Cookbook

Basic examples

Help!

ocrmypdf has built-in help.

ocrmypdf --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 --deskew. --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 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.

Note

ImageMagick 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.

Image processing

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-pages attempts to determine the correct orientation for each page and rotates the page if necessary.
  • --remove-background attempts 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.
  • --deskew will 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.
  • --clean uses 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-final uses 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.
  • -mask-barcodes will “cover up” any barcodes detected in the image of a page. Barcodes are known to confuse Tesseract OCR and interfere with the recognition of text on the same baseline as a barcode. The output file will contain the unaltered image of the barcode.

Note

In many cases image processing will rasterize PDF pages as images, potentially losing quality.

Warning

--clean-final and -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)

Deskew:

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

Redo existing OCR

To redo OCR on a file OCRed with other OCR software or a previous version of OCRmyPDF and/or Tesseract, you may use the --redo-ocr argument. (Normally, OCRmyPDF will exit with an error if asked to modify a file with OCR.)

This may be helpful for users who want to take advantage of accuracy improvements in Tesseract 4.0 for files they previously OCRed with an earlier version of Tesseract and OCRmyPDF.

ocrmypdf --redo-ocr input.pdf output.pdf

This method will replace OCR without rasterizing, reducing quality or removing vector content. If a file contains a mix of pure digital text and OCR, digital text will be ignored and OCR will be replaced. As such this mode is incompatible with image processing options, since they alter the appearance of the file.

In some cases, existing OCR cannot be detected or replaced. Files produced by OCRmyPDF v2.2 or earlier, for example, are internally represented as having visible text with an opaque image drawn on top. This situation cannot be detected.

If --redo-ocr does not work, you can use --force-ocr, which will force rasterization of all pages, potentially reducing quality or losing vector content.

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).

PDF optimization

By default OCRmyPDF will attempt to perform lossless optimizations on the images inside PDFs after OCR is complete. Optimization is performed even if no OCR text is found.

The --optimize N (short form -O) argument controls optimization, where N ranges from 0 to 3. --optimize 0 disables optimizations. 1 enables lossless optimizations that can be performed safely with no quality loss. 2 enables lossy optimizations such as image color quantizations. 3 enables more aggressive optimizations and targets a lower JPEG quality.

Optimization is improved when a JBIG2 encoder is available and when pngquant is installed. If either of these components are missing, then some types of images will not be optimized.

Currently optimization attempts to find more efficient encodings for images. The types of optimization available may expand over time. By default, OCRmyPDF compresses data streams inside PDFs, and will change inefficient encodings to more modern versions. A program like qpdf can be used to change encodings, e.g. to inspect the internals fo a PDF.

ocrmypdf --optimize 3 in.pdf out.pdf  # Make it small

Some users may consider enabling lossy JBIG2. See: Lossy mode JBIG2.