Originally Posted by SBT
I really should get that wiki page on image cleansing ready. A few hints re. Gimp:
* Colors->Levels to adjust black/white cutoff points
* Filters->Enhancement->Unsharp to improve clarity of ink/line drawings. A value of 0.2-0.4 is normally the best.
First of all, convert the image to gray levels (not RGB, and not indexed). Image->Mode->Grayscale.
Add a black layer. Layer->New Layer...->Foreground color (assuming it's black).
Set the black layer mode to "Burn" in the layers dialog. This makes everything in the underlying layer look black, except pure white pixels.
Now select the bottom layer to make changes on it, not on the black layer. Change color levels, remove speckles (with the eraser tool, or painting white on them), etc. Delete (or disable) the black layer before saving.
PS. Having curly quotes and apostrophes would also be nice.