: Isolating red ink with GIMP/Photoshop As a puzzle author, I often write puzzles with red ink and then test-solve them with pencil. What would be the most efficient way to remove the pencil

@Caterina889

a much easier solution is to use a piece of vellum or tracing paper when you are working on the draft. Simply lay the vellum over your red areas and write on it. When you're done the vellum is not actually part of the artwork and the red can be scanned without any need for alteration.

Vote Up Vote Down

@Looi7658678

For Gimp

To remove all content of a scan except red drawings we may do as follows:


Scan image in desired resolution



This image deliberately was a poor scan using a black and a red pencil to make it harder for us. Using a bright red felt pen will definitely make isolation much easier, but this probably is not what we have in reality.
Isolate red color with the Select by Color tool with an appropriate threshold to make sure only pixels on the red lines are going to be selected (here this was 10):


Select > Grow the selection by an appropriate value (5 pixels in my case):


Select > Feather the selection for a smoother transition (here by 5 px)
Select > Invert the selection
Press Del or Edit > Clear to remove everything in the background:

Vote Up Vote Down