Last active
October 21, 2024 06:05
-
-
Save petrklus/b1f427accdf7438606a6 to your computer and use it in GitHub Desktop.
Kelvin to RGB in python
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| """ | |
| Based on: http://www.tannerhelland.com/4435/convert-temperature-rgb-algorithm-code/ | |
| Comments resceived: https://gist.github.com/petrklus/b1f427accdf7438606a6 | |
| Original pseudo code: | |
| Set Temperature = Temperature \ 100 | |
| Calculate Red: | |
| If Temperature <= 66 Then | |
| Red = 255 | |
| Else | |
| Red = Temperature - 60 | |
| Red = 329.698727446 * (Red ^ -0.1332047592) | |
| If Red < 0 Then Red = 0 | |
| If Red > 255 Then Red = 255 | |
| End If | |
| Calculate Green: | |
| If Temperature <= 66 Then | |
| Green = Temperature | |
| Green = 99.4708025861 * Ln(Green) - 161.1195681661 | |
| If Green < 0 Then Green = 0 | |
| If Green > 255 Then Green = 255 | |
| Else | |
| Green = Temperature - 60 | |
| Green = 288.1221695283 * (Green ^ -0.0755148492) | |
| If Green < 0 Then Green = 0 | |
| If Green > 255 Then Green = 255 | |
| End If | |
| Calculate Blue: | |
| If Temperature >= 66 Then | |
| Blue = 255 | |
| Else | |
| If Temperature <= 19 Then | |
| Blue = 0 | |
| Else | |
| Blue = Temperature - 10 | |
| Blue = 138.5177312231 * Ln(Blue) - 305.0447927307 | |
| If Blue < 0 Then Blue = 0 | |
| If Blue > 255 Then Blue = 255 | |
| End If | |
| End If | |
| """ | |
| import math | |
| def convert_K_to_RGB(colour_temperature): | |
| """ | |
| Converts from K to RGB, algorithm courtesy of | |
| http://www.tannerhelland.com/4435/convert-temperature-rgb-algorithm-code/ | |
| """ | |
| #range check | |
| if colour_temperature < 1000: | |
| colour_temperature = 1000 | |
| elif colour_temperature > 40000: | |
| colour_temperature = 40000 | |
| tmp_internal = colour_temperature / 100.0 | |
| # red | |
| if tmp_internal <= 66: | |
| red = 255 | |
| else: | |
| tmp_red = 329.698727446 * math.pow(tmp_internal - 60, -0.1332047592) | |
| if tmp_red < 0: | |
| red = 0 | |
| elif tmp_red > 255: | |
| red = 255 | |
| else: | |
| red = tmp_red | |
| # green | |
| if tmp_internal <=66: | |
| tmp_green = 99.4708025861 * math.log(tmp_internal) - 161.1195681661 | |
| if tmp_green < 0: | |
| green = 0 | |
| elif tmp_green > 255: | |
| green = 255 | |
| else: | |
| green = tmp_green | |
| else: | |
| tmp_green = 288.1221695283 * math.pow(tmp_internal - 60, -0.0755148492) | |
| if tmp_green < 0: | |
| green = 0 | |
| elif tmp_green > 255: | |
| green = 255 | |
| else: | |
| green = tmp_green | |
| # blue | |
| if tmp_internal >=66: | |
| blue = 255 | |
| elif tmp_internal <= 19: | |
| blue = 0 | |
| else: | |
| tmp_blue = 138.5177312231 * math.log(tmp_internal - 10) - 305.0447927307 | |
| if tmp_blue < 0: | |
| blue = 0 | |
| elif tmp_blue > 255: | |
| blue = 255 | |
| else: | |
| blue = tmp_blue | |
| return red, green, blue | |
| if __name__ == "__main__": | |
| print("Preview requires matplotlib") | |
| from matplotlib import pyplot as plt | |
| step_size = 100 | |
| for i in range(0, 15000, step_size): | |
| color = list(map(lambda div: div/255.0, convert_K_to_RGB(i))) + [1] | |
| print(color) | |
| plt.plot((i, i), (0, 1), linewidth=step_size/2.0, linestyle="-", color=color) | |
| plt.show() | |
Oh bother, I found this minutes after I write a conversion myself. Oh well, great practice! Do you happen to have a pointer on linking colour temperature to time of day? I'm wanting to use this for a circadian clock project.
do you have by any change the reverse function?
hi @xalbertoisorna , I had a similar use-case and I've just eye-balled it - used around 5500K or even a little bluer for midday, then progressively going down.
No algorithm I am afraid.
I suggest using numpy for a much shorter code:
import numpy as np
def convert_K_to_RGB(colour_temperature: float) -> np.ndarray:
"""
Converts from K to RGB, algorithm courtesy of
http://www.tannerhelland.com/4435/convert-temperature-rgb-algorithm-code/
"""
# Range check.
colour_temperature = np.clip(colour_temperature, 1000, 40000)
tmp_internal = colour_temperature / 100.0
# Red.
if tmp_internal <= 66:
red = 255
else:
red = 329.698727446 * (tmp_internal - 60)**-0.1332047592
# Green.
if tmp_internal <= 66:
green = 99.4708025861 * np.log(tmp_internal) - 161.1195681661
else:
green = 288.1221695283 * (tmp_internal - 60)**-0.0755148492
# Blue.
if tmp_internal >= 66:
blue = 255
elif tmp_internal <= 19:
blue = 0
else:
blue = 138.5177312231 * np.log(tmp_internal - 10) - 305.0447927307
return np.clip((red, green, blue), 0, 255)I have also changed your main so that we can zoom in infinitely without seeing empty space between the color bars.
if __name__ == "__main__":
from matplotlib import pyplot as plt
STEP_SIZE = 100
temperatures = np.arange(0, 15000, STEP_SIZE)
colors = [convert_K_to_RGB(temperature)/255 for temperature in temperatures]
fig, ax = plt.subplots()
ax.set_xlim(temperatures[0], temperatures[-1])
ax.set_ylim(0, 1)
ax.bar(temperatures, height=1, width=STEP_SIZE, align="edge", color=colors)
fig.show()
With 10 more minutes of work, we could make the function support polymorphism so that it works on a whole numpy array at once.
If you are interested in the rgb_to_kelvin() I just reversed the values, with a step size of 100K, find it below as a header file to run it in C.
// temperature.h
#include <stdint.h>
#define HEIGHT 150
#define WIDTH 4
const unsigned colorTable[HEIGHT][WIDTH] = {
{181,205,255,14900},
{182,205,255,14800},
{182,206,255,14500},
{182,206,255,14600},
{182,206,255,14700},
{183,206,255,14300},
{183,206,255,14400},
{183,207,255,14200},
{184,207,255,13900},
{184,207,255,14000},
{184,207,255,14100},
{185,207,255,13800},
{185,208,255,13600},
{185,208,255,13700},
{186,208,255,13300},
{186,208,255,13400},
{186,208,255,13500},
{187,209,255,13000},
{187,209,255,13100},
{187,209,255,13200},
{188,209,255,12900},
{188,210,255,12700},
{188,210,255,12800},
{189,210,255,12400},
{189,210,255,12500},
{189,210,255,12600},
{190,211,255,12200},
{190,211,255,12300},
{191,211,255,12000},
{191,211,255,12100},
{192,212,255,11700},
{192,212,255,11800},
{192,212,255,11900},
{193,213,255,11500},
{193,213,255,11600},
{194,213,255,11300},
{194,213,255,11400},
{195,214,255,11100},
{195,214,255,11200},
{196,214,255,11000},
{196,215,255,10900},
{197,215,255,10700},
{197,215,255,10800},
{198,216,255,10600},
{199,216,255,10500},
{199,217,255,10400},
{200,217,255,10200},
{200,217,255,10300},
{201,218,255,10100},
{202,218,255,9900},
{202,218,255,10000},
{203,219,255,9800},
{204,219,255,9700},
{205,220,255,9500},
{205,220,255,9600},
{206,221,255,9400},
{207,221,255,9300},
{208,222,255,9200},
{209,222,255,9100},
{210,223,255,9000},
{211,223,255,8900},
{212,224,255,8800},
{213,225,255,8700},
{214,225,255,8600},
{215,226,255,8500},
{216,227,255,8400},
{217,227,255,8300},
{218,228,255,8200},
{220,229,255,8100},
{221,230,255,8000},
{223,231,255,7900},
{224,232,255,7800},
{226,233,255,7700},
{228,234,255,7600},
{230,235,255,7500},
{232,236,255,7400},
{234,237,255,7300},
{237,239,255,7200},
{240,240,255,7100},
{243,242,255,7000},
{246,244,255,6900},
{250,246,255,6800},
{254,249,255,6700},
{255,68,0,0},
{255,68,0,100},
{255,68,0,200},
{255,68,0,300},
{255,68,0,400},
{255,68,0,500},
{255,68,0,600},
{255,68,0,700},
{255,68,0,800},
{255,68,0,900},
{255,68,0,1000},
{255,77,0,1100},
{255,86,0,1200},
{255,94,0,1300},
{255,101,0,1400},
{255,108,0,1500},
{255,115,0,1600},
{255,121,0,1700},
{255,126,0,1800},
{255,132,0,1900},
{255,137,14,2000},
{255,142,27,2100},
{255,146,39,2200},
{255,151,50,2300},
{255,155,61,2400},
{255,159,70,2500},
{255,163,79,2600},
{255,167,87,2700},
{255,170,95,2800},
{255,174,103,2900},
{255,177,110,3000},
{255,180,117,3100},
{255,184,123,3200},
{255,187,129,3300},
{255,190,135,3400},
{255,193,141,3500},
{255,195,146,3600},
{255,198,151,3700},
{255,201,157,3800},
{255,203,161,3900},
{255,206,166,4000},
{255,208,171,4100},
{255,211,175,4200},
{255,213,179,4300},
{255,215,183,4400},
{255,218,187,4500},
{255,220,191,4600},
{255,222,195,4700},
{255,224,199,4800},
{255,226,202,4900},
{255,228,206,5000},
{255,230,209,5100},
{255,232,213,5200},
{255,234,216,5300},
{255,236,219,5400},
{255,237,222,5500},
{255,239,225,5600},
{255,241,228,5700},
{255,243,231,5800},
{255,244,234,5900},
{255,246,237,6000},
{255,248,240,6100},
{255,249,242,6200},
{255,251,245,6300},
{255,253,248,6400},
{255,254,250,6500},
{255,255,255,6600}
};
// function that takes an RGB value,
// checks the lowest distance to the colorTable and returns the temperature
unsigned rgb_to_kelvin(unsigned r, unsigned g, unsigned b) {
unsigned minDist = 0xFFFFFF;
unsigned minTemp = 0;
for (unsigned i = 0; i < HEIGHT; i++) {
unsigned rT = colorTable[i][0];
unsigned gT = colorTable[i][1];
unsigned bT = colorTable[i][2];
unsigned dist = (r-rT)*(r-rT) + (g-gT)*(g-gT) + (b-bT)*(b-bT);
if (dist < minDist) {
minDist = dist;
minTemp = colorTable[i][3];
}
}
return minTemp;
}
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Thank you so much for this!