Canon EOS R6 Mark II Mirrorless Camera with 24-105mm f/4-7.1 Lens - Manual (Page 272)

Long Exposure Noise Reduction
Noise such as dots of light or banding that tends to occur in long exposures at shutter
speeds of one sec. or slower can be reduced.
1.
Select [ : Long exp. noise reduction].
2.
Set a reduction option.
Auto
For images exposed for 1 sec. or longer, noise reduction is performed
automatically if noise typical of long exposures is detected. This setting
is effective enough in most cases.
Enable
Noise reduction is performed for all images exposed for 1 sec. or
longer. The [
Enable ] setting may reduce noise that cannot be detected
with the [ Auto ] setting.
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