title: edit canvas pixel coordinates
body: <p>Using canvas js, how can one edit canvas pixel coordinates?
  Tried </p>
  
  <pre><code>var pixelData = context.getImageData(0, 0, canvas.width, canvas.height);
      var length = pixelData.data.length;
      for (var i = 0; i &lt; length; i += 4) {
  
          pixelData.data[i] = pixelData.data[i] * ratio;
          pixelData.data[i + 1] = pixelData.data[i + 1] * ratio;
          pixelData.data[i + 2] = pixelData.data[i + 2] * ratio;
      }
      console.log(pixelData);
      context.putImageData(pixelData, 0, 0);
  </code></pre>
  
  <p>It changes pixel's color. But coordinates change is needed  </p>