title: recognizing punctuation in tesseract OCR
body: <p>I am running tesseract to extract text from pdf files in a context where it is important to distinguish between semicolons and commas.  I find that semi-colons often show up as commas after OCR.  The accuracy is otherwise pretty good.  I am looking for suggestions on how to improve accuracy in semicolon versus comma detection.  Following <a href="https://electricarchaeology.ca/2014/07/15/doing-ocr-within-r/" rel="nofollow noreferrer">this</a> suggestion, my procedure is to first convert a multipage pdf file to a ppm file using pdftoppm from Xpdf, then convert that to tif using imagemagick, then run tesseract on the .tif file.  I have set the resolution of the ppm file to 1000 DPI and used the <code>-sharpen</code> option in imagemagick in an effort to improve resolution, but neither seems to improve the semi-colon recognition.  Any suggestions for pre-processing the image files or is this just an tough hill to climb?</p>
  
  <p>Edit: here are links to the original <a href="https://dl.dropboxusercontent.com/u/45922619/ocr/camp-01.pdf" rel="nofollow noreferrer">pdf</a>, the <a href="https://dl.dropboxusercontent.com/u/45922619/ocr/camp-01.ppm" rel="nofollow noreferrer">.ppm</a> and <a href="https://dl.dropboxusercontent.com/u/45922619/ocr/camp-01.tif" rel="nofollow noreferrer">.tif</a> files, and the <a href="https://dl.dropboxusercontent.com/u/45922619/ocr/camp-01.txt" rel="nofollow noreferrer">.txt</a> output.  Note that this is copyrighted material which I do not own. </p>