Canon MARK IV User Manual (en)

Custom Function Settings
C.Fn II -3     Highlight tone priority
0: Disable
1: Enable
Improves the highlight detail. The dynamic range is expanded from the 
standard 18% gray to bright highlights. The gradation between the grays 
and highlights becomes smoother.
C.Fn II -4     Auto Lighting Optimizer
If the image comes out dark or the contrast is low, the brightness and 
contrast can be corrected automatically.
For details on the Auto Lighting Optimizer, see page 81.
0: Standard
2: Strong
1: Low
3: Disable
C.Fn II -5     E-TTL II flash metering
0: Evaluative flash metering
Fully automatic flash photography for all conditions, from low light to 
daylight fill-flash.
1: Average flash metering
The entire metered area is averaged. Since automatic flash exposure 
compensation will not be executed, you may have to set it yourself 
depending on the scene. This also applies if you use FE lock.
With setting 1, noise may be slightly more pronounced than usual.
With setting 1, the settable ISO speed range will be 200 - 12800.
Also, <H> will be displayed on the top LCD panel and in the viewfinder.