Color blindness simulator
Choose an image from your device or try the built-in sample. The original and four simulations appear side by side. The picture never leaves your browser.
Runs in your browser: nothing you enter is sent anywhere.
How to use it
- Press Choose file and pick a photo, chart or screenshot, or press Use a sample image.
- Compare the original with the four simulations.
- Look for places where two colors that you meant to be different look alike, such as red and green status indicators.
How it works
Each pixel is converted from sRGB to linear light, multiplied by a 3×3 matrix and converted back. The matrices for protanopia, deuteranopia and tritanopia come from Machado et al. 2009 (severity 1.0). White stays white because each matrix row adds up to 1. For achromatopsia the linear luminance 0.2126 R + 0.7152 G + 0.0722 B is written to all three channels.
Example
Pure red #ff0000 becomes a dark olive #6d5f00 under protanopia, and a mid grey #7f7f7f under achromatopsia.
Tips
- Never rely on color alone: add icons, labels, patterns or position.
- Test charts with several lines: different line styles survive better than different hues.
- Combine with the contrast checker to be sure the text is readable in all cases.
Frequently asked questions
Which method does the simulator use?
For protanopia, deuteranopia and tritanopia it uses the matrices of Machado, Oliveira and Fernandes (2009) at severity 1.0, meaning a complete absence of that cone type, applied to linear RGB values. Achromatopsia is shown as the relative luminance (Rec. 709 weights) in all three channels, since that model has no matrix for it.
Is my image uploaded anywhere?
No. The file is read with your browser and drawn on a canvas on this page. Nothing is sent to a server.
Does it show exactly what a colorblind person sees?
It is an approximation. Real color vision varies, and most people with a deficiency have a partial form, not the complete loss simulated here. Use it to spot colors that become hard to tell apart, not as a medical tool.
Which types are most common?
Red-green deficiencies, protanopia and deuteranopia and their milder forms, are by far the most common and mostly affect men. Tritanopia and complete color blindness are rare.
How large an image can I use?
Large photos are scaled down so the longest side is at most 800 pixels before simulation, which keeps it fast on phones.