Color-Blindness Simulator — See Any Image as Protanopia, Deuteranopia, Tritanopia and More

Free color-blindness simulator that runs in your browser. Preview an image as protanopia, deuteranopia, tritanopia, their milder forms or total color blindness, then find the colors that become indistinguishable. Nothing is uploaded.

What it does

Add an image and see how it looks to people with different kinds of color vision deficiency. You get eight conditions: protanopia, deuteranopia and tritanopia, their milder “-anomaly” forms (protanomaly, deuteranomaly, tritanomaly) with an adjustable severity, achromatopsia (no color at all) and blue-cone monochromacy.

Beyond the preview, the tool shows where an image changes the most, lists pairs of colors that look different to you but nearly identical to someone with the condition, and can adjust an image to make those differences easier to see. You can also paste a list of hex colors and test a palette without any image.

How it works

Your image is decoded in the browser and drawn to a canvas. Each pixel is converted from sRGB to linear light, multiplied by a 3×3 matrix that models the missing or shifted cone type, and converted back. Working in linear light matters: applying the matrix to gamma-encoded values gives visibly wrong colors.

Machado 2009 is the default method and covers every condition. Intermediate severities are produced by blending between normal vision and the full-severity matrix.
Viénot 1999 is offered for protan and deutan types. Tritan types always use Machado, and the tool tells you when that happens.
Achromatopsia converts each pixel to its luminance. Blue-cone monochromacy uses a simplified blue-weighted brightness model; it does not simulate the lower sharpness or rod involvement of the real condition.

To find confusing colors, the tool reduces the image to its dominant colors with a median-cut quantizer, then compares every pair using CIEDE2000, a standard measure of perceived color difference (ΔE). A pair is flagged when it differs clearly for normal vision but falls below your chosen ΔE threshold under the selected condition. The heatmap applies the same measure to every pixel.

The assist mode is a daltonization-style adjustment: it takes the information the condition loses and moves it into color channels the viewer can still use, with a strength slider. It is a heuristic and is labeled as one.

How to use it

Drop in one or more images, click to browse, or paste with Ctrl/Cmd+V.
Pick a condition from the list, or click a tile in the “All conditions” grid. For the “-anomaly” types, set the severity.
Choose a view: a draggable before/after slider, side by side, a heatmap of how much each area changes, or the assist view.
Hover or tap the image to read any pixel’s color under every condition.
Check the “Confusable colors” list and adjust the ΔE threshold to be stricter or looser.
Download the simulated image, copy it, export an all-conditions contact sheet, or export every condition as a ZIP (for one image or all of them).

Keyboard users can focus the preview and use the left and right arrow keys to move between conditions.

Test a palette without an image

Paste hex colors (#RGB or #RRGGBB, separated by spaces, commas or new lines) into the palette tester. It shows each color under all eight conditions and lists pairs that collide. This is useful for chart series, status colors and brand palettes. If you are checking text legibility rather than color confusion, the Image Color Contrast Matcher measures contrast directly, and the Color picker is a quick way to pull exact hex values from a screenshot first.

Supported formats

JPG, PNG, WebP, GIF (first frame), AVIF, BMP and SVG, as far as your browser can open them. Transparency in PNG and WebP is kept. Downloads can be PNG, JPG or WebP; JPG cannot hold transparency.

Privacy

Everything the simulator does is local. Your images are processed on your device and are never uploaded. To survive a refresh, images you add are stored in your browser’s own storage (IndexedDB) on your device; you can remove one image or clear all of them at any time with the buttons in the tool. There are no network features in this tool.

One detail: the first time you export a ZIP, the browser downloads a small public library (JSZip) from a CDN to build the archive. That request contains none of your images or data.

Limitations

These are approximations. Real color vision varies from person to person, and a screen cannot reproduce another person’s experience exactly. This is not a diagnostic tool.
Calculations assume a standard sRGB display. Images with other color profiles are converted by your browser first.
The preview is limited to about 1600 pixels on the long side for speed; downloads and exports use the full image size, up to your browser’s canvas limit.
Blue-cone monochromacy is a simplified model, and the assist adjustment may not help every image.

FAQ

Which type of color blindness is the most common?

Deuteranomaly, a mild green-weak form, affects roughly 5% of men. Altogether, red-green deficiencies affect around 8% of men and about 0.5% of women in many populations. Blue-yellow and total color blindness are much rarer.

What is the difference between protanopia and protanomaly?

The “-opia” types mean one cone type is missing entirely; the “-anomaly” types mean it is present but shifted, so the effect is milder. Use the severity slider to move from near-normal vision (0%) to the full dichromat simulation (100%).

Why does the simulation use linear light?

Screen colors are stored with a gamma curve, but cone responses add up in linear light. Doing the math on the encoded values distorts brightness and saturation, so the tool converts to linear light first and back afterwards.

Does the heatmap show where my design is inaccessible?

Not by itself. It shows where colors shift the most, which is only part of the story: a big shift is harmless if two things stay distinguishable. The “Confusable colors” list is the better indicator, since it looks for colors that were different and become alike.

Can I use this for charts and UI colors?

Yes. Use the palette tester to check a list of hex colors, and avoid relying on color alone: add labels, patterns, shapes or differences in lightness so information survives for everyone.

Is my image uploaded anywhere?

No. All processing happens in your browser, and saved images stay in your browser’s storage on your device until you remove them.