Show an updating image in just one window

Question

I want to show a jpg in a window which updates multiple times per second. I have coded a very very compact program with just 100 lines of code (a neural network which creates the image) and don't want to put in another 100 lines of code to just show the image. Is there anything I can do to solve this problem?

Many thx, jj

Just write the 100 lines and be done with it. That's why they invented modules. — Mark Ransom, Mar 13 '17 at 15:58
Take a look at the OpenCV library, it can update a jpg in a window very fast. — Martin Evans, Mar 13 '17 at 16:30
Do you have to load the jpgs? Or can you just use an already present numpy array? — mmensing, Mar 15 '17 at 14:53
@mmensing I use a numpy array which updates its values multiple times per second, and I want to show it (converted to an image) after every update to the user. — , Mar 17 '17 at 12:27

score 5 · Accepted Answer · answered Mar 17 '17 at 20:08

As it was stated in the comments that IO is not an issue, we shall go straight to the available standard image plot tools used in matplotlib, since it is the defacto standard plotting library for python. While not knowing the dimensions of typical images originating in neural networks, a quick comparison of the average time it would take to call e.g. imshow, pcolormesh and matshow for different image dimensions cannot hurt (pcolor is significantly slower, so it is omitted).

import matplotlib.pyplot as plt
import numpy as np
import timeit

n = 13
repeats = 20
timetable = np.zeros((4, n-1))
labellist = ['imshow', 'matshow', 'pcolormesh']

for i in range(1, n):
    image = np.random.rand(2**i, 2**i)
    print('image size:', 2**i)
    timetable[0, i - 1] = 2**i

    timetable[1, i - 1] = timeit.timeit("plt.imshow(image)", setup="from __main__ import plt, image", number=repeats)/repeats
    plt.close('all')
    timetable[2, i - 1] = timeit.timeit("plt.matshow(image)", setup="from __main__ import plt, image", number=repeats)/repeats
    plt.close('all')
    timetable[3, i - 1] = timeit.timeit("plt.pcolormesh(image)", setup="from __main__ import plt, image", number=repeats)/repeats
    plt.close('all')

for i in range(1, 4):
    plt.semilogy(timetable[0, :], timetable[i, :], label=labellist[i - 1])
    plt.legend()
    plt.xlabel('image size')
    plt.ylabel('avg. exec. time [s]')
    plt.ylim(1e-3, 1)

plt.show()

So, imshow it is. An elegant way to update or animate a plot in matplotlib is the animation framework it offers. That way one does not have to bother with many lines of code, as it was asked for. Here is a simple example:

import matplotlib.pyplot as plt
import numpy as np
import time
from matplotlib import animation

data = np.random.rand(128, 128)

fig = plt.figure()
ax = fig.add_subplot(1,1,1)

im = ax.imshow(data, animated=True)

def update_image(i):
    data = np.random.rand(128, 128)
    im.set_array(data)
    # time.sleep(.5)
    # plt.pause(0.5)
ani = animation.FuncAnimation(fig, update_image, interval=0)

plt.show()

In this example the neural network would be called out of the update function. The update behaviour under heavy computational work can be emulated by time.sleep. If your application is multi-threaded plt.pause might come in handy to give the other threads time to do their work. interval=0 basically makes the plot update as often as possible.

I hope this points you in the general direction and is helpful. If you do not want to utilize animations, canvas clearing and/or blitting need to be taken care of manually.

This doesn't work, `plt.show()` blocks the thread and then nothing happens. — Raphael Royer-Rivard, Jul 04 '18 at 20:19
Sorry for the late acceptance, I jus wanted to buy cigs quickly — , Jul 11 '18 at 12:22

Show an updating image in just one window

1 Answers1