Question

我正在尝试将一些绘图代码从gnuplot移植到matplotlib，并且正在努力移植由颜色名称指定的不连续颜色贴图。 有关如何在matplotlib中执行此操作的任何建议吗？

# Establish a 3-section color palette with lower 1/4 in the blues, 
# and middle 1/2 light green to yellow, and top 1/4 reds
set palette defined (0 'dark-blue', 0.5 'light-blue', \\
                     0.5 'light-green', 1 'green', 1.5 'yellow', \\
                     1.5 'red', 2 'dark-red')
# Establish that the palette range, such that the middle green range corresponds
# to 0.95 to 1.05
set cbrange [0.9:1.1]

Answer 1

我已经使用过这个脚本多年了，我真的不记得我得到它的方式或位置（编辑：经过一些搜索，this似乎是源代码，但它需要对Python3进行一些小改动，但它在快速创建自定义颜色贴图方面帮助了我很多。它允许您简单地指定具有位置（0..1）和颜色的字典，并创建一个线性颜色图;例如make_colormap({0:'w',1:'k'})创建从白色到黑色的线性颜色贴图。

import numpy as np
import matplotlib.pylab as pl

def make_colormap(colors):
    from matplotlib.colors import LinearSegmentedColormap, ColorConverter
    from numpy import sort

    z  = np.array(sorted(colors.keys()))
    n  = len(z)
    z1 = min(z)
    zn = max(z)
    x0 = (z - z1) / (zn - z1)

    CC = ColorConverter()
    R = []
    G = []
    B = []
    for i in range(n):
        Ci = colors[z[i]]      
        if type(Ci) == str:
            RGB = CC.to_rgb(Ci)
        else:
            RGB = Ci
        R.append(RGB[0])
        G.append(RGB[1])
        B.append(RGB[2])

    cmap_dict = {}
    cmap_dict['red']   = [(x0[i],R[i],R[i]) for i in range(len(R))]
    cmap_dict['green'] = [(x0[i],G[i],G[i]) for i in range(len(G))]
    cmap_dict['blue']  = [(x0[i],B[i],B[i]) for i in range(len(B))]
    mymap = LinearSegmentedColormap('mymap',cmap_dict)
    return mymap

test1 = make_colormap({0.:'#40004b',0.5:'#ffffff',1.:'#00441b'})
test2 = make_colormap({0.:'b',0.25:'w',0.251:'g',0.75:'y',0.751:'r',1:'k'})

data = np.random.random((10,10))

pl.figure()
pl.subplot(121)
pl.imshow(data, interpolation='nearest', cmap=test1) 
pl.colorbar()

pl.subplot(122)
pl.imshow(data, interpolation='nearest', cmap=test2) 
pl.colorbar()

Answer 2

巴特的功能非常好。但是，如果您想自己制作色彩映射表，可以使用字典按照custom_cmap example from the mpl website中的方式定义这样的色彩映射。

这是一个非常接近你的色彩映射的例子：

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

cdict = {'red':   ((0.0,  0.0, 0.0),   # From 0 to 0.25, we fade the red and green channels
                   (0.25, 0.5, 0.5),   # up a little, to make the blue a bit more grey

                   (0.25, 0.0, 0.0),   # From 0.25 to 0.75, we fade red from 0.5 to 1
                   (0.75, 1.0, 1.0),   # to fade from green to yellow

                   (1.0,  0.5, 0.5)),  # From 0.75 to 1.0, we bring the red down from 1
                                       # to 0.5, to go from bright to dark red

         'green': ((0.0,  0.0, 0.0),   # From 0 to 0.25, we fade the red and green channels
                   (0.25, 0.6, 0.6),   # up a little, to make the blue a bit more grey

                   (0.25, 1.0, 1.0),   # Green is 1 from 0.25 to 0.75 (we add red 
                   (0.75, 1.0, 1.0),   # to turn it from green to yellow)

                   (0.75, 0.0, 0.0),   # No green needed in the red upper quarter
                   (1.0,  0.0, 0.0)),

         'blue':  ((0.0,  0.9, 0.9),   # Keep blue at 0.9 from 0 to 0.25, and adjust its
                   (0.25, 0.9, 0.9),   # tone using the green and red channels

                   (0.25, 0.0, 0.0),   # No blue needed above 0.25
                   (1.0,  0.0, 0.0))

             }

cmap = colors.LinearSegmentedColormap('BuGnYlRd',cdict)

data = 0.9 + (np.random.rand(8,8) * 0.2)  # Data in range 0.9 to 1.1

p=plt.imshow(data,interpolation='nearest',cmap=cmap,vmin=0.9,vmax=1.1)

plt.colorbar(p)

plt.show()

将gnuplot颜色映射转换为matplotlib

2 个答案: