Specimen no. 04 · under a different light
Color blindness simulator
Check a chart, map, photo or screenshot the way people with the common types of color vision deficiency might see it, side by side with the original.
Drop an image on this sheet
or paste one with Ctrl+V (⌘+V on a Mac)
JPEG, PNG, WebP, GIF, AVIF or SVG. The image stays on your device.
No working green-sensitive (M) cones: reds, greens, oranges and browns are hard to tell apart.
Below 100% blends toward typical vision, a rough stand-in for the milder forms.
How the simulation works
Each pixel is converted from sRGB to linear light, multiplied by a 3 × 3 matrix, and converted back. For protanopia, deuteranopia and tritanopia the matrices come from the physiologically based model of Machado, Oliveira and Fernandes (2009), which shifts the sensitivity of the missing cone type and reprojects the result into what the remaining cones can tell apart. Achromatopsia keeps only relative luminance, so the image becomes a grey of the same lightness.
The full-strength setting simulates dichromacy, where one cone type is missing. Many more people have a milder, anomalous form (protanomaly, deuteranomaly, tritanomaly). Lowering the strength blends toward typical vision; the paper publishes separate matrices for each severity, so treat the blend as an approximation.
What to look for
Move the divider across anything that relies on color to carry meaning: chart series, map legends, error and success states, sale tags, cable colors. If two things you need to tell apart melt together, add a second cue such as a label, pattern, icon or a clear difference in lightness. Red-green types are by far the most common, so check deuteranopia and protanopia first.
A simulation is a model, not anyone's actual experience: color vision varies from person to person, and screens and lighting change what everyone sees.
Sources
- Machado GM, Oliveira MM, Fernandes LAF. A physiologically-based model for simulation of color vision deficiency. IEEE Transactions on Visualization and Computer Graphics 2009;15(6):1291–1298. doi:10.1109/TVCG.2009.113 (the severity 1.0 matrices).
- National Eye Institute, Color blindness: the types of color vision deficiency and how common they are.
- ITU-R Recommendation BT.709: the luminance weights (0.2126, 0.7152, 0.0722) used for achromatopsia.
For understanding and design checks only; it is not a medical or diagnostic tool.
Questions
Can this test whether I am color blind?
No. It shows how an image might look to someone else; it cannot measure your own vision. An eye care professional can test color vision properly.
Does it fix images for color-blind viewers?
No, it only simulates. The dependable fix is in the design itself: never let hue alone carry meaning, and back it up with text, shapes, patterns or contrast in lightness.
Why do bright reds turn so dark under protanopia?
The long-wavelength (red-sensitive) cones are the ones missing in protanopia, so deep reds send much less signal and look darker as well as less colorful. The model reproduces that loss of brightness.