Hello @eduardrudko,

PDF images have transparency:

$ vips colourspace thesis.pdf x.v b-w
$ vipsheader x.v
x.v: 595x842 uchar, 2 bands, b-w, pdfload

ie. you have an 8-bit GA (grey plus alpha) image. You need to drop the alpha with eg. flatten against white:

$ vips flatten x.v x2.v --background 255

Then when saving you need to ask tiffsave to save the 8-bit image as 1-bit:

$ vips tiffsave x2.v x.tif --bitdepth 1 --compression ccittfax4

Other savers (eg. the JPEG saver) will flatten for you if you pass an image with alpha, but of course TIFF supports everything (except ccittfax4 compression with alpha!), so it doesn't do much automatic conversion for you.

Perhaps selecting ccittfax4 compression should automatically convert to b-w, flatten, and set bitdepth to 1? Something for the todo list.