Slider picture fit to screen

Hi,
I’m building a full width one page website with Revolution Slider featured section.
(I’m using the slider only to show images so no layers, text, etc..)

How can I set the slider to show the images “fit to browser window”? So no cropping, no stretching and the full image is visible at any browser window size.

(I read the manuals and have played around with the settings for hours without luck..)

Thanks,
John