I've been looking for a long time for #Gimp "adaptive threshold" filter. Use-case: badly phone-camera'd printouts sent by teachers to be printed at home, with shadows, colors and such. If anyone knows of a plugin, I'm all ears.
OK, I found that "Divide" as a layer mode works even better than "Difference" for black&white source material. For "Divide", the "Invert" step is not required.
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