Resize the window to the picture's height and width

I just sent an email to fastpictureviewer support. However, maybe, it's better to put my functionality question here.
I am curious, how do I configure FastPictureViewer to resize the window to the picture's height and width? There is wasted Windows desktop real estate when flipping through unlike picture aspect ratios using FastPictureViewer (black borders between picture and window frame). I would prefer to see what's on my Windows desktop (in the background) instead of just wasted black filler/borders inside the window. The current picture viewer I use (Irfanview) does this already. Irfanview offers a variety of "Fit window to..." options. I dont see any of these types of options in FastPictureViewer (which is valuable for general picture viewing). Maybe this capability is called something else in FastPictureViewer?
Thanks in advance,
MKANET
I am curious, how do I configure FastPictureViewer to resize the window to the picture's height and width? There is wasted Windows desktop real estate when flipping through unlike picture aspect ratios using FastPictureViewer (black borders between picture and window frame). I would prefer to see what's on my Windows desktop (in the background) instead of just wasted black filler/borders inside the window. The current picture viewer I use (Irfanview) does this already. Irfanview offers a variety of "Fit window to..." options. I dont see any of these types of options in FastPictureViewer (which is valuable for general picture viewing). Maybe this capability is called something else in FastPictureViewer?
Thanks in advance,
MKANET