SVG to PNG problem no decode delegate for this image format `' @ error/blob.c/BlobToImage/364 !HELP!

gistfile1.txt

// PHP
$destinationPath = 'uploads/png/';
$filename = uniqid().'.png';
$svg = Input::get('canvas');
$path = $destinationPath.$filename;

$im = new Imagick();
$im->setBackgroundColor(new ImagickPixel('transparent'));
$im->readImageBlob($svg); // erro: "no decode delegate for this image format `' @ error/blob.c/BlobToImage/364"
$im->setImageFormat("png32");

File::put($path, $im); // criar ficheiro

// Javascript

var svg = $("#fita").prop('outerHTML');
//console.log(svg);
//var serializer = new XMLSerializer();
//var svgString = serializer.serializeToString(svg);
	
// tentativa de usar a biblioteca canvg e depois enviar o base64 da imagem para o servidor e criar o png
canvg('canvas', svg.toString());
var canvas = document.getElementById("canvas");
var img = canvas.toDataURL("image/png");

data.push({name: 'canvas', value: svg.toString()});
Backbone.ajax({
	type: 'POST',
	data: data,
	url: 'request',
	success: function(response) {

		if(response.status == 'ok') {
			Events.trigger('complete');
		}
				
	}
});