How protan / deutan / tritan see color & images · adjustable severity · Machado 2009
Normal vision
Simulated
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Single-color check
Original
Simulated
Common confusion pairs
The more alike the two swatches look, the harder that pair is for this type.
Method · formulas
Each pixel's sRGB value is first converted back to linear RGB (inverse gamma: c/12.92 if c≤0.04045, else ((c+0.055)/1.055)2.4), then multiplied by the 3×3 physiologically-based matrix of Machado et al. (2009), and re-encoded to sRGB. The model physically simulates how the retinal cone spectral sensitivities shift and collapse, so it is more accurate than a naive hue rotation.
There are three types: protan affects the L cone, deutan the M cone, tritan the S cone. Severity 0% is normal, 100% is full dichromacy, and intermediate values element-wise interpolate the two adjacent published matrices.
※ The protan and deutan models are reliable; the tritan model is less accurate above ~0.6 severity because tritan is rare and hard to characterize (the original paper says so). This tool is for design checking, not diagnosis. The matrix values match the DaltonLens reference.