How to remove convexity defects in a Sudoku square?

Question

I was doing a fun project: Solving a Sudoku from an input image using OpenCV (as in Google goggles etc). And I have completed the task, but at the end I found a little probl

Answer 1

To remove undected corners I applied gamma correction with a gamma value of 0.8.

The red circle is drawn to show the missing corner.

The code is:

gamma = 0.8
invGamma = 1/gamma
table = np.array([((i / 255.0) ** invGamma) * 255
                  for i in np.arange(0, 256)]).astype("uint8")
cv2.LUT(img, table, img)

This is in addition to Abid Rahman's answer if some corner points are missing.