You could also try adjusting the contrast a bit. I use an app called Genius Scan, which increases the contrast of the scanned image to reduce the number of bits needed per pixel. This reduces the size of the file quite a bit, although it obviously isn’t a true representation of the scanned document. The TextCleaner imagemagick plugin looks like it’s doing something similar.
I’m getting errors with the link you posted.
Here’s one from the Wayback Machine
https://web.archive.org/web/20190905152042/http://truegamer.net/SA_911/911 SATHREAD/index.html