Webcam openCV error: (-215) ssize.width > 0 && ssize.height > 0 in function resize

Question

I've seen the other stack exchange posts about this exact same error, but instead of reading from an image or a list of images, my script reads from a webcam. BTW, this script is copied, and i'm trying to get it working as an example for me to learn how it all works.

import numpy as np
import cv2

# set up HOG person detector and create hog object
hog = cv2.HOGDescriptor()
hog.setSVMDetector(cv2.HOGDescriptor_getDefaultPeopleDetector())

cv2.startWindowThread()

# set up video capture, make cap video stream object
cap = cv2.VideoCapture(0)

# write file output to output.avi in 640x480 size
out = cv2.VideoWriter(
    'output.avi',
    cv2.VideoWriter_fourcc(*'MJPG'),
    15.,
    (640,480))
if cap is not None:
    while(True):
        # read the webcam
        ret, frame = cap.read()

        # resizing for faster detection
        frame = cv2.resize(frame, (640, 480))
        # using a greyscale picture, also for faster detection
        gray = cv2.cvtColor(frame, cv2.COLOR_RGB2GRAY)

        # detect people in the image
        # returns the bounding boxes for the detected objects
        boxes, weights = hog.detectMultiScale(frame, winStride=(8,8) )

        boxes = np.array([[x, y, x + w, y + h] for (x, y, w, h) in boxes])

        for (xA, yA, xB, yB) in boxes:
            # display the detected boxes in the colour picture
            cv2.rectangle(frame, (xA, yA), (xB, yB),
            (0, 255, 0), 2)

        # Write the output video 
        out.write(frame.astype('uint8'))
        # Display the resulting frame
        cv2.imshow('frame',frame)
        if cv2.waitKey(1) & 0xFF == ord('q'):
            break

    # When everything done, release the capture
    cap.release()
    # and release the output
    out.release()
    # finally, close the window
    cv2.destroyAllWindows()
    cv2.waitKey(1)

I understand that the error is caused because there is no image for the resize function to resize, so I added the if cap is not None: statement, but I still get the same error. How can I fix this in this script?

Answer 1

From what I've gathered from your post above, you don't want to use a webcame in any sort of capacity. If so, You might be experiencing some errors with this portion of the script

# set up video capture, make cap video stream object
cap = cv2.VideoCapture(0)

# write file output to output.avi in 640x480 size
out = cv2.VideoWriter(
'output.avi',
cv2.VideoWriter_fourcc(*'MJPG'),
15.,
(640,480))

Here you are setting up a video stream, then loading in an avi. If you just want to read in an image you can use the below code.

import numpy as np
import cv2

# Load an color image in grayscale
img = cv2.imread('inputImage.jpg',0)

#Display the input image
cv2.imshow('image',img)
cv2.waitKey(0)
cv2.destroyAllWindows()

You can find more about images and Opencv below.

https://opencv-python-tutroals.readthedocs.io/en/latest/py_tutorials/py_gui/py_image_display/py_image_display.html