Lilliput PVM220S User Manual page 17

 Histogram
The horizontal axis of histogram represents the luminance, from left to right indicating low to high
luminance. The vertical axis of histogram indicates the number of pixels, from bottom to top indicating the
number of pixels from less to more. The higher the histogram bumps in a certain luminance range, the more
pixels there are in that luminance range. For example, if the histogram's bumps are mainly on the left side,
this means that the overall brightness of the image is low; if it is on the right side, the overall brightness is
high; if it is in the middle, the brightness is comfortable.
(Actual distribution is white, black for demonstration reference)
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