Matplotlib (pyplot) 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)

Asked By: tylerthemiler

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Source

Answer 1

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 By: Yann

Answer 2

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

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

Answered By: JAG2024

Answer 3

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()

Answered By: Jayhello

Answer 4

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 By: Behzad Sezari

Answer 5

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()

Answered By: Krish

Matplotlib (pyplot) savefig outputs blank image

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