var photo = new Image();
var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');

ctx.fillStyle = 'black';
ctx.font = '24px monospace';
ctx.fillText('Loading image...', 20, 40);

 function toasterGradient(width, height) {
   var texture = document.createElement('canvas');
   var ctx = texture.getContext('2d');

   texture.width = width;
   texture.height = height;

   // Fill a Radial Gradient
   // https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/createRadialGradient
   var gradient = ctx.createRadialGradient(width / 2, height / 2, 0, width / 2, height / 2, width * 0.6);

   gradient.addColorStop(0, "#804e0f");
   gradient.addColorStop(1, "#3b003b");

   ctx.fillStyle = gradient;
   ctx.fillRect(0, 0, width, height);

   return ctx;
 }

 function blend (background, foreground, width, height, transform) {
   var bottom = background.getImageData(0, 0, width, height);
   var top = foreground.getImageData(0, 0, width, height);

   for (var i = 0, size = top.data.length; i < size; i += 4) {
     // red
     top.data[i + 0] = transform(bottom.data[i + 0], top.data[i + 0]);
     // green
     top.data[i + 1] = transform(bottom.data[i + 1], top.data[i + 1]);
     // blue
     top.data[i + 2] = transform(bottom.data[i + 2], top.data[i + 2]);
     // the fourth slot is alpha. We don't need that (so skip by 4)
   }

   return top;
 }

 function render() {
   // Scale so that the image fills the container
   var width = window.innerWidth;
   var scale = width / photo.naturalWidth;
   var height = photo.naturalHeight * scale

   canvas.width = width;
   canvas.height = height;

   ctx.drawImage(photo, 0, 0, width, height);

   var gradient = toasterGradient(width, height);

   var screen = blend(ctx, gradient, width, height, function(bottomPixel, topPixel) {
     return 255 - (255 - topPixel) * (255 - bottomPixel) / 255;
   })

   ctx.putImageData(screen, 0, 0);
 }

 photo.onload = render;
 photo.crossOrigin = "Anonymous";
 photo.src = "https://s3.amazonaws.com/share.viget.com/images/viget-works.jpg?bust=true";