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Color Test
Check gray steps, near-black, near-white, color ramps, and a simple gamma match.
Merged steps mean the panel is crushing those shades.
More tests
What it measures
Steps
Gray, near-black, and near-white ramps. Merged steps mean crushed blacks or whites.
Gamma
A striped field next to flat patches. The patch that blends in is closest to the panel gamma.
Questions
What gamma should I see?
2.2 is the usual target for sRGB. Stand back if the stripes are too sharp to blend.
Bands in a gradient?
The panel or the browser is running out of shades. That is easier to see on the red, green, and blue ramps.