CODEWITHSUNDEEP
pythonnumpymatplotlib
Basj
Basj

Reputation: 46493

Overlay of two imshow plots on top of each other, with a slider to change the opacity of the layer

The code below works to overlay two imshow plots, and to create a slider which changes the value of the global variable OPACITY.

Unfortunately, img1.set_data(y); fig.canvas.draw_idle() doesn't redraw the new opacity.

How to make an overlay of two imshow plots with a slider to change the opacity of the 2nd layer?

enter image description here

import numpy as np, matplotlib.pyplot as plt, matplotlib.widgets as mpwidgets

OPACITY = 0.5

x = np.random.random((100, 50))
y = np.linspace(0, 0.1, 100*50).reshape((100, 50))

# PLOT
fig, (ax0, ax1) = plt.subplots(2, 1, gridspec_kw={'height_ratios': [5, 1]})
img0 = ax0.imshow(x, cmap="jet")
img1 = ax0.imshow(y, cmap="jet", alpha=OPACITY)

def update(value): 
    global OPACITY
    OPACITY = value
    print(OPACITY)
    img1.set_data(y)
    fig.canvas.draw_idle()

slider0 = mpwidgets.Slider(ax=ax1, label='opacity', valmin=0, valmax=1, valinit=OPACITY)
slider0.on_changed(update)

plt.show()

Upvotes: 4

Views: 1362

Answers (2)

Basj
Basj

Reputation: 46493

Based on the accepted answer and the answer from Overlay of two layers of different shapes with Matplotlib, here is a full example with opacity slider + plots of different shapes:

import numpy as np, matplotlib.pyplot as plt, matplotlib.widgets as mpwidgets, scipy.misc
x = scipy.misc.face(gray=False)     # shape (768, 1024, 3)
y = np.random.random((100, 133))    # shape (100, 133)
fig, (ax0, ax1) = plt.subplots(2, 1, gridspec_kw={'height_ratios': [5, 1]})
OPACITY = 0.5
img0 = ax0.imshow(x, cmap="jet")
img1 = ax0.imshow(y, cmap="jet", alpha=OPACITY, extent=img0.get_extent())
slider0 = mpwidgets.Slider(ax=ax1, label='opacity', valmin=0, valmax=1, valinit=OPACITY)
slider0.on_changed(lambda value: img1.set_alpha(value))
plt.show()

Upvotes: 0

MagnusO_O
MagnusO_O

Reputation: 1283

You can re-set the opacity of the overlaying img1 within the update function by img1.set_alpha():

enter image description here

enter image description here

Code:

import numpy as np, matplotlib.pyplot as plt, matplotlib.widgets as mpwidgets

OPACITY = 0.5

x = np.random.random((100, 50))
y = np.linspace(0, 0.1, 100*50).reshape((100, 50))

# PLOT
fig, (ax0, ax1) = plt.subplots(2, 1, gridspec_kw={'height_ratios': [5, 1]})
img0 = ax0.imshow(x, cmap="jet")
img1 = ax0.imshow(y, cmap="jet", alpha=OPACITY)


def update(value): 
    img1.set_alpha(value)    
    fig.canvas.draw_idle()

slider0 = mpwidgets.Slider(ax=ax1, label='opacity', valmin=0, valmax=1, valinit=OPACITY)
slider0.on_changed(update)

plt.show()

Upvotes: 2

Related Questions