Info:

[Wikinaut]

I developed a bash script make-tifpdf for converting (e.g.) 600 dpi 8-bit Grey scans using tumble to the format accepted and recommended by http://bitsavers.org .

Colored pages of scans will be added as 300 dpi jpg, black/white pages will be converted to 600 dpi 1-Bit as currently required by tumble.

The core is (see http://www.fmwconcepts.com/imagemagick/2colorthresh/index.php) the automatical thresholding of images to binary (b/w) format using an adaptive spatial subdivision color reduction technique (2COLORTHRESH).

convert "greyimage.ppm" -density 600 +dither -colors 2 -colorspace gray -contrast-stretch 0 -depth 1 "blackwhiteimage--600dpi.tif"

Perhaps my script can be helpful for those who need it.

The repo is https://github.com/Wikinaut/bitsavers-tools/ .

Example run: