Nikon D300 Complete Manual page 149

should avoid high levels of JPEG compression and high
levels of sharpening together. Put those three things
together—moiré, JPEG compression artifacts, and
sharpening artifacts—and you're asking for trouble. It'll be
extremely difficult to remove the color fringing that'll
occur.
• Higher JPEG compression produces more artifacts at
higher ISO levels. The noise on the D300 tends to be very
granular and visible at high ISO levels, and this triggers
the compression engine towards mosquito-type artifacts
on hard edges. Avoid JPEG basic and Size priority at
ISO 1600 and above. Still, the D300 is better than most
previous Nikon DSLRs in this regard.
• JPEG compression interacts with sharpening at high ISO
levels. It's the luminance noise that's the problem.
However, high degrees of sharpening can further trigger
excessive artifacts on edges. Again, avoid JPEG basic
and Size priority at ISO 1600 and above, and definitely
consider lowering the sharpening level as you increase the
ISO value.
In each of these cases you can create image defects that won't
be easily removed after the fact. Moiré can sometimes be
removed (or at least downplayed) by moiré removal tools (or
a bit of well-applied Gaussian Blur), but if JPEG edge artifacts
get melded into the image data along with moiré or
sharpening, all bets are off.
I'll describe these interactions more when I get to the shooting
suggestions later in this book.
Overall, however, the D300 exhibits almost no tendency
towards producing JPEG artifacts at the lower ISO values.
Only at high ISO values do I sometimes see mosquito-type
effects, and some of this is actually noise destruction of edges
that triggers JPEG rendering issues. JPEG blocks are almost
non-existent on the D300, probably because the data is kept
in the 12-bit realm while manipulating it.
Thom Hogan's Complete Guide to the Nikon D300
V1.02
Page 149