Convert LED brightness to PWM value based on CIE 1931 curve.

cie1931.py

# Generate lookup table for converting between perceived LED brightness and PWM

# Adapted from: https://jared.geek.nz/2013/feb/linear-led-pwm
# See also: https://ledshield.wordpress.com/2012/11/13/led-brightness-to-your-eye-gamma-correction-no/

from sys import stdout

TABLE_SIZE = 256 # Number of steps (brightness)
RESOLUTION = 2**10 # PWM resolution (10-bit = 1024)

def cie1931(L):
    L *= 100
    if L <= 8:
        return L / 902.3
    else:
        return ((L + 16) / 116)**3

x = range(0, TABLE_SIZE)
y = [cie1931(float(L) / (TABLE_SIZE - 1)) * (RESOLUTION - 1) for L in x]

stdout.write('const uint16_t CIE[%d] = {' % TABLE_SIZE)

for i, L in enumerate(y):
    if i % 16 == 0:
        stdout.write('\n')
    stdout.write('% 5d,' % round(L))

stdout.write('\n};\n')

Script output:

const uint16_t CIE[256] = {
    0,    0,    1,    1,    2,    2,    3,    3,    4,    4,    4,    5,    5,    6,    6,    7,
    7,    8,    8,    8,    9,    9,   10,   10,   11,   11,   12,   12,   13,   13,   14,   15,
   15,   16,   17,   17,   18,   19,   19,   20,   21,   22,   22,   23,   24,   25,   26,   27,
   28,   29,   30,   31,   32,   33,   34,   35,   36,   37,   38,   39,   40,   42,   43,   44,
   45,   47,   48,   50,   51,   52,   54,   55,   57,   58,   60,   61,   63,   65,   66,   68,
   70,   71,   73,   75,   77,   79,   81,   83,   84,   86,   88,   90,   93,   95,   97,   99,
  101,  103,  106,  108,  110,  113,  115,  118,  120,  123,  125,  128,  130,  133,  136,  138,
  141,  144,  147,  149,  152,  155,  158,  161,  164,  167,  171,  174,  177,  180,  183,  187,
  190,  194,  197,  200,  204,  208,  211,  215,  218,  222,  226,  230,  234,  237,  241,  245,
  249,  254,  258,  262,  266,  270,  275,  279,  283,  288,  292,  297,  301,  306,  311,  315,
  320,  325,  330,  335,  340,  345,  350,  355,  360,  365,  370,  376,  381,  386,  392,  397,
  403,  408,  414,  420,  425,  431,  437,  443,  449,  455,  461,  467,  473,  480,  486,  492,
  499,  505,  512,  518,  525,  532,  538,  545,  552,  559,  566,  573,  580,  587,  594,  601,
  609,  616,  624,  631,  639,  646,  654,  662,  669,  677,  685,  693,  701,  709,  717,  726,
  734,  742,  751,  759,  768,  776,  785,  794,  802,  811,  820,  829,  838,  847,  857,  866,
  875,  885,  894,  903,  913,  923,  932,  942,  952,  962,  972,  982,  992, 1002, 1013, 1023,
};