How PDF compression works
Updated 23 October 2026 · Zenvoq Labs
| DPI | Pixels (A4) | Readability on screen |
|---|---|---|
| 300 | 2480 × 3508 | Print quality |
| 150 | 1240 × 1754 | Sharp — ideal for uploads |
| 100 | 827 × 1169 | Clear for normal text |
| 72 | 595 × 842 | Readable; small print gets soft |
| 50 | 413 × 585 | Headings only — last resort |
The two dials: resolution and quality
Resolution decides how many pixels each page has. JPEG quality decides how aggressively those pixels are approximated. Lowering resolution helps most for big scans; lowering quality helps most for the last few kilobytes.
Hitting an exact target
FramePDF's compressor starts at 150 DPI and binary-searches JPEG quality between 35% and 92% to find the highest setting that fits. If even the lowest quality is too big, it steps down to 120, 100, 85, 72, 60, 50 and finally 40 DPI.
Lossless vs lossy
Operations like merging, splitting, rotating and reordering are lossless — pages are copied as-is. Compression of scanned pages is lossy, which is why you should keep your original.
Frequently asked questions
Handle PDFs offline on your phone
FramePDF makes PDFs smaller, combines and reorders pages, and saves any page as a photo — all on your Android phone, without uploading anything.
- Make PDFs smaller
- Edit pages offline
- Save pages to Photos
