python cv2.error: Unknown C++ exception from OpenCV code

Question

I have this code:

class CamThread(threading.Thread):

    def __init__(self, previewname, camid):
        threading.Thread.__init__(self)
        self.previewname = previewname
        self.camid = camid

    def run(self):
        print("Starting " + self.previewname)
        previewcam(self.previewname, self.camid)

# Function to preview the camera.
def previewcam(previewname, camid):
    cv2.namedWindow(previewname)
    cam = cv2.VideoCapture(camid)
    if cam.isOpened():
        rval, frame = cam.read()
    else:
        rval = False

    while rval:
        cv2.imshow(previewname, frame)
        rval, frame = cam.read()
        key = cv2.waitKey(20)
        if key == 27:  # Press ESC to exit/close each window.
            break
    cv2.destroyWindow(previewname)

when I run my python file, I get this error:

    self.run()
  File "swann.py", line 17, in run
    previewcam(self.previewname, self.camid)
  File "swann.py", line 21, in previewcam
    cv2.namedWindow(previewname)
cv2.error: Unknown C++ exception from OpenCV code
Assertion failed: (NSViewIsCurrentlyBuildingLayerTreeForDisplay() != currentlyBuildingLayerTree), function NSViewSetCurrentlyBuildingLayerTreeForDisplay, file NSView.m, line 13477.
zsh: illegal hardware instruction

I've never used the cv2 package before, so I'm not sure if I am doing something wrong. Could someone help me out?

Looks like maybe cv2 was not installed for the right architecture - this thread is similar: https://stackoverflow.com/questions/65383338/zsh-illegal-hardware-instruction-python-when-installing-tensorflow-on-macbook — Jeppe, Oct 30 '22 at 21:38
@Jeppe thanks for sharing. I'm not on M1 Mac, so it shouldn't apply to me... — bobthebuilder, Oct 30 '22 at 21:41
@Jeppe incase your curious, downgrading the version of cv2 fixed it — bobthebuilder, Oct 30 '22 at 23:00
Ah okay! Consider writing an answer with the bad/good versions. — Jeppe, Oct 31 '22 at 06:14

score 0 · Answer 1 · answered Nov 19 '22 at 13:58

0

This is known issue, see here. This is macOS specific problem, when cv2 tries to interact with UI in newly spawned thread, it throws this error. Use UI interactions on main thread only.

answered Nov 19 '22 at 13:58

Petr Novota

1

python cv2.error: Unknown C++ exception from OpenCV code

1 Answers1