A useful tool: BMP data viewer

[zedd151]

I'm really starting to think that this might have something to do with the dialog manager. I was considering using IsDialogMessage(), but since I don't have a message loop that won't do much good.

Have you thought about foregoing the dialog box and using either a Window, or even writing to stdout, in a console version? - At least for only the bitmap data...

I would isolate only the bitmap processing functions (you would still have to calculate where the bitmap data starts, of course - for the different flavors of bitmaps), omitting the header info display, and the mini bitmap display, to concentrate solely on making the bitmap data processing faster (use some form of timing mechanism, to verify just how much faster one algorithm is, versus another)
You already know that your bitmap headers info processing, and miniature bitmap processing works okay.

After you get that as fast as possible, then you can finish up the GUI code.    that's my tip/suggestion of the day.