Image processing library

Hi,
    I don't know whether the stuff I'm looking for even exists, but I
thought I'd ask anyway. I am after a library (or libraries) that allow
me to carry out a number of tasks:
* Read/Write image files in a number of formats
* Have a real-time display (so I get a snappy window where I can zoom
    in, out...)
* Have the ability to display histograms of images
* Let me select ROI with the mouse :-) (i.e., select the corners of a
    polygon)
* Is written (or callable) in C, C++, and runs on UN*X
* Is Free to use

    After some google-ing around, I have found that VXL might indeed
do all this (and more). It seems very complete, but the large amount
of sub-sub-sub-modules was a bit confusing :-) There was also Xite,
which looks like it could be handy.

    Many thanks,
    Jose