Lch is similar to it's cousin Cie-L*ab, except that it's been rearranged in the shape of a sphere which makes it useful for applications like high-end photo editing and retouching images. Read more about it here
Cie-L*ab is defined by lightness and the color-opponent dimensions a and b, which are based on the compressed Xyz color space coordinates. Lab is particularly notable for it's use in delta-e calculations. Read more about it here.
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Color conversions performed using the open source ColorMine library.