Modified Backstretch.js to keep image aspect ratio constant when container dimensions change

example.php

<?php $imgdata = wp_get_attachment_image_src( get_post_thumbnail_id(), "full");
  $imgurl = $imgdata[0]; // the url of the thumbnail picture
	$imgwidth = $imgdata[1]; // thumbnail's width
	$imgheight = $imgdata[2]; // thumbnail's height
	if ($imgheight > 0) {
		$ratio = $imgwidth / $imgheight;
	} else {
		$ratio = 1;
	}
?>
<img src="<?php echo $imgurl; ?>" alt="" data-ratio="<?php echo $ratio; ?>">

modifiedBackstretch.js

/*modified backstretch.js*/
(function($){

    //Adjust image size
    $.fn.stretchnow = function() {

      this.find('img').each( function() {
        var bgCSS = { left: 0, top: 0 },
          ratio = $(this).attr('data-ratio'),
          parentWidth = $(this).parent().innerWidth(),
          bgWidth = parentWidth,
          parentHeight = $(this).parent().innerHeight(),
          bgHeight = bgWidth / ratio,
          bgOffset;

        if ( bgHeight >= parentHeight ) {
          bgOffset = (bgHeight - parentHeight) / 2;
          bgCSS.top = '-' + bgOffset + 'px';
        } else {
          bgHeight = parentHeight;
          bgWidth = bgHeight * ratio;
          bgOffset = (bgWidth - parentWidth) / 2;
          bgCSS.left = '-' + bgOffset + 'px';
        }

        $(this).css({ width: bgWidth, height: bgHeight }).css(bgCSS);
      })
        
    };

})(jQuery);

$(document).ready(function() {
  $('.posts').stretchnow();
});

$(window).bind("resize", function() { 
  $('.posts').stretchnow();
});