Cleaning up microfilm, microfiche and aperture cards

[Blighty]

There are many ways to tackle this. I have listed 4, but I'm sure others will come up with more ways.

1. Contrast (about 40)
2. Levels (right hand white triangle to about 220)
3. Threshold (black triangle to about 190)
4. G'MIC : Repair > Repair scanned document

I also suspect that there will not be a single best method that applies to all images.