PyPlot ColorMesh创建具有错误颜色映射的图 [英] PyPlot ColorMesh creates plot with wrong color mapping

问题描述

我尝试以这种方式使用xy坐标和颜色的地图创建Color Mesh图:

I try to create a Color Mesh plot using a map of xy-coordinates and colors in this way:

from matplotlib.colors import ListedColormap
import numpy as np
%pylab inline

colors = ListedColormap(['red', 'blue', 'yellow'])
xx,yy = np.meshgrid(np.arange(1, 6, 1), np.arange(1, 6, 1))
zz = np.array([[1,1,1,1,1],
               [1,1,1,1,1],
               [1,1,1,1,1],
               [2,2,0,0,0],
               [2,2,0,0,0]])
pyplot.pcolormesh(xx, yy, zz, cmap = colors)

当存在三种颜色的列表并且我尝试将xy点映射到所有这些颜色时(如上面的代码中)，效果很好:

It works ok when there is a list of three colors and I try to map xy-points into all of that colors (like in the code above):

但是当有三种颜色列表时，我尝试仅将点映射到其中的两种，则映射会出错:

But when there is a list of three colors, and I try to map points only into two of them, mapping goes wrong:

zz = np.array([[1,1,1,1,1],
               [1,1,1,1,1],
               [1,1,1,1,1],
               [0,0,0,0,0],
               [0,0,0,0,0]])
pyplot.pcolormesh(xx, yy, zz, cmap = colors)

它应该映射为颜色0(红色)和1(蓝色)，但是我得到了0(红色)和 2(黄色)颜色的图.错误在哪里?

It should map into colors 0 (red) and 1 (blue), but I get plot with 0 (red) and 2 (yellow) colors. Where is the mistake?

推荐答案

色图在0到1之间进行归一化.在绘图中使用它们时，归一化将转换为数据的最小值和最大值.如果0和1是最小值和最大值，则0将是地图的第一个颜色(红色)，而1将是地图的最后一个颜色(黄色).

Colormaps are normalized between 0 and 1. When they are used in a plot, the normalization is transfered to the minimum and maximum value of the data. If 0 and 1 are minimum and maximum, 0 will be the first color of the map (red) and 1 will the last (yellow).

您需要的是一种标准化，它考虑了所需的颜色图行为.最简单的选择是使用 vmin 和 vmax

What you need is a normalization which takes the desired colormap behaviour into account. The easiest option is to use vmin and vmax

zz = np.array([[1,1,1,1,1],
               [1,1,1,1,1],
               [1,1,1,1,1],
               [0,0,0,0,0],
               [0,0,0,0,0]])
plt.pcolormesh(xx, yy, zz, cmap = colors, vmin=0,vmax=colors.N)

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