trimming white columns off a pf24bit bitmap

[bfa...@sentry-technology.com]

Greetings all.

I've got a program that captures the scan of an image to print later.
The bitmaps are typically 1600w x 1000px high, and there is generally
an "edge" on both the left and right that is purely white pixels that
i would like to be able to detect where the first column that is not
100% white pixels is, and trim off everything to the left, and then
find the last column that is not 100% white, and trim off everything
to the right, but i'm not certain how to do this.
I'm almost certain it would involve ScanLine, but i'm not good enough
of a programmer to know the proper way to do this.

TIA