Plustek V1.4 User Manual page 38

Chapter IV
B/W & Grayscale Scanning
If scanning B/W images, match the DPI to the resolution of
your printer, or scanner. For example, if you have a 300-dpi
scanner, then set the resolution to 300. If you have a 600-dpi
printer, set the scanning resolution to 600.
When not scanning using B/W, but rather Grayscale, we find
that a resolution of 150 works extremely well. Note: Sometimes
increasing the brightness and contrast can help improve and
lighten the grayscale image quality.
Color Scanning
When scanning in color, remember that 24 to 30 bits of
information take up a lot of disk space. If you
a color image and then print it out, scan at 200 dpi. If you are going
to scan a color image just to experiment, scan between 75 and 100
dpi to conserve hard disk space.
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e going to scan