Ok, I realize this is a little late in this thread, but I just found the thread. Assuming you are using photoshop... working in either B&W or grayscale, adjust the levels so that any artifacts like stray pencil lines are gone- this is done by moving the right slider (white) to the left, then moving the left (black) slider to the right to darken the remaining lines.
After this is done, use the magic wand to select the line work. Make sure it is not set to "contiguous", or you won't get everything- unless the art is one continuous line! I always find it easier to select the white of the page, then "invert" the selection in the "select" dropdown menu. (At this point I "save Selection" which makes it a channel- in case I need to select it again later).
After this is done, I copy the line art, then "paste into"- this creates a new layer. You can delete the original line art now if you wish. Make sure you are on the new line art only layer- in the Layers Pallette "lock" transparent pixels by clicking on the little checker board above the list of layers. Now "Select All" under the "Select" dropdown- then Fill with black, using either the paint bucket or shortcut (option+delete on a Mac- not sure for windows).
TA-DA! No more white bits!
http://quazar451.comicgenesis.com