This paper describes an experiment that studies perceived video quality, with the goal to get a better understanding of
whether a temporal or a spatial MPEG-2 based adaptation method should be used for video transmission over variable
bandwidth. The research focused on the relation between in-scene motion and camera motion on spatial as well as
temporal distortions in video sequences. Participants were tested on their sensitivity and appreciation for spatial and
temporal distortions using the scale paradigm of direct comparison. Footage was shot to create video material of three
scenes with a systematic manipulation of in-scene motion and camera motion, which produced twelve different video
sequences. Results show a relation trend between the two types of motion and the two types of distortion in video
sequences. The main result indicates that participants generally rated spatial distortions as better video quality than the
same video sequence containing temporal distortions; even though video sequences containing spatial distortions were
coded at an overall lower bitrate than video sequences containing temporal distortions.
KEYWORDS: Video, Signal to noise ratio, Cameras, Video processing, Video coding, Video compression, Image quality, Quantization, Plasma display panels, Plasma
To interpret the impressions of observers, it is necessary to understand the relationship between components that
influence perceived video quality. This paper addresses the effect of assessment methodology on the subjective
judgement for spatial and temporal impaired video material, caused by video adaptation methods that come into play
when there is variable throughput of video material (I-Frame Delay and Signal-to-Noise Ratio scalability). Judgement
strategies used are the double-stimulus continuous-quality scale (DSCQS) and the double stimulus impairment scale
(DSIS). Results show no evidence for an influence of spatial artifacts on perceived video quality with the presented
judgement strategies. Results for the influence of temporal artifacts are less easy to interpret, because it is not possible to
distinguish whether the non-linear relation between DSIS and DSCQS appeared because of the temporal artifacts
themselves or presented scene content.
JPEG compression of the left and right components of a stereo image pair is a way to save valuable bandwidth when transmitting stereoscopic images. This paper presents results on the effects of camera-base distance and JPEG-coding on overall image quality, perceived depth, perceived sharpness and perceived eye-strain. In the experiment, two stereoscopic still scenes were used, varying in depth (three different camera-base distances: 0, 8 and 12 cm) and compression ratio (4 levels: original, 1:30, 1:40 and 1:60). All levels of compression were applied to both the left and right stereo image, resulting in a 4x4 matrix of all possible symmetric and asymmetric coding combinations. We applied the single stimulus method for subjective testing according to the ITU 500-10 recommendations. The observers were asked to assess image quality, sharpness, depth and eye-strain. Results showed that JPEG coding had a negative effect on image quality, sharpness and eye-strain but had no effect on perceived depth. An increase in camera-base distance increased perceived depth and reported eye-strain but had no effect on perceived sharpness. Furthermore, both sharpness and eye-strain correlated highly with perceived image quality.
Three-dimensional television (3DTV) is often mentioned as a logical next step following high-definition television (HDTV). A high quality 3-D broadcast service is becoming increasingly feasible based on various recent technological developments combined with an enhanced understanding of 3-D perception and human factors issues surrounding 3DTV. In this paper, perceptually relevant issues, in particular stereoscopic image quality and visual comfort, in relation to 3DTV systems are reviewed. We discuss how the principles
of a quantitative measure of image quality for conventional 2-D images, based on identifying underlying attributes of image quality and quantifying the perceived strengths of each attribute, can be applied in image quality research for 3DTV. In this respect, studies
are reviewed that have focussed on the relationship between subjective attributes underlying stereoscopic image quality and the technical parameters that induce them (e.g. parameter choices in image acquisition, compression and display). More specifically, artifacts that may arise in 3DTV systems are addressed, such as keystone distortion, cross-talk, cardboard effect, puppet theatre effect, and blur. In conclusion, we summarize the perceptual requirements for 3DTV that can be extracted from the literature and address issues that require further investigation in order for 3DTV to be a success.
In this paper we evaluate two objective quality measures, the root-mean-square-error and a model based on the human visual system (HVS), on their ability to predict the perceived image quality for variations in bit-rate, processing method, and scene content. In theory quality metrics should be able to predict the perceived image quality independent of these variations. However, one can imagine that in practice this is not trivial to meet. But also subjects might have difficulties in making comparisons across processing methods or across scenes. In order to test whether subjects use separate quality scales for each identifiable scene and processing method or whether they use a single quality scale, we set up experiments in which the influence of bit-rate, processing method, and scene content was measured. In all experiments subjects were instructed to judge the quality difference between two simultaneously presented images.
Although the concept of image dissimilarity is very familiar in the context of instrumental measure for image quality, it is fairly uncommon to use it as an experimental paradigm. Most instrumental measures relate image quality to some distance, such as the root-mean-squared error (RMSE), between the original and the processed image, such that image dissimilarity arises naturally in this context. Dissimilarity can however also be judged consistently by subjects. In this paper we compare the performance of a number of representative instrumental models for image dissimilarity with respect to their ability to predict both image dissimilarity and image quality, as perceived by human subjects. Two sets of experimental data, one for images degraded by noise and blur, and one for JPEG-coded images, are used in the comparison. In none of the examined cases could a clear advantage of complicated distance metrics be demonstrated over simple measures such as RMSE.
In two experiments, dissimilarity data and numerical scaling data were obtained to determine the underlying attributes of image quality in baseline sequential JPEG coded imags. Although several distortions were perceived, i.e., blockiness, ringing and blur, the subjective data for all attributes where highly correlated, so that image quality could approximately be described by one independent attribute. We therefore proceeded by developing an instrumental measure for one of these distortions, i.e., blockiness. In this paper a single-ended blockiness measure is proposed, i.e., one that uses only the coded image. Our approach is therefore fundamentally different from most image quality models that use both the original and the degraded image. The measure is based on detecting the low- amplitude edges that result from blocking and estimating the amplitudes. Because of the approximate 1D of the underlying psychological space, the proposed blockiness measure also predicts the image quality of sequential baseline coded JPEG images.
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