@dichroma/core

Scientifically accurate color-vision-deficiency (CVD) simulation with zero runtime dependencies. All math runs in linear RGB, where the established models are actually defined: Viénot 1999 for full protanopia/deuteranopia, Machado 2009 for anomalous (partial-severity) protan/deutan trichromacy, Brettel 1997 two-half-plane projection for tritanopia, and a luminance blend for achromatopsia. It also generates equivalent SVG <filter> markup for whole-page simulation in browsers and computes WCAG contrast ratios in simulated color space.

npm install @dichroma/core

Or build it from this monorepo: pnpm install && pnpm build produces packages/core/dist.

Usage

import { simulateColor, buildSvgFilter, simulatedWcagRatio } from '@dichroma/core';

simulateColor([255, 0, 0], 'deutan', 1);        // -> [147, 147, 0]-ish yellow
simulateColor([255, 0, 0], 'protan', 0.5);      // partial severity (Machado 2009)

const filter = buildSvgFilter('tritan', 1);
document.body.insertAdjacentHTML('beforeend', `<svg width="0" height="0">${filter.markup}</svg>`);
document.documentElement.style.filter = filter.cssInline;   // or filter.cssDataUrl

simulatedWcagRatio([255, 0, 0], [0, 255, 0], 'deutan', 1);  // contrast as a deutan sees it

API

| Function | Purpose | | --- | --- | | simulateColor(srgb, type, severity?) | Simulate one 8-bit sRGB color ([r, g, b] → [r, g, b]). | | simulateImageData(data, type, severity?) | Simulate an RGBA pixel buffer in place (alpha untouched). | | buildSvgFilter(type, severity?, opts?) | SVG <filter> equivalent of the model (markup, svg, dataUrl, cssDataUrl, cssInline). | | resolveModel(type, severity?) | Resolve type + severity to the underlying linear-RGB model. | | simulateLinear(rgb, model) | Apply a resolved model to one linear-RGB color. | | relativeLuminance(srgb) | WCAG relative luminance. | | wcagRatio(fg, bg) | WCAG contrast ratio (1–21). | | simulatedWcagRatio(fg, bg, type, severity?) | WCAG contrast ratio under CVD simulation. | | compositeOver(fgRgba, bg) | Gamma-space alpha compositing (CSS default). | | srgbToLinear(c8) / linearToSrgb(c) / LINEAR_LUT | sRGB ↔ linear transfer functions. |

type is 'protan' | 'deutan' | 'tritan' | 'achromatopsia'; severity is 0–1 (default 1).

Accuracy

• The protan, deutan, and tritan routes are validated against DaltonLens-Python on the full 17³ sRGB grid for every model/severity combination: max per-channel delta ≤ 1/255.
• Achromatopsia is validated by unit-test fixed points (every color maps to its Rec. 709 luminance gray, ±1 after rounding); it has no external golden anchor.
• The SVG filters are verified pixel-for-pixel in headless Chrome (inline and data-URL delivery): max per-channel delta ≤ 3/255.

License

MIT