Matplotlib colorbar:如何手动设置间隔? [英] Matplotlib colorbar: how to manually set the intervals?

问题描述

我正在使用以下代码段创建自定义颜色栏:

I am using the following snippet to create a custom colorbar:

import pylab as pl
import numpy as np

a = np.array([[0,10000,100000,400000,500000]])
pl.figure(figsize=(9, 1.5))
mycmap = colors.ListedColormap(['yellow','orange','red','darkred'])
img = pl.imshow(a, cmap=mycmap)
pl.gca().set_visible(False)
cax = pl.axes([0.1, 0.2, 0.8, 0.6])
cbar=pl.colorbar(orientation='horizontal', cax=cax,spacing='proportional');
cbar.set_ticks([0,10000,100000,400000,500000])
cbar.set_ticklabels(['0','10000','100000','400000','500000'])

这虽然给我指定了 spacing ='proportional'，但仍以固定的间隔为我提供了一个彩条:

This is giving me a colorbar with regular intervals, although I have specified spacing='proportional':

预期的结果是:

0-10000: yellow
10001-100000: orange
100001-400000: red
400001-500000: dark red

我在做什么错了?

推荐答案

可以看到，当不使轴不可见时，颜色条正确地表示了图像中数据的颜色.

As can be seen when not turning the axes invisible, the colorbar is correctly representing the color of the data in the image.

如果这不是您想要的，则应首先确定图像中数据的表示方式.将数据归一化到色图范围通常是完成此操作的方法.在这里， BoundaryNorm 是有意义的.

If this is not what you want you should start by establishing how the data is represented in the image. Introducing a Normalization for the data to the colormap range is usually the way this is accomplished. Here a BoundaryNorm makes sense.

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

a = np.array([[0,10000,100000,400000,500000]])
plt.figure(figsize=(4, 2.5))

mycmap = matplotlib.colors.ListedColormap(['yellow','orange','red','darkred'])
norm = matplotlib.colors.BoundaryNorm(a[0], len(a[0])-1)
img = plt.imshow(a, cmap=mycmap, norm=norm)
cax = plt.axes([0.1, 0.1, 0.8, 0.1])
cbar=plt.colorbar(orientation='horizontal', cax=cax,spacing='proportional');

plt.show()

这现在给出了有意义的表示，在色彩范围的边缘带有刻度.

This now gives a meaningful representation with ticks at the edges of the colorranges.

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