this is inspired by ansel adams zone system, a way to think about a tone curve, i.e. modifying brightness of the output based on logarithmically spaced zones of input brightness.
it works similar to the tone equaliser aurelien implemented for darktable: the input image is partitioned into zones based on exposure values. these partitions are blurred to give us smooth blending. this is done by a guided filter which takes the original image as guide for the edges.
inputoutputdspythe quantised and filtered luminance to visualise the zones
radiusthis fraction of the image width will be the blur radiusepsilonthe edge weight for the guided filtergammathe gamma correction to apply before quantisation to zones. lower this value if you need more zones in the blacks, increase it for finer resolution in the highlights. this can be a great way to separate the image exactly where you need it.nzonesthe number of zones the image should be quantised intozonethe exposure compensation values for the zones from dark to bright.