How to center image vertically in lightbox

Lightbox image centering

// STEP 1:
// Inside the start function, at around line 170 I commented out the assignation of the 'top' property, like this:

// Position Lightbox
  var top  = $window.scrollTop() + this.options.positionFromTop;
  var left = $window.scrollLeft();
  this.$lightbox.css({
    // top: top + 'px', // comment out this line
    left: left + 'px'
  }).fadeIn(this.options.fadeDuration);
  
// STEP 2:
// Then inside the changeImage function, at line 232, after this declaration 

self.sizeContainer($image.width(), $image.height());

// STEP 3: 
// I added those lines:

 var window_height = windowHeight;
    var img_height = $image.height();
    var scroll_offset  = $(window).scrollTop();
    var view_offset = window_height/2 - img_height/2;
    var top_distance = scroll_offset + view_offset;

    self.$lightbox.css('top', top_distance+'px');
    
// More details
// https://github.com/lokesh/lightbox2/issues/172#issuecomment-228747592