how do I redraw an image using python's matplotlib?

Question

What I am trying to do seems to be fairly straightforward, but I'm having a heck of a time trying to get it to work. I am simply trying to draw an image using imshow and then re-draw it periodically as new data arrives.

I've started out with this:

fig = figure()
ax = plt.axes(xlim=(0,200),ylim=(0,200))
myimg = ax.imshow(zeros((200,200),float))

Then I'm assuming I can call set_data like this to update the image:

myimg.set_data(newdata)

I've tried many other things, for example I've called ax.imshow(newdata) instead or I've tried using figure.show() after set_data().

user2660966 · Accepted Answer · 2019-09-16 10:37:59Z

15

You can simply call figure.canvas.draw() each time you append something new to the figure. This will refresh the plot.

from matplotlib import pyplot as plt
from builtins import input

fig = plt.figure()
ax = fig.gca()
fig.show()

block = False
for i in range(10):
    ax.plot(i, i, 'ko')
    fig.canvas.draw()
    if block: 
        input('pause : press any key ...')
    else:
        plt.pause(0.1)
plt.close(fig)

edited Sep 16, 2019 at 10:37

answered Jan 5, 2014 at 18:29

user2660966

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4 Comments

kjgregory Over a year ago

This got me a step closer. When I run your code above, it opens a figure at the start of execution and draws the final plot only at the end of execution (rather than having a dot appear each time I hit return). I'm running python 2.7 in spider on windows 7, if that's of any consequence.

user2660966 Over a year ago

I don't know. I have tested it on both linux and windows7 and it works. This could maybe come from your version of matplotlib. I believe that the syntax may change between different versions. I am using matplotlib 1.2.0

kjgregory Over a year ago

I found out that if you do a plt.pause() in there, it gives the figure a chance to redraw before continuing execution. Other methods of inserting a wait don't do this.

brandon Feb 5 at 19:41

Is there a "pause until drawing everything"? 0.1 is way too long, and not long enough, depending on the plot. The canvas methods don't seem to wait for everything.

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