The purpose of this work is to assess lightness/brightness in displays consisting of a central target surface surrounded by a luminance gradient plus an homogeneous surround (disk-gradient-ring, DGR). The ecology of vision as well as laboratory phenomena (Agostini & Galmonte, 1997, Zavagno, 1996) suggest that DGR displays yield effects not observed in traditional disk-ring (DR) arrangements. A representative subset of the space of all possible DGR displays is defined by two parameters: the log ratio of target luminance to ring luminance (T/R) and the log ratio of the luminance of the inner end of the gradient to the luminance of the ring (G/R). The outer end of the gradient was constrained to be always equal to the ring. By sampling homogeneously from this space, we obtained a comprehensive assessment of the effect of gradient slope for two levels of relative gradient size and for both increments and decrements. A preliminary study of simple DR displays validated our method, yielding near-perfect ratio results for both increments and decrements. Luminance gradients yielded measurable deviations from ratio results in comparison with flat-gradient controls. For equal slopes, large gradients were more effective than small ones. Luminance gradients have dramatic and largely unexplored effects, possibily reflecting the operation of integrating relative luminance at different spatial scales in order to account for illumination and shading effects.
Towards a psychophysics of lightness/brightness in disk-gradient-ring displays: validation, slope, and size
GALMONTE, Alessandra;
1998-01-01
Abstract
The purpose of this work is to assess lightness/brightness in displays consisting of a central target surface surrounded by a luminance gradient plus an homogeneous surround (disk-gradient-ring, DGR). The ecology of vision as well as laboratory phenomena (Agostini & Galmonte, 1997, Zavagno, 1996) suggest that DGR displays yield effects not observed in traditional disk-ring (DR) arrangements. A representative subset of the space of all possible DGR displays is defined by two parameters: the log ratio of target luminance to ring luminance (T/R) and the log ratio of the luminance of the inner end of the gradient to the luminance of the ring (G/R). The outer end of the gradient was constrained to be always equal to the ring. By sampling homogeneously from this space, we obtained a comprehensive assessment of the effect of gradient slope for two levels of relative gradient size and for both increments and decrements. A preliminary study of simple DR displays validated our method, yielding near-perfect ratio results for both increments and decrements. Luminance gradients yielded measurable deviations from ratio results in comparison with flat-gradient controls. For equal slopes, large gradients were more effective than small ones. Luminance gradients have dramatic and largely unexplored effects, possibily reflecting the operation of integrating relative luminance at different spatial scales in order to account for illumination and shading effects.
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