How to make scan files smaller (without ruining them)
Published September 26, 2026
A scan that will not fit in an upload box is a solved problem wearing a scary face. File size comes from three dials — resolution, color, and compression — and understanding what each one does lets you shrink a file five- or ten-fold while keeping the text perfectly readable.
Dial one: resolution
Resolution sets how many pixels represent the page, and file size grows with the square of it — double the width and the file quadruples. For reading text on screen and ordinary office use, a page around 1500–2000 pixels wide is plenty. Higher resolution earns its size only for print, small type, or archival masters. The biggest single saving usually comes from not storing a 4000-pixel photo of a page you will only ever read at screen size.
Dial two: color
A color scan stores three values per pixel; grayscale stores one. If the document is black text on white paper — most are — B&W mode gives an immediate large saving with zero information lost, and typically improves legibility too. Keep color only where color carries meaning: stamps, signatures in blue ink, highlighted text, photos.
Dial three: compression
JPG quality settings run from paranoid to reckless. For document scans the sweet spot is moderate-high: at Scandut’s standard PDF quality, compression artifacts are invisible at reading size, and the file is a fraction of the high setting. Choose high quality only when the document will be printed or zoomed — legal fine print, technical drawings. Avoid recompressing repeatedly; export once at the right setting instead.
Practical recipes
Email attachment refused: export the PDF at standard quality, in Document or B&W mode — a 20-page scan lands well under typical 25 MB limits. Government portal with a tiny per-file cap: save pages as JPG individually and upload separately. Archiving hundreds of pages: standard-quality PDF per chapter or per month, grayscale where color adds nothing. And if a single page must be tiny (some forms cap uploads at 1–2 MB): JPG, grayscale, and it will fit with room to spare.