Computing the relevant colors that describe the color palette of paintings.

In this paper, we introduce an innovative parameter that allows us to evaluate the so-called "relevant colors" in a painting; in other words, the number of colors that would stand out for an observer when just glancing at a painting. These relevant colors allow us to characterize the color palette of a scene and, on this basis, those discernible colors that are colorimetrically different within the scene. We tried to carry out this characterization of the chromatic range of paints according to authors and styles. We used a collection of 4,266 paintings by 91 painters, from which we extracted various parameters that are exclusively colorimetric to characterize the range of colors. After this refinement of the set of selected colors, our algorithm obtained an average number of 18 relevant colors, which partially agreed with the total 11-15 basic color names usually found in other categorical color studies.

[Overweight and risk of overweight in schoolchildren aged 6-17 years old in Galicia (Spain)]. / Estudio del riesgo de sobrepeso y sobrepeso en escolares de Galicia entre 6 y 17 años.

BACKGROUND: Overweight and obesity currently represent one of the most important public health problems in industrialized countries and are also linked to cardiovascular disease and sleep apnea, as well as to orthopaedic and other complications. OBJECTIVES: To examine overweight and the risk of overweight in the school-aged population in Galicia in comparison with the nationally representative survey in the US population: the first National Health and Nutrition Examination Survey (NHANES-1). METHODS: We performed a cross sectional study including a sample of 1105 boys and girls (50 % from a rural environment and 50 % from urban areas) in Galicia, northwest Spain. RESULTS: The 50th percentile for boys and girls in Galicia was higher than the corresponding percentile in the NHANES-1 for all the ages studied. In general, the 85th and 95th percentiles for children's body mass index in Galicia were higher in the group aged 6-14 years. CONCLUSIONS: In Galicia body mass index values in the 50th, 85th and 95th percentiles were higher in girls than in boys. For the 50th percentile, both boys and girls in Galicia had higher values than those of the NHANES-1 for all ages. In areas with risk of excess weight (85th percentile) and prevailing excess weight (95th percentile) the same was true in the 6 to 13-14 age group for both sexes.

Parallel detection of violations of color constancy.

The perceived colors of reflecting surfaces generally remain stable despite changes in the spectrum of the illuminating light. This color constancy can be measured operationally by asking observers to distinguish illuminant changes on a scene from changes in the reflecting properties of the surfaces comprising it. It is shown here that during fast illuminant changes, simultaneous changes in spectral reflectance of one or more surfaces in an array of other surfaces can be readily detected almost independent of the numbers of surfaces, suggesting a preattentive, spatially parallel process. This process, which is perfect over a spatial window delimited by the anatomical fovea, may form an early input to a multistage analysis of surface color, providing the visual system with information about a rapidly changing world in advance of the generation of a more elaborate and stable perceptual representation.

Color and spectral analysis of daylight in southern Europe.

We have analyzed the colorimetric and spectral characteristics of 2600 daylight spectra (global spectral irradiances on a horizontal surface) measured for all sky states during a 2-year period at Granada, Spain. We describe in detail the chromaticity coordinates, correlated color temperatures (CCT), luminous efficacies, and relative UV and IR contents of Granada daylight. The chromaticity coordinates of Granada daylight lie far above the CIE locus at high CCTs (>9,000 K), and a CCT of 5,700 K best typifies this daylight. Our principal-components analysis shows that Granada daylight spectra can be adequately represented by using six-dimensional linear models in the visible, whereas seven-dimensional models are required if we include the UV or near-IR. Yet on average only three-dimensional models are needed to reconstruct spectra that are colorimetrically indistinguishable from the original spectra.

Optical measurement of cardiac rhythm using a personal computer with telediagnosis possibilities.

A system that enables the automatic measurement of cardiac rhythm and the quantity of oxygen in the blood has been designed, constructed, and patented. Equipped with the appropriate software, this system registers this information and represents it numerically, in the form of a graph, which can then be printed as a detailed record of cardiac rhythm. This system aids in the determination of cardiac pathologies, and also enables the information to be sent to medical professionals to perform telediagnosis. The apparatus is based on the measurement (sampling) of noninvasive medical parameters. The apparatus is intended to cover a broad range of requirements and needs, as can be used by medical professionals (to detect pathologies related to the pumping and circulation of blood in the body) as well as by lay people who might wish to monitor or gain information concerning their cardiac rhythm and the general functioning of their heart. Thus, the system is designed to be clear and concise in its information as well as easy to use, especially for people unrelated to the medical profession. The way to constructing this system is explained in detail.

Stochastic independence of color-vision mechanisms confirmed by a subthreshold summation paradigm.

We have used a subthreshold summation protocol to analyze spatial color-color interaction. By means of a CRT color monitor, we measured the threshold contours for a spatial frequency of 0.5 cycles/degree. Heterochromatic flicker photometry was used to obtain isoluminance. The results suggest that the blue-yellow (b-y) and red-green (r-g) contrast thresholds remained unchanged by the addition of fixed r-g and b-y subthreshold pedestals. Our subthreshold summation data then support the stochastic independence of colorvision mechanisms derived from Mullen and Sankeralli's work [Vision Res. 39, 733 (1999)] despite the differences that exist between the two experimental methods.

Response of the human visual system to variable illuminant conditions: an analysis of opponent-colour mechanisms in colour constancy.

Illuminant changes in a scene generally cause displacements in the chromaticity and luminance of the objects of which the scene is composed; however, the visual system is capable of maintaining a constant object colour appearance independently of the illuminant. This is the phenomenon traditionally known as colour constancy. A classical asymmetric colour-matching experiment is reported to address two aspects of colour constancy: successive colour constancy and the role of opponent mechanisms in it. To this end, colour matches are made with chromatically complex backgrounds under different illuminants and with an equal-energy light source as standard. The results are analysed in the cone-excitation space, separately along the L-2M and S dimensions. Data are presented showing that colour-vision mechanisms respond differently to illuminant changes when colour constancy is considered at both receptoral and post-receptoral levels. The L- and M-cones tend to adapt so as to support colour constancy, whereas S-cones are strongly influenced by the illuminant changes. In addition, the data suggest good approaches to colour constancy linked particularly to the yellow-blue mechanism.

Visual system's adjustments to illuminant changes: heuristic-based model revisited.

This study evaluates the effect of illuminant changes along the two post-receptoral mechanisms: red-green (L - 2M) and yellow-blue (L + M - S). By means of a CRT colour monitor, Mondrian-type scenes were simulated and a series of asymmetric colour matches were made with five test illuminants. The standard objects comprising the scenes were simulations of surfaces under equal-energy illuminant and were selected according to lines of equal excitation of the red-green and the yellow-blue mechanisms. Results show that observers' matches are well predicted by assuming affine transformations between test and standard illuminant conditions. The best linear fits derived from the data corroborates the previous heuristic-based algorithms [Zaidi Q. (1998) Journal of the Optical Society of America A. 7. 1767-1776] although some discrepancies were found. Results along red-green mechanism confirm that the significant effect of the illuminant is an additive change along this axis, while data for yellow-blue mechanism suggest that illuminant induces not only multiplicative changes along this axis but additive too. In addition, we found that memory factors involved in the experiment could influence the observers' matches and would be taken into account as responsible of the differences found between the yellow-blue and the red-green systems.

Testing linear models on spectral daylight measurements.

We have analyzed the results of the reconstruction quality of 252 daylight spectral curves measured at Granada, Spain, using four bases obtained from measurements in different areas of the world. For these reconstructions we used two different methods (orthogonality of characteristic vectors and chromaticity coordinates) to study the influence of the wavelength range and spectral resolution. The reconstruction method from chromaticity coordinates presents difficulties for the spectral recovery of daylight spectral power distributions regardless of the basis used. The orthogonality method makes clear that the best bases were those proposed by the CIE, but more than two characteristic CIE vectors were needed for good reconstruction.

Human processing of colour information in the chromatic-frequency domain.

On the basis of MacAdam's data, we have computed a psychophysical function which characterizes the transference of the colour information processed by the human visual system in the chromatic frequency domain. This function, obtained using chromatic-discrimination criteria, shows a cut-off frequency between 0.01375 and 0.02 c/nm, depending upon the colour-tolerance units adopted.