It's the night before a deadline and the portal says "Maximum file size: 1 MB." Your passport scan is 6 MB. Here's how to fix it without turning the document into an unreadable blur.
Why scans are so big
Phone scanners and copiers save at high resolution, often in PNG or uncompressed formats. A single A4 page at 600 DPI in colour can be many megabytes.
The levers, in order of impact
- Resolution: 150–200 DPI is legible for most text documents. Halving the DPI roughly quarters the pixel count.
- Format: JPEG (or WebP) is much smaller than PNG for scans and photos.
- Quality: JPEG quality 70–80 is usually indistinguishable from 100 for documents.
- Colour: grayscale is fine for text-only documents unless colour is required (passports, stamps).
- Cropping: remove the table and background around the page.
Quick method
Crop to the document edges
Every pixel of desk you keep costs bytes.
Resize
An A4 page about 1,700 px wide is roughly 200 DPI.
Compress
Use my Image Compressor. It runs in your browser, so your documents aren't uploaded to a server.
Check legibility
Zoom to 100%. Can you read the smallest text and see stamps and signatures?
Multi-page documents
Transcripts and degree certificates usually go as one PDF:
- Compress each page image first, then combine into a PDF.
- On macOS, Preview can export with a "Reduce File Size" filter, though it can be aggressive, so check the result.
Sensitive documents
Passports, bank statements, and IDs are sensitive. Prefer:
- In-browser tools (no upload)
- Offline software
- Deleting copies from shared or cloud folders after submission