Canon EOS-1D X Instruction Manual page 45

Setting View Assist
Canon Log gamma is a movie characteristic to attain wide dynamic
range. As a result, the image displayed on the LCD monitor has low
contrast and is somewhat dark compared to when a Picture Style is set.
With View Assist, the movie image will be displayed on the LCD monitor
with a conspicuous characteristic. This makes it easier to check the
angle of view, details, etc.
Note that even if View Assist is set, it will not affect the movie recorded
to the card. (The movie will be recorded to the card with Canon Log
gamma.)
View Assist display with HDMI output
If [View Assist.] is set to [On] and you shoot a movie in H, the
View Assist will also apply to the HDMI output (p.53 to 54) image.
Note that View Assist will not work with a movie-recording quality
other than H.
Setting the Canon Log Gamma
Select [View Assist.].
Turn the <5> dial to select [View
Assist.], then press <0>.
Turn the <5> dial to select [On],
then press <0>.
The View Assist display will appear
when you shoot a movie.
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