Interactively plot image mean over time in matplotlib

Question

I have been trying to make a small tool to plot the mean of a region of a stack of images dynamically using matplotlib in Python. I have used the rectangle selector widget, similar to that used in Persistent rectangle selector

here is the code:

fig, (ax1,ax2) = plt.subplots(2)
ax1.imshow(im[:100].mean(axis=0))
line, =ax2.plot(im.mean(axis=1).mean(axis=1))

def line_select_callback(eclick, erelease):
    global x1, y1 , x2, y2
    'eclick and erelease are the press and release events'
    x1, y1 = eclick.xdata, eclick.ydata
    x2, y2 = erelease.xdata, erelease.ydata
    print("(%3.2f, %3.2f) --> (%3.2f, %3.2f)" % (x1, y1, x2, y2))
    print(" The button you used were: %s %s" % (eclick.button, erelease.button))
    verts=np.array([x1, y1, x2, y2],np.uint16)
    prof=im[:,verts[1]:verts[3],verts[0]:verts[2]].mean(axis=1).mean(axis=1)
    ax2.plot(prof)
    ax2.draw()


def toggle_selector(event):
    global returned
    print(' Key pressed.')
    if event.key in ['Q', 'q'] and toggle_selector.RS.active:
        print(' RectangleSelector deactivated.')
        toggle_selector.RS.set_active(False)
    if event.key in ['A', 'a'] and not toggle_selector.RS.active:
        print(' RectangleSelector activated.')
        toggle_selector.RS.set_active(True)
    if event.key in ['Y', 'y'] and not toggle_selector.RS.active:
        returned=True

plt.connect('key_press_event', toggle_selector)

toggle_selector.RS = RectangleSelector(ax1, line_select_callback,
                                           drawtype='box', useblit=True,
                                           button=[1, 3],  # don't use middle button
                                           minspanx=5, minspany=5,
                                           spancoords='pixels',
                                           interactive=True)
fig.show()

I have 2 issues with this: 1) the plot doesn't automatically update when i release my mouse drag 2) The rectangle selector tool seems to stick to my mouse even when I release my left mouse button.

score 0 · Answer 1 · answered Jul 14 '17 at 21:58

It's not entirely clear in which environment this is supposed to work. So assuming you are running this as a script, you would show the figure with plt.show() and draw the updates with fig.canvas.draw_idle().

import matplotlib.pyplot as plt
from matplotlib.widgets import RectangleSelector
import numpy as np

im = np.random.rand(100,100)
fig, (ax1,ax2) = plt.subplots(2, gridspec_kw=dict(height_ratios=[5,1]))
ax1.imshow(im, cmap="summer")
line, =ax2.plot(im.mean(axis=1))

def line_select_callback(eclick, erelease):
    global x1, y1 , x2, y2
    'eclick and erelease are the press and release events'
    x1, y1 = eclick.xdata, eclick.ydata
    x2, y2 = erelease.xdata, erelease.ydata
    print("(%3.2f, %3.2f) --> (%3.2f, %3.2f)" % (x1, y1, x2, y2))
    print(" The button you used were: %s %s" % (eclick.button, erelease.button))
    verts=np.array([x1, y1, x2, y2],np.uint16)
    prof=im[verts[1]:verts[3],verts[0]:verts[2]].mean(axis=1)
    line.set_data(np.arange(int(min(y1,y2)), int(max(y1,y2))), prof)
    fig.canvas.draw_idle()


def toggle_selector(event):
    global returned
    print(' Key pressed.')
    if event.key in ['Q', 'q'] and toggle_selector.RS.active:
        print(' RectangleSelector deactivated.')
        toggle_selector.RS.set_active(False)
    if event.key in ['A', 'a'] and not toggle_selector.RS.active:
        print(' RectangleSelector activated.')
        toggle_selector.RS.set_active(True)
    if event.key in ['Y', 'y'] and not toggle_selector.RS.active:
        returned=True

plt.connect('key_press_event', toggle_selector)

toggle_selector.RS = RectangleSelector(ax1, line_select_callback,
                                           drawtype='box', useblit=True,
                                           button=[1, 3],  # don't use middle button
                                           minspanx=5, minspany=5,
                                           spancoords='pixels',
                                           interactive=True)
plt.show()

Interactively plot image mean over time in matplotlib

1 Answers1