Nikon D4S - Manual (Page 330)

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If On is selected, photographs taken at
shutter speeds slower than 1 s will be
processed to reduce noise (bright spots,
randomly-spaced bright pixels, or fog). The
time required for processing roughly doubles;
during processing, “l m” will flash in the
shutter speed/aperture displays and pictures
can not be taken (if the camera is turned off before processing is
complete, the picture will be saved but noise reduction will not be
performed). In continuous release mode, frame rates will slow and
while photographs are being processed, the capacity of the
memory buffer will drop.
Photographs taken at high ISO sensitivities can be processed to
reduce noise.
Long Exposure NR
(Long Exposure Noise Reduction)
G button
➜ C shooting menu
High ISO NR
G button
➜ C shooting menu
Option Description
High
Reduce noise (randomly-spaced bright pixels, lines, or fog),
particularly in photographs taken at high ISO sensitivities.
Choose the amount of noise reduction performed from High,
Normal, and Low.
Normal
Low
Off
Noise reduction is performed only at ISO sensitivities of 6400
and higher. The amount of noise reduction is less than the
amount performed when Low is selected for High ISO NR.