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About this tool
Simulate protanopia, deuteranopia, tritanopia and achromatopsia on your own images in real time, with an adjustable severity slider and side-by-side comparison.
Color Blindness Simulator re-renders an image or interface screenshot as someone with protanopia, deuteranopia, tritanopia or achromatopsia would see it, using the Viénot–Brettel–Mollon dichromacy model in LMS cone space. It is for designers and developers checking whether a chart, a status badge or a red/green button pair still reads when one cone type is missing. A severity slider covers the anomalous forms too — around 0.5 approximates deuteranomaly and protanomaly, where the cone is shifted rather than absent.
Open Color Blindness Simulator on AltFTool — it loads instantly in your browser.
Load a picture first: click the Drop Image to Analyze card or press Choose Files, paste one with Ctrl+V, or click one of the six Quick Pick thumbnails such as Ishihara Style or Spectral Chart. The controls only appear once an image is on the canvas.
Pick a deficiency in Filter Modes — Normal Vision, Protanopia, Protanomaly, Deuteranopia (the one loaded by default), Deuteranomaly, Tritanopia, Tritanomaly or Achromatopsia — then dial Simulation Intensity, Brightness, Contrast and Saturation in Adjustments. The Reset Settings button in that card's corner returns all four sliders to 100% and the mode to Deuteranopia.
Drag the Slide to Compare handle across the canvas to wipe between Original on the left and Simulated on the right, then keep the result with Export Simulation in the preview footer or Download HD in Quick Export — both write a full-resolution PNG named altftool-cvd-<mode>-<timestamp>.png. The Remove image bin in the header clears the canvas for the next file.
Simulation runs in LMS cone space via linear RGB, not by rotating hues in sRGB, so the result matches how a dichromat actually confuses colours.
Anomalous trichromacy is far more common than full dichromacy; the slider covers the whole range from 0 to 1 instead of only the extreme.
A draggable divider puts the original and the simulation on the same pixels, which is the only reliable way to spot a distinction that has collapsed.
About 8% of men and 0.5% of women of Northern European descent have a red-green deficiency — roughly 1 in 12 men. Deuteranomaly (shifted green cone) is the most common form by a wide margin. Tritanopia is far rarer, under 0.01%, and unlike the red-green forms it affects men and women equally because the gene is not on the X chromosome.
Protanopia is the absence of L (long-wavelength, red) cones; deuteranopia is the absence of M (medium, green) cones. Both collapse reds and greens toward yellows, but protanopes also see red as much darker — pure red comes out near RGB 115,115,0 in this simulation, a dim olive, which is why red-on-black text can vanish entirely for them.
Never carry meaning in hue alone. Pair colour with a shape, icon, label or pattern; keep a contrast ratio of at least 4.5:1 for body text so the distinction survives in achromatopsia mode; and avoid red/green and blue/purple as your only differentiator. Checking the design in achromatopsia mode is the fastest test — if it still works with no colour at all, it works for every deficiency.
No. The image is drawn to a canvas in your own browser and each pixel is transformed in JavaScript; nothing is sent to a server, so unreleased designs and screenshots stay on your machine.