(02-12-2018, 01:13 AM)udif Wrote: Using GIMP threshold tool :
You can easily see that even if you let part of the picture become black, some other section is still too bright.
No global threshold level across all the picture can separate all the text from the background.
Canonical technique:
- duplicate layer, blur heavily top copy so that text disappears
- set top copy to grain extract
- Layer>New from visible
- Apply threshold
Personal remark: there are two kinds of "camera scans". Those taken with even lighting and good equipment (copy stand, DSLR...) and those shot handheld with a smartphone under available light. In the former the picture is clean and algorithms work well. In the latter, the picture is mercilessly postprocessed by the camera and the generated artifacts although not always visible will often trip algorithms (on the lesser smartphones, this a pixel soup...). So, better test your thing with real-life photos.