How to detect if an image generated via canvas is blank (transparent PNG)?

Question

I am working on an application in which an image is created/edited on a HTML5 canvas and then saved into a file-store/cloud. The problem is that of \"saving efficiency\". On sav

Answer 1

HTML:

SCRIPT:

isCanvasTransparent(document.getElementById("canvas_img"));

function isCanvasTransparent(canvas) { // true if all pixels Alpha equals to zero
  var ctx=canvas.getContext("2d");
  var imageData=ctx.getImageData(0,0,canvas.offsetWidth,canvas.offsetHeight);
  for(var i=0;i

UPDATE:

Dont use CSS style declarations like border: 1px solid black; for CANVAS, because border included into canvas image, and, as result, alpha chanel is always not equals to zero.