RGB到XYZ和LAB颜色转换

我很确定 ^ 是javascript中的按位xor,而不是幂运算符。我想 Math.pow 就是你想要的。

/**
 * Converts RGB color to CIE 1931 XYZ color space.
 * https://www.image-engineering.de/library/technotes/958-how-to-convert-between-srgb-and-ciexyz
 * @param  {string} hex
 * @return {number[]}
 */
export function rgbToXyz(hex) {
    const [r, g, b] = hexToRgb(hex).map(_ => _ / 255).map(sRGBtoLinearRGB)
    const X =  0.4124 * r + 0.3576 * g + 0.1805 * b
    const Y =  0.2126 * r + 0.7152 * g + 0.0722 * b
    const Z =  0.0193 * r + 0.1192 * g + 0.9505 * b
    // For some reason, X, Y and Z are multiplied by 100.
    return [X, Y, Z].map(_ => _ * 100)
}

/**
 * Undoes gamma-correction from an RGB-encoded color.
 * https://en.wikipedia.org/wiki/SRGB#Specification_of_the_transformation
 * https://stackoverflow.com/questions/596216/formula-to-determine-brightness-of-rgb-color
 * @param  {number}
 * @return {number}
 */
function sRGBtoLinearRGB(color) {
    // Send this function a decimal sRGB gamma encoded color value
    // between 0.0 and 1.0, and it returns a linearized value.
    if (color <= 0.04045) {
        return color / 12.92
    } else {
        return Math.pow((color + 0.055) / 1.055, 2.4)
    }
}

/**
 * Converts hex color to RGB.
 * https://stackoverflow.com/questions/5623838/rgb-to-hex-and-hex-to-rgb
 * @param  {string} hex
 * @return {number[]} [rgb]
 */
function hexToRgb(hex) {
    const match = /^#?([a-f\d]{2})([a-f\d]{2})([a-f\d]{2})$/i.exec(hex)
    if (match) {
        match.shift()
        return match.map(_ => parseInt(_, 16))
    }
}

/**
 * Converts CIE 1931 XYZ colors to CIE L*a*b*.
 * The conversion formula comes from <http://www.easyrgb.com/en/math.php>.
 * https://github.com/cangoektas/xyz-to-lab/blob/master/src/index.js
 * @param   {number[]} color The CIE 1931 XYZ color to convert which refers to
 *                           the D65/2° standard illuminant.
 * @returns {number[]}       The color in the CIE L*a*b* color space.
 */
// X, Y, Z of a "D65" light source.
// "D65" is a standard 6500K Daylight light source.
// https://en.wikipedia.org/wiki/Illuminant_D65
const D65 = [95.047, 100, 108.883]
export function xyzToLab([x, y, z]) {
  [x, y, z] = [x, y, z].map((v, i) => {
    v = v / D65[i]
    return v > 0.008856 ? Math.pow(v, 1 / 3) : v * 7.787 + 16 / 116
  })
  const l = 116 * y - 16
  const a = 500 * (x - y)
  const b = 200 * (y - z)
  return [l, a, b]
}

/**
 * Converts Lab color space to Luminance-Chroma-Hue color space.
 * http://www.brucelindbloom.com/index.html?Eqn_Lab_to_LCH.html
 * @param  {number[]}
 * @return {number[]}
 */
export function labToLch([l, a, b]) {
    const c = Math.sqrt(a * a + b * b)
    const h = abToHue(a, b)
    return [l, c, h]
}

/**
 * Converts a and b of Lab color space to Hue of LCH color space.
 * https://stackoverflow.com/questions/53733379/conversion-of-cielab-to-cielchab-not-yielding-correct-result
 * @param  {number} a
 * @param  {number} b
 * @return {number}
 */
function abToHue(a, b) {
    if (a >= 0 && b === 0) {
        return 0
    }
    if (a < 0 && b === 0) {
        return 180
    }
    if (a === 0 && b > 0) {
        return 90
    }
    if (a === 0 && b < 0) {
        return 270
    }
    let xBias
    if (a > 0 && b > 0) {
        xBias = 0
    } else if (a < 0) {
        xBias = 180
    } else if (a > 0 && b < 0) {
        xBias = 360
    }
    return radiansToDegrees(Math.atan(b / a)) + xBias
}

function radiansToDegrees(radians) {
    return radians * (180 / Math.PI)
}

function degreesToRadians(degrees) {
    return degrees * Math.PI / 180
}

以下是RGB的一些函数->XYZ、XYZ->实验室,实验室->XYZ、XYZ->RGB中。

function RGBtoXYZ([R, G, B]) {
    const [var_R, var_G, var_B] = [R, G, B]
        .map(x => x / 255)
        .map(x => x > 0.04045
            ? Math.pow(((x + 0.055) / 1.055), 2.4)
            : x / 12.92)
        .map(x => x * 100)

    // Observer. = 2°, Illuminant = D65
    X = var_R * 0.4124 + var_G * 0.3576 + var_B * 0.1805
    Y = var_R * 0.2126 + var_G * 0.7152 + var_B * 0.0722
    Z = var_R * 0.0193 + var_G * 0.1192 + var_B * 0.9505
    return [X, Y, Z]
}

function XYZtoRGB([X, Y, Z]) {
    //X, Y and Z input refer to a D65/2° standard illuminant.
    //sR, sG and sB (standard RGB) output range = 0 ÷ 255

    let var_X = X / 100
    let var_Y = Y / 100
    let var_Z = Z / 100

    var_R = var_X *  3.2406 + var_Y * -1.5372 + var_Z * -0.4986
    var_G = var_X * -0.9689 + var_Y *  1.8758 + var_Z *  0.0415
    var_B = var_X *  0.0557 + var_Y * -0.2040 + var_Z *  1.0570

    return [var_R, var_G, var_B]
        .map(n => n > 0.0031308
            ? 1.055 * Math.pow(n, (1 / 2.4)) - 0.055
            : 12.92 * n)
        .map(n => n * 255)
}

const ref_X =  95.047;
const ref_Y = 100.000;
const ref_Z = 108.883;

function XYZtoLAB([x, y, z]) {
    const [ var_X, var_Y, var_Z ] = [ x / ref_X, y / ref_Y, z / ref_Z ]
        .map(a => a > 0.008856
            ? Math.pow(a, 1 / 3)
            : (7.787 * a) + (16 / 116))

    CIE_L = (116 * var_Y) - 16
    CIE_a = 500 * (var_X - var_Y)
    CIE_b = 200 * (var_Y - var_Z)

    return [CIE_L, CIE_a, CIE_b]
}

function LABtoXYZ([l, a, b]) {

    const var_Y = (l + 16) / 116
    const var_X = a / 500 + var_Y
    const var_Z = var_Y - b / 200

    const [X, Y, Z] = [var_X, var_Y, var_Z]
        .map(n => Math.pow(n, 3) > 0.008856
            ? Math.pow(n, 3)
            : (n - 16 / 116) / 7.787)

    return [X * ref_X, Y * ref_Y, Z * ref_Z]
}

参考文献: http://www.easyrgb.com/en/math.php

function xyzc(c){return ((c/255)>0.04045)?Math.pow((((c/255)+0.055)/1.055),2.4)*100:(c/255)/12.92*100;}

此行将rgb通道转换为XYZ