Canon EOS 5D MARK III Instruction Manual page 45

Noise Reduction Settings*
I_ With [Auto] and [Enable], after the picture is taken, the noise reduction
orocess may take the same amount of time as the exposure. During
noise reduction, shooting is still possible as long as the maximum burst
indicator in the viev,!finder shows "1" or higher.
Images taken at SO 1600 or higher may look grainier with the [Enable]
setting than with tile [Disable] and [Auto] settings.
With [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.)
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