[plt colormap] #plot #python

colormap.py

# https://matplotlib.org/3.1.1/gallery/color/colormap_reference.html
import numpy as np
import matplotlib.pyplot as plt

cm = plt.get_cmap('Reds')
print(cm.N)  # how many color levels in this cm

# cm takes list or single value in [0,N-1] or [0.0, 1.0], depending on the value type
# value lower or bigger than boundary are default to boundry color

cm([-1, 0 ,1, 255, 256])
cm([-1, 0, 0.5, 1, 1.5])

# self defined pure color cmap with alpha changes
from matplotlib.colors import ListedColormap
pure_colors = []
for i in range(256):
    pure_colors.append([1.0,0,0, i/255])
pure_colors = np.array(pure_colors)
purecm = ListedColormap(pure_colors)