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M L de Mattiello

Publications and source records attributed to M L de Mattiello.

6 recordsLinked to original sources
PubMed1985

Suprathreshold contrast perception at different luminance levels.

Magnitude estimation experiments show that the perceived contrast of sine waves is a linear function of stimulus contrast at some mean luminance (Lm), spatial frequency and contrast levels, but not at others. For monocular vision at both low and high contrast levels, linearity is observed within a limited zone which, at high Lm levels, does not include intermediate frequencies. Binocular vision gives similar results at high contrast levels, while for low levels, the linearity zone comprises intermediate frequencies in a wide Lm range. It is demonstrated that if a threshold correction is introduced into the obtained psychophysical functions, the described linearity zones extend to wider Lm and contrast ranges.

Adult↗
PubMed1981

Saturation constancy in surface colors.

The level of reflectance of pigmented surfaces observed in daylight affects saturation growth in different ways, depending on the wavelength of the samples. Numerical and matching judgments collected in previous experiments were replotted in families of monochromatic (constant hue) saturation power functions for blue, green, yellow, and red. For each hue the set of functions intersected at a point at which the colorimetric purity and saturation were invariant with reflectance. The points of intersection were: blues, 0.081 colorimetric purity (Pc) and 2.7 cromes; greens, 0.257 Pc and 4.6 cromes; yellows, 0.694 Pc and 8.3 cromes; and reds, 0.144 Pc and 3.6 cromes. A straight line fitted to these four intersecting points makes it possible to interpolate other intersecting points for other hues. Two additional experiments were designed to compare a function of saturation with a function of lightness for a set of different hues (heterochromatic functions). Observers judged saturation in one experiment and lightness in the other. Lightness grows linearly with reflectance, and saturation increases as the 0.5 power of Pc, suggesting a different perceptual discrimination for the two dimensions. The relation between changes in quantity and percentage of color perceived was tested in an additional experiment. Observers assigned the following saturation values to the samples with Pc close to the converging points: 13% of color for blues, 20% for reds, 25% for greens, and 40% for yellows.

Color↗
PubMed1977

Saturation of colored samples at various levels of reflectance.

The dependence of saturation on the level of reflectance of colored surfaces was measured by numerical estimation and by matching judgments. Four sets of chromatic samples, one for each hue--blue, 460 nm, green, 510 nm, yellow, 580 nm, and red, 620 nm--within a range between 4% and 65% reflectance, were presented to the observers. The largest changes of saturation were observed at the high and low values of reflectance. The effect is more pronounced for the yellows than for the reds and greens, and relatively less apparent for the blues. For each hue, saturation grows faster at intermediate values of reflectance. The four families of saturation functions permitted us to draw a map of equal-purity contours. There are values of colorimetric purity for which saturation remains constant for all levels of reflectance.

Color Perception↗