Stereoscopic displays are known to offer a number of key advantages in visualizing complex 3D structures or datasets.
The large majority of studies that focus on evaluating stereoscopic displays for professional applications use completion
time and/or the percentage of correct answers to measure potential performance advantages. However, completion time
and accuracy may not fully reflect all the benefits of stereoscopic displays. In this paper, we argue that perceived
workload is an additional valuable indicator reflecting the extent to which users can benefit from using stereoscopic
displays. We performed an experiment in which participants were asked to perform a visual path-tracing task within a
convoluted 3D wireframe structure, varying in level of complexity of the visualised structure and level of disparity of the
visualisation. The results showed that an optimal performance (completion time, accuracy and workload), depend both
on task difficulty and disparity level. Stereoscopic disparity revealed a faster and more accurate task performance,
whereas we observed a trend that performance on difficult tasks stands to benefit more from higher levels of disparity
than performance on easy tasks. Perceived workload (as measured using the NASA-TLX) showed a similar response
pattern, providing evidence that perceived workload is sensitive to variations in disparity as well as task difficulty. This
suggests that perceived workload could be a useful concept, in addition to standard performance indicators, in
characterising and measuring human performance advantages when using stereoscopic displays.
Some people report visual discomfort when watching 3D displays. For both the objective measurement of visual fatigue
and the subjective measurement of visual discomfort, we would like to arrive at general indicators that are easy to apply
in perception experiments. Previous research yielded contradictory results concerning such indicators. We hypothesize
two potential causes for this: 1) not all clinical tests are equally appropriate to evaluate the effect of stereoscopic viewing
on visual fatigue, and 2) there is a natural variation in susceptibility to visual fatigue amongst people with normal vision.
To verify these hypotheses, we designed an experiment, consisting of two parts. Firstly, an optometric screening was
used to differentiate participants in susceptibility to visual fatigue. Secondly, in a 2×2 within-subjects design (2D vs 3D
and two-view vs nine-view display), a questionnaire and eight optometric tests (i.e. binocular acuity, fixation disparity
with and without fusion lock, heterophoria, convergent and divergent fusion, vergence facility and accommodation
response) were administered before and immediately after a reading task.
Results revealed that participants found to be more susceptible to visual fatigue during screening showed a clinically
meaningful increase in fusion amplitude after having viewed 3D stimuli. Two questionnaire items (i.e., pain and
irritation) were significantly affected by the participants' susceptibility, while two other items (i.e., double vision and
sharpness) were scored differently between 2D and 3D for all participants. Our results suggest that a combination of
fusion range measurements and self-report is appropriate for evaluating visual fatigue related to 3D displays.
KEYWORDS: Stereoscopic displays, Surgery, Visualization, 3D image processing, 3D displays, 3D modeling, Stereoscopy, Computed tomography, Blood vessels, Magnetic resonance imaging
In 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.
The 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.
We tend to think of our body image as fixed. However, human brains appear to support highly negotiable body images.
As a result, our brains show a remarkable flexibility in incorporating non-biological elements (tools and technologies)
into the body image, provided reliable, real-time intersensory correlations can be established, and artifacts can be
plausibly mapped onto an already existing body image representation. A particularly interesting and relevant
phenomenon in this respect is a recently reported crossmodal perceptual illusion known as the rubber-hand illusion
(RHI). When a person is watching a fake hand being stroked and tapped in precise synchrony with his or her own unseen
hand, the person will, within a few minutes of stimulation, start experiencing the fake hand as an actual part of his or her
own body. In this paper, we will review recent work on the RHI and argue that such experimental transformation of the
intimate ties between body morphology, proprioception and self-perception enhances our fundamental understanding of
the phenomenal experience of self. Moreover, it will enable us to significantly improve the design of interactive media,
including the design of avatars in virtual environments and digital games, as well as a range of human-like telerobotic
devices.
KEYWORDS: Image quality, 3D displays, 3D image processing, Visualization, 3D modeling, Systems modeling, Imaging systems, Eye, Visual process modeling, 3D visualizations
The image quality circle is a commonly accepted framework to model the relation between the technology variables of a display and the resulting image quality. 3D-TV systems, however, go beyond the concept of image quality. Research has shown that, although 3D scenes are clearly more appreciated by subjects, the concept 'image quality' does not take this added value of depth into account. Concepts as 'naturalness' and 'viewing experience' have turned out to be more useful when assessing the overall performance of 3D displays. In this paper, experiments are described that test 'perceived depth', 'perceived image quality' and 'perceived naturalness' in images with different levels of blur and different depth levels. Results show that naturalness incorporates both blur level as well as depth level, while image quality does not include depth level. These results confirm that image quality is not a good measure to assess the overall performance of 3D displays. Naturalness is a more promising concept.
Visual discomfort has been the subject of considerable research in relation to stereoscopic and autostereoscopic displays, but remains an ambiguous concept used to denote a variety of subjective symptoms potentially related to different underlying processes. In this paper we clarify the importance of various causes and aspects of visual comfort.
Classical causative factors such as excessive binocular parallax and accommodation-convergence conflict appear to be of minor importance when disparity values do not surpass one degree limit of visual angle, which still provides sufficient range to allow for satisfactory depth perception in consumer applications, such as stereoscopic television. Visual discomfort, however, may still occur within this limit and we believe the following factors to be the most pertinent in contributing to this: (1) excessive demand of accommodation-convergence linkage, e.g., by fast motion in depth, viewed at short distances, (2) 3D artefacts resulting from insufficient depth information in the incoming data signal yielding spatial and temporal inconsistencies, and (3) unnatural amounts of blur. In order to adequately characterize and understand visual discomfort, multiple types of measurements, both objective and subjective, are needed.
KEYWORDS: 3D image processing, Image quality, 3D displays, 3D vision, Eye, Cameras, 3D modeling, Autostereoscopic displays, Error analysis, Televisions
The term 'image quality' is often used to measure the performance of an imaging system. Recent research showed however that image quality may not be the most appropriate term to capture the evaluative processes associated with experiencing 3D images. The added value of depth in 3D images is clearly recognized when viewers judge image quality of unimpaired 3D images against their 2D counterparts. However, when viewers are asked to rate image quality of impaired 2D and 3D images, the image quality results for both 2D and 3D images are mainly determined by the introduced artefacts, and the addition of depth in the 3D images is hardly accounted for. In this experiment we applied and tested the more general evaluative concepts of 'naturalness' and 'viewing experience'. It was hypothesized that these concepts would better reflect the added value of depth in 3D images. Four scenes were used varying in dimension (2D and 3D) and noise level (6 levels of white gaussian noise). Results showed that both viewing experience and naturalness were rated higher in 3D than in 2D when the same noise level was applied. Thus, the added value of depth is clearly demonstrated when the concepts of viewing experience and naturalness are being evaluated. The added value of 3D over 2D, expressed in noise level, was 2 dB for viewing experience and 4 dB for naturalness, indicating that naturalness appears the more sensitive evaluative concept for demonstrating the psychological impact of 3D displays.
The emergence and proliferation of email, mobile communication devices, internet chatrooms, shared virtual environments, advanced tele-conferencing platforms and other telecommunication systems underline the importance of developing measurement methods that are sensitive to the human experience with these systems. In this paper, we discuss the concepts of social presence and connectedness as complementary notions, each relating to a different set of media properties that serve distinct communication needs. We aim to broaden the scope of current presence technologies and applications, illustrating the various factors that play a role in establishing, enhancing, and enriching the experience of human connectedness through communication media. Based on existing literature, we discuss a number of user requirements for home communication and awareness systems. To make these ideas tangible, we finish the paper by briefly discussing the ASTRA project as a case study in designing and evaluating an awareness system for the home.
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 will present the concept of a modular three dimensional broadcast chain, that allows for an evolutionary introduction of depth perception into the context of 2D digital TV. The work is performed within the framework of the European Information Society Technologies (IST) project "Advanced Three-dimensional Television System Technologies" (ATTEST), bringing together the expertise of industries, research centers and universities to design a backwards-compatible, flexible and modular broadcast 3D-TV system. This three dimensional broadcast chain includes content creation, coding, transmission and display. Research in human 3D perception will be used to guide the development process.
The goals of the project towards the optimized 3D broadcast chain comprise the development of a novel broadcast 3D camera, algorithms to convert existing 2D-video material into 3D, a 2D-compatible coding and transmission scheme for 3D-video using MPEG-2/4/7 technologies and the design of two new autostereoscopic displays.
The 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 becoming 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.
Despite many benefits that stereoscopic displays are known to have, there is evidence that stereoscopic displays can potentially cause discomfort to the viewer. The experiment reported in this paper was motivated by the need to quantify the potential subjective discomfort of viewing stereoscopic TV images. Observers provided direct subjective ratings of eye strain and quality in response to stereoscopic still images that varied in camera separation, convergence distance and focal length. Display duration of the images was varied between 1 an d15 seconds. Before and after the experiment, observers filled out a symptom checklist to assess any subjective discomfort resulting from the total experiment. Reported eye strain was on average around 'perceptible, but not annoying' for natural disparities. As disparity values increased reported eye strain increased to 'very annoying' and quality rating solved off and eventually dropped. This effect was most pronounced for the stereoscopic images that were produce using a short convergence distance. This effect may be attributed to an increase in keystone distortion in this condition. No significant effect of display duration was found. The results of the symptom checklist showed a slight increase in reported negative side-effects, with most observers reporting only mild symptoms of discomfort. Finally, our results showed that subjective stereoscopic image quality can be described as a function of reported eye strain and perceived depth.
Previously we reported a study into the effect of stereoscopic filing 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 image 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 1 to 15 seconds. The result 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 judgments to monoscopic images and stereoscopic images with unnatural disparity values as exposure duration increases.
Within the area of broadcasting and entertainment, stereoscopic displays are used to heighten the viewer's sense of excitement and quality. To evaluate these subjective experiences, an appreciation-oriented approach seems to be appropriate. Within this framework, this paper reports on two experiments in which we investigated the influence of image disparity, convergence distance and focus length on the subjective assessment of depth, naturalness, quality and eye-strain. Twelve observers with normal or corrected-to-normal vision and good stereopsis viewed a fully randomized presentation of stereoscopic still images that varied systematically in image disparity, convergence distance and focus length. In the first experiment observers were asked to rate, in separate counterbalanced sessions, their impression of depth, naturalness of depth and quality of depth. In the second experiment observers were asked to rate the eye-strain they experienced on a five point rating scale. Results indicate that observers prefer a stereoscopic presentation of images over a monoscopic presentation. A clear optimum for quality and naturalness judgments was found at 4 cm image disparity, which was also rated by observers as the stereoscopic condition that produced the least eye-strain. Extreme image disparities were found to be annoying, producing low quality and naturalness ratings accordingly. Although there was a strong linear relationship between naturalness and quality (a correlation of r equals 0.96), a small but systematic shift could be observed. This quality-naturalness shift is discussed in relation to similar, yet more pronounced findings in the color domain.
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