llap: local contrast, shadows, and highlights

parameters

sigma this controls the center region of the tonality, i.e. it determines what are mid tones and what are extremal values. increasing sigma will make more pixels be considered as mid tones. this can be useful if you mainly care about contrast in the image. it will make the clarity slider more powerful. decreasing sigma will remove from the area where clarity has a big effect and instead consider a larger range of pixels as shadows or highlights, giving more power to the corresponding sliders.
shadows this setting is used to control the shadows of the image. pulling shadows to 0 means shadows will disappear. increasing the shadow value will pull more pixels into the shadows.
hilights this is similar but for highlights. use it to control the sharpness of your speculars.
clarity this controls the amount of local contrast. it can also be used to smooth the image if you dial in a negative number.

this employs local laplacian pyramids, with a few extra tweaks for improved quality, and in a glsl implementation for speed.

it works on the luminance channel only (Y channel of XYZ), and reconstructs colours later by applying the method of Mantiuk 2009.