var c = document.createElement("canvas");
c.width = 128;
c.height = 128;
var g = c.getContext("2d");
var data = g.getImageData(0,0,128,128);
console.log(data);
c.style.position = fixed;
c.style.top = "0px";
c.style.left = "0px";
document.body.appendChild(c);
for(var i =0;i< data.data.length;i+=4) {
  
data.data[i+0] = data.data[i+1] = data.data[i+2] = Math.floor(Math.random()*0xff); 
  data.data[i+3] = 10;

}
g.putImageData(data,0,0);