The advance of technology continuously enables new luminaire designs and concepts. Evaluating such designs has
traditionally been done using actual prototypes, in a real environment. The iterations needed to build, verify, and
improve luminaire designs incur substantial costs and slow down the design process. A more attractive way is to evaluate
designs using simulations, as they can be made cheaper and quicker for a wider variety of prototypes. However, the
value of such simulations is determined by how closely they predict the outcome of actual perception experiments.
In this paper, we discuss an actual perception experiment including several lighting settings in a normal office
environment. The same office environment also has been modeled using different software tools, and photo-realistic
renderings have been created of these models. These renderings were subsequently processed using various tonemapping
operators in preparation for display. The total imaging chain can be considered a simulation setup, and we have
executed several perception experiments on different setups. Our real interest is in finding which imaging chain gives us
the best result, or in other words, which of them yields the closest match between virtual and real experiment.
To answer this question, first of all an answer has to be found to the question, "which simulation setup matches the real
world best?" As there is no unique, widely accepted measure to describe the performance of a certain setup, we consider
a number of options and discuss the reasoning behind them along with their advantages and disadvantages.
In the design of professional luminaires, improving visibility has always been a core target. Recently, it has become
clearer that especially for consumer lighting, generating an appropriate atmosphere and pleasant feeling is of almost
equal importance. In recent studies it has been shown that the perception of an atmosphere can be described by four
variables: cosiness, liveliness, tenseness, and detachment. In this paper we compare the perception of these lighting
characteristics when viewed in reality with the perception when viewing a simulated picture. Replacing reality by a
picture on a computer screen such as an LCD monitor, or a piece of paper, introduces several differences. These include
a reduced dynamic range, reduced maximum brightness and quantization noise in the brightness levels, but also in a
different viewing angle, and a different adaption of the human visual system. Research has been done before to compare
simulations with photographs, and simulations with reality. These studies have focused on 'physical variables', such as
brightness and sharpness, but also on naturalness and realism. We focus on the accuracy of a simulation for the
prediction of the actual goal of a lot of luminaires: atmosphere creation. We investigate the correlation between
perceptual characteristics of the atmosphere of a real-world scene and a simulated image of it. The results show that for
all 4 tested atmosphere words similar main effects and similar trends (over color temperature, fixtures, intensities) can be
found in both the real life experiments and the simulation experiments. This implies that it is possible to use simulations
on a screen or printout for the evaluation of atmosphere characteristics.
It is well known that LEDs have problems with color consistency and color stability over time. Two perception
experiments were conducted in order to determine guidelines for the color and luminance deviations between LEDs that
are allowed. The first experiment determined the visibility threshold of hue, saturation, and luminance deviations of one
LED in an array of LEDs and the second experiment measured the visibility threshold of hue, saturation, and luminance
gratings for different spatial frequencies. The results of the first experiment show that people are most sensitive for color
deviations between LEDs when a white color is generated. The visibility threshold for white was 0.004 &Dgr;u'v' for a
deviation in the hue of the LED primaries, 0.007 &Dgr;u'v' for a deviation in the saturation of the LED primaries and 0.006 &Dgr;u'v' for a deviation in the luminance of the LED primaries. The second experiment showed that the visibility of hue
gratings is independent of spatial frequency in the range of 0.4 to 1.2 cycles/degree. However, for saturation and
luminance gratings there was a significant effect of spatial frequency on the visibility threshold. Both experiments show
that observers are more sensitive to hue than to saturation deviations.
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.
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.
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.