python - pytesseract can't read dot-punched numbers

Question

I am trying to use pytesseract to read images like this:

I thought that should be rather easy, but I can't get it to work so far. I tried different sorts of preprocessing but it doesn't work:

image = cv2.imread('number.png')
custom_config = r'-c tessedit_char_whitelist=0123456789 --psm 10'

text_i = pytesseract.image_to_string(img, config=custom_config)
gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
text_g = pytesseract.image_to_string(img, config=custom_config)
thresh = cv2.threshold(image, 50, 255, cv2.THRESH_BINARY)[1]
text_t = pytesseract.image_to_string(img, config=custom_config)

plt.axis('off')
plt.imshow(image)
plt.show()
print("Recognized number: ", text_i)

plt.axis('off')
plt.imshow(gray)
plt.show()
print("Recognized number: ", text_g)

plt.axis('off')
plt.imshow(thresh)
plt.show()
print("Recognized number: ", text_t)

In all cases, the returned string is empty. Does anyone have an idea, what to do?

Answer 1

Using erode was the key to success. My script looks now as follows:

# Load image
img = cv2.imread('number.png')
img = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
plt.axis('off')
plt.imshow(img, cmap='gray')
plt.show()

# Set number pool
pool = [31138796, 31130796]

# Set time limit
time_limit = 3

# Set config for pytesseract
custom_config = r'-c tessedit_char_whitelist=0123456789 --psm 10'

while True:
    start = time.time()
    # Iterate over kernel sizes for erode
    for k_erode in range(10, 1, -1):
        # Iterate over thresholds
        for thresh in range(20, 81, 10):
            
            # Check if time limit is exceeded
            if time.time() > start + time_limit:
                print("Time limit exceeded. Make a better picture! ;)")
                break
                
            # Preprocess image
            img_erode = cv2.erode(img, np.ones((k_erode, k_erode), dtype=np.uint8), 1)
            img_out = cv2.threshold(img_erode, thresh, 255, cv2.THRESH_BINARY)[1]
            number = pytesseract.image_to_string(img_out, config=custom_config)
            if number == 'x0c':
                continue
                
            # Check if number is in pool
            if int(number) in pool:
                print("The number is:", str(number))
                print("Is this your number? (y/n)")
                time_curr1 = time.time()
                answer = input()
                time_curr2 = time.time()
                time_limit += time_curr2 - time_curr1
                if answer == "y":
                    plt.axis('off')
                    plt.imshow(img_out, cmap='gray')
                    plt.show()
                    break
                else:
                    pool.remove(int(number))
                    continue
        else:
            continue
        break
    break