Refresh image in Tkinter window

Question

I am building an application to continuously display an image fetched from an IP camera. I have figured out how to fetch the image, and how to also display the image using Tkinter. But I cannot get it to continuously refresh the image. Using Python 2.7+.

Here is the code I have so far.

import urllib2, base64
from PIL import Image,ImageTk
import StringIO
import Tkinter

URL = 'http://myurl.cgi'
USERNAME = 'myusername'
PASSWORD = 'mypassword'

def fetch_image(url,username,password):
    # this code works fine
    request = urllib2.Request(url)
    base64string = base64.encodestring('%s:%s' % (username, password)).replace('\n', '')
    request.add_header("Authorization", "Basic %s" % base64string)   
    result = urllib2.urlopen(request)
    imgresp = result.read()
    img = Image.open(StringIO.StringIO(imgresp))
    return img

root = Tkinter.Tk()
img = fetch_image(URL,USERNAME,PASSWORD)
tkimg = ImageTk.PhotoImage(img)
Tkinter.Label(root,image=tkimg).pack()
root.mainloop()

How should I edit the code so that the fetch_image is called repeatedly and its output updated in the Tkinter window?

Note that I am not using any button-events to trigger the image refresh, rather it should be refreshed automatically, say, every 1 second.

Answer 1

Here is a solution that uses Tkinter's Tk.after function, which schedules future calls to functions. If you replace everything after your fetch_image definition with the snipped below, you'll get the behavior you described:

root = Tkinter.Tk()
label = Tkinter.Label(root)
label.pack()
img = None
tkimg = [None]  # This, or something like it, is necessary because if you do not keep a reference to PhotoImage instances, they get garbage collected.

delay = 500   # in milliseconds
def loopCapture():
    print "capturing"
#    img = fetch_image(URL,USERNAME,PASSWORD)
    img = Image.new('1', (100, 100), 0)
    tkimg[0] = ImageTk.PhotoImage(img)
    label.config(image=tkimg[0])
    root.update_idletasks()
    root.after(delay, loopCapture)

loopCapture()
root.mainloop()