Local Laplacian Filters constitute an interesting algorithm for manipulating the local and global contrast of images while minimizing halos. I wanted to experiment with this technique since quite a while, and now I have finally wrote some code to see what one can get.
Local laplacian filters are available in Darktable, and most of the code I have used is derived from there. However, I have decided to follow the original paper(s) more than DT’s implementation:
- the algorithm is applied to the log-luminance, and not to the Lab channel as in DT
- I am not using the speed-up proposed by Aubry et al., instead I am using the original version from the Paris et al. paper(s)
- I have used up to now the most simple version of the remapping function, totally clipping the values above the user-defined threshold
- the output image is “beautified” with a simple gain+power adjustment, applied to the image linear luminance to avoid color shifts. Again, this follows the suggestions of Paris et al.
My implementation is still far from perfect, and I am still getting some artifacts that I need to understand. Also, the code is rather slow, too slow to think about implementing it in PhF. But results are nevertheless interesting, so let me show few examples from “difficult” images that have been posted in this forum in the past:
This is work in progress, so comments/suggestions are very much appreciated!