js-rook

<canvas id="canvas">canvas unsupported</canvas>
<script type="text/JavaScript">

var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");

var img = new Image();
img.src = "PICTURE_NAME.jpg";

var width = canvas.width = img.width;

js-rook

<canvas id="canvas">canvas unsupported</canvas>
<script type="text/JavaScript">
     
var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");

canvas.width = 256;
canvas.height = 256;

var dst = ctx.createImageData(canvas.width, canvas.height);