//by @plugnburn
function str2png(datastr) { //string as input, ready compressed PNG data URI as output
	var data = unescape(encodeURIComponent(datastr));
	var dlen = data.length;
	var dim = Math.ceil(Math.sqrt(dlen/3))
	var cnv = document.createElement("canvas");
	cnv.width=cnv.height=dim;
	var ctx=cnv.getContext("2d");
	var idata=ctx.createImageData(dim,dim);
	var p = -1;
	for(var i=0;i<dlen*3;i+=4)
	{
		idata.data[i]=data.charCodeAt(++p);
		idata.data[i+1]=data.charCodeAt(++p);
		idata.data[i+2]=data.charCodeAt(++p);
		idata.data[i+3]=255;
	}
	ctx.putImageData(idata,0,0);
	return cnv.toDataURL("image/png");
}

function png2str(imglink, cb) { //PNG data URI as input, decompressed string as output (to callback)
	var img = new Image();
	img.onload = function() {
		var cnv = document.createElement("canvas");
		var ctx=cnv.getContext("2d");
		cnv.width = this.width;
		cnv.height = this.height;
		ctx.drawImage(this,0,0);
		var idata=ctx.getImageData(0,0,this.width,this.height).data;
		var data = [];
		for(var i=0;i<idata.length;i++)
			if(((i+1)&3)&&idata[i]) data.push(String.fromCharCode(idata[i]));
		cb(decodeURIComponent(escape(data.join(''))));
	}
	img.src=imglink;
}

function loadfile(fileobj, cb) { //local file object as input, data URI as output (to callback)
	var reader = new FileReader();
	reader.onload = function(e){cb(e.target.result)}
	reader.readAsDataURL(fileobj);
}