Side by Side A/B view

[uncpotato]

It is a great feature!
With today's digital camera technology, I will usually take several shots of the same scene.
With this side by side view, I can determine which picture to keep in 1 second. Previously I have to either open two image viewer or click NEXT/PREV ZOOM in/OUT several times before the decision.

XnView outperform FastStone Image Viewer in terms of speed, but lacks quite a number of features.

The CTRL-DRAG in FastStone Viewer is great when your two photos is not in perfectly matched layout/structured.
You can also do CTRL-ZOOM RATIO in FSV to adjust ZOOM RATIO independently, which is great if you are comparing images taken by two cameras with different MEGA pixels.

EXIF info in FSV sometimes help to determine which picture to keep too.

The size of seperator in middle of XNView seems a bit too wide... a waste of valuable screen area when today's picture are so huge. The same applies to the bottom boarder just to hold the [ OK ] button, which I don't think is necessary as you always have the [X] at the top.

The "USE TABS" options could be placed together with the buttons ZOOM etc. When you say USE TABS, it applies to all pictures anyway, just like clicking ZOOM, it applies to all pictures at the same time.