Slide show like real slides: zoom into square target area

[lalaka]

When showing a slide show of images in full screen I miss the following: I want all images to appear in the same way as they would if they were real slides - all pictures appear at the same size regardless of their orientation. With real slides this is naturally the case, the projection area is square, no individual resizing done etc.
For a digital image viewer like XnView this could work simlarly by choosing the smaller (vertical) resolution of the screen (or the smaller side of the window in windowed mode) as length for a (thought) square bounding box to which all (or larger) images are fitted.
I know that images in landscape format will not use the full screen resolution that way, but that's the whole point: I don't want landscape images to appear larger than portrait images!

I hope I made clear what I meant though I find it difficult to describe - even though the feature seems very straightforward to me. I haven't found a single viewer which is able to do this, though, not even XnView

I know I can achieve something similar by resizing the window so that the image area is a square size and choosing 'fit image to window' mode. But this is a bit too cumbersome IMHO...

[Olivier_G]

all pictures appear at the same size regardless of their orientation. With real slides this is naturally the case, the projection area is square

I would be interested by this feature as well.