A filter that performs optical character recognition on video frames.

ocr.Recognize(clip clip[, string datapath="", string language="", string[] options])

This function runs Tesseract on each video frame and adds the following properties:

The OCR result as UTF-8 string.
Confidence value for each recognized word as an array of integers in range 0-100. The number of confidence values should correspond to the number of space-delimited words in OCRString.


Clip to be processed. Must be grayscale with 8 bits per sample.
Path containing Tesseract’s data files. Must have a trailing slash. Uses Tesseract’s default data path if unset.
An ISO 639-3 language string. Uses Tesseract’s default language if unset (usually eng). The language may be a string of the form [~]<lang>[+[~]<lang>]*, indicating that multiple languages are to be loaded. E.g. hin+eng will load Hindi and English. Languages may specify internally that they want to be loaded with one or more other languages, so the ~ sign is available to override that. E.g. if hin were set to load eng by default, then hin+~eng would force loading only hin. The number of loaded languages is limited only by memory, with the caveat that loading additional languages will impact both speed and accuracy, as there is more work to do to decide on the applicable language, and there is more chance of hallucinating incorrect words.

Options to be passed to Tesseract, as a list of (key, value) pairs. Available options are documented in tesseractclass.h of Tesseract’s source code.


Tesseract is not completely thread-safe. Changing any of the options starting with classify or textord will change them for all instances of this filter.


ret = core.ocr.Recognize(src, language="eng", options=["tessedit_char_whitelist", "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ.:;,-!?\"'"])


This only really works on frames that contain nothing but text, so make sure to filter the input appropriately if this is not the case.