Nikon D300s - Manual (Page 344)

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U
D Retouching Copies
Most options can be applied to copies created using other retouch
options, although with the exceptions of
Image overlay and Edit movie
each option can only be applied once (note that multiple edits may
result in loss of detail). Options that can not be applied to the current
image are grayed out and unavailable.
A Image Quality
Except in the case of copies created with
Trim, Image overlay, NEF
(RAW) processing, and Resize, copies created from JPEG images are
the same size and quality as the original, copies created from NEF (RAW)
photos are saved as large fine-quality JPEG images, and copies created
from TIFF (RGB) photos are saved as fine-quality JPEG images of the
same size as the original. Size-priority compression is used when copies
are saved in JPEG format.