Identify and Calculate Free Area in Vanning Slot Image Using OpenCV

I am working on a project where I need to identify and calculate the free area within a vanning slot in a warehouse. The vanning slot is marked with yellow color, and there are pallets occupying some of the space within this yellow-marked area.

I have already implemented a Python code using OpenCV to isolate the yellow color and extract the gray area covered by the yellow lines. The code is provided below:

    from PIL import Image    from IPython.display import display    # Replace 'your_image_path.jpg' with the actual path to your image file    image_path = 'C:/Users/CSR/Desktop/tracking_images/Half Vanning.jpg'    # Open the image file    img = Image.open(image_path)    # Display the image    display(img)    import cv2    import numpy as np    from PIL import Image    from IPython.display import display    # Load the image    image_path = 'C:/Users/CSR/Desktop/tracking_images/Half Vanning.jpg'    image = cv2.imread(image_path)    # Convert the image to grayscale    gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)    # Define the lower and upper bounds for the yellow color in HSV    lower_yellow = np.array([20, 100, 100], dtype=np.uint8)    upper_yellow = np.array([40, 255, 255], dtype=np.uint8)    # Convert the image to HSV color space    hsv = cv2.cvtColor(image, cv2.COLOR_BGR2HSV)    # Create a binary mask for the yellow color    yellow_mask = cv2.inRange(hsv, lower_yellow, upper_yellow)    # Apply a bitwise AND operation to extract the gray area covered by yellow lines    gray_area = cv2.bitwise_and(gray, gray, mask=yellow_mask)    # Save the result    output_path = 'C:/Users/CSR/Desktop/04-08-2023/bz.jpg'  # Change this to the desired output path    cv2.imwrite(output_path, gray_area)    print("Result image saved to:", output_path)    # Open the image file    img = Image.open(output_path)    # Display the image    display(img)

input imageMy output image

However, I am struggling to determine the free area within this yellow-marked vanning slot – the area not occupied by pallets. I would like to calculate and visualize this free space. Could you please provide guidance on how to achieve this? Specifically, how can I identify and calculate the unoccupied (free) area within the yellow-marked vanning slot?

sample imageexpected output