openmv/tools/gen_rgb2lab.py
2021-02-14 16:47:45 +02:00

77 lines
2.3 KiB
Python
Executable File

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# This file is part of the OpenMV project.
#
# Copyright (c) 2013-2021 Ibrahim Abdelkader <iabdalkader@openmv.io>
# Copyright (c) 2013-2021 Kwabena W. Agyeman <kwagyeman@openmv.io>
#
# This work is licensed under the MIT license, see the file LICENSE for details.
#
# This script generates RGB to LAB lookup table.
# See https://en.wikipedia.org/wiki/SRGB (The reverse transformation)
def lin(c):
return 100 * ((c/12.92) if (c<=0.04045) else pow((c+0.055)/1.055, 2.4))
import sys, math
sys.stdout.write("#include <stdint.h>\n")
l_list = []
a_list = []
b_list = []
sys.stdout.write("const int8_t lab_table[98304] = {\n") # 65536 * 3 / 2
for i in range(65536):
r = ((((i >> 11) & 31) * 255) + 15.5) // 31
g = ((((i >> 5) & 63) * 255) + 31.5) // 63
b = (((i & 31) * 255) + 15.5) // 31
# https://en.wikipedia.org/wiki/SRGB (The reverse transformation)
r_lin = lin(r / 255.0)
g_lin = lin(g / 255.0)
b_lin = lin(b / 255.0)
x = (r_lin * 0.4124) + (g_lin * 0.3576) + (b_lin * 0.1805);
y = (r_lin * 0.2126) + (g_lin * 0.7152) + (b_lin * 0.0722);
z = (r_lin * 0.0193) + (g_lin * 0.1192) + (b_lin * 0.9505);
# https://en.wikipedia.org/wiki/Lab_color_space (CIELAB-CIEXYZ conversions)
def f(t):
return pow(t, (1/3.0)) if (t>0.008856) else ((7.787037*t)+0.137931)
x = f(x / 095.047)
y = f(y / 100.000)
z = f(z / 108.883)
l = int(round(116 * y)) - 16;
a = int(round(500 * (x-y)));
b = int(round(200 * (y-z)));
l_list.append(int(round(116 * y)) - 16)
a_list.append(int(round(500 * (x-y))))
b_list.append(int(round(200 * (y-z))))
lab = list(zip(l_list, a_list, b_list))
for i, (x, y) in enumerate(zip(lab[0::2], lab[1::2])):
out = [(i1 + i2)/2.0 for i1, i2 in zip(x, y)]
sys.stdout.write(" %4d, %4d, %4d" % (out[0], out[1], out[2]))
if (i + 1) % 4:
sys.stdout.write(", ")
elif i != 65535//2:
sys.stdout.write(",\n")
else:
sys.stdout.write("\n};\n")
sys.stdout.write("const float xyz_table[256] = {\n")
for i in range(256):
if not (i % 8):
sys.stdout.write(" ")
sys.stdout.write("%9.6ff" % lin(i / 255.0))
if (i + 1) % 8:
sys.stdout.write(", ")
elif i != 255:
sys.stdout.write(",\n")
else:
sys.stdout.write("\n};\n")