title: Name a PNG file saved from Canvas using an "open with" dialog
body: <p>I am working with canvas and I would be able to save my Canvas to png.</p>
  
  <p>By looking around, I discover the great toDataURL() function given by the W3C.</p>
  
  <p>I am also already using the canvas2image from  nihilogic that we can found on this page : <a href="http://www.nihilogic.dk/labs/canvas2image/" rel="noreferrer">http://www.nihilogic.dk/labs/canvas2image/</a></p>
  
  <p>I noticed that on canvas2image, the developpers use the "image/octet-stream" which open the "open with" dialog box but give some problem :</p>
  
  <p>-picture name is the ascii returned by toDataUrl().</p>
  
  <p>-file extension is .part when downloaded</p>
  
  <p>In short, I would prompt the "open with" dialog box with something like "myImage.png" when clicking on a button.</p>
  
  <p>Is it possible ? Any help would be appreciated.</p>
  
  <p>Edit : I have the contraint to use only Javascript, I can't use <a href="http://www.permadi.com/blog/2010/10/html5-saving-canvas-image-data-using-php-and-ajax/" rel="noreferrer">some nice PHP trick</a></p>