get-dominant-colour-in-image.js

var Jimp = require('jimp');

const fileName = process.argv[2];
const width = process.argv[3];
const height = process.argv[4];

Jimp.read(fileName)
    .then(photo => {
        let colours = {};
        for (let x = 0; x < width; x++) {
            for (let y = 0; y < height; y++) {
                const colour = photo.getPixelColor(x, y);
                colours[colour.toString(16).padStart(8, '0')] = colours[colour] ? ++colours[colour] : 1;
            }
        }

        let [mostFrequentColourHex, ] = Object.entries(colours)
            .reduce(([mostFrequentColourThusFar, highestFrequencyThusFar], [colour, frequency]) => {
                if (Math.max(frequency, highestFrequencyThusFar)) {
                    return [colour, frequency];
                }

                return [mostFrequentColourThusFar, highestFrequencyThusFar];
            });

        console.log(Jimp.intToRGBA(Number("0x" + mostFrequentColourHex)));
        console.log(mostFrequentColourHex);

        new Jimp(256, 256, mostFrequentColourHex, (err, imageWithDominantColour) => {
            // Write an image file with the dominant colour
            imageWithDominantColour.write('dominant.png');
        });
    })
    .catch(err => {
        console.error(err);
    });