Don't confuse halftone screening with halftone scanning. Halftone scanning refers to methods used to scan images such as photos in a book or magazine that have been screened for printing.
Halftone screening is the process of applying a screen (during or after scanning) that applies a pattern of dots or lines that when printed, simulates shades of gray. Normally you would apply a halftone screen to a grayscale (or color) image that you need to print on a black and white printer.
Applying a halftone screen to a black and white line art sketch results in a totally new look for the image. Use the option to achieve special effects or for pencil and charcoal sketches to be printed on a black and white printer.
Because the resulting image is 1-bit, black and white only, follow the same guidelines presented for scanning in line art mode: scan at the resolution of the output device and at the final desired size.
Also see:
The above images simulate the same black and white sketch image scanned in with two different halftone screens.
