voluptasquisquam/src/image/transform/cmyk.js

Image processing and manipulation in JavaScript

// http://www.easyrgb.com/index.php?X=MATH&H=18#text18
// check rgbToHsl : https://bgrins.github.io/TinyColor/docs/tinycolor.html

import {RGB, CMYK} from '../model/model';
import Image from '../Image';

/**
 * Make a copy of the current image and convert the color model to CMYK
 * The source image has to be RGB !
 * @memberof Image
 * @instance
 * @return {Image} - New image in CMYK color model
 * @example
 * var cmykImage = image.cmyk();
 * // we can create one image per channel
 * var channels = cmykImage.split();
 */
export default function cmyk() {
    this.checkProcessable('cmyk', {
        bitDepth: [8, 16],
        alpha: [0, 1],
        colorModel: [RGB]
    });

    let newImage = Image.createFrom(this, {
        components: 4,
        colorModel: CMYK
    });

    let ptr = 0;
    let data = this.data;
    for (let i = 0; i < data.length; i += this.channels) {
        let red = data[i];
        let green = data[i + 1];
        let blue = data[i + 2];

        let black = Math.min(this.maxValue - red, this.maxValue - green, this.maxValue - blue);
        let cyan = (this.maxValue - red - black) / (1 - black / this.maxValue);
        let magenta = (this.maxValue - green - black) / (1 - black / this.maxValue);
        let yellow = (this.maxValue - blue - black) / (1 - black / this.maxValue);

        newImage.data[ptr++] = cyan;
        newImage.data[ptr++] = magenta;
        newImage.data[ptr++] = yellow;
        newImage.data[ptr++] = black;
        if (this.alpha) {
            newImage.data[ptr++] = data[i + 3];
        }
    }

    return newImage;
}