Question

I’m working on a program (python ,opencv) in which I use the spacebar to go to the next frame, and Esc to exit the program. These are the only two keys i’ve got working. I tried to find out about more keys , tried various codes for them but didnt work. especially arrow keys.

I found this about waitkey, but it doesn’t work.

So my question is, How do I catch other keys besides esc and spacebar to trigger certain functions in my python-opencv program?

Answer 1

You can use ord() function in Python for that.

For example, if you want to trigger ‘a’ key press, do as follows :

if cv2.waitKey(33) == ord('a'):
   print "pressed a"

See a sample code here: Drawing Histogram

UPDATE :

To find the key value for any key is to print the key value using a simple script as follows :

import cv2
img = cv2.imread('sof.jpg') # load a dummy image
while(1):
    cv2.imshow('img',img)
    k = cv2.waitKey(33)
    if k==27:    # Esc key to stop
        break
    elif k==-1:  # normally -1 returned,so don't print it
        continue
    else:
        print k # else print its value

With this code, I got following values :

Upkey : 2490368
DownKey : 2621440
LeftKey : 2424832
RightKey: 2555904
Space : 32
Delete : 3014656
...... # Continue yourself :)