Having problem with digits recognition in python using opencv, tesseract

Question

I'm trying crop an image using opencv and then let tesseract read it, but even the image is quite clear it is not able to recognize numbers out of that image, here are lines of code for the action:

screen_img = cv2.imread(f'data\\screenshot\\{e_name}.png')
crop_img = screen_img[350:385,185:270]
crop_img = cv2.cvtColor(crop_img,cv2.COLOR_BGR2GRAY)
cv2.imwrite(f'data\\screenshot{e_name}.png',crop_img)
cv2.imshow('ad',crop_img)
cv2.waitKey(0)
text = pytesseract.image_to_string(crop_img)
print(text)

The output of cv2.imshow('ad',crop_img) look something like this:

But the output of print(text) is nothing other a new blank line in the console.

I really appreciate for your help (I may making silly mistake since i'm not a professional programmer, then i'm sorry about that).

EDIT1: I've added a few line thanks to the comments:

screen_img = cv2.imread(f'data\\screenshot\\{e_name}.png')
crop_img = screen_img[350:385,185:270]
crop_img = cv2.cvtColor(crop_img,cv2.COLOR_BGR2GRAY)
crop_img = cv2.bitwise_not(crop_img)
ret, thresh1 = cv2.threshold(crop_img, 120, 255, cv2.THRESH_BINARY + cv2.THRESH_OTSU)
cv2.imshow('ad',thresh1)
cv2.waitKey(0)
text = pytesseract.image_to_string(thresh1)

The output now look much more promising:

But the result seem to remain the same,i've check some random text image from the internet and most of them work just fine.

Apply inverse binary threshold (Otsu), to make sure the text is in black — Jeru Luke
– Jeru Luke, Commented May 17, 2022 at 10:51
Tesseract needs black text on white background. Invert the image before passing it to the OCR engine. — stateMachine
– stateMachine, Commented May 17, 2022 at 11:27

Rotem · Accepted Answer · 2022-05-17 21:11:32Z

4

A magic happens when adding config='--psm 6'.

According to Tesseract OCR options page:

6 Assume a single uniform block of text.

Code sample:

crop_img = cv2.imread('crop_img.png')
text = pytesseract.image_to_string(crop_img, config='--psm 6')
print(text)

Result:
73.9

answered May 17, 2022 at 21:11

Rotem

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