oklch_visible_cull_getdata.py

# usage: python3 cull.py HUE
# where HUE is a number
#
# Get datasets faster using multiple threads, like:
# seq 360 | xargs --max-procs=8 -n 1 python cull.py

# Copyright © 2022 CuriousTorvald
#
# Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

import colour # pip install colour-science
import math
import sys

def lch_to_lab(l,c,h):
    hrad = h * math.pi / 180.0
    a = c * math.cos(hrad)
    b = c * math.sin(hrad)
    return [l, a, b]

def lab_to_xyz(L,a,b):
    if (L < 0.000001):
        return [0.0, 0.0, 0.0]
    #FIXME D65 only!

    l = math.pow(0.99999999845051981432*L + 0.39633779217376785678*a + 0.21580375806075880339*b, 3.0)
    m = math.pow(1.0000000088817607767*L - 0.1055613423236563494*a - 0.063854174771705903402*b, 3.0)
    s = math.pow(1.0000000546724109177*L - 0.089484182094965759684*a - 1.2914855378640917399*b, 3.0)

    X = 1.227013851103521026*l - 0.5577999806518222383*m + 0.28125614896646780758*s
    Y = -0.040580178423280593977*l + 1.1122568696168301049*m - 0.071676678665601200577*s
    Z = -0.076381284505706892869*l - 0.42148197841801273055*m + 1.5861632204407947575*s

    return [X, Y, Z]

def lch_to_xyz(l,c,h):
    lab = lch_to_lab(l,c,h)
    return lab_to_xyz(lab[0],lab[1],lab[2])

def vis(xyz):
    return colour.is_within_visible_spectrum(xyz)

print("sys.executable = "+sys.executable)

#print(vis(colour.xyY_to_XYZ([0.05, 0.8, 0.05])))
#print(vis(colour.xyY_to_XYZ([0.05, 0.8, 0.55])))

llimits = 1000
RECURSION_DEPTH = 16 # precision: 1/2^(n+1) because chromahigh is set to 0.5. 9 seems to be the absolute minimum acceptable precision for llimits=100

climits = [0]*(llimits+1)
H = float(sys.argv[1]) #153

if (H - int(sys.argv[1]) == 0):
    H = int(sys.argv[1])


filename = "ChromaLimits-H"+str(H)+"-Lcnt"+str(llimits)+"-Clim"+str(2**(RECURSION_DEPTH+1))+".txt"
print("filename: "+filename)


for l in range(1,llimits): # 1..99
    lightness = l / llimits

    sys.stdout.write("Chroma limits for L="+str(lightness)+", H="+str(H)+"... ")

    chromalow = 0.0
    chromahigh = 0.5
    chromamid = -1.0
    recursion_count = 0
    while recursion_count < RECURSION_DEPTH:
        chromamid = (chromalow + chromahigh) / 2.0
        col = lch_to_xyz(lightness, chromamid, H)
        if (vis(col)):
            chromalow = chromamid
        else:
            chromahigh = chromamid
        recursion_count += 1

    climits[l] = chromamid
    sys.stdout.write(str(chromamid)+"\n")

print("Chroma limits by Lightness for H="+str(H)+":")
print(climits)

with open(filename, "w") as f:
    numbers = ''.join(map(lambda x: str(x)+",", climits))
    f.writelines('"'+str(H)+'"'+":["+numbers[0:-1]+"],")