Canon EOS-1D X Mark III Advanced User's Manual page 224

3.
Set [HDR assist disp: shooting].
Converted images are displayed on the screen in Live View shooting,
giving an impression similar to how they would appear on an HDR
display device.
Select [Exposure prior. (mid-tones)] or [Tones prior. (highlights)].
[ ] Exposure prior. (mid-tones)
Provides reference display that emphasizes exposure of subjects (such
as people) with intermediate brightness.
[ ] Tones prior. (highlights)
Provides reference display that emphasizes gradation of bright subjects
(such as the sky).
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