8bpp BMP files

[cheesey]

Hello,

Situation: I have a 32-bit BMP file, which (for long and unpleasant reasons) is monochrome. I am attempting to convert this into an 8-bit BMP. (It needs to be 8-bit, even though it is monochrome; I'm interacting with something with a hideously broken image loader. Fixing said image loader is not *really* an option).

Doing this:

convert in.bmp -type palette -depth 8 foo/out.bmp

Always gives me a 2bpp bitmap (according to a hex editor). I've tried adding -colors 256 to it, as well.

What am I doing wrong?

[fmw42]

what is your version of IM?

do you need the alpha channel? if not try

convert inputimage.bmp -alpha off -depth 8 -type grayscale resultimage.bmp

[cheesey]

-type grayscale doesn't work here. -alpha off makes no difference at all. There is no alpha information in the BMP, so the entire channel can be thrown away if need be.

I've reproduced on:

Version: ImageMagick 6.5.7-8 2009-11-26 Q16 http://www.imagemagick.org
Version: ImageMagick 6.6.1-3 2010-04-16 Q16 http://www.imagemagick.org
The debian package imagemagick 8:6.6.0.4-3

Which were the ones in package management on the machines I happen to have kicking around here at the moment.

[fmw42]

Perhaps I misunderstand. Is this a 32-bit single channel image or an 8-bit per channel with 4 channels rgba?

Perhaps it would be best if you post a link to your image (or a small subsection of it), so others can test with it.

IM may recognize it is binary and ignore the -type grayscale and keep it binary.

[Chipper]

I am trying to force IM to create 4BPP and 8BPP bmp files too and all I can get is 24BPP files.

Did you ever figure this out?

Using ImageMagick 6.7.2-9 2011-09-23 Q16

[Chipper]

Posted too soon.... this did the trick...

example:

convert -size 800x480 gradient:green-yellow -depth 8 -alpha off -compress NONE -colors 256 BMP3:gr_green-yellow.bmp

Not sure if I needed all the options... but it worked.