save canvas to image in IE7/8

[Abhishek Dubey]

Dear all group member,

I am software developer and facing to much trouble of save canvas
image in server for IE7 and 8 version .Its working in all browser but
not working in above broser please help me .
in this i am stuck in .toDataurl <error was object not supported>
i am using code for this .
please provide me any solution i am facing to much trouble .
thanks in advance .
var oCanvas=document.getElementById('mychart').firstChild;
var canvasData = oCanvas.toDataURL("image/png");
var ajax = new XMLHttpRequest();
ajax.open("POST",'testSave.php',false);
ajax.setRequestHeader('Content-Type', 'application/upload');
ajax.send(canvasData);
document.pdf.submit();