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<li class="toctree-l3"><a class="reference internal" href="#ocr-and-correct-document-skew-crooked-scan">OCR and correct document skew (crooked scan)</a></li>
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<div class="section" id="cookbook">
<h1>Cookbook<a class="headerlink" href="#cookbook" title="Permalink to this headline">¶</a></h1>
<div class="section" id="basic-examples">
<h2>Basic examples<a class="headerlink" href="#basic-examples" title="Permalink to this headline">¶</a></h2>
<div class="section" id="help">
<h3>Help!<a class="headerlink" href="#help" title="Permalink to this headline">¶</a></h3>
<p>ocrmypdf has built-in help.</p>
<div class="highlight-bash"><div class="highlight"><pre><span></span>ocrmypdf --help
</pre></div>
</div>
</div>
<div class="section" id="add-an-ocr-layer-and-convert-to-pdf-a">
<h3>Add an OCR layer and convert to PDF/A<a class="headerlink" href="#add-an-ocr-layer-and-convert-to-pdf-a" title="Permalink to this headline">¶</a></h3>
<div class="highlight-bash"><div class="highlight"><pre><span></span>ocrmypdf input.pdf output.pdf
</pre></div>
</div>
</div>
<div class="section" id="add-an-ocr-layer-and-output-a-standard-pdf">
<h3>Add an OCR layer and output a standard PDF<a class="headerlink" href="#add-an-ocr-layer-and-output-a-standard-pdf" title="Permalink to this headline">¶</a></h3>
<div class="highlight-bash"><div class="highlight"><pre><span></span>ocrmypdf --output-type pdf input.pdf output.pdf
</pre></div>
</div>
</div>
<div class="section" id="modify-a-file-in-place">
<h3>Modify a file in place<a class="headerlink" href="#modify-a-file-in-place" title="Permalink to this headline">¶</a></h3>
<p>The file will only be overwritten if OCRmyPDF is successful.</p>
<div class="highlight-bash"><div class="highlight"><pre><span></span>ocrmypdf myfile.pdf myfile.pdf
</pre></div>
</div>
</div>
<div class="section" id="correct-page-rotation">
<h3>Correct page rotation<a class="headerlink" href="#correct-page-rotation" title="Permalink to this headline">¶</a></h3>
<p>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.</p>
<div class="highlight-bash"><div class="highlight"><pre><span></span>ocrmypdf --rotate-pages myfile.pdf myfile.pdf
</pre></div>
</div>
<p>You can increase (decrease) the parameter <code class="docutils literal"><span class="pre">--rotate-pages-threshold</span></code> to make page rotation more (less) aggressive.</p>
</div>
<div class="section" id="ocr-languages-other-than-english">
<h3>OCR languages other than English<a class="headerlink" href="#ocr-languages-other-than-english" title="Permalink to this headline">¶</a></h3>
<p>By default OCRmyPDF assumes the document is English.</p>
<div class="highlight-bash"><div class="highlight"><pre><span></span>ocrmypdf -l fre LeParisien.pdf LeParisien.pdf
ocrmypdf -l eng+fre Bilingual-English-French.pdf Bilingual-English-French.pdf
</pre></div>
</div>
<p>Language packs must be installed for all languages specified. See <a class="reference internal" href="languages.html#lang-packs"><span class="std std-ref">Installing additional language packs</span></a>.</p>
</div>
</div>
<div class="section" id="ocr-images-not-pdfs">
<h2>OCR images, not PDFs<a class="headerlink" href="#ocr-images-not-pdfs" title="Permalink to this headline">¶</a></h2>
<p>Use a program like <a class="reference external" href="https://gitlab.mister-muffin.de/josch/img2pdf">img2pdf</a> to convert your images to PDFs, and then pipe the results to run ocrmypdf:</p>
<div class="highlight-bash"><div class="highlight"><pre><span></span>img2pdf my-images*.jpg <span class="p">|</span> ocrmypdf - myfile.pdf
</pre></div>
</div>
<p>If given a single image as input, OCRmyPDF will try converting it to a PDF on its own. This feature may be removed at some point, because OCRmyPDF does not specialize in converting images to PDFs.</p>
<p>You can also use Tesseract 3.04+ directly to convert single page images or multi-page TIFFs to PDF:</p>
<div class="highlight-bash"><div class="highlight"><pre><span></span>tesseract my-image.jpg output-prefix pdf
</pre></div>
</div>
</div>
<div class="section" id="image-processing">
<h2>Image processing<a class="headerlink" href="#image-processing" title="Permalink to this headline">¶</a></h2>
<p>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.</p>
<ul class="simple">
<li><code class="docutils literal"><span class="pre">--rotate-pages</span></code> attempts to determine the correct orientation for each page and rotates the page if necessary.</li>
<li><code class="docutils literal"><span class="pre">--remove-background</span></code> 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.</li>
<li><code class="docutils literal"><span class="pre">--deskew</span></code> will correct pages were scanned at a skewed angle by rotating them back into place. Skew determination and correction is performed using <a class="reference external" href="http://www.leptonica.com/skew-measurement.html">Postl’s variance of line sums</a> algorithm as implemented in <a class="reference external" href="http://www.leptonica.com/index.html">Leptonica</a>.</li>
<li><code class="docutils literal"><span class="pre">--clean</span></code> uses <a class="reference external" href="https://www.flameeyes.eu/projects/unpaper">unpaper</a> 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.</li>
<li><code class="docutils literal"><span class="pre">--clean-final</span></code> 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.</li>
</ul>
<div class="section" id="ocr-and-correct-document-skew-crooked-scan">
<h3>OCR and correct document skew (crooked scan)<a class="headerlink" href="#ocr-and-correct-document-skew-crooked-scan" title="Permalink to this headline">¶</a></h3>
<div class="highlight-bash"><div class="highlight"><pre><span></span>ocrmypdf --deskew input.pdf output.pdf
</pre></div>
</div>
</div>
</div>
<div class="section" id="hot-watched-folders">
<h2>Hot (watched) folders<a class="headerlink" href="#hot-watched-folders" title="Permalink to this headline">¶</a></h2>
<p>To set up a “hot folder” that will trigger an OCR operation for every file inserted, use a program like Python <a class="reference external" href="https://pypi.python.org/pypi/watchdog">watchdog</a> (supports all major OS).</p>
<div class="highlight-bash"><div class="highlight"><pre><span></span>apt-get install python-watchdog
</pre></div>
</div>
<p>watchdog installs the command line program <code class="docutils literal"><span class="pre">watchmedo</span></code>, which can be told to run <code class="docutils literal"><span class="pre">ocrmypdf</span></code> on any .pdf added to the current directory (<code class="docutils literal"><span class="pre">.</span></code>) and place the result in the previously created <code class="docutils literal"><span class="pre">out/</span></code> folder.</p>
<div class="highlight-bash"><div class="highlight"><pre><span></span><span class="nb">cd</span> hot-folder
mkdir out
watchmedo shell-command <span class="se">\</span>
--patterns<span class="o">=</span><span class="s2">"*.pdf"</span> <span class="se">\</span>
--ignore-directories <span class="se">\</span>
--command<span class="o">=</span><span class="s1">'ocrmypdf "${watch_src_path}" "out/${watch_src_path}" '</span> <span class="se">\</span>
. <span class="c1"># don't forget the final dot</span>
</pre></div>
</div>
<p>For more complex behavior you can write a Python script around to use the watchdog API.</p>
<p>On file servers, you could configure watchmedo as a system service so it will run all the time.</p>
<div class="section" id="caveats">
<h3>Caveats<a class="headerlink" href="#caveats" title="Permalink to this headline">¶</a></h3>
<ul class="simple">
<li><code class="docutils literal"><span class="pre">watchmedo</span></code> may not work properly on a networked file system, depending on the capabilities of the file system client and server.</li>
<li>This simple recipe does not filter for the type of file system event, so file copies, deletes and moves, and directory operations, will all be sent to ocrmypdf, producing errors in several cases. Disable your watched folder if you are doing anything other than copying files to it.</li>
<li>If the source and destination directory are the same, watchmedo may create an infinite loop.</li>
</ul>
</div>
</div>
<div class="section" id="batch-jobs">
<h2>Batch jobs<a class="headerlink" href="#batch-jobs" title="Permalink to this headline">¶</a></h2>
<p>Consider using the excellent <a class="reference external" href="https://www.gnu.org/software/parallel/">GNU Parallel</a> to apply OCRmyPDF to multiple files at once.</p>
<p>Both <code class="docutils literal"><span class="pre">parallel</span></code> and <code class="docutils literal"><span class="pre">ocrmypdf</span></code> will try to use all available processors. To maximize parallelism without overloading your system with processes, consider using <code class="docutils literal"><span class="pre">parallel</span> <span class="pre">-j</span> <span class="pre">2</span></code> to limit parallel to running two jobs at once.</p>
<p>This command will run all ocrmypdf all files named <code class="docutils literal"><span class="pre">*.pdf</span></code> in the current directory and write them to the previous created <code class="docutils literal"><span class="pre">output/</span></code> folder.</p>
<div class="highlight-bash"><div class="highlight"><pre><span></span>parallel -j <span class="m">2</span> ocrmypdf <span class="s1">'{}'</span> <span class="s1">'output/{}'</span> ::: *.pdf
</pre></div>
</div>
<p>If you have thousands of files to work with, contact the author.</p>
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