How to Simulate Color Blindness — Free Online Tool (2026)

You can simulate how people with colour vision deficiency see your images for free using brevio Color Blindness Simulator. Upload any image and instantly see four views — original, protanopia, deuteranopia, and tritanopia — all processed in your browser without uploading.

How to Simulate Colour Blindness

1. Open brevio Color Blindness Simulator. No account required.
2. Drop your image or click to choose a file. JPG, PNG, and WebP are all supported. The file never leaves your browser.
3. Review the four views: Original, Protanopia (red-blind), Deuteranopia (green-blind), and Tritanopia (blue-blind).
4. Download any simulated view by clicking the download link beneath it, or compare them directly on screen.

The three main types of colour blindness

Protanopia (red-blind)

Absence of L-cone (long-wavelength, red-sensitive) photoreceptors. Reds appear very dark, and the red-green distinction is lost. Affects approximately 1% of males. Red text on black backgrounds becomes nearly invisible. Traffic lights: only the bottom green light is distinguishable by position — the red and orange are both perceived as dark.

Deuteranopia (green-blind)

Absence of M-cone (medium-wavelength, green-sensitive) photoreceptors. The most common form of colour blindness, affecting approximately 1% of males. Like protanopia, red-green confusion occurs, but green appears darker rather than red. Together, protanopia and deuteranopia account for the majority of colour vision deficiency in the population.

Tritanopia (blue-blind)

Absence of S-cone (short-wavelength, blue-sensitive) photoreceptors. Very rare (affects fewer than 0.01% of people). Blue appears greenish, yellow appears pinkish, and the blue-yellow distinction is lost. Unlike the red-green deficiencies, tritanopia affects males and females equally.

How the simulation works

The tool applies a 3×3 colour transformation matrix to each pixel. The matrix values are derived from the Dalton model, which maps the response functions of the missing or impaired cone type to approximate the visual experience. For each pixel [R, G, B], the output is:

R_out = m[0]*R + m[1]*G + m[2]*B
G_out = m[3]*R + m[4]*G + m[5]*B
B_out = m[6]*R + m[7]*G + m[8]*B

These are simplified matrices that produce an approximate simulation. More accurate models (such as those from Machado et al., 2009) require non-linear gamma correction steps. This tool prioritises real-time performance over clinical accuracy — the results are useful for design review but should not be used for medical or scientific purposes.

Designing for colour-blind users

• Never rely on colour alone to convey information. Always pair colour with shape, pattern, text label, or icon.
• Avoid red-green combinations for critical UI states (error vs. success). Use icons, border styles, or blue-orange instead.
• Check contrast ratios across simulations. A pair of colours that passes WCAG AA contrast in the original may fail when simulated for deuteranopia.
• Test your charts and data visualisations. Line charts and heat maps are particularly affected — use both distinct colours and distinct line styles (solid, dashed, dotted).
• Use tools like the WCAG Contrast Checker alongside colour blindness simulation for a complete accessibility review.

Frequently Asked Questions

Are the simulations medically accurate?

The simulations are approximate. They use simplified Dalton matrices and do not apply gamma correction, which means very bright and very dark colours may not be simulated with full accuracy. For publishable accessibility research, use tools based on the Machado 2009 model (available in MATLAB or as open-source Python libraries).

Does the tool simulate anomalous trichromacy (protanomaly, deuteranomaly)?

No. The tool simulates full dichromacy (complete absence of one cone type), which represents the more severe end of colour vision deficiency. Anomalous trichromacy (reduced sensitivity rather than absence) affects a larger portion of the population and produces milder colour confusion. A full simulation set would include both dichromacy and anomalous trichromacy variants.

Can I use the simulated images in accessibility reports?

Yes, with the caveat that these are approximations. For formal accessibility audits, note that the simulation uses the simplified Dalton model. The images are suitable for design review and stakeholder communication.

Is my image uploaded anywhere?

No. All four simulations are generated in your browser using the HTML Canvas API. No image data is sent over the network.