OCRmyPDF/ROADMAP.md

Recoding in 5 python modules

• Less platform dependent implementation
• Higher versality (wrt addition of new intput / output file tytes)

The functionality of each module is described below:

Normalize inputs (inputs can be a pdf file, an image, a folder containing images)

• For pdf:
  • Identify if image already contains fonts
  • If the page needs to be OCRed:
    • Extract the image corresponding to the page and save it in a tmp folder. 3 approaches to extract images:
    • extract raw image from pdf and rotate it according to pdf page rotation
      • if not possible: identify resolution and rasterize
      • if not possible: use default resolution and rasterize
  • If not:
    • Save the page AS-IS in the tmp folder that should contained the final page
• For image(s):
  • Just copy the images with standardized name into the tmp folder containing pages to be OCRed

Preprocess normalized inputs (perform jobs in parallel)

• Orientation (if requested by user)
  • Correct orientation
• Skew angle (if requested by user)
  • Correct skew angle
• Cleaning (if requested by user)
  • Clean image

Perform OCR (perform jobs in parallel)

• Perform OCR and save resulting hocr file for each respective page (perfom jobs in parallel)

Generate output for each page

• For pdf (if output file has a "pdf" extension):
  • Generate pdf pages from hocr files (note: pdf pages can already exist if OCR has been skipped for them)

Build final output

• For pdf:
  • Concatenate pdf pages
  • Converte to pdf/1-a
  • Verify conformity to pdf/1-a

Tmp folder structure

• tmp_xxxxx/
  • a_raw_images (either from images or extracted from pdf file)
  • b_preprocessed_images (after deswing anf cleaning)
  • c_ocr_out
  • d_output_pages (one file per page (at first 1 pdf file per page. Later on other formats might be supported)
  • e_output_final (concatenate output pages and conversion into PDF/1-a standard, Later on support other formats)

ocrmypdf arguments

• Overall parameters
  • [-h] : Display this help message
  • [-v] : Increase the verbosity (this option can be used more than once) (e.g. -vvv)
  • [-k] : Do not delete the temporary files
  • [-g] : Activate debug mode (max verbosity, keep tmp files, generate debug pages)
• Nomalization parameters:
  • [-o dpi] : If page resolution is lower x dpi, provide OCR engine with an oversampled image. (Can improve OCR results)
  • [-f] : Force to OCR the whole document, even if some page already contain font data
  • [-s] : If pages contain font data, do not OCR that page, but include the page (as is) in the final output.
• Prepocessing parameters:
  • [-r] : Correct orientation before performing OCR
  • [-d] : Deskew each page before performing OCR
  • [-c] : Clean each page before performing OCR
  • [-i] : Incorporate cleaned image in final output
• OCR parameters:
  • [-l lan1[+lan2...] : Document language(s). Multiple languages may be specified, separated by '+' characters.
  • [-C cfg] : Pass an additional cofg file to the tesseract OCR engine. (this option can be used more than once)
• output generation parameters:
  • None by now
• input files:
  • inputpath : path to image, pdf file or folder to be processed
• output files:
  • outputfile1 [outputfile2 ...] : *.pdf file or *.txt file to be generated (this argumente can be repeated if both pdf and txt file should be generated