ocr image cleansing with python opencv

Question

I'm currently learning about computer vision OCR. I have an image that needs to be scan. I face a problem during the image cleansing.

I use opencv2 in python to do the things. This is the original image:

image = cv2.imread(image_path)
cv2.imshow("imageWindow", image)

I want to cleans the above image, the number at the middle (64) is the area I wanted to scan. However, the number got cleaned as well.

image[np.where((image > [0,0,105]).all(axis=2))] = [255,255,255]
cv2.imshow("imageWindow", image)

What should I do to correct the cleansing here? I wanted to make the screen where the number 64 located is cleansed coz I will perform OCR scan afterwards.

Please help, thank you in advance.

Answer 1

What you're trying to do is called "thresholding". Looks like your technique is recoloring pixels that fall below a certain threshold, but the LCD digit darkness varies enough in that image to throw it off.

I'd spend some time reading about thresholding, here's a good starting place: Thresholding in OpenCV with Python . You're probably going to need an adaptive technique (like Adaptive Gaussian Thresholding), but you may find other ways that work for your images.