Biomedical subjects

Françoise Viénot

Publications and source records attributed to Françoise Viénot.

3 recordsLinked to original sources

PubMed2005

Regulation of chromatic induction by neighboring images.

We deal with the regulation of chromatic contrast when the induction of a second stimulus (one of five neighboring surrounds) opposes the induction from a first stimulus (one of two remote vivid peripheral fields). Using a hue cancellation judgment, we show that, although every neighboring surround that we used has the same average chromatic content, the resulting color appearance of the target differs between surrounds, and this may be ascribed to the spatiochromatic organization of the surround. So, rather than the chromatic contrast amplitude or the frequential structure of the surround, it is the structure of proximity that matters.

Adaptation, Ocular↗

PubMed2004

Difference scaling of gloss: nonlinearity, binocularity, and constancy.

Gloss is an attribute of visual appearance that originates from the geometrical distribution of the light reflected by the surface. We used the maximum likelihood difference scaling (MLDS) procedure (L.T. Maloney & J. N. Yang, 2003) to estimate gloss scales over an extended range. Observers' judgments were obtained for a series of 10 black, coated samples for two directions of illumination, in binocular and monocular vision. The results showed a nonlinear relation between gloss percept and instrumental specular gloss values. Sensitivity is higher at extreme scale values than in the middle. In binocular vision, the sensitivity to gloss is higher than in monocular vision exclusively for high gloss levels. Lastly, we found that gloss difference scales, when expressed in terms of the samples rather than the photometric characteristics, vary little with the direction of illumination. Gloss scaling thus seems to be independent of the geometrical variations of the luminous flux at the surface of the sample. By analogy with the term "color constancy," we call this property "gloss constancy."

Humans↗

PubMedDate not supplied

Convergence of experimental multiple Rayleigh matches to peak L- and M-photopigment sensitivity estimates.

Shift in the wavelength of peak sensitivity of the cone photo pigments is a major cause of inter-individual variations in the Rayleigh match. Normal color observers performed multiple Rayleigh matches (i.e., a series of seven Rayleigh-type color matches using various sets of test and primary lights) in order to derive estimates of the M- and L-photo pigment wavelengths of maximum absorbance. We predicted the ratio of incident radiances Pr/Pg for a range of plausible values in terms of wavelength of the peak sensitivity of the M-cone and L-cone. An algorithm allowed us to adjust the values of the peak wavelength of the cone photo pigments in order to minimize the sum of squared differences between predicted and real results of matches. To create candidate M-cone and L-cone photo pigments that best predict the set of equation values, we used the low density spectral absorbance curves of the M-cone and L-cone photo pigments respectively, as tabulated by Stockman and Sharpe (2000), and shifted each template along a logarithmic wavelength scale. For all observers, the system of seven Rayleigh-like equations converges to a unique solution. M- and L-cone photo pigments are estimated separately. The distribution of the wavelength of maximum sensitivity of the photo pigments includes a cluster. Only a few women's results lie outside the cluster. The choice of the template has a considerable influence on the convergence of the algorithm.

Adult↗