tutorials: cleaning up red pencil
Typically, I sketch with red pencil and ink over the artwork with pen and ink. Here's what we have today.
I scan my original in color, 600 dpi minimum, and open the image in Photoshop.
I open Hue/Saturation with CMND+U (you'll find it from the top menu: Image > Adjustments > Hue/Saturation). I click on the Master drop-down menu and boost the lightness of both red and magenta channels to +100.
(Note: IF you're sketching with a blue pencil, the same logic applies, you just boost the blue and cyan channels to +100.)
As you can see, the red sketch just blasts off, boom!
The image is still a little bleak, so I use either Levels or Curves to adjust the contrast. This should delete most of the dust and other specks, but it's usually worth doing a quick check and cleaning up your mess where you don't want it.
To finish things off, I convert the image to grayscale. If you're using my Photoshop Action Set, the Red Out action ends here. Mainly because I want the action to work for both black & white linework and grayscale images. I don't want the action to convert a grayscale image to bitmap automatically.