<canvas width="1366" height="768"></canvas>
<script>
var canvas = document.querySelector('canvas');
var ctx = canvas.getContext('2d');

var imageData = ctx.getImageData(0, 0, canvas.width, canvas.height);
var data = imageData.data;

for (var i = 0; i < data.length; i += 4) {
      data[i]     = 0;
      data[i + 1] = 0;
      data[i + 2] = 0;
    }
ctx.putImageData(imageData, 0, 0);
</script>