<!DOCTYPE html>
<html>
<body>
<canvas id="c" width="500" height="1000">
</canvas>
<script>
var ctxt = document.getElementById('c').getContext('2d');
for (var k = 0; k < 100; ++j) {
  for (var j = 0; j < 10; ++j) {
    for (var i = 0; i < 1000; ++i) {
      gradient = ctxt.createLinearGradient(0,0,200,i);
      gradient.addColorStop(0,'black');
      gradient.addColorStop(1,'rgba(0, 255*k/100, 0, 0.1)');
      ctxt.fillStyle = gradient;
      ctxt.fillRect(j*50, 2*i, 50, 2);
    }
  }
}
</script>
</body>
</html>