# Can you match two shades of grey?

Match the shade of the right tile across five deceptive optical surrounds, then connect the tiles to reveal the physical reality and measure how severely your visual cortex distorts lightness.

[Open the interactive experiment](https://mariuscomper.uk/cele-doua-griuri/en/)

## The Premise

The human eye is not a photometer. The retina and visual cortex do not record absolute photon flux; they compute local spatial contrast along surface borders and infer lighting conditions.

## The Five Rounds

1. **Classic Simultaneous Contrast:** Left tile on pitch black, right tile on pure white. The left tile appears far brighter despite sharing an identical 50% physical reflectance.
2. **Gradient Ramp:** A smooth continuous luminance ramp induces an illusory gradient inside an otherwise uniform patch.
3. **Cylinder Shadow (Adelson):** The visual cortex discounts three-dimensional cast shadow, heavily boosting the perceived lightness of the shaded check.
4. **White's Illusion:** T-junctions assign grey bars to distinct depth planes, inverting the standard prediction of lateral inhibition.
5. **Cornsweet Edge:** An opposed edge gradient spanning only a few pixels tricks the visual system into filling in an illusory tone across two identical expanses.

## Scoring and Measurement

Each round records the signed delta between the target's physical reflectance and your chosen shade. The final profile computes your mean contrast error, directional bias, and an interactive 5-swatch comparison strip.

All computations are deterministic and remain strictly local to your browser.

Research and implementation: Marius Comper, September 2026.