matplotlib颜色图提供重复的值

Question

Recently I was using this method to basically select 6 equally values along this colormap.

import matplotlib.pyplot as plt
import numpy as np
ints = np.linspace(0,255,6)
ints = [int(x) for x in ints]
newcm = plt.cm.Accent(ints)

Normally this would return the colormap values no problem. Now when I run this, the output I get for newcm is:

Out[25]: 
array([[ 0.49803922,  0.78823529,  0.49803922,  1.        ],
       [ 0.4       ,  0.4       ,  0.4       ,  1.        ],
       [ 0.4       ,  0.4       ,  0.4       ,  1.        ],
       [ 0.4       ,  0.4       ,  0.4       ,  1.        ],
       [ 0.4       ,  0.4       ,  0.4       ,  1.        ],
       [ 0.4       ,  0.4       ,  0.4       ,  1.        ]])

So now things are not plotting right. I have also tried bytes=True but the behaviour is the same. Do others get the same result or is it some funny setting on my matplotlib that has gone awry?

Moreover - it seems this is happening in particular on the Accent colormap, but not necessarily others.

Answer 1

In general, a colormap ranges between 0 and 1. In np.linspace(0,255,6) all values except the first are larger than 1, hence you get the output corresponding to the maximum value 1 for all but the first item of that list.

If instead you use numbers = np.linspace(0,1,6) , you will get 6 different values from that colormap.

import matplotlib.pyplot as plt
import numpy as np

numbers = np.linspace(0,1,6)
newcm = plt.cm.Accent(numbers)
print(newcm)

produces

[[ 0.49803922  0.78823529  0.49803922  1.        ]
 [ 0.74509804  0.68235294  0.83137255  1.        ]
 [ 1.          1.          0.6         1.        ]
 [ 0.21960784  0.42352941  0.69019608  1.        ]
 [ 0.74901961  0.35686275  0.09019608  1.        ]
 [ 0.4         0.4         0.4         1.        ]]