Hi, moster67
Thank you for your response.
Yes, I am aware OpenCV and also Tesseract. From what I had learned, OpenCV and Tesseract can be complimentary in text detection: OpenCV does pre-processing to an image and hands off the result to Tesseract for text recognition. Google Play Service Vision offers simpler usage and without increasing app size cause the API is built in Google Play Services. The speed and detection result are good. Whenever pre-processing is needed I can just let the camera app in the phone to do that; so far I've never had a need to do that. Perhaps, Google Play Service Vision is just OpenCV + Tesseract. I don't know.
Thanks,