■On. When exposures are eight seconds or longer, the Nikon D7000 takes a sec-
ond, blank exposure to compare that to the first image. (While the second image
is taken, the warning Job nr appears on the monochrome LCD panel and in the
viewfinder.) Noise (pixels that are bright in a frame that shouldbe completely black)
in the “dark frame” image is subtracted from your original picture, and only the
noise-corrected image is saved to your memory card. Because the noise-reduction
process effectively doubles the time required to take a picture, you won’t want to
use this setting when you’re rushed. Some noise can be removed later on, using
tools like the noise reduction features built into Bibble Pro, many image editors,
or Nikon Capture NX2.
High ISO NR
Noise can also be caused by higher ISO sensitivity settings, and the Nikon D7000,
which offers settings up to ISO 6400 (and thence up to the equivalent of ISO 12800
and 25600 with the Hi 1.0 and Hi 2.0 settings) has a loftier ISO ceiling than many
cameras. Even so, high ISO noise reduction, which can be set with this menu option,
may be a good option in many cases. You can choose Off when you want to preserve
detail at the cost of some noise graininess, and the D7000 will apply high ISO NR only
at the “boosted” settings of Hi 0.3 and above. Or, you can select On, which is applied
when ISO sensitivity has been set to ISO 800 or higher.
The effects of high ISO noise are something like listening to a CD in your car, and then
rolling down all the windows. You’re adding sonic noise to the audio signal, and while
increasing the CD player’s volume may help a bit, you’re still contending with an unfa-
vorable signal to noise ratio that probably mutes tones (especially higher treble notes)
that you really want to hear.
The same thing happens when the analog image signal is amplified: You’re increasing
the image information in the signal, but boosting the background fuzziness at the same
time. Tune in a very faint or distant AM radio station on your car stereo. Then turn up
the volume. After a certain point, turning up the volume further no longer helps you
hear better. There’s a similar point of diminishing returns for digital sensor ISO increases
and signal amplification as well.
As the captured information is amplified to produce higher ISO sensitivities, some ran-
dom noise in the signal is amplified along with the photon information. Increasing the
ISO setting of your camera raises the threshold of sensitivity so that fewer and fewer
photons are needed to register as an exposed pixel. Yet, that also increases the chances
of one of those phantom photons being counted among the real-life light particles, too.
Fortunately, the Nikon D7000’s CMOS sensor and its EXPEED digital processing chip
are optimized to produce the low noise levels, so ratings as high as ISO 1600 to ISO
3200 can be used routinely (although there will be some noise, of course), and even
Chapter 8 ■Setup: Playback and Shooting Menus 265