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Sunday, December 25, 2011

How to Save a Canvas as PNG

In yesterday's post, I showed how to render an image into an HTML5 canvas element (and then operate on it with canvas API calls). When you've made changes to a canvas image, the time may come when you want to save the canvas as a regular PNG image. As it turns out, doing that isn't hard at all.

The key is to use canvas.toDataURL('image/png') to serialize the image as a data URI, which you can (of course) open in a new window with window.open( uri ). Once the image is open in a new window (note: you may have to instruct your browser to allow popups), you can right-click on the image to get the browser's Save Image As... command in a context menu. From there, you just save the image as you normally would.

The following code can be added to yesterday's example in order to create a button on the page called Open as PNG...

function createPNGButton( ) {

 var button = document.createElement("input");
 button.setAttribute("type","button");
 button.setAttribute("value","Open as PNG...");
 button.setAttribute("onclick",
  "window.open(canvas.toDataURL('image/png'))" );
 document.body.appendChild( button );
}

As you can see, there's no rocket science involved. Just a little HTML5 magic.