fit 5th degree polynomial to color ramp values

polyfit_colorramp.py

import numpy as np
from numpy.polynomial import Polynomial
from numpy.polynomial.polynomial import polyval

# colorramp rgb values at steps of 1/16 from 0.0 to 1.0:
colors = [
    (45,24,40),
    (42,77,117),
    (25,120,170),
    (24,158,205),
    (15,190,217),
    (48,217,219),
    (79,234,213),
    (135,243,199),
    (179,242,184),
    (215,227,171),
    (244,199,154),
    (254,167,131),
    (253,123,94),
    (237,79,57),
    (210,47,31),
    (172,22,12),
    (121,9,1),
    ]

# scale colors to 0.0-1.0 range:
x = [t/16.0 for t in range(17)]
yr = [c[0]/255.0 for c in colors]
yg = [c[1]/255.0 for c in colors]
yb = [c[2]/255.0 for c in colors]

# fit the curve:
degree = 5
pr = Polynomial.fit(x, yr, degree, window=[0,1])
pg = Polynomial.fit(x, yg, degree, window=[0,1])
pb = Polynomial.fit(x, yb, degree, window=[0,1])

# compare the output at the given x positions:
polyval(x,pr.coef)*255.0
polyval(x,pg.coef)*255.0
polyval(x,pb.coef)*255.0

# print the coefficients to use:
pr.coef
pg.coef
pb.coef