Why phone scans look grey, and how to fix them

Photos of paper often come out grey, shadowed and uneven. Phone cameras expose for the whole scene, so a white page in dim light is rendered as mid-grey, and any shadow becomes a dark patch that swallows text.

Fix it before you shoot

Use daylight from a window or a lamp at an angle that does not put your own shadow on the page. Hold the phone directly above the page so the camera is parallel to it; a tilted shot stretches the far side and makes text harder to read. Put the page on a dark, plain surface so you can see its edges when you crop.

Then clean the image

Crop the photo to the page in your phone gallery, then use Scanned Document to Clean PDF. It converts to grayscale, finds the darkest and lightest areas of the image and stretches them, which turns grey paper white and makes ink darker. You can add several photos and get one multi-page PDF.

Grayscale or black and white?

Grayscale keeps signatures, stamps, pencil and photographs, so use it for forms and anything with marks. Black and white makes typed pages very crisp and small, but faint pencil, light highlighter and colored stamps can disappear. If you are unsure, try grayscale first and compare.

Limits to know

The tool does not straighten a crooked page, crop it, or make the text searchable. Text in the PDF is an image. Very uneven lighting, such as a hard shadow across half the page, will still leave a visible difference, so re-shoot if the result is patchy. Large photos are scaled to about 2000 pixels on the long side, roughly 170 dpi on an A4 page, which is comfortable to read. If the file is still too large, run it through PDF Compress.

Related: all guides and all tools.