python - 绘制和保存大量图形时如何加速 matplotlib？

Question

我正在处理来自许多天线基线的观测数据。目前我正在做的是绘制 ~ 40 个图形，每个图形都有 4x5 的子图区域。我发现在循环中使用 matplotlib 绘制和保存图形时速度很慢。这是我的代码:

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

    PLT_PAGE_NUM = 39 # default is 39
    SUB_PLT_NUM = 20 # default is 20

    for pp in xrange(0,PLT_PAGE_NUM):

        plt.figure(figsize=(20,12))

        start_time = time.clock() 
        for kk in xrange(0,SUB_PLT_NUM):
            plt.subplot(5,4,kk+1)
            plt.plot(np.arange(0,TIME_LENGTH), xcor_real_arr[20*pp+kk,0:],'r-',
                     range(0,TIME_LENGTH), xcor_imag_arr[20*pp+kk,0:],'b-')
            plt.title('XCOR of '+ ind_arr[20*pp+kk], color='k') 

        plt.savefig('test_imag_real'+str(pp)+'.png',format='png',dpi=100)
        print 'Fig-'+str(pp)+' has been saved'
        print "Excution time:", time.clock()-start_time

执行时间信息是:

######### Check your inputs setting #########
You have selected 2 files.
The time interval is From 2011-10-20_14:28:38 to 2011-10-20_15:10:54
Your time resolution is set to 1.125s
The total plot points number is: 100
Your frequency channel is: ch2
######### Hardworking...please wait #########
Fig-0 has been saved
Excution time: *2.52576639619*
Fig-1 has been saved
Excution time: *2.59867230708*
Fig-2 has been saved
Excution time: *2.81915188482*
Fig-3 has been saved
Excution time: *2.83102198991*
Program ends

如您所见，我只绘制了 4 个数字，耗时约 11 秒。绘制和保存所有 39 个数字大约需要 2 分钟。我不知道瓶颈在哪里。你能帮忙让它更快吗？谢谢!

Answer 1

我已经修改了您的代码以使其可运行:

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

PLT_PAGE_NUM = 39 # default is 39
SUB_PLT_NUM = 20 # default is 20
TIME_LENGTH = 1000

xcor_real_arr = np.random.random((SUB_PLT_NUM*PLT_PAGE_NUM,TIME_LENGTH))
xcor_imag_arr = np.random.random((SUB_PLT_NUM*PLT_PAGE_NUM,TIME_LENGTH))
for pp in xrange(0,PLT_PAGE_NUM):

    plt.figure(figsize=(20,12))

    start_time = time.time() 
    for kk in xrange(0,SUB_PLT_NUM):
        plt.subplot(5,4,kk+1)
        plt.plot(np.arange(0,TIME_LENGTH), xcor_real_arr[SUB_PLT_NUM*pp+kk,0:],'r-',
                 range(0,TIME_LENGTH), xcor_imag_arr[SUB_PLT_NUM*pp+kk,0:],'b-')
        plt.title('XCOR of '+ str(SUB_PLT_NUM*pp+kk), color='k') 

    plt.savefig('test_imag_real'+str(pp)+'.png',format='png',dpi=100)
    print 'Fig-'+str(pp)+' has been saved'
    print "Excution time:", time.time()-start_time

在我的机器上，每个图形大约需要 3 秒:

Fig-0 has been saved
Excution time: 3.01798415184
Fig-1 has been saved
Excution time: 3.08960294724
Fig-2 has been saved
Excution time: 2.9629740715

使用来自 Matplotlib Animations Cookbook 的想法(Joe Kington，here 也进行了演示)，我们可以通过重复使用相同的轴并简单地重新定义每个图的 y 数据，将速度提高约 33%(每个图 1 秒):

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

PLT_PAGE_NUM = 39 # default is 39
SUB_PLT_NUM = 20 # default is 20
TIME_LENGTH = 1000

xcor_real_arr = np.random.random((SUB_PLT_NUM*PLT_PAGE_NUM,TIME_LENGTH))
xcor_imag_arr = np.random.random((SUB_PLT_NUM*PLT_PAGE_NUM,TIME_LENGTH))
plt.figure(figsize=(20,12))

ax = {}
line1 = {}
line2 = {}

for pp in xrange(0,PLT_PAGE_NUM):
    start_time = time.time() 
    for kk in xrange(0,SUB_PLT_NUM):
        if pp == 0:
            ax[kk] = plt.subplot(5,4,kk+1)
            line1[kk], line2[kk] = ax[kk].plot(np.arange(0,TIME_LENGTH),
                                   xcor_real_arr[SUB_PLT_NUM*pp+kk,0:],'r-',
                                   range(0,TIME_LENGTH),
                                   xcor_imag_arr[SUB_PLT_NUM*pp+kk,0:],'b-')
        else:
            line1[kk].set_ydata(xcor_real_arr[SUB_PLT_NUM*pp+kk,0:])
            line2[kk].set_ydata(xcor_imag_arr[SUB_PLT_NUM*pp+kk,0:])
        plt.title('XCOR of '+ str(SUB_PLT_NUM*pp+kk), color='k') 

    plt.savefig('test_imag_real'+str(pp)+'.png',format='png',dpi=100)
    print 'Fig-'+str(pp)+' has been saved'
    print "Excution time:", time.time()-start_time

产生这些执行时间:

Fig-0 has been saved
Excution time: 3.0408449173
Fig-1 has been saved
Excution time: 2.05084013939
Fig-2 has been saved
Excution time: 2.01951694489

(第一个图仍然需要 3 秒来设置初始图。在后续图上我们可以节省一些时间。)