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

Historical prospective of human cytogenetics: from microscope to microarray.

Item does not contain fulltextAfter the fundamental discovery in 1956 that normal human cells contain 46 chromosomes, clinical cytogenetics was born and studies into the relation of chromosomal defects and disease could begin. Although many technical advances have been made over this long period, including the introduction of molecular techniques, until now, all cytogenetic studies have been performed through regular microscopes, which was throughout the years the most important equipment of a cytogenetic laboratory. However, recently a new technique has been introduced based on comparative genomic hybridization on an array of thousands of different probes (array-CGH). This technique enables an increase in the sensitivity of detecting chromosomal aberrations far beyond the detection limit of regular banding techniques. Furthermore, it gives us the possibility to detect genomic changes in malignant cells in cases where aberrations are too complex to study or when chromosomes are not available at all. Cytogenetic laboratories are now challenged to introduce and incorporate this new application next to the various well-established microscopical techniques to provide optimal diagnostic services

Mentale retardatie

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Mentale retardatie

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In search of disease genes. Array CGH as a molecular cytogenetic diagnostic tool.

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Unique mosaicism of structural chromosomal rearrangement: is chromosome 18 preferentially involved?

The mentally normal mother of a 4-year-old boy with del(18)(q21.3) syndrome was tested cytogenetically to study the possibility of an inherited structural rearrangement of chromosome 18. She was found to carry an unusual mosaicism involving chromosomes 18 and 21. Two unbalanced cell lines were seen as derivatives of a reciprocal translocation t(18;21), resulting in mosaicism of two cell lines, one with partial monosomy 18q and one with partial trisomy 18q. A literature review revealed that mosaicism of two or more cell lines with different unbalanced structural aberrations is extremely rare; moreover, chromosome 18 appeared to be involved in the majority of cases. We discuss possible mechanisms for the origin of this distinctive chromosomal constitution

Intramuscular vitamin K and cytogenetic toxicity

Item does not contain fulltextInternational Symposium Base

Comparative genomic hybridization analysis of human sarcomas: I. Occurrence of genomic imbalances and identification of a novel major amplicon at 1q21-q22 in soft tissue sarcomas

Contains fulltext : 21733___.PDF (publisher's version ) (Open Access

Comparative genomic hybridization analysis of human sarcomas: II. Identification of novel amplicons at 6p and 17p in osteosarcomas

Contains fulltext : 21734___.PDF (publisher's version ) (Open Access