how to covert image to 8-bit bmp

[loosen]

first to be here to ask help...
i just want to know how to covert image to 8-bit bmp ? I searched in the old posts, but no one helps
It doesn't work when using command like 'convert xxx.jpg -colors 256 xxx.bmp' .
Do i need to edit coders/bmp.c ? how ?

[fmw42]

do you want 8-bit pseudocolor or 8-bits per r,g,b channel (24-bits total)?

for the former, try

convert image -depth 8 -type palette image.bmp

for the latter try

convert image -depth 8 -type truecolor image.bmp