I'm looking at presentation by Timothy Lottes where he derives a generic tonemapper (slides 37 and following).
Although the purpose of the different parameters is explained nicely I find it quite hard to adjust them properly. I wrote a simple script to compare different tonemappers and have trouble to find reasonable settings for the generic tonemapper.
Generally I cannot get the shoulder of the curve to behave comparable to the other operators. Maybe it is a mistake in my implementation (original source code is in the slides).
def generic(x):
a = 1.2 # contrast
d = 1.1 # shoulder
mid_in = 1
mid_out = 0.18
hdr_max = 16
# It seems to work better when omitting the minus
b = (-math.pow(mid_in, a) + math.pow(hdr_max, a) * mid_out) / (math.pow(math.pow(hdr_max, a), d) - math.pow(math.pow(mid_in, a), d) * mid_out)
c = (math.pow(math.pow(hdr_max, a), d) * math.pow(mid_in, a) - math.pow(hdr_max, a) * math.pow(math.pow(mid_in, a), d) * mid_out) / (math.pow(math.pow(hdr_max, a), d) - math.pow(math.pow(mid_in, a), d) * mid_out)
z = math.pow(x, a)
y = z / (math.pow(z, d) * b + c)
return y
Has anybody experimented with this by chance?
