I just found out about this awesome fiddle. You input the color you need in hex, and it gives you your filter code. Very pratical: https://codepen.io/sosuke/pen/Pjoqqp.
The javascript to calculate it is:
'use strict';
class Color {
constructor(r, g, b) {
this.set(r, g, b);
}
toString() {
return `rgb(${Math.round(this.r)}, ${Math.round(this.g)}, ${Math.round(this.b)})`;
}
set(r, g, b) {
this.r = this.clamp(r);
this.g = this.clamp(g);
this.b = this.clamp(b);
}
hueRotate(angle = 0) {
angle = angle / 180 * Math.PI;
const sin = Math.sin(angle);
const cos = Math.cos(angle);
this.multiply([
0.213 + cos * 0.787 - sin * 0.213,
0.715 - cos * 0.715 - sin * 0.715,
0.072 - cos * 0.072 + sin * 0.928,
0.213 - cos * 0.213 + sin * 0.143,
0.715 + cos * 0.285 + sin * 0.140,
0.072 - cos * 0.072 - sin * 0.283,
0.213 - cos * 0.213 - sin * 0.787,
0.715 - cos * 0.715 + sin * 0.715,
0.072 + cos * 0.928 + sin * 0.072,
]);
}
grayscale(value = 1) {
this.multiply([
0.2126 + 0.7874 * (1 - value),
0.7152 - 0.7152 * (1 - value),
0.0722 - 0.0722 * (1 - value),
0.2126 - 0.2126 * (1 - value),
0.7152 + 0.2848 * (1 - value),
0.0722 - 0.0722 * (1 - value),
0.2126 - 0.2126 * (1 - value),
0.7152 - 0.7152 * (1 - value),
0.0722 + 0.9278 * (1 - value),
]);
}
sepia(value = 1) {
this.multiply([
0.393 + 0.607 * (1 - value),
0.769 - 0.769 * (1 - value),
0.189 - 0.189 * (1 - value),
0.349 - 0.349 * (1 - value),
0.686 + 0.314 * (1 - value),
0.168 - 0.168 * (1 - value),
0.272 - 0.272 * (1 - value),
0.534 - 0.534 * (1 - value),
0.131 + 0.869 * (1 - value),
]);
}
saturate(value = 1) {
this.multiply([
0.213 + 0.787 * value,
0.715 - 0.715 * value,
0.072 - 0.072 * value,
0.213 - 0.213 * value,
0.715 + 0.285 * value,
0.072 - 0.072 * value,
0.213 - 0.213 * value,
0.715 - 0.715 * value,
0.072 + 0.928 * value,
]);
}
multiply(matrix) {
const newR = this.clamp(this.r * matrix[0] + this.g * matrix[1] + this.b * matrix[2]);
const newG = this.clamp(this.r * matrix[3] + this.g * matrix[4] + this.b * matrix[5]);
const newB = this.clamp(this.r * matrix[6] + this.g * matrix[7] + this.b * matrix[8]);
this.r = newR;
this.g = newG;
this.b = newB;
}
brightness(value = 1) {
this.linear(value);
}
contrast(value = 1) {
this.linear(value, -(0.5 * value) + 0.5);
}
linear(slope = 1, intercept = 0) {
this.r = this.clamp(this.r * slope + intercept * 255);
this.g = this.clamp(this.g * slope + intercept * 255);
this.b = this.clamp(this.b * slope + intercept * 255);
}
invert(value = 1) {
this.r = this.clamp((value + this.r / 255 * (1 - 2 * value)) * 255);
this.g = this.clamp((value + this.g / 255 * (1 - 2 * value)) * 255);
this.b = this.clamp((value + this.b / 255 * (1 - 2 * value)) * 255);
}
hsl() {
// Code taken from https://stackoverflow.com/a/9493060/2688027, licensed under CC BY-SA.
const r = this.r / 255;
const g = this.g / 255;
const b = this.b / 255;
const max = Math.max(r, g, b);
const min = Math.min(r, g, b);
let h, s, l = (max + min) / 2;
if (max === min) {
h = s = 0;
} else {
const d = max - min;
s = l > 0.5 ? d / (2 - max - min) : d / (max + min);
switch (max) {
case r:
h = (g - b) / d + (g < b ? 6 : 0);
break;
case g:
h = (b - r) / d + 2;
break;
case b:
h = (r - g) / d + 4;
break;
}
h /= 6;
}
return {
h: h * 100,
s: s * 100,
l: l * 100,
};
}
clamp(value) {
if (value > 255) {
value = 255;
} else if (value < 0) {
value = 0;
}
return value;
}
}
class Solver {
constructor(target, baseColor) {
this.target = target;
this.targetHSL = target.hsl();
this.reusedColor = new Color(0, 0, 0);
}
solve() {
const result = this.solveNarrow(this.solveWide());
return {
values: result.values,
loss: result.loss,
filter: this.css(result.values),
};
}
solveWide() {
const A = 5;
const c = 15;
const a = [60, 180, 18000, 600, 1.2, 1.2];
let best = { loss: Infinity };
for (let i = 0; best.loss > 25 && i < 3; i++) {
const initial = [50, 20, 3750, 50, 100, 100];
const result = this.spsa(A, a, c, initial, 1000);
if (result.loss < best.loss) {
best = result;
}
}
return best;
}
solveNarrow(wide) {
const A = wide.loss;
const c = 2;
const A1 = A + 1;
const a = [0.25 * A1, 0.25 * A1, A1, 0.25 * A1, 0.2 * A1, 0.2 * A1];
return this.spsa(A, a, c, wide.values, 500);
}
spsa(A, a, c, values, iters) {
const alpha = 1;
const gamma = 0.16666666666666666;
let best = null;
let bestLoss = Infinity;
const deltas = new Array(6);
const highArgs = new Array(6);
const lowArgs = new Array(6);
for (let k = 0; k < iters; k++) {
const ck = c / Math.pow(k + 1, gamma);
for (let i = 0; i < 6; i++) {
deltas[i] = Math.random() > 0.5 ? 1 : -1;
highArgs[i] = values[i] + ck * deltas[i];
lowArgs[i] = values[i] - ck * deltas[i];
}
const lossDiff = this.loss(highArgs) - this.loss(lowArgs);
for (let i = 0; i < 6; i++) {
const g = lossDiff / (2 * ck) * deltas[i];
const ak = a[i] / Math.pow(A + k + 1, alpha);
values[i] = fix(values[i] - ak * g, i);
}
const loss = this.loss(values);
if (loss < bestLoss) {
best = values.slice(0);
bestLoss = loss;
}
}
return { values: best, loss: bestLoss };
function fix(value, idx) {
let max = 100;
if (idx === 2 /* saturate */) {
max = 7500;
} else if (idx === 4 /* brightness */ || idx === 5 /* contrast */) {
max = 200;
}
if (idx === 3 /* hue-rotate */) {
if (value > max) {
value %= max;
} else if (value < 0) {
value = max + value % max;
}
} else if (value < 0) {
value = 0;
} else if (value > max) {
value = max;
}
return value;
}
}
loss(filters) {
// Argument is array of percentages.
const color = this.reusedColor;
color.set(0, 0, 0);
color.invert(filters[0] / 100);
color.sepia(filters[1] / 100);
color.saturate(filters[2] / 100);
color.hueRotate(filters[3] * 3.6);
color.brightness(filters[4] / 100);
color.contrast(filters[5] / 100);
const colorHSL = color.hsl();
return (
Math.abs(color.r - this.target.r) +
Math.abs(color.g - this.target.g) +
Math.abs(color.b - this.target.b) +
Math.abs(colorHSL.h - this.targetHSL.h) +
Math.abs(colorHSL.s - this.targetHSL.s) +
Math.abs(colorHSL.l - this.targetHSL.l)
);
}
css(filters) {
function fmt(idx, multiplier = 1) {
return Math.round(filters[idx] * multiplier);
}
return `filter: invert(${fmt(0)}%) sepia(${fmt(1)}%) saturate(${fmt(2)}%) hue-rotate(${fmt(3, 3.6)}deg) brightness(${fmt(4)}%) contrast(${fmt(5)}%);`;
}
}
function hexToRgb(hex) {
// Expand shorthand form (e.g. "03F") to full form (e.g. "0033FF")
const shorthandRegex = /^#?([a-f\d])([a-f\d])([a-f\d])$/i;
hex = hex.replace(shorthandRegex, (m, r, g, b) => {
return r + r + g + g + b + b;
});
const result = /^#?([a-f\d]{2})([a-f\d]{2})([a-f\d]{2})$/i.exec(hex);
return result
? [
parseInt(result[1], 16),
parseInt(result[2], 16),
parseInt(result[3], 16),
]
: null;
}
$(document).ready(() => {
$('button.execute').click(() => {
const rgb = hexToRgb($('input.target').val());
if (rgb.length !== 3) {
alert('Invalid format!');
return;
}
const color = new Color(rgb[0], rgb[1], rgb[2]);
const solver = new Solver(color);
const result = solver.solve();
let lossMsg;
if (result.loss < 1) {
lossMsg = 'This is a perfect result.';
} else if (result.loss < 5) {
lossMsg = 'The is close enough.';
} else if (result.loss < 15) {
lossMsg = 'The color is somewhat off. Consider running it again.';
} else {
lossMsg = 'The color is extremely off. Run it again!';
}
$('.realPixel').css('background-color', color.toString());
$('.filterPixel').attr('style', result.filter);
$('.filterDetail').text(result.filter);
$('.lossDetail').html(`Loss: ${result.loss.toFixed(1)}. <b>${lossMsg}</b>`);
});
});
