If you've ever looked at the settings in a digital camera, or have experience with image processing programs like GIMP, then you may have seen a colour histogram. This is a simple graph that shows the amount of different shades of colour are present in the image.
They are created by looking at the number of colours in a given image and them mapping their red, green and blue values against a the frequency of their occurrence in the image.
Colour histograms are useful for looking at the overall colour distribution within an image and can also be used to simplify the colours of an image by restricting how much of a certain colour is allowed based on its frequency.
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