Vasco M. N. de Almeida

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Color matching experiments use, in general, stimuli that are poor representations of the natural world. The aim of this work was to compare the degree of color constancy for a range of illuminant pairs using a new matching technique that uses both real objects and three-dimensional (3-D) real scenes. In the experiment, observers viewed a 3-D real scene(More)
The effect of scene complexity on colour constancy was tested with a novel technique in which a virtual image of a real 3-D test object was projected into a real 3-D scene. Observers made discriminations between illuminant and material changes in simple and complex scenes. The extent of colour constancy achieved varied little with either scene structure or(More)
Relational color constancy refers to the constancy of the perceived relations between the colors of surfaces of a scene under changes in the spectral composition of the illuminant. Spatial ratios of cone excitations provide a natural physical basis for this constancy, as, on average, they are almost invariant under illuminant changes for large collections(More)
In a complex natural scene the colour and intensity of the illumination may vary considerably across the scene. Changes in intensity can easily be detected but the same does not seem to be true of colour changes. We investigated the extent to which chromatic changes of the illuminant are detected and the relation of detection performance with colour(More)
The effect of scene dimensionality on colour constancy was tested with real scenes and objects. Observers viewed a three-dimensional (3-D) scene, or its two-dimensional (2-D) planar projection, through a large beam-splitter that projected the virtual image of a real test object (a cube or its 2-D projection) so that it appeared part of the scene. Test(More)
Human iris recognition systems are an attractive form of non-intrusive bio-identification with many potential applications. However, the accuracy of these systems is still limited due to challenges presented by iris surface deformation. This paper provides an introduction to the physiology of the iris, describes the problem of iris deformation, and presents(More)
Traditional color vision tests use luminance contrast noise to mask cues that could improve color discrimination. Recent computerised color vision tests use dynamic luminance contrast noise to mask the colored target. The impact of such masking wasn't yet assessed. The purpose of this work was to assess the masking effect of dynamic luminance contrast noise(More)
The aim of this work was to assess the influence of dynamic luminance contrast noise masking (LCNM) on color discrimination for color normal and anomalous trichromats. The stimulus was a colored target on a background presented on a calibrated CRT display. In the static LCNM condition, the background and target consisted of packed circles with variable size(More)
Performance on a visual search task depends on the conspicuity of the target in relation to the distracters. If these have different colors, performance can reveal the perceptual structure of the color space. The aim of this work was to test how perceptual models of color deficiencies predict the performance of dichromats and anomalous trichromats on a(More)
The purpose of this work was to evaluate existing perceptual models of inherited red-green color deficiencies by assessing the extent to which they predict color discrimination. For dichromacy, the model was the one proposed by Brettel at al. (1997 J. Opt. Soc. Am. A, 2647). For anomalous trichromacy, the assumption tested was that equal stimulations of(More)
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