Canon EOS-1D X Mark III Advanced User's Manual page 250

Live View image
Under low- or bright-light conditions, the displayed image may not reflect the
brightness of the captured image.
Although noise may be noticeable in Live View images under low light (even at low
ISO speeds), there will be less noise in your shots, due to differences in image
quality between Live View images and captured images.
The screen may flicker if the light source (lighting) changes. In this case, stop Live
View shooting temporarily before you continue shooting under the light source you
will use.
Pointing the camera at different direction may momentarily prevent correct display
of brightness. Wait until the brightness level stabilizes before shooting.
If there is a very bright light source in the image, the bright area may appear black
on the screen. However, the actual captured image will correctly show the bright
area.
Under low light, bright [ : Disp. brightness] settings may cause noise or irregular
colors in Live View images. However, the noise or irregular colors will not be
recorded in the captured image.
When you magnify the image, the image sharpness may look more pronounced
than in the actual image.
Custom Functions
Some Custom Functions are not available in Live View shooting (some settings
have no effect).
Lens and flash
If the attached lens has an Image Stabilizer and you set the Image Stabilizer switch
to < >, the Image Stabilizer will operate at all times even if you do not press
the shutter button halfway. The Image Stabilizer consumes battery power and may
decrease the number of available shots depending on the shooting conditions.
When the Image Stabilizer is not necessary, such as when using a tripod, it is
recommended that you set the Image Stabilizer switch to <
Focus preset is available in Live View shooting only when using (super) telephoto
lenses equipped with this function released in and after the second half of 2011.
Modeling flash is not available when a Speedlite is used.
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