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OCR

Under Review

This article is currently under review. Some content may be incomplete or inaccurate.

Category: Processing

The OCR activity extracts machine-readable text from each page image. That text feeds Split, Classify, and Extract, and is also used to locate field values on the page.

PDF text layer​

Many PDFs are digitally born and already contain exact text. The PDF Text Layer setting controls how the OCR step treats it:

  • Auto (default): each PDF page is checked individually. Digitally-born pages use their embedded text directly, which is exact and does not consume OCR capacity. Scanned pages, scans that carry a hidden text layer from another OCR tool, and pages whose text layer is unreadable are sent to the OCR engine as usual. Mixed files work naturally: the digital pages of a file use embedded text while its scanned pages are recognized.
  • Always run OCR: every page is recognized by the OCR engine, and embedded text is ignored.
  • Prefer embedded text: any substantial text layer is trusted, including text layers added by another OCR tool. Choose this if your documents were already processed by an OCR you trust.

This setting applies to PDF sources only; images (TIFF, JPEG, PNG, ...) always use the OCR engine. Barcode recognition works together with the PDF text layer: when Microsoft barcodes are selected, the Microsoft call still runs to read barcodes, while the page text is taken from the PDF. Note that the PDF text layer requires an OCR engine to be selected; with "Skip OCR" pages get no text at all.

To see what actually happened, open the transaction's Activity Log: the OCR step entry shows where the text of each page came from (embedded PDF text or the OCR engine that recognized it). In Auto mode it also lists the per-page decision reasons, for example "digital text" or "scanned page", which helps when investigating why a page was or was not read from its PDF text layer.

Notes​

  • OCR can optionally detect barcodes on each page for use in splitting or extraction.
  • The document language is detected automatically and stored with each page's results, at no extra cost. It is used, for example, as the document language of PDF/A-3a archival exports. Microsoft engines detect it on the same call; RapidOCR reports its script model; Tesseract reports the configured recognition language when a single one is selected.
  • With the Tesseract engine, select the recognition language(s) in the step settings. The list offers the language packs installed in your deployment; selecting several recognizes mixed-language documents at some accuracy cost.
  • Text quality depends on the Import DPI: low-resolution scans produce weaker OCR.