Gradients and Edges
Edges cause big changes in appearance
On the bottom an edge [display digits 160/200] causes an change in appearance from middle gray to dark gray.
Gradients cause small changes in appearance
On the top a gradual change in luminance [display digits 160/200] causes a nearly invisible change in appearance from middle gray to slightly darker middle gray.
The visibility of gradients is independent of the rate of change of luminance on the retina.
J. J. McCann, R. L. Savoy, J. A. Hall and J. J. Scarpetti,
“Visibility of Continuous Luminance Gradients”,
Vis. Research, 14, 917-927, 1974.
The visibility of low-spatial frequency sine waves is dependent on the number of cycles of sinewave stimulus.
R. L. Savoy and J.J. McCann,
“Visibility of low spatial-frequency sine-wave targets: dependence on number of cycles”,
J. opt. Soc. Am., 65, No. 3, 343-350, 1975.
J. J. McCann, R. L. Savoy and J. A. Hall, Jr.,
“Visibility of Low Frequency Sine-Wave Targets, Dependence on Number of Cycles and Surround Parameters”,
Vis. Research, 18, 891-894, 1978.
J.J. McCann,
“Visibility of gradients and low-spatial frequency sinusoids: Evidence for a distance constancy mechanism”,
J. Photogr. Sci.Eng., 22, 64-68, (1978).
R. L. Savoy,
“Low Spatial Frequencies and Low Number of Cycles at Low Luminances”,
J. Photogr. Sci. Eng., 22, 76-79, 1978.
J.J. McCann and J. A. Hall, Jr.,
“Effects of average-luminance surrounds on the visibility of sine-wave gratings”,
J. opt. Soc. Am., 70, 212-219, 1980.