Glossary · Hardware

Scanner

A scanner is a device that converts a physical document or image into a digital file by sweeping light across it and recording the reflected light.

Updated October 6, 2026

A scanner is an input device that converts a physical page, photo, or film into a digital image by moving a light source and a sensor across it and recording the reflected or transmitted light. Most consumer models use a CCD or CIS sensor under a glass flatbed, and many office models add an automatic document feeder (ADF).

Why it matters

Scanning is how paper becomes searchable, shareable data. Quality depends on optical resolution (measured in dpi), colour depth, and software. Adding optical character recognition (OCR) turns a scanned image into selectable text, which is what makes archives searchable.

Example

Common settings for typical jobs:

Text document, OCR     300 dpi, grayscale or black and white
Colour photo print     600 dpi
Small slide or film    2400 dpi or higher (film scanner)

A 300 dpi scan of an A4 page is about 2,480 by 3,508 pixels. Saving it as a PDF keeps multiple pages together; saving as TIFF or PNG avoids repeated JPEG compression.

Common mistakes

  • Trusting interpolated resolution figures. Only the optical resolution reflects real detail.
  • Scanning everything at the maximum dpi, which creates huge files with no readability gain.
  • Skipping OCR, leaving a PDF that is only pictures of text.
  • Forgetting that scans of IDs or contracts are sensitive files and should be stored and shared accordingly.

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