I ‘m using Tesseract OCR engine in an iPhone application to read specific numeric fields from bill invoice photos.
Using a lot of photo pre-processing (adaptive thresholding, artifact cleaning, etc) the results are finally fairly accurate but there are still some cases I want to improve.
If the user takes a photo in low-light conditions and there is some noise or artifacts in the picture, the OCR engine interprets these artifacts as additional digits. In some rear cases it can read e.g. a numeric amount of “32,15” EUR as “5432,15” EUR and this is not at all good for the final user confidence in the product.
I assume that, if there is an internal OCR engine read-error associated to each character read, it will be higher on the “54” digits of my previous example as they are recognized over small noise-pixels, and if I had access to this reading-error values I will be able to easily discard the erroneous digits.
Do you know of any method to get a reading error magnitude (or any “accuracy factor” value) for each individual character returned from tesseract OCR engine?
It is called “confidence” value in Tesseract terminology. Search for that term in tesseract-ocr Group turned up many answers that mention about a TesserractExtractResult method.
The hOCR output also contains this value.