Your visual system pays close attention to boundaries. A simple illusion exposes that habit.
WHY CARE?This is here to help you understand the idea and use it—not merely finish a page.WHAT NEXT?Read the first section, explain it in your own words, then try the small task below.
OPEN ONLY WHAT YOU NEED.Start with the short answer. Expand each idea for examples, mistakes and the fuller explanation. Slides or video are added when they genuinely make the subject clearer.
01 · THE BIG IDEARead deeper+
IN PLAIN ENGLISH
Brightness perception depends partly on nearby contrast. A sharp boundary can make a difference stand out; concealing that boundary can change how the same areas look.
02 · EXAMPLERead deeper+
IN PLAIN ENGLISH
The Exploratorium's Gray Step demonstration uses matching grey gradients side by side. At the join, a dark edge meets a light edge. Cover that join and the apparent difference can weaken.