Tips by document type

Different documents need slightly different approaches to get a clean scan.

Receipts: thermal paper is thin and low-contrast. Place the receipt on a dark background and use a flash or hold a lit screen behind the paper to improve contrast. Enable Enhance mode to push the text toward pure black.
Books with tight spines: photograph at a slight angle rather than forcing the book fully flat — the perspective correction will straighten it. Press the pages gently to reduce shadow in the gutter. Scan one page at a time for best results.
Multi-page contracts: keep the camera at a consistent height and use the same lighting for every page. Consistent exposure gives uniform scan quality across the assembled PDF so pages don't look mismatched.
Whiteboards: stand directly in front of the board and use Enhance mode. Avoid capturing harsh reflections from overhead lights by shooting at a slight downward angle.

How perspective correction works

When you photograph a document at an angle, the image is a trapezoid rather than a rectangle. The scanner detects the four corners of the document and applies a projective homography transform — a mathematical mapping that stretches and warps each point in the trapezoid to its corresponding position in a flat rectangle. The result looks as if the camera was positioned directly above the document, regardless of the actual shooting angle. The same technique is used in satellite imagery to correct for the curvature of Earth and oblique camera angles.

What Enhance mode does

Enhance mode applies adaptive thresholding to the image. Instead of converting every pixel above a single global brightness value to white, adaptive thresholding calculates a local threshold for each small region of the image independently. This compensates for uneven lighting, shadows across the page, and yellowed or off-white paper — all of which would fool a global threshold. The result is clean black ink on a white background, ideal for printed text and typed documents. Enhance is less effective on pencil, faded ink, or images where you want to preserve tonal gradations.

Your documents never leave your device

Photos are captured to an in-browser canvas and assembled into a PDF using a JavaScript library running entirely in your browser. No images or PDF files are ever uploaded to a server. The tool works fully offline once the page has loaded.