Does anyone know how to isolate line art cleanly that's been scanned into the computer. In particular I'm trying to create a layer of colored prismacolor pencil line art (it's very dark prismacolor line art). Whenever I do it using the magic wand, or auto select/image luminance (or any of the options under the auto select menu) I'm able to isolate the line art but it's got a halo of light area around it. I've also tried selecting it in the above manner then transforming it to a path-based selection and trying to isolate it in that way but without luck. I want to retain the crispness of the original line. Can anyone help on this?

Thanks,
PG