I am trying to create a heat map with python. For this I have to assign an RGB value to every value in the range of possible values. I thought of changing the color from blue (minimal value) over green to red (maximal value).
The picture example below explains how I thought of the color composition: We have a range from 1 (pure blue) to 3 (pure red), 2 is in between resembled by green.
I read about linear interpolation and wrote a function that (more or less) handles the calculation for a certain value in the range between a minimum and a maximum and returns an RGB tuple. It uses if
and elif
conditions (which does not make me completely happy):
def convert_to_rgb(minimum, maximum, value):
minimum, maximum = float(minimum), float(maximum)
halfmax = (minimum + maximum) / 2
if minimum <= value <= halfmax:
r = 0
g = int( 255./(halfmax - minimum) * (value - minimum))
b = int( 255. + -255./(halfmax - minimum) * (value - minimum))
return (r,g,b)
elif halfmax < value <= maximum:
r = int( 255./(maximum - halfmax) * (value - halfmax))
g = int( 255. + -255./(maximum - halfmax) * (value - halfmax))
b = 0
return (r,g,b)
However I wonder if one could write a function for each color value without using if
conditions. Does anybody have an idea? Thank you a lot!
def rgb(minimum, maximum, value):
minimum, maximum = float(minimum), float(maximum)
ratio = 2 * (value-minimum) / (maximum - minimum)
b = int(max(0, 255*(1 - ratio)))
r = int(max(0, 255*(ratio - 1)))
g = 255 - b - r
return r, g, b