Edit: links scrubbed because "Your post looks too spamy for a new user, please remove off-site URLs." What a bunch of baloney. There are better spam detection methods than that, and the signup process was plenty onerous enough. So rather than linking to the papers in question I'm giving the full titles, hope folks can find them.

I wish the G'MIC plugin had visible scripts for helping with scanned documents and other bilevel images.

The Otsu thresholding already built in to G'MIC is already a big improvement on manual thresholding. Unfortunately AFAIK the only way to use it in the GIMP is to use "custom code (global)", replace whatever's there with -otsu, and set value range to "normalize." It'd be nice to have it along with other binarization methods in a menu item. One possible place to start would be with adding efficient Sauvola local thresholding as described in Shafait et al, "Efficient Implementation of Local Adaptive Thresholding Techniques Using Integral Images."

The median filter is helpful for dealing with bilevel noise- more so, I think than opening+closing/closing+opening/other morphological ops. I don't know that any of G'MIC's other noise removal stuff is very applicable to bilevel or to greyscale images intended for bilevel output. There are more sophisticated methods for bilevel noise out there- one that looks promising is Hoang et al, "Edge Noise Removal In Bilevel Graphical Document Images" but I don't know much about what's been done in that field.

nice first post !

there is also a introduce yourself subforum

The filter 'Black & White / Stamp' gives some tools to binarize an image, including the Otsu method (option 'Auto-threshold').
This may also help.

It kept you from posting a link though, didn't it? It is an extremely effective anti-spam mechanism and works very well for our purposes. Please feel free to create your own site and use whatever anti-spam method you prefer.