Free Color Blindness Simulator – See Colors as CVD Users Do

What a Color Blindness Simulator Does and How It Works

A colour blindness simulator shows how a colour, a palette, or a whole image would look to someone with a colour vision deficiency, so you can judge whether your design still works for them. Colour vision deficiency is common: roughly eight percent of men and about half a percent of women have some form of it, which across a large audience is a meaningful slice of people who may not perceive your colours the way you do. The tool takes a single colour or an uploaded image and produces a side-by-side view, normal on one side and simulated on the other, so the difference is obvious at a glance. It also includes a pair-checker that warns you when two colours you rely on to mean different things collapse into nearly the same appearance under a given deficiency, which is the core accessibility question. The simulation is a proper colour-space transformation rather than a crude filter. First the sRGB values are converted from their gamma-encoded form to linear RGB, because the maths of human cone response works in linear light. The linear RGB is then converted into the LMS colour space, which represents the response of the long, medium, and short wavelength cones in the eye. In that space the relevant cone response is removed or altered depending on the deficiency, the result is converted back to linear RGB, and finally gamma is re-applied to return to normal sRGB for display. This LMS-based method follows the transformation approach described by Brettel, Viénot, and Mollon, which is the widely cited basis for accurate dichromacy simulation rather than a simple hue swap. Different deficiencies remove different cones. Protanopia is the absence of the long-wavelength (L) cones, deuteranopia the absence of the medium (M) cones, and tritanopia the absence of the short (S) cones; these three are the dichromacies, where one cone type is missing entirely. The anomalous trichromacies, protanomaly, deuteranomaly, and tritanomaly, are milder: the cone still works but is shifted, so the simulator models them by blending the original colour partway toward the full dichromat result, giving a reduced rather than total loss. Achromatopsia, total colour blindness, is modelled by reducing the image to luminance only, so it appears in shades of grey. Presenting all of these lets you check a design against the range of conditions your audience may have. The practical uses centre on accessibility. A designer checks that a red error message and a green success message do not look identical to someone with deuteranopia, which is the most common form, and adds an icon or text label if they do. A data-visualisation author simulates a chart to confirm that adjacent categories in a legend stay distinguishable, then switches to a colourblind-safe palette if they do not. A product team runs a whole interface screenshot through the simulator to spot buttons or status colours that lose meaning. A teacher checks that a worksheet's colour coding still communicates when a colourblind student uses it. In each case the pair-checker's warning is the actionable signal: if two meaningful colours become indistinguishable, add a second cue rather than relying on colour alone. A few caveats keep expectations realistic. A simulation is a model, not a perfect reproduction of any individual's vision, since real deficiencies vary in severity and no two people see identically, so treat it as strong guidance rather than a guarantee. The result also depends on your own display's calibration, so a shade may render slightly differently on another monitor. The most robust design does not depend on colour alone anyway: pairing colour with text, icons, patterns, or position keeps meaning intact for everyone regardless of how they perceive hue. Everything here, including any image you upload, is processed locally in your browser, so nothing is transmitted to a server; the simulation runs on your device, keeps working offline once the page has loaded, and no colour or image you test is uploaded, logged, or stored anywhere.

Color Blindness Simulator Formula & Method

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