Matplotlib 颜色图显示不正确的颜色

Question

I need to make a colormap with 256 colors from red to white and display the red channel in Python but it looks like this thing it's done wrong and I don't understand why. This is my code:

import numpy as np
import matplotlib as mpl
import matplotlib.pyplot as plt

# How to create an array filled with zeros
img = np.zeros([256,256])
colormap1 = np.zeros([256,1])
#image:
for i in range(256):
    img[:,i] = i #on all columns I have the same value
    #to go from red to white we'll have: [1,0,0]...,[1,0.5,0.5],..[1,1,1]
for i in range(128):
    colormap1[i,1] = i/127     

#display the thing:  
colormap1 = mpl.colors.ListedColormap(colormap1)
plt.figure(), plt.imshow(img, cmap = colormap1)

Answer 1

You can answer it like that :

import numpy as np
import matplotlib as mpl
import matplotlib.pyplot as plt

# How to create an array filled with zeros
img = np.zeros([256,256])
colormap = np.zeros([256,3])

#image:
for i in range(256):
    img[:,i] = i #on all columns I have the same value
    
#color map:
for i in range(256):
    colormap[i,0] = 1
    colormap[i,1] = (i+1)/256
    colormap[i,2] = (i+1)/256
    
#display the thing:
colormap = mpl.colors.ListedColormap(colormap)
plt.figure(), plt.imshow(img, cmap = colormap)

almost like you did in here Colormap it's not composed of correct color . You just need to write the second part of your code (from red to white) and do it in 256 moves instead of 128.