🎨 Colorblind Vision Simulator

♿ Accessibility: Color-Safe Enhancement

This tab shifts red and green hues in your figure toward colorblind-safe alternatives (vermillion/orange for reds; blue-green/teal for greens), while leaving all other colors, luminance, and detail unchanged. Use the slider to control the degree of shift, optionally preview how the corrected image looks to colorblind viewers, then download.

📖 Background: Color Vision Deficiency and Scientific Figures

What is color vision deficiency?

Color vision deficiency (CVD) results from absent or non-functional cone photoreceptors in the retina. The human eye has three cone types sensitive to long (L, "red"), medium (M, "green"), and short (S, "blue") wavelengths. Deficiencies arise when one or more cone classes is absent (dichromacy) or shifted in sensitivity (anomalous trichromacy).

The most prevalent forms involve L and M cones and are X-linked, affecting approximately 8% of males of Northern European descent but only ~0.5% of females. In a typical scientific audience, roughly 1 in 12 male attendees or readers may have difficulty distinguishing certain color combinations — most critically, red from green.

Types simulated by this tool

• Deuteranopia — absent M (green) cones; the most common form (~5% of males). Red and green are confused; both tend to appear as shades of yellow-brown or olive.
• Protanopia — absent L (red) cones (~1% of males). Red appears very dark; green and red are confused with characteristic darkening of long wavelengths.
• Tritanopia — absent S (blue) cones (very rare, ~0.003%). Blue and yellow are confused.
• Deuteranomaly — shifted M cones (partial green weakness; ~5% of males). Milder than deuteranopia.
• Protanomaly — shifted L cones (partial red weakness; ~1% of males). Milder than protanopia.
• Achromatopsia — complete absence of functional cones (very rare). Vision is entirely grayscale.

Why does this matter for scientific figures?

The red-green color pair is one of the most frequently used in science — stop/go, inhibit/activate, control/treatment, low/high — yet it is precisely the pair most invisible to the most common forms of colorblindness. Journals increasingly require or recommend colorblind-accessible figures. Institutions receiving federal funding in the United States also have accessibility obligations under Section 508 and the ADA that extend to instructional and research materials, making colorblind-accessible figures a matter of both inclusion and compliance.

How the Accessibility tab color shift works

Each pixel is converted to HSL (hue, saturation, lightness) color space and targeted hue rotation is applied to the two most problematic ranges:

• Reds (hues ~330°–30°) are rotated toward vermillion/orange (~18°) — distinguishable from green by both normal and dichromatic viewers.
• Greens (hues ~75°–165°) are rotated toward blue-green/teal (~165°) — distinguishable from orange/vermillion even for red-green dichromats.

All other hues and all luminance values are preserved. The strength slider blends original (0%) and fully shifted (100%) values, allowing the minimum intervention necessary. Output is always the same pixel dimensions as the input image.

Recommended colorblind-safe palette

The Wong (2011) eight-color palette:

For two-color stop/go situations, blue + orange is the most reliable replacement for red + green.

Additional tips

• Use filled vs. open symbols in addition to color for data series.
• Use solid vs. dashed lines to differentiate curves.
• Add direct labels to lines rather than relying on color-coded legends.
• Avoid rainbow/jet colormaps; use perceptually uniform colormaps such as viridis, cividis, or inferno.
• Check figures in grayscale — if elements are indistinguishable in grayscale, they may also be indistinguishable to colorblind viewers.
• For heatmaps, use blue-white-orange diverging palettes rather than green-red.

How the simulation works

The Simulator tab uses linear RGB transformation matrices derived from the Vienot, Brettel, and Mollon (1999) dichromacy simulation model. Pipeline per pixel: (1) convert sRGB to linear light (remove gamma); (2) apply 3x3 matrix redistributing the missing cone contribution to remaining cones; (3) re-apply gamma correction. Anomalous trichromacy (deuteranomaly, protanomaly) is simulated by blending 60% of the dichromatic result with 40% of the original. All processing is local — no image data is transmitted to any server.

References

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