Capture HTML Canvas as gif/jpg/png/pdf?

Is it possible to capture or print what’s displayed in an html canvas as an image or pdf?

I’d like to generate an image via canvas, and be able to generate a png from that image.

Original answer was specific to a similar question. This has been revised:

var canvas = document.getElementById("mycanvas");
var img    = canvas.toDataURL("image/png");

with the value in IMG you can write it out as a new Image like so:

document.getElementById("existing-image-id").src = img;

or

document.write('<img src="'+img+'"/>');