PNG alpha support for Internet Explorer

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Introduction

Internet Explorer doesn�t support the alpha channel in PNG images. However the fix is to use the "AlphaImageLoader" filter. This script replaces all PNG images on the page with a blank image (blank.gif) and adds the "AlphaImageLoader" filter with the original image source. The blank image is to avoid the "broken image" picture to display above the filter. This script also supports printing and changing the source image at runtime.

Source

//Array containing all PNG images on the page

var PNGimageArray = new Array();
var isPrinting = false;

//Path to the blank image (1x1 transparent)

var blankSrc = "blank.gif";

//Captures print events

window.attachEvent("onbeforeprint", function () { beforePrint(); } );
window.attachEvent("onafterprint", function () { afterPrint(); } );
//Tests if element is a PNG image, and if so fixes it

function addPngImage(element){
  if (/\.png$/i.test(element.src)) {
    fixImage(element);
    element.attachEvent("onpropertychange", function () 
      { propertyChanged(); } );
    PNGimageArray[PNGimageArray.length] = element;
  }
}

//Applies filter and changes source to blank

function fixImage(element) {
  element.runtimeStyle.filter = 
   "progid:DXImageTransform.Microsoft.AlphaImageLoader(
      src='" + element.src + "')";
  element.src = blankSrc;
}

//If property "src" is changed fixs image (not 

//if it is changed to blank though)

function propertyChanged() {
  if (isPrinting) return;
  var element = event.srcElement;
  var pName = event.propertyName;
  if (pName != "src") return;
  if (!new RegExp(blankSrc).test(element.src))
    fixImage(element);

}

//Turns image back to original before print (Explorer can't print filters)

function beforePrint() {
  isPrinting = true;
  var element;
  for(var i = 0; i < PNGimageArray.length; i++){
    element = PNGimageArray[i];
    element.src = element.filters[0].src;
    element.runtimeStyle.filter = "";
  }

}

//Fixes image after print

function afterPrint() {
  isPrinting = false;
  var element;
  for(var i = 0; i < PNGimageArray.length; i++){
    element = PNGimageArray[i];
    fixImage(element);

  }
}

Style that makes all images run the addPngImage function. I use "expression" instead of "behavior" to avoid some security issues in Internet Explorer.

<style type="text/css"> img { filter:expression(addPngImage(this)); }
</style>