[Python] How do I go about the detection of this low contrast calibration checkerboard?

I'm trying to calibrate a camera. I have a very low-contrast image of a checkerboard. I've tried applying Contrast Limited Adaptive Histogram Equalization (CLAHE) to the image, but I'm still struggling to detect the checkerboard.

I've also tried Mrcal with no luck as well.

Here's the image of the checkerboard and the minimum reproducible example.



import cv2

pattern_size=(26, 20)

image = cv2.imread("denoised_image_checkboard_recentered.png")

image = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
clahe = cv2.createCLAHE(clipLimit=4, tileGridSize=(8,8))
image = clahe.apply(image)

flags = cv2.CALIB_CB_EXHAUSTIVE + cv2.CALIB_CB_ACCURACY
ret, corners = cv2.findChessboardCornersSB(image, pattern_size, flags=flags)
print(ret)
print("---")
print(corners)

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