chroma-js/src/io/hsi/rgb2hsi.js

JavaScript library for color conversions

import { unpack, TWOPI } from '../../utils/index.js';
const { min, sqrt, acos } = Math;

const rgb2hsi = (...args) => {
    /*
    borrowed from here:
    http://hummer.stanford.edu/museinfo/doc/examples/humdrum/keyscape2/rgb2hsi.cpp
    */
    let [r, g, b] = unpack(args, 'rgb');
    r /= 255;
    g /= 255;
    b /= 255;
    let h;
    const min_ = min(r, g, b);
    const i = (r + g + b) / 3;
    const s = i > 0 ? 1 - min_ / i : 0;
    if (s === 0) {
        h = NaN;
    } else {
        h = (r - g + (r - b)) / 2;
        h /= sqrt((r - g) * (r - g) + (r - b) * (g - b));
        h = acos(h);
        if (b > g) {
            h = TWOPI - h;
        }
        h /= TWOPI;
    }
    return [h * 360, s, i];
};

export default rgb2hsi;