PubMed · 10182375
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D Swartz. 1998. Basic medical digital imaging.. https://pubmed.ncbi.nlm.nih.gov/10182375/
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Distinct physical processes can change the spectrum of the illumination that impinges on a surface. Here we consider two such changes. The first is a change in the spectrum of the light source that provides the scene illumination (light source change). The second is a change in the reflectance of a surface located near a test surface of interest (reflected light change). A color constant visual system must compensate for changes caused by both of these physical processes. We report measurements of constancy with respect to reflected light changes and compare them to results from a recent experiment that examines constancy across light source changes. Observers viewed synthetic images rendered from three-dimensional scene descriptions and displayed on a CRT-based stereoscope. They made achromatic adjustments to test surfaces embedded in the images. The degree of constancy varied with the color direction of the illuminant change, and the variation was similar for reflected light and light source changes. The overall level of constancy was lower for reflected light changes than for light source changes. A second experiment suggests that for our conditions, constancy across reflected light changes is driven almost entirely by changes in the local surround of the test. In a third experiment, observers made asymmetric matches across both types of illuminant change. Here the matches were essentially identical across both types of illuminant change.
The extent of the Maillard reaction was studied by measuring furosine and color formation in infant and enteral formula-resembling model systems prepared by mixing calcium caseinate, laboratory-obtained or commercial whey protein with lactose or dextrinomaltose (ingredients similar to those used in infant and enteral formula manufacture) and heating the mixture at 100, 120, or 140 degrees C for 0-30 min. The furosine determination was performed by HPLC and the color determination by measuring colorimetric parameters L, a, and b in a reflection photometer. The first steps of the Maillard reaction could be followed by furosine determination when initial ingredients had low thermal damage. Hence, furosine may be an indicator of low thermal damage in ingredients with <100 mg/100 g of protein. At the concentrations used in these model systems, similar to those in infant and enteral formulas, furosine values (indirect measure of lysine losses) were higher in lactose than in dextrinomaltose systems, in which only glucose, maltose, maltotriose, and maltotetraose among all of the sugars present showed reactivity with casein. Finally, the advanced steps could be followed by color determination when the initial ingredients had high thermal damage or the model systems were heated at high temperature or for a long time. Among the parameters assayed, b was the most sensitive.
Recent findings show that colour processing, like most other sensory attributes, is shaped by experience. While such studies can reveal the mechanisms of development, can they also help uncover the mechanisms of perception?