What image processing operation should I use to remove fuzzy black area
You can perform local averaging/blurring of the picture and then use a threshold to remove all areas that are too dark:
img = cv2.imread('k1aqp.png')
figure(figsize=(20,20))
subplot(2,2,1);
imshow(img)

subplot(2,2,2);
B = cv2.blur(img, (55,55), 0)
imshow(B)

subplot(2,2,3)
mask = B &gt; 150
imshow(mask)

subplot(2,2,4)
img2 = img.copy()
img2[~mask] = 255
imshow(img2)


you need to play around with the blur size and the threshold. But in general, this is one way to go.