Soft shadows has its independent sampling space.
Texture filters are applied.
spp = [8, 128], threshold = 1e-6.
samples for shadow = [8, 32], threshold = 1e-4.
time: 54s using openmp.
spec: Ubuntu 18.04 on i5-8250U @ 1.6GHz x 8 with 20G memory
Trying second order average for all the samples
Looks almost the same. If we diff the images and extremize contrast,
Soon I found out that this is just random error by diffing two regular images.