create_schwarzwald_cmap.py

# download http://soliton.vm.bytemark.co.uk/pub/cpt-city/wkp/schwarzwald/wiki-schwarzwald-cont.pg

with open('schwarzwald.txt') as cmap:
    lines = cmap.read().splitlines()
    colormap = [list(map(int, line.split())) for line in lines if not line.startswith('#')][1:]

new_cmap = []
nb = len(colormap)
cmap = [[round((ix / nb) * 257), cp] for ix, cp in enumerate(colormap[::-1])]

for ix in range(len(cmap)):
    cp = cmap[ix]
    new_cmap.append(cp)  
    if ix == len(cmap) - 1:
        continue
    
    cnext = cmap[ix + 1]

    diff = cnext[0] - cp[0] - 1
    if diff > 1:
        continue
    for ii in range(diff):
        
        xc = diff
        ycR = cnext[1][0] - cp[1][0]
        ycG = cnext[1][1] - cp[1][1]
        ycB = cnext[1][2] - cp[1][2]

        mR = ycR / (diff + 1)
        mG = ycG / (diff + 1)
        mB = ycB / (diff + 1)

        newId = ii + 1
        mC = [
            newId + cp[0], 
            [
                round(mR*newId) + cp[1][0],
                round(mG*newId) + cp[1][1],
                round(mB*newId) + cp[1][2],                        
            ]
        ]
        new_cmap.append(mC)  

for c in new_cmap:
    print(f'{c[0]} {c[1][0]} {c[1][1]} {c[1][2]}')

not really proud of this scripts but it worked ;-)