Effects of texture on color difference evaluation of surface color

The parametric effects of texture on supratheshold color tolerance thresholds were investigated in two psychophysical experiments using simulated textures presented on a CRT. Textured images were created from scanned photographs of physical texture samples with semi-random textured pattern. Differences in appearance were created by varying the illumination geometry during the image capture stage. Two conditions were simulated: diffuse illumination of a standard light booth and directional lighting which accentuates texture relief. In the first experiment observers matched average perceived lightness of grayscale textured images by adjusting the lightness of a uniform gray field. Images varied in their average L*. The results showed that, on average, there was no statistically significant difference between the observer match and the average L of the image. The only exception was found for darker images of coarse texture. In the second experiment, an array of color images was created from three texture patterns: one simulating diffuse lighting conditions and two simulating directional illumination. The CTELAB coordinates of the images were centered around the five CEE color centers recommended for color tolerance research. Color differences were varied in the lightness, chroma, and hue dimensions. Color tolerance thresholds were measured in each dimension for each texture type and uniform patches. An adaptive psychophysical technique, QUEST, was utilized to determine color tolerances in a greater than/less than task using test pairs in comparison to a fixed anchor pair of 1 unit AE*94. The results indicated that the presence of texture increases tolerance thresholds for hue irrespective of the texture pattern. The chroma dimension remained unaffected. Less conclusive results were found for lightness dimension with a strong trend toward increased tolerance thresholds for textured stimuli. When the different textures were compared, it was found that the L* thresholds were significantly higher for the images simulating directional lighting compared to the images of diffusely illuminated surface. No differences in tolerances for chroma and hue were found in that case

Using an illumination discrimination paradigm to investigate the role of illumination priors in colour perception

PhD ThesisPrevious studies suggest human colour constancy is optimised for natural daylight illuminations - a \blue bias" for colour constancy - but it is unclear how such a bias is encoded in the visual system. We use an illumination discrimination task to test two hypothesised mechanisms. Both hypotheses suggest that the human visual system has a prior expectation that illuminations are more likely to vary in a bluer region of chromaticity space. One hypothesis (the nature hypothesis) suggests this has developed in the human visual system through evolution, with selection of colour mechanisms that have reduced sensitivity to global bluer changes across a scene (a species prior). The second hypothesis suggests that the prior is learnt through experience with illuminations (the nurture hypothesis - an individual prior). In Chapter 3 we expand on previous results showing a \blue bias" for colour constancy when the illumination varies from a neutral reference, to show that the \blue bias" prevails in variants of the task where the illuminations are all chromatically biased. This result supports the nature hypothesis. However, depending on the chromatic bias, di erent biases can emerge in the threshold data that are more supportive of the nurture hypothesis. In Chapter 4 we explore individual di erences in illumination discrimination ability, compare illumination discrimination ability with chromatic contrast detection ability, and develop ideal observer models for the task. The results in this Chapter are mostly in support of the nurture hypothesis. In Chapter 5 we show that illumination priors may play a role in the recent visual illusion of a dress photograph that appeared blue and black to some observers but white and gold to others. Finally, in Chapter 6, we search for evidence that observers can learn an illumination prior during a psychophysical task. We conclude that the \blue bias" is likely governed by both a learnt prior over the characteristics of daylight illuminations (the nurture hypothesis) and a generic reduction in sensitivity to bluer changes in an illumination (the nature hypothesis)

Perceptual Fidelity for Digital Color Imagery

The problem of measuring the fidelity of digital color images in a manner that corresponds to human perceptual assessments is addressed. Experiments are performed to validate human visual system (HVS) models, which provide access to a \u27perceptual space\u27 in which visual distortions may be measured, and then a model is proposed for assessing the perceptual fidelity of digital color image. Color Mach bands are produced in the first experiment, demonstrating that, as in the brightness channel, low spatial frequency attenuation occurs in the chromatic channels of the HVS. In the second experiment, a correlation between the chromatic channels of the HVS model and color discrimination axes of color blind observers is demonstrated. Removing variation from one of the chromatic channels of a natural image produces a color-distorted image which the color blind subjects cannot distinguish from the original. Removing variation from the other chromatic channel produces an image that appears colorful to normally-sighted observers, but monochrome to the color blind observers. The third experiment shows that a Gabor filter-based HVS model produces illusory contours in several illusory contour stimuli. These results provide a unique validation of multiple-channel HVS models which process the image in multiple spatial frequency bands that are tuned to match measured sensitivities of neurons in the primary visual cortex of cats and monkeys. Finally, the multiple-channel processing used in the illusory contour experiment is combined with the color vision model from the first two experiments to produce a multiple-channel, color HVS model for measuring perceptual fidelity of color images. A demonstration of the model shows that the structure of the new model is correct. However, inaccurate parameter values for the multiple-channel processing of the chromatic channels cause over-prediction of visible differences in these channels

Crowd-sourced data and its applications for new algorithms in photographic imaging

This thesis comprises two main themes. The first of these is concerned primarily with the validity and utility of data acquired from web-based psychophysical experiments. In recent years web-based experiments, and the crowd-sourced data they can deliver, have been rising in popularity among the research community for several key reasons – primarily ease of administration and easy access to a large population of diverse participants. However, the level of control with which traditional experiments are performed, and the severe lack of control we have over web-based alternatives may lead us to believe that these benefits come at the cost of reliable data. Indeed, the results reported early in this thesis support this assumption. However, we proceed to show that it is entirely possible to crowd-source data that is comparable with lab-based results. The second theme of the thesis explores the possibilities presented by the use of crowd-sourced data, taking a popular colour naming experiment as an example. After using the crowd-sourced data to construct a model for computational colour naming, we consider the value of colour names as image descriptors, with particular relevance to illuminant estimation and object indexing. We discover that colour names represent a particularly useful quantisation of colour space, allowing us to construct compact image descriptors for object indexing. We show that these descriptors are somewhat tolerant to errors in illuminant estimation and that their perceptual relevance offers even further utility. We go on to develop a novel algorithm which delivers perceptually-relevant, illumination-invariant image descriptors based on colour names

Attention Restraint, Working Memory Capacity, and Mind Wandering: Do Emotional Valence or Intentionality Matter?

Attention restraint appears to mediate the relationship between working memory capacity (WMC) and mind wandering (Kane et al., 2016). Prior work has identifed two dimensions of mind wandering—emotional valence and intentionality. However, less is known about how WMC and attention restraint correlate with these dimensions. Te current study examined the relationship between WMC, attention restraint, and mind wandering by emotional valence and intentionality. A confrmatory factor analysis demonstrated that WMC and attention restraint were strongly correlated, but only attention restraint was related to overall mind wandering, consistent with prior fndings. However, when examining the emotional valence of mind wandering, attention restraint and WMC were related to negatively and positively valenced, but not neutral, mind wandering. Attention restraint was also related to intentional but not unintentional mind wandering. Tese results suggest that WMC and attention restraint predict some, but not all, types of mind wandering

In-vitro studies on the color stability and masking ability of composite cores and the influence of posts and cores on the shades of all-ceramic systems

Master'sMASTER OF SCIENC

A Competency Model for Judges

Throughout most modern and contemporary legal scholarship there appears an unbridgeable division between two dominant approaches to judicial decision making. Put succinctly, legal scholars argue that there exist either objective, foundational, ultimate groundings for legal theory and decisions or legal theory and practice inevitably follow a path to relativism and skepticism. This dissertation argues for a theory of evaluation grounded in the Pragmatic, practical ontology and epistemology. Grounding the theory in this fashion avoids the philosophical views of extreme objectivism and extreme subjectivism. In contrast to these conventional stances, which are rooted in philosophical dualism, the view argued for in this dissertation perceives the ontological and epistemological relationship between humans and their environment as inherently interconnected or relational. This philosophical relationship is characterized as intentional, perspectival, and dialectical and embodied. Consonant with the Pragmatic Ontology, the dissertation argues for a conception of rationality termed embodied reason. Unlike abstract versions of rationality, embodied reason is characterized by its concreteness, situatedness, and intersubjective validation. The theory clarifies the concept of legal reasoning and develops meta-theory underlining practical, expert based, holistic, narrative, argumentative, intuitive dimensions. Additionally, given the embodied and perspectival characteristic of judicial decision making the importance of individual differences, especially context-dependent, holistic thinking style is underlined

Spatiotemporal occupancy in building settings

This thesis presents an investigation of methods to capture and analyze spatiotemporal occupancy patterns of high resolution, demonstrating their value by measuring behavioral outcomes over time. Obtaining fine-grain occupancy patterns is particularly useful since it gives researchers an ability to study such patterns not just with respect to the geometry of the space in which they occur, but also to study how they change dynamically in time, in response to the behavior itself. This research has three parts: The first is a review of the traditional methods of behavioral mapping utilized in architecture research, as well as the existing indoor positioning systems, offering an assessment of their comparative potential, and a selection for the current scenario. The second is an implementation of scene analysis analyses using computer vision to capture occupancy patterns on one week of surveillance videos over twelve corridors in a hospital in Chile. The data outcome is occupancy in a set of hospital corridors at a resolution of one square foot per second. Due to the practical detection errors, a two-part statistical model was developed to compute the accuracy on recognition and precision of location, given certain scenario conditions. These error rates models can be then used to predict estimates of patterns of occupancy in an actual scenario. The third is a proof-of-concept study of the usefulness of a new spatiotemporal metric called the Isovist-minute, which describes the actual occupancy of an Isovist, over a specified period of time. Occupancy data obtained using scene-analyses, updated with error-rate models of the previous study, are used to compute Isovist-minute values per square feet. The Isovist-minute is shown to capture significant differences in the patient surveillance outcome in the same spatial layout, but different organizational schedule and program.Ph.D

Modelling chromatic processes in human vision

This investigation programme has concentrated on a number of topics concerning visual function in humans, with particular emphasis on the processing of chromatic information. The programme included an investigation of colour constancy which was carried out using a computer - controlled colour display. A new dynamic colour matching method was developed and the experimental conditions arranged so as to test the constancy of colour appearance. The technigue makes possible the definition of an index of colour constancy which simplifies the interpretation of experimental results. Various spatial, temporal and chromatic parameters of the stimulus configuration were investigated and the results show the importance of the stimulus boundary and near surround in determining the magnitude of the constancy effects observed. Pupillary function was investigated in normal and amblyopic observers. The results suggest that the pupil light reflex is essentially of normal amplitude in amblyopic eyes, although a latency anomaly does exist. Pupillary responses to achromatic, sinusoidal grating stimuli were anomalous in the affected eyes of many amblyopic subjects. Interestingly, certain response parameters were found to be anomalous in the normal eyes of amblyopic observers. Pupillary responses in normal observers were measured following stimulation with isoluminant, red - green chromatic gratings. Responses were found to vary systematically with grating spatial frequency, and broadly reflect the way in which detection thresholds for the same stimuli vary with spatial frequency. Response latencies were approximately 80 ms longer than for equivalent responses to achromatic gratings. No responses were observed when the same experiments were carried out with a protanope. Chromatic discrimination thresholds were measured using a spatio - temporal luminance masking technique. The technique is implemented on a carefully calibrated colour monitor and obviates the requirement of stimulus isoluminance. Preliminary experiments employing psychophysical and pupillometric procedures illustrate the use of the technique in the subjective and objective assessment of colour vision. The rapid changes in visual sensitivity which occur following an intense flash of light were investigated by measuring increment thresholds for a small, brief test stimulus. Results are presented which show the dependence of the sensitivity changes on various spatial, temporal and chromatic parameters. An attempt is made to relate the experimental findings to the properties of retinal neurones