Canon EOS-1D X Mark III Advanced User's Manual page 296

View Assist.
When played on the camera, these movies may look darker and have lower contrast than
movies recorded with a Picture Style applied, due to Canon Log image characteristics,
which are intended to ensure a wide dynamic range. For clearer display that makes it easier
to check details, set [View Assist.] to [On].
Setting this feature to [On] does not affect movies recorded to the card, which are
recorded using Canon Log. Similarly, HDMI video output has Canon Log characteristics,
and View Assist is not used for it.
Note
[ ] is shown on the information display screen during movie recording with View
Assist.
When set to [On], View Assist is also used with magnified display.
Color Matrix
Using a color matrix, you can specify how colors are reproduced, to plan for postproduction
processing.
Cinema EOS Original
Reproduces colors equivalent to those of the EOS-1D C.
Neutral
Reproduces colors similar to actual subject colors.
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