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§ · free tool

Color blindness simulator. Eight ways of seeing.

Preview any image, or a text / background color pair, through all eight color-vision deficiency types. Adjust severity, check WCAG contrast per mode, download the result. Nothing is uploaded; everything runs locally in your browser.

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A free online tool by Digital Heroes
Drop an image here
or click to browse, JPG, PNG, WebP
Files never leave your browser, all simulation happens locally on your device.

Color-pair tester

Check how a text / background pair holds up under every vision type, with the WCAG contrast ratio recalculated per mode (uses the severity slider above).

AA = ratio ≥ 4.5 (normal text) · AA-L = ratio ≥ 3 (large text ≥ 24px / 18.66px bold)

How the simulation works

Each vision type is approximated with an established 3×3 RGB color matrix (the widely used Colorjack / Machado-style daltonization matrices), applied pixel-by-pixel on a canvas. Around 8% of men and 0.5% of women have some form of color-vision deficiency, deuteranomaly (green-weak) is by far the most common. Everything runs locally; your image never touches a server. Free forever.

§ 02 · what you can do

Everything a simulator should do.

  • Simulate 8 vision types, protanopia, protanomaly, deuteranopia, deuteranomaly, tritanopia, tritanomaly, achromatopsia and achromatomaly, on any image.
  • Adjust severity from 0% to 100% to show partial or full color-vision deficiency, ideal for the “-anomaly” types.
  • Compare 4 views side by side in a 2×2 grid: the original plus any three vision modes of your choice.
  • Test any color pair and see the WCAG contrast ratio recalculated for every deficiency type at once, with AA and AA-Large pass/fail flags.
  • Download the simulated image or a labeled 2×2 comparison grid as PNG, JPG or WebP, at full resolution or capped at 1600 / 1200 / 800 px.
  • Export a report, copy a plain-text summary or download a CSV of contrast ratios across all vision types for accessibility audits.
§ 03 · how to use it

Five steps, no upload.

  1. Drop an image (or click to browse). The file never leaves your device, decoding and simulation happen on a local canvas.
  2. Pick a vision type and drag the severity slider to preview partial or full deficiency.
  3. Switch to 2×2 compare to see the original next to three modes at once, choosing which modes fill the slots.
  4. Use the color-pair tester to check a text / background combination, the WCAG ratio is recalculated for every vision type.
  5. Download the result as PNG, JPG or WebP (with optional burned-in labels), copy the report, or export the CSV.
§ 04 · faq

Frequently asked questions.

Is the Color Blindness Simulator free?
Yes, completely free for everyone. No sign-up, no account and no usage limits.
Is it private? Are my images uploaded anywhere?
No upload, ever. The simulator runs entirely in your browser on your own device, images are decoded onto a local canvas and never leave your computer.
Which vision types does it simulate?
Eight: protanopia and protanomaly (red-blind / red-weak), deuteranopia and deuteranomaly (green-blind / green-weak), tritanopia and tritanomaly (blue-blind / blue-weak), plus achromatopsia and achromatomaly (total and partial color blindness). The severity slider blends any of them toward normal vision.
How accurate is the simulation?
It uses established 3×3 RGB transformation matrices (the widely used Colorjack / Machado-style daltonization approach) applied per pixel. That is a solid approximation for design and accessibility checks, but it is not a medical instrument, individual perception varies, so use it to catch problems, not to diagnose anyone.
What do the AA and AA-L badges mean?
They are WCAG 2 contrast thresholds: AA requires a ratio of at least 4.5:1 for normal text, and AA-L (large text, 24px or 18.66px bold and up) requires at least 3:1. The tester recalculates the ratio after simulating both colors through each vision type, so a pair that passes for typical vision can still fail for, say, deuteranopia.
Does it work offline?
Yes, once the page has loaded, simulation, contrast testing and downloads all work without a connection, because every calculation runs locally in your browser.

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