of so....

bmp files save as 24 bit (8 bits per for R G B)
jpg is 32 bit (R G B and alpha)
unless i'm farther off than i think :P anyways
once a texture is loaded, say jpg, then wouldn't it use more memory per pixel than bmp?
so jpg uses 1024x1024x32=4mb and bmp 1024x1024x24=3mb?

if i'm not insanely far off track so far, then a format saving 8 bits per pixel would be
1024x1024x8=1mb, and be better use for when i make my bump maps, correct?
since they are just greyscale, R=G=B, which is accually a waste of room

so if i'm not crazy :P whats a file format thats just 8 bits of info?
reason i ask, is i'm making a map 8192x8192 for a poster :) 64mb vs 256mb o_o hmm