ocrmypdf has built-in help.
Add an OCR layer and convert to PDF/A¶
ocrmypdf input.pdf output.pdf
Add an OCR layer and output a standard PDF¶
ocrmypdf --output-type pdf input.pdf output.pdf
Create a PDF/A with all color and grayscale images converted to JPEG¶
ocrmypdf --output-type pdfa --pdfa-image-compression jpeg input.pdf output.pdf
Modify a file in place¶
The file will only be overwritten if OCRmyPDF is successful.
ocrmypdf myfile.pdf myfile.pdf
Correct page rotation¶
OCR will attempt to automatic correct the rotation of each page. This can help fix a scanning job that contains a mix of landscape and portrait pages.
ocrmypdf --rotate-pages myfile.pdf myfile.pdf
You can increase (decrease) the parameter
--rotate-pages-threshold to make page rotation more (less) aggressive.
If the page is “just a little off horizontal”, like a crooked picture, then you want
--rotate-pages is for when the cardinal angle is wrong.
OCR languages other than English¶
By default OCRmyPDF assumes the document is English.
ocrmypdf -l fra LeParisien.pdf LeParisien.pdf ocrmypdf -l eng+fra Bilingual-English-French.pdf Bilingual-English-French.pdf
Language packs must be installed for all languages specified. See Installing additional language packs.
Produce PDF and text file containing OCR text¶
This produces a file named “output.pdf” and a companion text file named “output.txt”.
ocrmypdf --sidecar output.txt input.pdf output.pdf
OCR images, not PDFs¶
If you are starting with images, you can just use Tesseract 3.04 or later directly to convert images to PDFs:
tesseract my-image.jpg output-prefix pdf
# When there are multiple images tesseract text-file-containing-list-of-image-filenames.txt output-prefix pdf
Tesseract’s PDF output is quite good – OCRmyPDF uses it by internally by default. However, OCRmyPDF has many features not available in Tesseract like like image processing, metadata control, and PDF/A generation.
Use a program like img2pdf to convert your images to PDFs, and then pipe the results to run ocrmypdf. The - tells ocrmypdf to read standard input.
img2pdf my-images*.jpg | ocrmypdf - myfile.pdf
img2pdf is recommended because it does an excellent job at generating PDFs without transcoding images.
For convenience, OCRmyPDF can also convert single images to PDFs on its own. If the resolution (dots per inch, DPI) of an image is not set or is incorrect, it can be overridden with
--image-dpi. (As 1 inch is 2.54 cm, 1 dpi = 0.39 dpcm).
ocrmypdf --image-dpi 300 image.png myfile.pdf
If you have multiple images, you must use
img2pdf to convert the images to PDF.
convert can also convert a group of images to PDF, but in the author’s experience it takes a long time, transcodes unnecessarily and gives poor results.
OCRmyPDF perform some image processing on each page of a PDF, if desired. The same processing is applied to each page. It is suggested that the user review files after image processing as these commands might remove desirable content, especially from poor quality scans.
--rotate-pagesattempts to determine the correct orientation for each page and rotates the page if necessary.
--remove-backgroundattempts to detect and remove a noisy background from grayscale or color images. Monochrome images are ignored. This should not be used on documents that contain color photos as it may remove them.
--deskewwill correct pages were scanned at a skewed angle by rotating them back into place. Skew determination and correction is performed using Postl’s variance of line sums algorithm as implemented in Leptonica.
--cleanuses unpaper to clean up pages before OCR, but does not alter the final output. This makes it less likely that OCR will try to find text in background noise.
--clean-finaluses unpaper to clean up pages before OCR and inserts the page into the final output. You will want to review each page to ensure that unpaper did not remove something important.
In many cases image processing will rasterize PDF pages as images, potentially losing quality.
-remove-background may leave undesirable visual artifacts in some images where their algorithms have shortcomings. Files should be visually reviewed after using these options.
OCR and correct document skew (crooked scan)¶
ocrmypdf --deskew input.pdf output.pdf
Image processing commands can be combined. The order in which options are given does not matter. OCRmyPDF always applies the steps of the image processing pipeline in the same order (rotate, remove background, deskew, clean).
ocrmypdf --deskew --clean --rotate-pages input.pdf output.pdf
Don’t actually OCR my PDF¶
If you set
--tesseract-timeout 0 OCRmyPDF will apply its image processing without performing OCR, if all you want to is to apply image processing or PDF/A conversion.
ocrmypdf --tesseract-timeout=0 --remove-background input.pdf output.pdf
To redo OCR on a file OCRed with other OCR software or a previous version of OCRmyPDF and/or Tesseract, you may use the
--force-ocr argument. Normally, OCRmyPDF does not modify files that already appear to contain OCR text.
ocrmypdf --force-ocr input.pdf output.pdf
Note that the method above will force rasterization of all pages, potentially reducing quality or losing vector content.
To ensure quality is preserved, one could extract all of the images and rebuild the PDF for a lossless transformation. This recipe does not work when PDFs contain multiple images per page, as many do in practice. It will also lose any page rotation information.
pdfimages -all old-ocr.pdf prefix # extract all images img2pdf -o temp.pdf prefix* # construct new PDF from the images # review the new PDF to ensure it visually matches the old one ocrmypdf --output-type pdf temp.pdf new-ocr.pdf
--output-type pdf is used here to avoid using Ghostscript which will also rasterize images.
Improving OCR quality¶
The Image processing features can improve OCR quality.
Rotating pages and deskewing helps to ensure that the page orientation is correct before OCR begins. Removing the background and/or cleaning the page can also improve results. The
--oversample DPI argument can be specified to resample images to higher resolution before attempting OCR; this can improve results as well.
OCR quality will suffer if the resolution of input images is not correct (since the range of pixel sizes that will be checked for possible fonts will also be incorrect).