1,721,035 research outputs found
Influence of chroma variations on naturalness and image quality of stereoscopic images
No full textThe computational view on image quality of Janssen and Blommaert states that the quality of an image is determined by the degree to which the image is both useful (discriminability) and natural (identifiability). This theory is tested by creating two manipulations. Firstly, multiplication of the chroma values of each pixel with a constant in the CIELab color space, i.e., chroma manipulation, is expected to increase only the usefulness by increasing the distances between the individual color points, enhancing the contrast. Secondly, introducing stereoscopic depth by varying the screen disparity, i.e., depth manipulation, is expected to increase both the usefulness and the naturalness. Twenty participants assessed perceived image quality, perceived naturalness and perceived depth of the manipulated versions of two natural scenes. The results revealed a small, yet significant shift between image quality and naturalness as a function of the chroma manipulation. In line with previous research, preference in quality was shifted to higher chroma values in comparison to preference in naturalness. Introducing depth enhanced the naturalness scores, however, in contrast to our expectations, not the image quality scores. It is argued that image quality is not sufficient to evaluate the full experience of 3D. Image quality appears to be only one of the attributes underlying the naturalness of stereoscopic images.Man-Machine InteractionElectrical Engineering, Mathematics and Computer Scienc
Alone or together: Measuring users' viewing experience in different social contexts
Get PDFIn the past decades, a lot of effort has been invested in predicting the users’ Quality of Visual Experience (QoVE) in order to optimize online video delivery. So far, the objective approaches to measure QoVE have been mainly based on an estimation of the visibility of artifacts generated by signal impairments at the moment of delivery and on a prediction of how annoying these artifacts are to the end user. Recently, it has been shown that other aspects, such as user interest or viewing context, also have a crucial influence on QoVE. Social context is one of these aspects, but it has been poorly investigated in relation to QoVE so far. In this paper, we report the outcomes of an experiment that aims at unveiling the role that social context, and in particular co-located co-viewing, plays within the visual experience and the annoyance of coding artifacts. The results show that social context significantly influences user’s QoVE, whereas the appearance of artifacts doesn’t have impact on viewing experience, although users can still notice them. The results suggest that quantifying the impact of social context on user experience is of major importance to accurately predict QoVE towards video delivery optimizationIntelligent SystemsElectrical Engineering, Mathematics and Computer Scienc
Interactions of visual attention and quality perception
Get PDFSeveral attempts to integrate visual saliency information in quality metrics are described in literature, albeit with contradictory results. The way saliency is integrated in quality metrics should reflect the mechanisms underlying the interaction between image quality assessment and visual attention. This interaction is actually two-fold: (1) image distortions can attract attention away from the Natural Scene Saliency (NSS), and (2) the quality assessment task in itself can affect the way people look at an image. A subjective study was performed to analyze the deviation in attention from NSS as a consequence of being asked to assess the quality of distorted images, and, in particular, whether, and if so how, this deviation depended on the distortion kind and/or amount. Saliency maps were derived from eye-tracking data obtained during scoring distorted images, and they were compared to the corresponding NSS, derived from eye-tracking data obtained during freely looking at high quality images. The study revealed some structural differences between the NSS maps and the ones obtained during quality assessment of the distorted images. These differences were related to the quality level of the images; the lower the quality, the higher the deviation from the NSS was. The main change was identified as a shrinking of the region of interest, being most evident at low quality. No evident role for the kind of distortion in the change in saliency was found. Especially at low quality, the quality assessment task seemed to prevail on the natural attention, forcing it to devi te in order to better evaluate the impact of artifactsElectrical Engineering, Mathematics and Computer Scienc
The impact of interactive manipulation on the recognition of objects
Get PDFA new application for VR has emerged: product development, in which several stakeholders (from engineers to end users) use the same VR for development and communicate purposes. Various characteristics among these stakeholders vary considerably, which imposes potential constraints to the VR. The current paper discusses the influence of three types of exploration of objects (i.e., none, passive, active) on one of these characteristics: the ability to form mental representations or visuo-spatial ability (VSA). Through an experiment we found that all users benefit from exploring objects. Moreover, people with low VSA (e.g., end users) benefit from an interactive exploration of objects opposed to people with a medium or high VSA (e.g. engineers), who are not sensitive for the type of exploration. Hence, for VR environments in which multiple stakeholders participate (e.g. for product development), differences among their cognitive abilities (e.g., VSA) have to be taken into account to enable an efficient usage of VR
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No full textAlthough the concept of image dissimilarity is very familiar in the context of instrumental measures 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 (such as the Sarnoff model and RMSE) 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 (such as the Sarnoff model) be demonstrated over simple measures such as RMSE
The intensity JND comes from Poisson neural noise: Implications for image coding
No full textWhile the problems of image coding and audio coding have frequently
been assumed to have similarities, specific sets of relationships
have remained vague. One area where there should be a meaningful
comparison is with central masking noise estimates, which
define the codec's quantizer step size.
In the past few years, progress has been made on this problem
in the auditory domain (Allen and Neely, J. Acoust. Soc. Am.,
{\bf 102}, 1997, 3628-46; Allen, 1999, Wiley Encyclopedia of
Electrical and Electronics Engineering, Vol. 17, p. 422-437,
Ed. Webster, J.G., John Wiley \& Sons, Inc, NY).
It is possible that some useful insights might now be obtained
by comparing the auditory and visual cases.
In the auditory case it has been shown, directly from psychophysical
data, that below about 5 sones
(a measure of loudness, a unit of psychological intensity),
the loudness JND is proportional to the square root of the loudness
\DL(\L) \propto \sqrt{\L(I)}.
This is true for both wideband noise and tones, having
a frequency of 250 Hz or greater.
Allen and Neely interpret this to mean that the internal noise is
Poisson, as would be expected from neural point process noise.
It follows directly that the Ekman fraction (the relative loudness JND),
decreases as one over the square root of the loudness, namely
\DL/\L \propto 1/\sqrt{\L}.
Above {\L} = 5 sones, the relative loudness JND
\DL/\L \approx 0.03 (i.e., Ekman law).
It would be very interesting to know if this same
relationship holds for the visual case between brightness \B(I)
and the brightness JND \DB(I). This might be tested by measuring
both the brightness JND and the brightness as a function of
intensity, and transforming the intensity JND into a brightness JND, namely
\DB(I) = \B(I+ \DI) - \B(I)
\approx \DI \frac{d\B}{dI}.
If the Poisson nature of the loudness relation (below 5 sones)
is a general result of central neural noise, as is anticipated,
then one would expect that it would also hold in vision,
namely that \DB(\B) \propto \sqrt{\B(I)}.
%The history of this problem is fascinating, starting with Weber and Fechner.
It is well documented that the exponent in the S.S. Stevens' power
law is the same for loudness and brightness (Stevens, 1961)
\nocite{Stevens61a}
(i.e., both brightness \B(I) and loudness \L(I) are proportional to
). Furthermore, the brightness JND data are more like
Riesz's near miss data than recent 2AFC studies of JND measures
\cite{Hecht34,Gescheider97}
Evaluation of optimal sharpness enhancement for different image content and different display technologies
No full textThis paper presents a subjective experiment performed to determine the optimal level of sharpness enhancement for various image content and two display technologies. For the experiment, a peaking algorithm was used as sharpness enhancement method and its gain parameter, which controls the amount of sharpness enhancement, was optimized. Eleven still images were used as image material, and for each original, eight levels of sharpness enhancement were shown. Subjects were asked to select the image that they prefer most on overall image quality. To study the effect of the display technology, the experiment was performed on a CRT monitor and LCD panel. The results show an effect of content: lower gains were preferred for faces and content with flat areas, while higher gains were preferred for highly textured images. We also found an effect of display: in general for a given image, the averaged gain preferred on the CRT was equal or higher than on the LCD. The results can be used to optimize sharpness enhancement algorithms to image content and display type in agreement with the averaged preference of viewers
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No full textPreviously we reported a study into the effect of stereoscopic filming parameters on perceived quality, naturalness and eye strain. In a pilot experiment, using 25 seconds exposure duration, a marked shift occurred between naturalness and quality ratings as a function of camera separation. This shift was less clearly present in the main experiment, in which we used an exposure duration of 5 seconds. This suggests a potential effect of exposure duration on observer appreciation of stereoscopic images. To further investigate this, we performed an experiment using exposure durations of both 5 and 10 seconds. For these durations, twelve observers rated naturalness of depth and quality of depth for stereoscopic still images varying in camera separation, convergence distance and focal length. The results showed no significant main effect of exposure duration. A small yet significant shift between naturalness and quality was found for both duration conditions. This result replicated earlier findings, indicating that this is a reliable effect, albeit content-dependent. A second experiment was performed with exposure durations ranging from I to 15 seconds. The results of this experiment showed a small yet significant effect of exposure duration. Whereas longer exposure durations do not have a negative impact on the appreciative scores of optimally reproduced stereoscopic images, observers do give lower judgements to monoscopic images and stereoscopic images with unnatural disparity values as exposure duration increases
Presence : concept, determinants and measurement
No full textThe concept of presence, i.e. the sensation of 'being there' in a mediated environment, has received substantial attention from the virtual reality community, and is becaming increasingly relevant both to broadcasters and display developers. Although research into presence is still at an early stage of development, there is a consensus that presence has multiple determinants. To identify and test which parameters affect presence, a reliable, robust and valid means of measuring presence is required. In this paper, we describe the categories of factors thought to have an impact on presence.
Furthermore, we present an overview of various approaches taken to measuring presence, which can be divided into two general categories: subjective measures and objective corroborative measures. Since presence is a subjective experience, the most direct way of assessment is through users' subjective report. This approach has serious limitations however, and should be used judiciously. Objective measures, such as postural, physiological or social responses to media. can be used to corroborate subjective measures, thereby overcoming some of their limitations. At present, the most promising direction for presence measurement is to develop and use an aggregate measure of presence that is comprised of both subjective and objective components, tailored to the specific medium under study
Stereoscopic displays in the medical domains: a review of perception and performance effects
No full textIn this paper we review empirical studies that investigate performance effects of stereoscopic displays for medical applications. We focus on four distinct application areas: diagnosis, pre-operative planning, minimally invasive surgery (MIS) and training/teaching. For diagnosis, stereoscopic displays can augment the understanding of complex spatial structures and increase the detection of abnormalities. Stereoscopic viewing of medical data has proven to increase the detection rate in breast imaging. A stereoscopic presentation of noisy and transparent images in 3D ultrasound results in better visualization of the internal structures, however more empirical studies are needed to confirm the clinical relevance. For MRI and CT, where images are frequently rendered in 3D perspective, the added value of binocular depth has not yet been convincingly demonstrated. For MIS, stereoscopic displays can decrease surgery time and increase accuracy of surgical procedures. Performance of surgical procedures is similar when high resolution 2D displays are compared with lower resolution stereoscopic displays, indicating an image quality improvement for stereoscopic displays. Training and surgical planning already use computer simulations in 2D, however more research is needed to the benefit of stereoscopic displays in those applications. Overall there is a clear need for more empirical evidence that quantifies the added value of stereoscopic displays in medical domains, such that the medical community will have ample basis to invest in stereoscopic displays in all or some of the described medical applications
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