How to simulate color blindness on an image
- Drop in a screenshot, chart, photo or design, choose a file, or paste one from the clipboard.
- See it with normal vision next to protanopia, deuteranopia, tritanopia and achromatopsia, or choose one type to compare with the original using the slider.
- Lower Severity for the milder forms (protanomaly, deuteranomaly, tritanomaly), then download one simulation or the side-by-side sheet.
Designing for colour blind readers
The simulation shows where colours collapse into one. The usual fixes are simple:
- Don’t use colour alone. Add labels, icons, patterns or line styles to anything that carries meaning, such as chart series, form errors and status badges.
- Vary lightness, not just hue. Two colours of the same brightness, like a mid red and a mid green, look identical to many colour blind people. A dark colour next to a light one stays distinct for everyone; the achromatopsia view shows lightness alone, so it is a quick test.
- Avoid the classic pairs. Red with green, green with brown, blue with purple and light green with yellow are the most often confused. Blue and orange are a safer pair for two-colour charts.
- Check text contrast too. Colour blindness and low contrast are different problems; test text separately with the colour contrast checker.
How the simulation works
Each type is a 3 × 3 matrix from Machado, Oliveira and Fernandes, “A Physiologically-based Model for Simulation of Color Vision Deficiency” (IEEE TVCG, 2009). The model shifts the sensitivity of one cone type until, at full severity, it overlaps with another, then works out the colour the eye would see. The matrices act on linear light, so the image’s sRGB values are linearised first and converted back afterwards; skipping that step, as some simulators do, makes the result too dark in the mid-tones.
Between the published 10% steps the matrix is interpolated linearly, as the authors recommend. Achromatopsia is simulated by replacing each pixel with its luminance, using the standard sRGB weights (21% red, 72% green, 7% blue).
Side by side or one at a time
All shows normal vision and the four simulations together, each with its own download button; the file in the list is a single comparison sheet for sharing with a team. Choose one type instead to compare it with the original using the slider, which is the quickest way to spot the exact areas that change. Protan, Deutan and Tritan show protanopia, deuteranopia and tritanopia at 100% severity and protanomaly, deuteranomaly and tritanomaly below it; No colour shows achromatopsia.