I went and looked at photoshop and it only supports bmp to 24.  So I thought
maybe I was missing something and did a quick google and found this:
http://www.aha-soft.com/ahaview/bmp-info.htm maybe it will help?

Ron

-----Original Message-----
From: squeak-dev-bounces at lists.squeakfoundation.org
[mailto:squeak-dev-bounces at lists.squeakfoundation.org] On Behalf Of Cees De
Groot
Sent: Wednesday, October 26, 2005 4:49 AM
To: The general-purpose Squeak developers list
Subject: Re: Help needed: 16 and 32 bit BMP files

On 10/25/05, Andreas Raab <andreas.raab at gmx.de> wrote:
> I need some help for fixing an issue in BMPReadWriter. For writing
> proper test cases I need to have both, a 16 and a 32 bit version of the
> attached (24bit) bmp file.

I wanted to do this with the netpbm tools, but ppmtobmp only accepts
bpp values of 1,2,4,8 and 24... So I'm at a loss as to what software
actually can produce these.