# 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. 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 `--deskew`. `--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 <lang-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

Note

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 `--skip-big` or `--tesseract-timeout`, those pages will not be in the sidecar.

If you don’t want to generate the output PDF, use `--output-type=none` to avoid generating one. Set the output filename to `-` (i.e. redirect to stdout).

To extract all text from a PDF, whether generated from OCR or otherwise, use a program like Poppler’s `pdftotext` or `pdfgrep`.

### 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.

#### Not recommended

We caution against using ImageMagick or Ghostscript to convert images to PDF, since they may transcode images or produce downsampled images, sometimes without warning.

## 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 that were scanned at a skewed angle by rotating them back into place.

- `--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.

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.

### Example: 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 (by causing OCR to time out). This works if all you want to is to apply image processing or PDF/A conversion.

    ocrmypdf --tesseract-timeout 0 --remove-background input.pdf output.pdf

Changed in version v14.1.0: Prior to this version, `--tesseract-timeout 0` would prevent other uses of Tesseract, such as deskewing, from working. This is no longer the case. Use `--tesseract-non-ocr-timeout` to control the timeout for non-OCR operations, if needed.

### Remove all text or OCR from my PDF

This is getting ridiculous, but OCRmyPDF can complete strip all textual information from a PDF and reconstruct it as a “bag of images” PDF.

    ocrmypdf --tesseract-timeout 0 --force-ocr input.pdf output.pdf

Why would you want to do this? Perhaps you have a PDF where OCR fails to produce useful results, and just want to get rid of all OCR information. This command also removes OCR generated by third party tools.

### 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

### Process only certain pages

You can ask OCRmyPDF to only apply image processing and 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 overlapping 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. If your list of pages is out of numerical order, OCRmyPDF will sort it for you.

Regardless of the argument to `--pages`, OCRmyPDF will optimize all pages/images in the file and convert it to PDF/A, unless you disable those options. Both of these steps are “whole file” operations. In this example, we want to OCR only the title and otherwise change the PDF as little as possible:

    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 `--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 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 inclusive, analogous to the optimization levels in the GCC compiler. `-O1` is the default.

For further details, see the section on PDF optimization.

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

Some users may consider enabling lossy JBIG2. See: `jbig2-lossy`.

Note

Image processing and PDF/A conversion can also introduce lossy transformations to your PDF images, even when `--optimize 1` is in use.

## Digitally signed PDFs

OCRmyPDF cannot preserve digital signatures in PDFs and also add OCR to them. By default, it will refuse to modify a signed PDF regardless of other settings. You can override this behavior with `--invalidate-digital-signatures`; as the name suggests, any digital signatures will be invalidated.

OCRmyPDF cannot open documents that are encrypted with a digital certificate.

Versions of OCRmyPDF prior to 14.4.0 would invalidate existing digital signatures without warning.