbing jerkiness. In order to effectively get rid of the unwanted camera movements, an estimate of the global motion between adjacent frames is necessary. This paper presents a novel approach for estimating the global motion between frames using a curve warping technique known as dynamic time warping. The proposed algorithm guarantees robustness also in presence of sharp illumination changes and moving objects.

Abstract: The developers and users of interactive computer graphics (CG), such as 3D games and virtual reality, are demanding ever more realistic computer generated imagery delivered at high frame rates, to enable a greater perceptual experience for the user. As more computational power and/or transmission bandwidth are not always available, special techniques are applied that trade off fidelity in order to reduce computational complexity, while trying to minimise the perceptibility of the resulting visual defects. Research on human visual perception has promoted the development of perception driven CG techniques, where knowledge of the human visual system and its weaknesses are exploited when rendering/displaying 3D graphics. It is well known in the human perception community that many factors, including audio stimuli, may influence the amount of cognitive resources available to perform a visual task. In this paper we investigate the influence sound effects have on the perceptibility of motion smoothness in an animation (i.e. on the perception of delivered frame rate). Forty participants viewed pairs of computer-generated walkthrough animations (with the same visual content within the pair) displayed at five different frame rates, in all possible combinations. Both walkthroughs in each test pair were either silent or accompanied by sound effects and the participant had to detect the one that had a smoother motion (i.e. was delivered at higher frame rate). A significant effect of sound effects on the perceived smoothness was revealed. The participants who watched the audiovisual walkthroughs gave more erroneous answers while performing their task compared to the subjects in the "No Sound" group, regardless of their familiarity with animated CG. Especially the unfamiliar participants failed to notice motion smoothness variations which were apparent to them in the absence of sound. The effect of the type of camera movement in the scene (translation or rotation) on the viewers' perception of the motion smoothness/jerkiness was also investigated, but no significant association between them was found. Our results should lead to new insights in 3D graphics regarding the requirements for the delivered frame rate in a wide range of applications.

Abstract: In making any movement (say, for instance, reaching for an object) our limbs usually take a smooth trajectory. That has been taken to mean that the body's motor system minimizes jerkiness. Instead, however, smoothness may be a by-product of a more fundamental computational goal of the motor system -- that of balancing speed and accuracy when activity-dependent ‘noise' in the neural control systems is taken into account.