The largest resolution setting is not automatically the best setting for every scan. It can create more data without improving the information you need. Start by deciding whether the file is for reading, printing, text recognition or later enlargement.

Identify the difficult part of the original

Look for small type, faint punctuation, fine diagrams or another detail that must survive. Select a representative page rather than the cleanest page in the stack. Check whether the receiving organisation specifies resolution or another file requirement; that requirement takes priority over a general rule of thumb.

Epson's Scan 2 guidance suggests 200 to 300 dpi for common printing, faxing, OCR and searchable-PDF tasks. It also explains that higher resolutions produce larger files and advises using the lowest resolution that gives acceptable quality. Treat the range as a starting point, not a guarantee for every original.

Scan the sample at a supported setting in that range. Keep the colour mode, page area and file format unchanged so the comparison answers a resolution question rather than changing several variables at once.

Compare the saved result

Open the saved file and inspect the smallest necessary detail at a practical reading size. If it fails, make a second sample at a higher supported resolution and compare the same area. Check actual file sizes as well as image quality.

For a document that will be printed, print the sample at the intended final size. For OCR, test a few difficult words or numbers. If later enlargement is planned, evaluate the enlarged result rather than judging only the small screen preview.

Do not keep increasing resolution to compensate for a dirty scan surface, cropped text or a blurred original. Those problems require a different correction. Likewise, reducing resolution cannot recover detail that was never captured.

Record the accepted setting with the document type and intended use. Repeat the sample when the originals change, especially when moving from clear typed pages to small receipts, photographs or faint handwriting.

Sources: Epson Scan 2 resolution guidance.