sRGB linearisation of a channel
C_lin = C ÷ 12.92 if C ≤ 0.04045, otherwise ((C + 0.055) ÷ 1.055)^2.4
C is the channel value scaled to 0–1 (value ÷ 255).
Color blindness simulator
Upload an image and locally simulate protanopia, deuteranopia, tritanopia or achromatopsia.
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Add a PNG, JPEG, or WebP image. The file stays on your device and all edits run locally in your browser.
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How does this tool work?
About 8% of men and 0.5% of women of Northern European descent have trouble telling some colours apart, most often red and green. This simulator shows how an image, a mock-up or a chart may look with seven types of colour vision deficiency, so you can spot a legend, a status or a button that differs only by colour before you publish it.
Import a PNG, JPEG or WebP image, pick a Simulation type and click Apply simulation. You get three dichromacies, where one type of cone is missing (protanopia for red, deuteranopia for green, tritanopia for blue), three milder and more common anomalous trichromacies (protanomaly, deuteranomaly, tritanomaly) and achromatopsia, which keeps only brightness.
Each pixel is first converted from sRGB to linear light, then multiplied by the 3 × 3 matrix published by Machado, Oliveira and Fernandes (2009) for the chosen type: severity 1.0 for dichromacies and 0.6 for anomalies. The result is encoded back to sRGB. Achromatopsia replaces each colour with its relative luminance.
The simulated image is limited to 1600 px on its longest side, which is enough for a visual check. Before / after and Side by side compare the original with the simulation. All the processing stays in your browser.
How to use this tool
Import the image
Drop a screenshot, a mock-up or a chart in PNG, JPEG or WebP.
Choose the type
Select for example Deuteranopia, the most common form of red-green colour blindness, then apply the simulation.
Compare and download
Switch to Before / after to compare, then download the simulated image if you want to share it.
How the simulation is calculated
Machado's matrices apply to linear light: each channel is linearised, transformed and encoded back to sRGB.
Colour transformation
(R', G', B') = M × (R_lin, G_lin, B_lin)
The result is clamped to 0–1 and encoded back to sRGB with the inverse function.
- C
- value of the red, green or blue channel, from 0 to 1
- M
- 3 × 3 matrix of the chosen deficiency
- R', G', B'
- perceived colour, in linear light
Use cases
Charts and dashboards
Check that the red and green lines of a chart can still be told apart without reading the legend.
Interfaces and forms
Make sure a field in error or an "approved" status stays visible without its colour.
Maps and print
Test a map, a transit diagram or a poster before it goes to print.
Examples
Dashboard red and green with deuteranopia
Both colours turn into two almost identical olives: their red channels differ by a single step. A status shown only by colour becomes unreadable; add an icon or a label.
Input
"Error" dot #E53935 and "success" dot #43A047, Deuteranopia (no green) simulationResult
Simulated red #98892E (152, 137, 46); simulated green #978A4E (151, 138, 78)The same colours with achromatopsia
The relative luminance of the two colours is close, so without colour the difference in grey is small. A stronger brightness contrast would help every reader.
Input
#E53935 and #43A047, Achromatopsia (no color) simulationResult
Grey #7B7B7B (123) and grey #8D8D8D (141)Tips and best practices
- Test at least deuteranopia and protanopia: red-green deficiencies account for most cases.
- Before trying another type, go back to the original with Undo (Ctrl+Z); otherwise the new simulation is applied to the already simulated image.
- Information must never rely on colour alone (WCAG 2.2, success criterion 1.4.1): add a shape, a pattern or a label.
- The simulation is an average model: perception varies from person to person and from screen to screen. It does not replace testing with real users.
Sources and references
- G. M. Machado, M. M. Oliveira, L. A. F. Fernandes, A Physiologically-based Model for Simulation of Color Vision Deficiency (opens in a new tab), IEEE Transactions on Visualization and Computer Graphics, 2009Page in English
- W3C, Web Content Accessibility Guidelines (WCAG) 2.2 — Use of Color (opens in a new tab)Page in English
Frequently asked questions
What is the difference between protanopia and protanomaly?
In protanopia the red-sensitive cones are missing; in protanomaly they are present but shifted. The tool simulates the latter at severity 0.6, so the effect is milder.
Which type should I test first?
Deuteranomaly and deuteranopia, then protanomaly and protanopia. Tritanopia and achromatopsia are much rarer.
Which model does the simulation use?
The matrices of Machado, Oliveira and Fernandes (2009), applied in linear RGB. Achromatopsia uses the relative luminance defined for sRGB.
Why is the downloaded image smaller?
The simulation is computed on a copy limited to 1600 px on its longest side. It is meant to check a design, not to replace your file.
Does the simulation correct the colours?
No. It shows a likely rendering; you then change the colours, contrast or labels of your original design.
Is my image uploaded to a server?
No. The pixel-by-pixel calculation runs in your browser and the image stays on your device.
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