Canon EOS 6D Instruction Manual page 240

B: Shooting Information Display
About the Highlight Alert
When [33: Highlight alert] is set to [Enable], overexposed
highlight areas will blink. To obtain more image detail in the
overexposed areas, set the exposure compensation to a negative
amount and shoot again.
About the AF Point Display
When [33: AF point disp.] is set to [Enable], the AF point that
achieved focus will be displayed in red. If automatic AF point
selection was used, multiple AF points may be displayed in red.
About the Histogram
The brightness histogram shows the exposure level distribution and
overall brightness. The RGB histogram is for checking the color
saturation and gradation. The display can be switched with [33:
Histogram disp].
[Brightness] Display
This histogram is a graph showing the
distribution of the image's brightness level. The
horizontal axis indicates the brightness level
(darker on the left and brighter on the right),
while the vertical axis indicates how many
pixels exist for each brightness level. The more
pixels there are toward the left, the darker the
image. The more pixels there are toward the
right, the brighter the image. If there are too
many pixels on the left, the shadow detail will be
lost. If there are too many pixels on the right, the
highlight detail will be lost. The gradation in-
between will be reproduced. By checking the
image and its brightness histogram, you can
see the exposure level inclination and the
overall gradation.
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Sample Histograms
Dark image
Normal brightness
Bright image