Nikon D90 - Manual (Page 234)

214
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Monochrome
Copy photographs in Black-and-white, Sepia, or Cyanotype
(blue and white monochrome).
Selecting Sepia or Cyanotype displays a preview of
the selected image; press
1 to increase color
saturation, 3 to decrease. Press J to create a
monochrome copy.
Increase
saturation
Decrease
saturation