Canon MARK IV User Manual (en)

Custom Function Settings
C.Fn II: Image/Flash exposure/Display
C.Fn II -1     Long exposure noise reduction
0: Off
1: Auto
For 1 sec. or longer exposures, noise reduction is performed 
automatically if noise typical of long exposures is detected. This [Auto
setting is effective in most cases.
2: On
Noise reduction is performed for all exposures of 1 sec. or longer. The 
[On] setting may be effective for noise that cannot be detected or 
reduced with the [Auto] setting.
C.Fn II -2     High ISO speed noise reduction
Reduces the noise generated in the image. Although noise reduction is applied at all 
ISO speeds, it is particularly effective at high ISO speeds. At low ISO speeds, the 
noise in the shadow areas is further reduced. Change the setting to suit the noise level.
0: Standard
2: Strong
1: Low
3: Disable
With setting 1 and 2, after the picture is taken, the noise reduction 
process may take the same amount of time as the exposure. During the 
noise reduction, shooting is still possible as long as the maximum burst 
indicator in the viewfinder shows “1” or higher.
At ISO 1600 and higher, noise might be more pronounced with setting 2 
than with setting 0 or 1.
With setting 2, if a long exposure is shot during Live View display, “BUSY” will be 
displayed during the noise reduction process and the Live View display will not 
appear until the noise reduction is completed. (You cannot take another picture.)
With setting 2, the maximum burst for continuous shooting will greatly decrease.
This function does not work with movies. However, the noise reduction 
setting will be applied to still photos taken during movie shooting.
If you playback a RAW or RAW+JPEG image with the camera or print 
the image directly, the effect of the high ISO speed noise reduction may 
look minimal. You can check the noise reduction effect or print noise-
reduced images with Digital Photo Professional (provided software).