Limit characters tesseract is looking for

Question

Is it possible to limit the set of characters that tesseract is looking for (e.g. search only for letters a-z)? That would improve my results greatly.

Answer 1

Create a config file (e.g "letters") in tessdata/configs directory - usually /usr/share/tesseract/tessdata/configs
or
/usr/share/tesseract-ocr/tessdata/configs

And add this line to the config file:

tessedit_char_whitelist abcdefghijklmnopqrstuvwxyz 

...or maybe [a-z] works. I don't know. Then call tesseract similar to this:

tesseract input.tif output nobatch letters   

That will limit tesseract to recognize only the wanted characters.