title: putImageData alpha lost
body: <p>i spend a lot of time to change color of png file with transparent background.
  I know how set color in getImageData(ctx,0,0,100,100).data; 
  but when i want save new PNG image i've got white background... </p>
  
  <p>i've got something like:</p>
  
  <pre><code>    var el = document.getElementById('before');
      var ctx = el.getContext('2d');
      var img=new Image();
  img.src='src';
      ctx.drawImage(img,0,0,150,150);
      var imgData=ctx.getImageData(0, 0, 150, 150);
      for (var i=0;i&lt;imgData.data.length;i+=4){
          imgData.data[i]=135;
          imgData.data[i+1]=222;
          imgData.data[i+2]=115;
      }
      var es = document.getElementById('after');
      var cts = es.getContext('2d');
      cts.putImageData(imgData,0,0);
  </code></pre>
  
  <p><a href="http://jsfiddle.net/6aZ7L/1/" rel="nofollow">EXAMPLE</a>
  (i dont know why it was here putImageData)</p>
  
  <p>in other project (ex. <a href="https://crosspop.in/croquis" rel="nofollow">https://crosspop.in/croquis</a> )it is posible, but i cant find where is solution.</p>
  
  <p>Do You know how create canvas from modyfited getImageData with transparent background?</p>
  
  <p>regards</p>