Scanner apps that produce a document, not a photograph
A scanner app does four things a camera does not: finds the edges of the page, corrects the angle so the result is rectangular, flattens the lighting so shadows disappear, and outputs a small multi-page PDF instead of a large image. Doing all four well is harder than it sounds, which is why the field is smaller than the app store suggests.
What separates a good scan
| Step | What goes wrong without it |
|---|---|
| Edge detection | The desk, the floor and your hand end up in the document |
| Perspective correction | The page is a trapezoid and the text curves |
| Contrast flattening | Half the page is in shadow and unreadable |
| Compression | A five-page document arrives as a 40 MB attachment |
| OCR | The text cannot be searched or copied |
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The apps
The most accurate edge detection of any of them and a strong OCR engine. The free tier adds a watermark, which is the trade.
The best free tier: no watermark on basic scans, good batch mode, and export to PDF without an account.
Its built-in scan mode is surprisingly good and puts the result straight into a notebook, which suits receipts and reference material.
Includes scanning alongside its office tools, useful if you are already using it and would rather not add another app.
Technique beats app choice
The difference between a good scan and a bad one is mostly lighting and background, not software.
- Put the page on a contrasting surface Dark table, white paper. Edge detection works by finding that boundary.
- Light it from the side, not from above Overhead light puts your own shadow on the page. A window to one side is ideal.
- Hold the phone parallel to the page Correction can fix a small angle, and it degrades text at a large one.
- Use black and white mode for text It compresses far better and reads more clearly than a colour photo of a white page.
- Check the result before you send it Zoom to a corner and confirm the small print is legible.
- Under 1 MB per page
- Straight edges, square corners
- Uniform background
- Text readable at 100 percent zoom
- Full-resolution colour photo
- Visible shadow across the page
- Keystone distortion
- The desk visible around the edges
Where your documents go
Scanner apps handle identity documents, contracts and bank statements, which makes them a category where the privacy policy is worth two minutes of your time. Several upload every scan for cloud OCR by default.
If you scan anything sensitive, look for an offline mode, check whether OCR happens on the device, and prefer an app that does not require an account at all. For a passport or a payslip, a watermark on a free tier is a smaller problem than an unnecessary upload.
Dark surface, side lighting, phone parallel to the page, black-and-white mode. Then the app choice barely matters.
Frequently asked questions
Can I scan without an account?
Genius Scan and the office suites work without one. Several of the larger apps require sign-in before exporting.
Does OCR work offline?
In some apps yes, in others the text recognition happens on a server. Check before scanning anything private.
Why is my scanned PDF enormous?
It is storing colour photographs at full resolution. Switch to document or black-and-white mode and the size drops by an order of magnitude.
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