CODEWITHSUNDEEP
pythonmatplotlib
ahelm
ahelm

Reputation: 702

Matplotlib: no effect of set_data in imshow for the plot

I have a strange error which I can't fix without your help. After I set an image with imshow in matplotlib it stays the same all the time even if I change it with the method set_data. Just take a look on this example:

import numpy as np
from matplotlib import pyplot as plt


def newevent(event):
    haha[1,1] += 1
    img.set_data(haha)
    print img.get_array()    # the data is change at this point
    plt.draw()

haha = np.zeros((2,2))
img = plt.imshow(haha)
print img.get_array()        # [[0,0],[0,0]]
plt.connect('button_press_event', newevent)
plt.show()

After I plot it, the method set_data doesn't change anything inside the plot. Can someone explain me why?

EDIT

Just added a few lines to point out what I actually want to do. I want to redraw the data after I press a mouse button. I don't want to delete the whole figure, because it would be stupid if only one thing changes.

Upvotes: 16

Views: 19489

Answers (2)

Redoubts
Redoubts

Reputation: 843

The problem is because you have not updated the pixel scaling after the first call.

When you instantiate imshow, it sets vmin and vmax from the initial data, and never touches it again. In your code, it sets both vmin and vmax to 0, since your data, haha = zeros((2,2)), is zero everywhere.

Your new event should include autoscaling with img.autoscale() , or explicitly set new scaling terms by setting img.norm.vmin/vmax to something you prefer.

The function to set the new vmin and vmax is:

img.set_clim(vmin=new_vim, vmax=new_vmax)

Upvotes: 25

Levon
Levon

Reputation: 143032

Does this give you the output you expect?

import numpy as np
from matplotlib import pyplot as plt

haha = np.zeros((2,2))
img = plt.imshow(haha)
print img.get_array()        # [[0,0],[0,0]]
haha[1,1] += 1

img.set_data(haha)    
img = plt.imshow(haha)       # <<------- added this line  
print img.get_array()        # [[0,0],[0,1]]
plt.show()

When I display the plot twice (once before the change to haha, and at the end), it does change.

Upvotes: 3

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