title: Rendering video frame to canvas lost some pixel color information
body: <p>Hello all,</p>
  
  <p>I render a frame of video to the canvas and when I do that I noticed next this. I check RGB value before rendering and after and noticed that value is different.</p>
  
  <pre><code>&lt;video id="video" width="400" height="300" controls&gt;
      &lt;source src="save.mp4" type="video/mp4"&gt;
    &lt;/video&gt;
    &lt;button onclick="draw()"&gt;Draw&lt;/button&gt;
    &lt;canvas id="canvas"&gt;&lt;/canvas&gt;
    &lt;script&gt;
  
      function draw() {
        const video = document.getElementById('video'),
          canvas = document.getElementById('canvas'),
          canvasContext = canvas.getContext('2d');
          canvas.width = video.offsetWidth;
          canvas.height = video.offsetHeight;
  
          canvasContext.drawImage(video, 0, 0, video.offsetWidth, video.offsetHeight);
      }
  
    &lt;/script&gt;
  </code></pre>