Scans too big? Fix it at the scanner, not afterwards
5 min read
Oversized scan files are ten times easier to prevent at scan time than to repair afterwards.
300dpi is the standard for documents
Resolution acts on file size quadratically: a 600dpi scan is four times the bytes of a 300dpi one. For ordinary documents that will be read on screen and printed, 300dpi is fully sufficient, and even 200dpi keeps text crisp.
600dpi and up is for originals with very small print you'll need to magnify, or where photographic detail matters. If your scanner defaults to 600dpi, dropping to 300 alone cuts files to a quarter.
Color mode moves the needle most
The same page scanned in color can be three times the size of grayscale and over ten times the size of black-and-white. Unless stamps, seals, or highlighter marks matter, grayscale is usually enough.
For text-only pages, black-and-white (bilevel) mode is smallest and often renders letter edges sharper. But it flattens stamps, signatures, and shading — never use it for contracts where a seal matters.
Check the scanner's own file format settings
Some multifunction printers save scans uncompressed or barely compressed by default. At the same 300dpi color settings, output size can differ severalfold depending on this. Look for options like “PDF (high compression)” or a JPEG quality slider and set them to a middle level.
In an office that scans in volume, this one setting changes cumulative storage significantly. Do one test scan to confirm quality, then save it as the default.
For files that are already too big
Files you've already received oversized are the compression tool's job. Scans are image-dominated, so compression works well on them — modest quality reduction often halves the size or better.
Afterwards, verify the small print is still readable, and keep the original. Compression discards information and cannot be reversed.