Correct handling of alpha layers in PNG files with IE

Okay, per Gizmo's advice I went in search of a javascript that forces IE to properly handle png graphics. As usual I found our sexy admin to be correct. There is a javascript that forces IE to handle the alpha layers of a PNG graphic correctly. Wow!!! This is really cool as up till now it was gif or nothing to hit the main stream. Below is the code. Can anyone explain it to me?

Code

// Correctly handle PNG transparency in Win IE 5.5 or higher.
// http://homepage.ntlworld.com/bobosola. Updated 02-March-2004

function correctPNG() 
   {
   for(var i=0; i<document.images.length; i++)
      {
	  var img = document.images[i]
	  var imgName = img.src.toUpperCase()
	  if (imgName.substring(imgName.length-3, imgName.length) == "PNG")
	     {
		 var imgID = (img.id) ? "id='" + img.id + "' " : ""
		 var imgClass = (img.className) ? "class='" + img.className + "' " : ""
		 var imgTitle = (img.title) ? "title='" + img.title + "' " : "title='" + img.alt + "' "
		 var imgStyle = "display:inline-block;" + img.style.cssText 
		 if (img.align == "left") imgStyle = "float:left;" + imgStyle
		 if (img.align == "right") imgStyle = "float:right;" + imgStyle
		 if (img.parentElement.href) imgStyle = "cursor:hand;" + imgStyle		
		 var strNewHTML = "<span " + imgID + imgClass + imgTitle
		 + " style=\"" + "width:" + img.width + "px; height:" + img.height + "px;" + imgStyle + ";"
	     + "filter:progid:DXImageTransform.Microsoft.AlphaImageLoader"
		 + "(src=\'" + img.src + "\', sizingMethod='scale');\"></span>" 
		 img.outerHTML = strNewHTML
		 i = i-1
	     }
      }
   }
window.attachEvent("onload", correctPNG);

I may have known it exists but i'm not sure how to explain it, our good friend Ian Spence would be able to give you a hand me thinks... He's been toying with stuff like this forever...

Code

// Correctly handle PNG transparency in Win IE 5.5 or higher.
// http://homepage.ntlworld.com/bobosola. Updated 02-March-2004

function correctPNG() 
   {
   // Loop through all the images in a page
   for(var i=0; i<document.images.length; i++)
      {
      	  // img = the number i image of the page
	  var img = document.images[i]
	  
	  // imgname = uppercase version of url
	  var imgName = img.src.toUpperCase()
	  
	  // If url ends in PNG	  
	  if (imgName.substring(imgName.length-3, imgName.length) == "PNG")
	     {
	         // If the image has an id, add it to the html we're creating
		 var imgID = (img.id) ? "id='" + img.id + "' " : ""
		 
		 // Same thing for class name
		 var imgClass = (img.className) ? "class='" + img.className + "' " : ""
		 
		 // As well as title attribute
		 var imgTitle = (img.title) ? "title='" + img.title + "' " : "title='" + img.alt + "' "
		 
		 // Make the img display correctly, transfer style attribute
		 var imgStyle = "display:inline-block;" + img.style.cssText 
		 
		 // If the image was aligned, float the div
		 if (img.align == "left") imgStyle = "float:left;" + imgStyle
		 if (img.align == "right") imgStyle = "float:right;" + imgStyle
		 
		 // If the image was inside a link, add the pointing cusor
		 if (img.parentElement.href) imgStyle = "cursor:hand;" + imgStyle	
		 
		 // Put together all the html with what we created	
		 var strNewHTML = "<span " + imgID + imgClass + imgTitle
		 + " style=\"" + "width:" + img.width + "px; height:" + img.height + "px;" + imgStyle + ";"
	     + "filter:progid:DXImageTransform.Microsoft.AlphaImageLoader"
		 + "(src=\'" + img.src + "\', sizingMethod='scale');\"></span>" 
		 
		 // Add the html to the document
		 img.outerHTML = strNewHTML
		 
		 // Honestly, this confuses me
		 i = i-1
	     }
      }
   }
   
// Run this function as soon as the page loads
window.attachEvent("onload", correctPNG);

See, told you he'd know

Ian thanks for the break down.