Panasonic Lumix DMC-FZ200 User Manual page 196

Here in this example of a "high key" image where there are more areas
of white in the image the "skew" of the histogram is more towards the
highlight end of the chart.
The histogram only displays the distribution of pixel values in the scene
to be photographed; you still have to interpret the indicated result.
Here in Aperture priority mode with -4/3 EV you can see the light areas
are not aligned with the right hand side giving an indication of
underexposure in the image.
White gap
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