Savefig outputs blank image

Question

I am trying to save plots I make using matplotlib; however, the images are saving blank.

Here is my code:

plt.subplot(121)
plt.imshow(dataStack, cmap=mpl.cm.bone)

plt.subplot(122)
y = copy.deepcopy(tumorStack)
y = np.ma.masked_where(y == 0, y)

plt.imshow(dataStack, cmap=mpl.cm.bone)
plt.imshow(y, cmap=mpl.cm.jet_r, interpolation='nearest')

if T0 is not None:
    plt.subplot(123)
    plt.imshow(T0, cmap=mpl.cm.bone)

    #plt.subplot(124)
    #Autozoom

#else:
    #plt.subplot(124)
    #Autozoom

plt.show()
plt.draw()
plt.savefig('tessstttyyy.png', dpi=100)

And tessstttyyy.png is blank (also tried with .jpg)

score 479 · Accepted Answer · answered Jan 26 '12 at 01:05

479

First, what happens when T0 is not None? I would test that, then I would adjust the values I pass to plt.subplot(); maybe try values 131, 132, and 133, or values that depend whether or not T0 exists.

Second, after plt.show() is called, a new figure is created. To deal with this, you can

Call plt.savefig('tessstttyyy.png', dpi=100) before you call plt.show()
Save the figure before you show() by calling plt.gcf() for "get current figure", then you can call savefig() on this Figure object at any time.

For example:

fig1 = plt.gcf()
plt.show()
plt.draw()
fig1.savefig('tessstttyyy.png', dpi=100)

In your code, 'tesssttyyy.png' is blank because it is saving the new figure, to which nothing has been plotted.

answered Jan 26 '12 at 01:05

Yann

33,811
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70

Forgot to remove the T0 part...it was commented previously. – tylerthemiler Jan 26 '12 at 01:18
27

A special case of this occurs in `jupyter` notebooks with `%matplotlib inline` enabled: the `savefig` call must be in the same cell as the plot creation method. – ijoseph Jan 06 '18 at 01:31
8

Interesting to see `plt.show()` generates a new image. Indeed, this solved the issue. – user989762 Aug 15 '18 at 08:21
1

Interestingly, if you type plt.plot, plt.savefig, plt.show one by one in terminal such as spyder, it will not show fig. Put all command in a script and run in one go. It shows the plot. – CKM Oct 09 '18 at 06:57
@CKM Hi. Do you happen to know why this happens? I was thinking it's actually a problem that causes functions like `plt.ylabel()` create a new figure instead of applying to the current one (posted [here](https://stackoverflow.com/questions/62794236/matplotlib-pyplot-functions-creating-new-figures-instead-of-applyting-to-the-cur)), and also saving figures blank. I plotted a figure and saved it in the same line (separated by `;`) and it worked. Is this just a problem with Spyder? – TheSprinter Jul 10 '20 at 14:20

score 252 · Answer 2 · edited Jan 23 '20 at 08:53

252

plt.show() should come after plt.savefig()

Explanation: plt.show() clears the whole thing, so anything afterwards will happen on a new empty figure

edited Jan 23 '20 at 08:53

PV8

5,799
7
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answered Nov 17 '17 at 03:57

JAG2024

3,987
7
29
58

score 30 · Answer 3 · answered Aug 07 '19 at 16:04

30

change the order of the functions fixed the problem for me:

first Save the plot
then Show the plot

as following:

plt.savefig('heatmap.png')

plt.show()

answered Aug 07 '19 at 16:04

Behzad Sezari

728
8
11

score 7 · Answer 4 · edited Dec 30 '19 at 23:07

7

Calling savefig before show() worked for me.

fig ,ax = plt.subplots(figsize = (4,4))
sns.barplot(x='sex', y='tip', color='g', ax=ax,data=tips)
sns.barplot(x='sex', y='tip', color='b', ax=ax,data=tips)
ax.legend(['Male','Female'], facecolor='w')

plt.savefig('figure.png')
plt.show()

edited Dec 30 '19 at 23:07

Behzad Sezari

728
8
11

answered Dec 07 '19 at 07:30

Krish

131
2
3

score 3 · Answer 5 · answered Jul 20 '18 at 09:33

let's me give a more detail example:

import numpy as np
import matplotlib.pyplot as plt


def draw_result(lst_iter, lst_loss, lst_acc, title):
    plt.plot(lst_iter, lst_loss, '-b', label='loss')
    plt.plot(lst_iter, lst_acc, '-r', label='accuracy')

    plt.xlabel("n iteration")
    plt.legend(loc='upper left')
    plt.title(title)
    plt.savefig(title+".png")  # should before plt.show method

    plt.show()


def test_draw():
    lst_iter = range(100)
    lst_loss = [0.01 * i + 0.01 * i ** 2 for i in xrange(100)]
    # lst_loss = np.random.randn(1, 100).reshape((100, ))
    lst_acc = [0.01 * i - 0.01 * i ** 2 for i in xrange(100)]
    # lst_acc = np.random.randn(1, 100).reshape((100, ))
    draw_result(lst_iter, lst_loss, lst_acc, "sgd_method")


if __name__ == '__main__':
    test_draw()

Savefig outputs blank image

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