Canon EOS-1D X Mark III DSLR Camera (Body Only) - Manual (Page 506)

[Brightness] display
This histogram is a graph showing the distribution of the image's brightness level, with
the horizontal axis indicating the brightness level (darker on the left and brighter on the
right) and the vertical axis indicating the pixel count at each brightness level. The more
pixels there are toward the left, the darker the image, and the more pixels there are
toward the right, the brighter the image. If there are too many pixels on the left, detail in
shadows will be lost, and if there are too many pixels on the right, detail in highlights 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.
Sample histograms
Dark image
Normal brightness
Bright image
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