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
to make page rotation more (less) aggressive. The threshold number is the ratio
of how confidence the OCR engine is that the document image should be changed,
compared to kept the same. The default value is quite conservative; on some files
it may not attempt rotations at all unless it is very confident that the current
rotation is wrong. A lower value of
2.0 will produce more rotations, and
more false positives. Run with
-v1 to see the confidence level for each
page to see if there may be a better value for your files.
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¶
OCRmyPDF assumes the document is in English unless told otherwise. OCR quality may be poor if the wrong language is used.
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.
Unfortunately, the Tesseract OCR engine has no ability to detect the language when it is unknown.
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
The sidecar file contains the OCR text found by OCRmyPDF. If the document
contains pages that already have text, that text will not appear in the
sidecar. If the option
--pages is used, only those pages on which OCR
was performed will be included in the sidecar. If certain pages were skipped
because of options like
--tesseract-timeout, those pages
will not be in the sidecar.
To extract all text from a PDF, whether generated from OCR or otherwise,
use a program like Poppler’s
OCR images, not PDFs¶
Option: use Tesseract¶
If you are starting with images, you can just use Tesseract 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, in some cases. However, OCRmyPDF has many features not available in Tesseract like image processing, metadata control, and PDF/A generation.
Option: use img2pdf¶
You can also 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.
Option: use OCRmyPDF (single images only)¶
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.
We caution against using ImageMagick or Ghostscript to convert images to PDF, since they may transcode images or produce downsampled images, sometimes without warning.
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
Example: 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
Optimize images without performing OCR¶
You can also optimize all images without performing any OCR:
ocrmypdf --tesseract-timeout=0 --optimize 3 --skip-text input.pdf output.pdf
Perform OCR only certain pages¶
You can ask OCRmyPDF to only apply OCR to certain pages.
ocrmypdf --pages 2,3,13-17 input.pdf output.pdf
Hyphens denote a range of pages and commas separate page numbers. If you prefer
to use spaces, quote all of the page numbers:
--pages '2, 3, 5, 7'.
OCRmyPDF will warn if your list of page numbers contains duplicates or overlap pages. OCRmyPDF does not currently account for document page numbers, such as an introduction section of a book that uses Roman numerals. It simply counts the number of virtual pieces of paper since the start.
Regardless of the argument to
--pages, OCRmyPDF will optimize all pages in
the file and convert it to PDF/A, unless you disable those options. In this
example, we want to OCR only the title and otherwise change the PDF as little
ocrmypdf --pages 1 --output-type pdf --optimize 0 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
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.
--redo-ocr does not work, you can use
--force-ocr, which will
force rasterization of all pages, potentially reducing quality or losing
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).
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.
--optimize N (short form
-O) argument controls optimization,
N ranges from 0 to 3 inclusive, analogous to the optimization
levels in the GCC compiler.
Enables lossless optimizations, such as transcoding images to more efficient formats. Also compress other uncompressed objects in the PDF and enables the more efficient “object streams” within the PDF.
All of the above, and enables lossy optimizations and color quantization.
All of the above, and enables more aggressive optimizations and targets lower image 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 cannot be optimized.
The types of optimization available may expand over time. By default,
OCRmyPDF compresses data streams inside PDFs, and will change
inefficient compression modes 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.