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Provides a histogram data structure from PNG, JPEG or GIF files using canvas. This library works in nodejs and in any canvas supporting browser using histogram.min.js. In the browser histogram will be available in window.histogram You can also use require.js instead, keeping your global scope clean.

Example usage


var histogram = require('histogram');
histogram(fileName || Buffer, function (err, data) {
    console.log(filePath + ' has ' + data.colors.rgba + ' colors');

Browser with require.js

require(['path/to/histogram.min.js'], function (err, histogram) {
    histogram(URL || FileReader.result, function (data) {
        console.log(filePath + ' has ' + data.colors.rgba + ' colors');

Vanilla browser

<script src="path/to/histogram.min.js"></script>
    histogram(URL || FileReader.result, function (err, data) {
        console.log(filePath + ' has ' + data.colors.rgba + ' colors');

Data structure

    red: new Array(256), // Count of the number of times a value appears in the red channel 
    green: new Array(256), // Count of the number of times a value appears in the green channel 
    blue: new Array(256), // Count of the number of times a value appears in the blue channel 
    alpha: new Array(256), // Count of the number of times a value appears in the alpha channel 
    colors: {
        rgb: 0, // Number of unique RGB colors 
        rgba: 0 // Number of unique RGBA colors 
    palettes: {
        rgb: [], // Array of unique colors in hex notation 
        rgba: [] // Array of unique colors in hexa notation 
    greyscale: true, // Indicates whether all colors are greyscale or not 
    alphachannel: false // Indicates that one or more pixels are translucent 


This software is licensed under the beerware license. Do whatever you want with it. If we meet some day, and you think this stuff is worth it, you can buy me a beer in return.

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