Slideshow Qestion Can anyone help?

  I can’t find the setting that makes the wallpaper slideshow do a random real slow zoom in, zoom out or fade ins does anyone know how to set this up?  I never set anything to do this just thought it was a really cool default.  I applied some animated deskscapes,  but when I went back to slideshow it wasn’t doing any of this. 

  It looks like you could do picture by picture, but I never did that a single picture.  All 40 pics in the folder were just randomly doing slow animated effects in the 30sec interval before starting a newly animated wallpaper.  Your help would be most appreciated.