canvas filter

gistfile1.js

function process(img) {
	var oCanvas = document.getElementById('canvas'),
		oCtx = oCanvas.getContext("2d"),
		width, height, imgData, dataURL;

	width = img.offsetWidth;
	height = img.offsetHeight;

	oCanvas.width = width;
	oCanvas.height = height;

	oCtx.filter = 'invert(100%)';
	
	oCtx.drawImage(img, 0, 0);

	// ImageData.data is PNG BLOB usable as shown @ http://stackoverflow.com/a/26595628
	// imgData = oCtx.getImageData(0, 0, width, height);

	dataURL = oCanvas.toDataURL();

	return dataURL;
}

function start() {
	var src = document.querySelector('img'),
		pre = document.querySelector('pre');

	if (src) {
		pre.innerHTML = process(src);
	} else {
		console.warn(' Something Went Wrong ');
	}
}