Document Scanning
What document scanning is, how it differs from photographing documents, and how scanning connects to OCR and searchable PDFs.
Document scanning converts paper pages into digital files. The source is a flatbed or sheet-fed scanner, or a phone camera with a scanning app. Scanner resolution is measured in DPI, and 300 DPI is a common setting for text documents.
Scanning apps usually run several steps on each page: detect the page edges, correct perspective, crop, adjust contrast or convert to black and white, and save the pages as a PDF or as images. Many apps can also run OCR to add selectable text.
On a Mac, Continuity Camera can scan pages with a nearby iPhone or iPad and insert them into supported apps.
Scanning vs photographing
A plain photo of a page keeps the camera angle, shadows and background. A scan, or a scanning app, flattens the page to a rectangle, evens out the lighting and crops the edges. Scans are easier to read, print and run through OCR. A phone photo also uses the camera's default format, which on iPhone is often HEIC.
Where document scanning is used
- Receipts, invoices and contracts for records.
- Signed forms that must be returned digitally.
- Notes and handouts for study.
- Archives of letters and printed manuals.
Scanning and OCR
A scan without OCR is an image-only PDF. Its text cannot be searched, copied or read by a screen reader, even though it looks like text. OCR adds an invisible text layer aligned with the words on the page.
Screenshots of on-screen documents have the same issue, because they are also images of text. Temposhot runs OCR when it exports a PDF from the results pane, so the exported file is searchable.
Common mistakes
- Scanning text at low resolution, which lowers OCR accuracy.
- Leaving pages skewed or with dark borders.
- Saving each page as a separate file instead of one PDF.
- Assuming a PDF is searchable without testing a search.
Turning pages into a PDF?
Combine images into one file with Image to PDF, or make screenshots searchable with Screenshot to Searchable PDF. For iPhone photos, HEIC to PDF Converter converts HEIC files.
Common questions
What DPI should I use?
300 DPI suits most text. Use a higher setting for small print or fine detail.
Can I scan a document that is already on screen?
Capture it as screenshots and export a searchable PDF. See save screenshots as PDF on Mac.
Sources
Related resources
- Export formats: searchable PDF export.
- OCR misses equations, footnotes and diagrams: limits of OCR.
Taking the same screenshots again and again?
Temposhot captures a screen, window or area on a timer and exports the set as a PDF, images, ZIP or MP4. The free browser tools fix single images.
Related resources
Related terms
- OCRWhat OCR is, how it works, where it's used, and common mistakes to avoid when making screenshots and scans searchable.
- Searchable PDFWhat makes a PDF searchable, how to tell if yours is, and common mistakes when working with image-only PDFs.
- Image-Only PDFWhat an image-only PDF is, why it limits search and accessibility, and how to make it searchable.
- HEICWhat HEIC is, how it compares to JPG, and how to handle Apple's default photo format in cross-platform workflows.