Figure 1: the gradient test image – download and play with it in darktable
People using image editors or similar (raster) graphics editors are probably familiar with histograms. You also have them in almost all digital cameras. In darktable you can find it very prominently in the top right corner of darkroom mode, but also as a backdrop of modules like levels, tonecurve and similar.
From a mathematical point of view they are a diagram displaying the amount of pixels in the image that have a specific colour, lightness, value or similar measure.
This is a companion discussion topic for the original entry at https://www.darktable.org/2013/12/of-histograms-and-waveforms/
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