Handling user input from a keyboard
OpenCV has simple and clear way to handle input from a keyboard. This functionality is organically built into the cv2.waitKey function. Let's see how we can use it.
Getting ready
You need to have OpenCV 3.x installed with Python API support.
How to do it...
You will need to perform the following steps for this recipe:
- As done previously, open an image and get its width and height. Also, make a copy of the original image and define a simple function that returns a random point with coordinates inside our image:
import cv2, numpy as np, random
image = cv2.imread('../data/Lena.png')
w, h = image.shape[1], image.shape[0]
image_to_show = np.copy(image)
def rand_pt():
return (random.randrange(w),
random.randrange(h))- Now when the user presses P, L, R, E, or T draw points, lines, rectangles, ellipses, or text, respectively. Also, we will clear an image when the user hits C and closes the application when the Esc key is pushed:
finish = False
while not finish:
cv2.imshow("result", image_to_show)
key = cv2.waitKey(0)
if key == ord('p'):
for pt in [rand_pt() for _ in range(10)]:
cv2.circle(image_to_show, pt, 3, (255, 0, 0), -1)
elif key == ord('l'):
cv2.line(image_to_show, rand_pt(), rand_pt(), (0, 255, 0), 3)
elif key == ord('r'):
cv2.rectangle(image_to_show, rand_pt(), rand_pt(), (0, 0, 255), 3)
elif key == ord('e'):
cv2.ellipse(image_to_show, rand_pt(), rand_pt(), random.randrange(360), 0, 360, (255, 255, 0), 3)
elif key == ord('t'):
cv2.putText(image_to_show, 'OpenCV', rand_pt(), cv2.FONT_HERSHEY_SIMPLEX, 1, (0, 0, 0), 3)
elif key == ord('c'):
image_to_show = np.copy(image)
elif key == 27:
finish = TrueHow it works...
As you can see, we just analyze the waitKey() return value. If we set a duration and no key is pressed, waitKey() would return -1.
After launching the code and pressing the P, L, R, E, and T keys a few times, you will get an image close to the following:
