Contrast Illusion

Manipulate[Graphics[{Thickness[thickness],GrayLevel[brightness],Table[Line[{{n,0},{n,1}}],{n,zoom,1,zoom}],
Table[Line[{{0,n},{1,n}}],{n,zoom,1,zoom}],
White,
If[disks,Table[Disk[{n,m},thickness/(Sqrt[2])],{n,zoom,1,zoom},{m,zoom,1,zoom}],{}]
},PlotRange->{{0,1},{0,1}},Background->Black],
{{zoom,0.144},0.1,0.2},
{{thickness,0.03},0.01,0.1},
{disks,{True,False}},
{{brightness,0.5},0.1,1}]

CAPTION

How bright are the intersections between the lines? With white circles on them, some appear to have black circles. Remove the circles and some appear to have dark smudges. But in fact all are the same.

Try different sizes and contrasts for the strongest effect.

THIS NOTEBOOK IS THE SOURCE CODE FROM

"Contrast Illusion" from the Wolfram Demonstrations Project
 http://demonstrations.wolfram.com/ContrastIllusion/

Contributed by: Jon McLoone

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