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8-bit Grayscale BMP
Posted: 2007-03-07T16:42:04-07:00
by compmaniac
I have two 8-bit grayscale bmps.
I want to composite one over the other, and still maintain the 8-bit and grayscale (in bmp format)
How would I maintain the grayscale and 8-bit, or if that's not possible, could somebody tell me how to convert an RGB 24-bit bmp to grayscale 8-bit? Thanks.
Re: 8-bit Grayscale BMP
Posted: 2007-03-07T21:22:19-07:00
by anthony
See IM Examples, Misc Formats, BMP
http://www.imagemagick.org/Usage/formats/#bmp
Basically make sure your image is 8bit index compatible (eg less that 256 colors)
by using a "-colors 256" operation.
If BM is GIF-like with transparency handling (I don't know for BMP) you may need
Code: Select all
-quantize transparent -colors 254 -channel A -threshold 50%
instead.
This is actually what IM does automatically for GIF with thransparency, it just has other options with BMP, so you may need to DIY.
Re: 8-bit Grayscale BMP
Posted: 2007-03-08T05:19:19-07:00
by compmaniac
Thanks, but after the -colors 256 operation on a 192kb file, the file is now around 3kb ish...
Am I supposed to type the following command to get it back to 65kb?
convert test.bmp bmp3:test.bmp
?
Sorry if I'm not doing it correctly.
I need to get an 8-bit file (around 65kb) from a 24-bit, regular grayscale BMP ( around 192kb)
I'm using 256x256 images.