Como aplicar efeito fade nesse java

<script type="text/javascript">// <![CDATA[

	var imageCount = 0;

	var currentImage = 0;

	var images = new Array();

	images[0] = 'fotos/1.png';

	images[1] = 'fotos/2.png';

	images[2] = 'fotos/3.png';

	images[3] = 'fotos/4.png';

	images[4] = 'fotos/5.png';

	var preLoadImages = new Array();

	for (var i = 0; i < images.length; i++)

	{

	   if (images* == "")*

*

**
   preLoadImages** = new Image();*
*
   preLoadImages.src = images;*
*
   imageCount++;*
*
}
*

*

**
function startSlideShow()*
*
{*
*
   if (document.body && imageCount > 0)*
*
   {*
*
      document.body.style.backgroundImage = "url("+images[currentImage]+")";    *
*
      document.body.style.backgroundAttachment = "fixed";*
*
      document.body.style.backgroundRepeat = "no-repeat";*
*
      document.body.style.backgroundPosition = "center center";*
*
      document.body.style.backgroundSize  = "100% 100%";*
*
      currentImage = currentImage + 1;*
*
      if (currentImage > (imageCount-1))*
*
      {*
*
         currentImage = 0;*
*
      }*
*
      setTimeout('startSlideShow()', 3000);*
*
   }*
*
}*
*
startSlideShow();*
*
// ]]></script>
*