should i set picture resolution for tesseract?

[elige...@gmail.com]

Hi  Guys, 

        I have a task that convert pdf image into textual file.   

        The first thing i convert pdf to png by poppler-utils, it has better resolution than imagemagick. 

        The second thing, i specify the input png picture for tesseract to recognize words. But there are many errors. 

        I don't know whether different image formats influent ocr, tiff/png/jpeg?  Can tesseract automatically resize picture to the best resolution, for example zoom in upto 100%?

Regards,
Levin