Reducing size of scanned pages

[R. G. Newbury]

I am scanning old files and papers for archiving (and shredding the 
paper). In the past, under OS/2, I could convert the original scans from 
  24 bit color to one bit black and white scans by converting to dcx 
format (and back to jpg). This reduced the image file from 1MB to abojut 
55-60KB.

Can anyone suggest a similar sort of conversion methodology which I can 
use on Fedora? I have no idea what programs are available which might be 
capable of these sorts of conversions.

Geoff