Parallax WordPress thumbnail

Functions.php:

function add_parallax($post) {
    $parallax = "<div id='parallax-banner'>";
		$parallax .= get_the_post_thumbnail( $post, 'full' );
		// $parallax .= "<span class='title'>".get_the_title($post)."</span>";
	$parallax .= "</div>";

	echo $parallax;
}

CMS Control PHP code:

<?php
	if( is_singular() ) {
		add_parallax($parallax[0]->ID);
    }
?>

<script>
  jQuery(window).load(function(){
	var $banner = jQuery("#parallax-banner"), $image = $banner.find("img"), height = 0, max = 0;

	//let's find the best height for it
	height = $banner.find("img").height() / 3;
	$banner.height(height);

	//this is the maxiumum amount of scroll for still visible banner, cached to improve performance
	max = ($banner.offset()).top + height;

	//let's position our title in the middle of the Area
	$banner.find(".title").css({
		"top": ((height - $banner.find(".title").height()) / 2) + "px"
	});

	jQuery(window).scroll(function() {
	   parallax_image(max, $image);
	});
});

function parallax_image(max, $image) {
	var imgTop = 0, scrollPos = jQuery(this).scrollTop();

	//rule of thirds to find the new top position for image
	imgTop = (scrollPos / max) * (2/3) * $image.height();

	$image.css({
		"top": -(imgTop)+"px"
	});
}
</script>

CMS Control CSS Code:

#parallax-banner {
	position: relative;
	width: 100%;
	margin-left: 0;
	overflow: hidden;
}
#parallax-banner img {
		position: absolute;
}

#parallax-banner .title {
	position: absolute;
	padding: 5px 0;
	top: 0;
	left: 0;
	width: 100%;
	text-align: center;
	text-transform: uppercase;
	font-weight: bold;
	background-color: transparent;
	background-color: rgba(255, 255, 255, 0.8);

	-ms-filter: "progid:DXImageTransform.Microsoft.gradient(startColorstr=#ccffffff,endColorstr=#ccffffff)";

	-moz-box-shadow: 0 0 4px #000;
	-webkit-box-shadow: 0 0 4px #000;
	box-shadow: 0 0 4px #000;
}