Grayscale is an 8-bit scanning mode. The computer/scanner sees the parts of the image in shades of gray resulting in smoother or fuzzy edges. Grayscale mode results in much larger file sizes and is usually not the best choice for scanning strictly black and white drawings.
However, if the original line art is a pencil or charcoal sketch, use grayscale to capture the subtle shading of those types of drawings.
The above illustration simulates (left to right):
- sketch scanned in grayscale mode
- portion of first image in zoomed view - shows gray pixels that make up the image
- sketch scanned in grayscale mode then resized (50% increase) after scanning.
While grayscale mode is more forgiving when resizing it still has disadvantages:
- Files of the same dimensions have much larger file sizes as grayscale.
- Small changes in size may not be noticeable but large changes - for example, reducing a snapshot size image to postage stamp size (or the reverse) results in a very degraded or blurry image.
- Soft edges created by anti-aliasing change the flavor of the image making it less suitable for the intended purpose.
- To print to a desktop printer you will need to apply a halftone screen (or use the printer's halftoning) to simulate the grayscale -- further changing the appearance of the image.