How to select ROI in video input in OpenCV (Python)?

Question

I'm working on sign language recognition (hand gestures) using OpenCV. I want to select a particular region (ROI) as input from the entire frame and give it to the model. Right now, I'm able to do the same with the entire frame but can't have ROI. This is the code I've tried so far :

_, image_frame = cam_capture.read()

r = cv2.rectangle(image_frame, upper_left, bottom_right, (100, 50, 200), 5)
rect_img = image_frame[upper_left[1] : bottom_right[1], upper_left[0] : bottom_right[0]]

sketcher_rect = rect_img
sketcher_rect = sketch_transform(sketcher_rect)



cv2.resize(sketcher_rect, (28,28), interpolation = cv2.INTER_AREA)
pred_probab, pred_class = keras_predict(model, sketcher_rect)
print(pred_class, pred_probab)
cv2.imshow('image_frame',sketcher_rect)

Any help ?

Answer 1

If I understand you correctly you simply want to cut a region from the image right? This should work:

def crop_image(image, x, y, width, height):
    """
    image: a cv2 frame
    x, y, width, height: the region to cut out
    """
    return image[y:y + height, x:x + width]

Remember that cv2 images are simply numpy arrays. Cutting a region of the image is the same as extracting the indexes from the array.