Find contours of a square table (matrix shape) in an image using Python OpenCV

Question

I am new and I wonder how can I find the contours of the image like the below with Python OpenCV (cv2 library):

I am going to fill in each square a number and then convert it into numpy array, so I think I need to figure out how to get the contours of each square in the matrix first (maybe the coordinates of the square in the picture)

I try to use some code snippet:

img = cv2.imread(img_path, 1)

gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)

binary = cv2.bitwise_not(gray)

contours, hierarchy = cv2.findContours(binary, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_NONE)

for contour in contours:
    (x, y, w, h) = cv2.boundingRect(contour)
    cv2.rectangle(img, (x, y), (x + w, y + h), (0, 255, 0), 2)

But it doesn't work

Answer 1

Try this:

img = cv2.imread(img_path, 1)
gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
gauss = cv2.adaptiveThreshold(gray,255,cv2.ADAPTIVE_THRESH_GAUSSIAN_C, cv2.THRESH_BINARY, 3, 0)
ret,thresh = cv2.threshold(gauss,0,255,cv2.THRESH_BINARY|cv2.THRESH_OTSU)
rev=255-thresh

_ ,contours, hierarchy = cv2.findContours(thresh, cv2.RETR_LIST ,cv2.CHAIN_APPROX_SIMPLE)
print(contours)
min_rect_len = 15
max_rect_len = 20

for contour in contours:
    (x, y, w, h) = cv2.boundingRect(contour)
    if h>min_rect_len and w>min_rect_len:
        cv2.rectangle(img, (x, y), (x + w, y + h), (255, 0, 0), 1)
cv2.imwrite(img_path[:-4] + "_with_contours.jpg", img)

It produces the following image for the given image :

Answer 2

Maybe using hough line would do the job : -> check here

Regards