Brother MFC-890 User Manual page 278

Colour Type
Black & White—Set the image Type to Black & White for text or line
art. For photographic images, set the image type to Grey (Error
diffusion) or True Grey.
Grey (Error Diffusion)—is used for documents with photographic
images or graphics. (Error Diffusion is a method for creating
simulated grey images by placing black dots instead of the true grey
dots in a specific matrix instead of true grey dots.)
True Grey—is used for documents with photographic images or
graphics. This mode is more exact because it uses up to 256 shades
of grey. It requires the most memory and takes the longest transfer
time.
Colors—Choose either 8-bit Colour, which scans up to 8-bit colors or
24-bit colour which scans up to 16.8 million colors. Although using
24-bit colour creates an image with the most accurate colors, the
image file will be about three times larger than a file created with 8-bit
Colour.
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USING YOUR MACHINE WITH A MACINTOSH 19 - 18