Subpixel anti-aliased text on HTML5's canvas element

Question

I\'m a bit confused with the way the canvas element anti-aliases text and am hoping you all can help.

In the following screenshot the top \"Quick Brown Fox\" is an

Answer 1

Matt, I sat with the (same/similar) problem last week, which, in my case, turned out to be because of differences in pixel densities on the devices I was testing; I wrote about it tonight - http://joubert.posterous.com/crisp-html-5-canvas-text-on-mobile-phones-and

The link at posterous is dead, so here is the gist with the source code: https://gist.github.com/joubertnel/870190

And the snippet itself:

  // Output to Canvas without consideration of device pixel ratio
  var naiveContext = $('#naive')[0].getContext('2d');    
  naiveContext.font = '16px Palatino';
  naiveContext.fillText('Rothko is classified as an abstract expressionist.', 10, 20);

  // Output to Canvas, taking into account devices such as iPhone 4 with Retina Display
  var hidefCanvas = $('#hidef')[0];
  var hidefContext = hidefCanvas.getContext('2d');

  if (window.devicePixelRatio) {
    var hidefCanvasWidth = $(hidefCanvas).attr('width');
    var hidefCanvasHeight = $(hidefCanvas).attr('height');
    var hidefCanvasCssWidth = hidefCanvasWidth;
    var hidefCanvasCssHeight = hidefCanvasHeight;

    $(hidefCanvas).attr('width', hidefCanvasWidth * window.devicePixelRatio);
    $(hidefCanvas).attr('height', hidefCanvasHeight * window.devicePixelRatio);
    $(hidefCanvas).css('width', hidefCanvasCssWidth);
    $(hidefCanvas).css('height', hidefCanvasCssHeight);
    hidefContext.scale(window.devicePixelRatio, window.devicePixelRatio);               
  }

  hidefContext.font = "16px Palantino";
  hidefContext.fillText("Rothko is classified as an abstract expressionist.", 10, 20);