scanimage to the rescue

As I have an old CanoScan LiDE 30 and troubles under Ubuntu with SANE I have to use scanimage. It is know as as

scanimage --help
-- last line --
plustek:libusb:002:002

To scan a A4 which is the standard paper size over here is need to use

scanimage -l 0 -t 0 -x 215 -y 297 --resolution 150 > myimage.ppm

gives file size of 6 MB

Problem's I have so far is in the output size of the above line. The mode defaults to color so the scans are huge.

scanimage -l 0 -t 0 -x 215 -y 297 --resolution 150 --mode Lineart > myimage.ppm

gives file size of 300 KB but this looks ugly for a scanned document.

So use your gray matter

scanimage -l 0 -t 0 -x 215 -y 297 --resolution 150 --mode Gray > myimage.ppm

gives file size of 2 MB.

Color equals 3 times Grey equals 20 (?) times Black and White. Hmm.

Color Depth defaults to 8 bits. So I cannot explain the 20 times difference in size between Gray and Lineart.