1,913 research outputs found
Colour Relations in Form
The orthodox monadic determination thesis holds that we represent colour relations by virtue of representing colours. Against this orthodoxy, I argue that it is possible to represent colour relations without representing any colours. I present a model of iconic perceptual content that allows for such primitive relational colour representation, and provide four empirical arguments in its support. I close by surveying alternative views of the relationship between monadic and relational colour representation
Visual Aftereffect Of Texture Density Contingent On Color Of Frame
An aftereffect of perceived texture density contingent on the color of a surrounding region is reported. In a series of experiments, participants were adapted, with fixation, to stimuli in which the relative density of two achromatic texture regions was perfectly correlated with the color presented in a surrounding region. Following adaptation, the perceived relative density of the two regions was contingent on the color of the surrounding region or of the texture elements themselves. For example, if high density on the left was correlated with a blue surround during adaptation (and high density on the right with a yellow surround), then in order for the left and right textures to appear equal in the assessment phase, denser texture was required on the left in the presence of a blue surround (and denser texture on the right in the context of a yellow surround). Contingent aftereffects were found (1) with black-and-white scatter-dot textures, (2) with luminance-balanced textures, and (3) when the texture elements, rather than the surrounds, were colored during assessment. Effect size was decreased when the elements themselves were colored, but also when spatial subportions of the surround were used for the presentation of color. The effect may be mediated by retinal color spreading (Pöppel, 1986) and appears consistent with a local associative account of contingent aftereffects, such as Barlow\u27s (1990) model of modifiable inhibition
Change blindness: eradication of gestalt strategies
Arrays of eight, texture-defined rectangles were used as stimuli in a one-shot change blindness (CB) task where there was a 50% chance that one rectangle would change orientation between two successive presentations separated by an interval. CB was eliminated by cueing the target rectangle in the first stimulus, reduced by cueing in the interval and unaffected by cueing in the second presentation. This supports the idea that a representation was formed that persisted through the interval before being 'overwritten' by the second presentation (Landman et al, 2003 Vision Research 43149–164]. Another possibility is that participants used some kind of grouping or Gestalt strategy. To test this we changed the spatial position of the rectangles in the second presentation by shifting them along imaginary spokes (by ±1 degree) emanating from the central fixation point. There was no significant difference seen in performance between this and the standard task [F(1,4)=2.565, p=0.185]. This may suggest two things: (i) Gestalt grouping is not used as a strategy in these tasks, and (ii) it gives further weight to the argument that objects may be stored and retrieved from a pre-attentional store during this task
High-fidelity colour reproduction for high-dynamic-range imaging
The aim of this thesis is to develop a colour reproduction system for high-dynamic-range (HDR)
imaging. Classical colour reproduction systems fail to reproduce HDR images because current characterisation
methods and colour appearance models fail to cover the dynamic range of luminance
present in HDR images. HDR tone-mapping algorithms have been developed to reproduce HDR
images on low-dynamic-range media such as LCD displays. However, most of these models have
only considered luminance compression from a photographic point of view and have not explicitly
taken into account colour appearance. Motivated by the idea to bridge the gap between crossmedia
colour reproduction and HDR imaging, this thesis investigates the fundamentals and the
infrastructure of cross-media colour reproduction. It restructures cross-media colour reproduction
with respect to HDR imaging, and develops a novel cross-media colour reproduction system for
HDR imaging. First, our HDR characterisation method enables us to measure HDR radiance values
to a high accuracy that rivals spectroradiometers. Second, our colour appearance model enables us
to predict human colour perception under high luminance levels. We first built a high-luminance
display in order to establish a controllable high-luminance viewing environment. We conducted a
psychophysical experiment on this display device to measure perceptual colour attributes. A novel
numerical model for colour appearance was derived from our experimental data, which covers the
full working range of the human visual system. Our appearance model predicts colour and luminance
attributes under high luminance levels. In particular, our model predicts perceived lightness
and colourfulness to a significantly higher accuracy than other appearance models. Finally, a complete
colour reproduction pipeline is proposed using our novel HDR characterisation and colour
appearance models. Results indicate that our reproduction system outperforms other reproduction
methods with statistical significance. Our colour reproduction system provides high-fidelity colour
reproduction for HDR imaging, and successfully bridges the gap between cross-media colour reproduction
and HDR imaging
The Computation of Surface Lightness in Simple and Complex Scenes
The present thesis examined how reflectance properties and the complexity of surface mesostructure (small-scale surface relief) influence perceived lightness in centresurround displays. Chapters 2 and 3 evaluated the role of surface relief, gloss, and interreflections on lightness constancy, which was examined across changes in background albedo and illumination level. For surfaces with visible mesostructure (“rocky” surfaces), lightness constancy across changes in background albedo was better for targets embedded in glossy versus matte surfaces. However, this improved lightness constancy for gloss was not observed when illumination varied. Control experiments compared the matte and glossy rocky surrounds to two control displays, which matched either pixel histograms or a phase-scrambled power spectrum. Lightness constancy was improved for rocky glossy displays over the histogram-matched displays, but not compared to phase-scrambled variants of these images with equated power spectrums. The results were similar for surfaces rendered with 1, 2, 3 and 4 interreflections. These results suggest that lightness perception in complex centre-surround displays can be explained by the distribution of contrast across space and scale, independently of explicit information about surface shading or specularity. The results for surfaces without surface relief (“homogeneous” surfaces) differed qualitatively to rocky surfaces, exhibiting abrupt steps in perceived lightness at points at which the targets transitioned from being increments to decrements. Chapter 4 examined whether homogeneous displays evoke more complex mid-level representations similar to conditions of transparency. Matching target lightness in a homogeneous display to that in a textured or rocky display required varying both lightness and transmittance of the test patch on the textured display to obtain the most satisfactory matches. However, transmittance was only varied to match the contrast of targets against homogeneous surrounds, and not to explicitly match the amount of transparency perceived in the displays. The results suggest perceived target-surround edge contrast differs between homogeneous and textured displays. Varying the mid-level property of transparency in textured displays provides a natural means for equating both target lightness and the unique appearance of the edge contrast in homogeneous displays
Modelling of colour appearance
A colour may have a different appearance under different viewing conditions. This
causes many problems in the colour reproduction industry. Thus the importance of
prediction of colour appearance has arisen. In this study, a mathematical model to
predict colour appearance was developed based on the investigation of the changes of
colour appearance under a wide range of media and viewing conditions.
The media studied included large cut-sheet transparency films, 35mm projected
slides, reflection samples and monitor colours. The viewing conditions varied were light
source, luminance level and viewing background. Colour appearance was studied using
the magnitude estimation technique.
In general, colours appeared more colourful, lighter and brighter with an increase
in luminance level. Background and flare light had considerable influence on colour
appearance for cut-sheet transparency media. Simultaneous contrast effects occurred
when a monitor colour was displayed against a chromatic surround. The monitor colour
appeared lighter with a darker induction field. When a coloured area was enlarged,
lightness tended to increase while colourfulness tended to decrease. Colour appearance
was also affected by the closest neighbouring colour. In this case, the hue of the colour
largely shifted towards the direction of the opponent hue of the induction colour.
The data obtained were applied to test three colour spaces and two colour
appearance models. For reflection media, the Hunt91 model performed the best.
However it was not satisfactory when applied to transmissive media. Based on these
results, the Hunt93 model was developed by modification of the Hunt91 model. The new
model widens the application range of the Hunt91 and is reversible
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