get_playfield_corners.py

 def get_playfield_corners(frame):
        """Identifies coordinates of the playfield corners from the frame.
        Parameters
        ----------
        frame : numpy.ndarray
            The frame read in by the VideoCapture
        Returns
        -------
        corners_coordinates : list
            List of coordinates of the identified playfield corners
        """

        corner_coordinates = []

        blurred_frame = cv2.GaussianBlur(frame, config.GAUSSIAN_BLUR_KERNEL_SIZE, 0)
        # Change to HSV colorspace for color thresholding
        hsv = cv2.cvtColor(blurred_frame, cv2.COLOR_BGR2HSV)

        # Split frame into two parts to analyze different colors and reduce noise
        [top, bottom] = np.split(hsv, 2, axis=0)

        # Color threshold masks (top of playfield has yellow corner markers and bottom of playfield has blue corner
        # markers)
        yellow_mask = cv2.inRange(top, np.array(config.CORNER_LOWER_YELLOW), np.array(config.CORNER_UPPER_YELLOW))
        blue_mask = cv2.inRange(bottom, np.array(config.CORNER_LOWER_BLUE), np.array(config.CORNER_UPPER_BLUE))
        # Combining masks to retrieve full frame mask
        mask = np.vstack((yellow_mask, blue_mask))

        # Extract targeted colors from original frame in grayscale
        extracted_colors = cv2.bitwise_and(blurred_frame, blurred_frame, mask=mask)
        extracted_colors_gray = cv2.cvtColor(extracted_colors, cv2.COLOR_BGR2GRAY)

        # Find contours in the image
        contours, _ = cv2.findContours(extracted_colors_gray, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)
        for c in contours:
            area = cv2.contourArea(c)
            perim = cv2.arcLength(c, True)
            approx = cv2.approxPolyDP(c, config.CONTOUR_APPROXIMATION_COEFFICIENT * perim, True)
            if config.CORNER_CONTOUR_AREA_MIN < area < config.CORNER_CONTOUR_AREA_MAX and len(approx) == 4:
                m = cv2.moments(c)
                x = int(m["m10"] / m["m00"])
                y = int(m["m01"] / m["m00"])
                corner_coordinates.append([x, y])

        return corner_coordinates