matplotlib 色图：不要调整大小

Question

我正在使用matplotlib绘制一个混淆矩阵：

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

conf_arr_hs = [[90, 74],
                [33, 131]]
norm_conf_hs = []
for i in conf_arr_hs:
    a = 0
    tmp_arr = []
    a = sum(i, 0)
    for j in i:
        tmp_arr.append(float(j)/float(a))
    norm_conf_hs.append(tmp_arr)


confmatmap=cm.binary    
fig = plt.figure()


plt.clf()
ax = fig.add_subplot(111)
res = ax.imshow(np.array(norm_conf_hs), cmap=confmatmap, interpolation='nearest')
for x in xrange(2):
    for y in xrange(2):
        textcolor = 'black'
        if norm_conf_hs[x][y] > 0.5:
            textcolor = 'white'
        ax.annotate("%0.2f"%norm_conf_hs[x][y], xy=(y, x),  horizontalalignment='center', verticalalignment='center', color=textcolor)]

但是matplotlib似乎会自动调整颜色变化的范围：左下角的格子应该是浅灰色，因为它对应的值是0.2，而不是0.0。同样，右下角的格子应该是深灰色，因为它是0.8，而不是1。

我觉得我漏掉了设置颜色映射动态范围的步骤。我查阅了一些matplotlib的文档，但没有找到我想要的内容。

Answer 1

如果你想明确设置颜色映射的范围，可以使用 set_clim 这个命令：

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

plt.ion()

conf_arr_hs = [[90, 74],
                [33, 131]]
norm_conf_hs = []
for i in conf_arr_hs:
    a = 0
    tmp_arr = []
    a = sum(i, 0)
    for j in i:
        tmp_arr.append(float(j)/float(a))
    norm_conf_hs.append(tmp_arr)

confmatmap=plt.cm.binary    
fig = plt.figure()

plt.clf()
ax = fig.add_subplot(111)
res = ax.imshow(np.array(norm_conf_hs), cmap=confmatmap, interpolation='nearest')
res.set_clim(0,1) # set the limits for your color map

for x in xrange(2):
    for y in xrange(2):
        textcolor = 'black'
        if norm_conf_hs[x][y] > 0.5:
            textcolor = 'white'
        ax.annotate("%0.2f"%norm_conf_hs[x][y], xy=(y, x),  horizontalalignment='center', verticalalignment='center', color=textcolor)

想了解更多，可以查看这里: http://matplotlib.org/api/cm_api.html