Canon EOS REBEL T6i Instruction Manual page 139

[Auto]

For exposures of 1 sec. or longer, noise reduction is performed
automatically if noise typical of long exposures is detected. This
[Auto] setting is effective in most cases.
[Enable]

Noise reduction is performed for all exposures of 1 sec. or longer.
The [Enable] setting may reduce noise that cannot be detected with
the [Auto] setting.
With [Auto] and [Enable], the noise reduction process after the picture is

taken may take the same amount of time as that for the exposure. You
cannot take another picture until the noise reduction process is
completed.
Images taken at ISO 1600 or higher may look grainier with the [Enable]

setting than with the [Disable] or [Auto] setting.
With [Auto] and [Enable], if a long exposure is shot with the Live View

image displayed, "BUSY" will be displayed during the noise reduction
process. The Live View display will not appear until the noise reduction is
completed. (You cannot take another picture.)
Set the desired setting.
2
Select the desired setting, then press

<0>.
Take the picture.
3
The image will be recorded with noise

reduction applied.
3 Setting Noise ReductionK
139