DPI by Use Case
| DPI | Use case | A4 page size (px) | Notes |
| 72 | Web/email, minimal size | 595 x 842 | Text readable, images soft |
| 96 | Screen reading | 794 x 1123 | Standard screen resolution |
| 150 | General purpose | 1240 x 1754 | Good balance of quality and size |
| 200 | Detailed viewing | 1654 x 2339 | Sharp diagrams and charts |
| 300 | Print quality | 2480 x 3508 | Professional printing standard |
How DPI Affects File Size
Doubling the DPI quadruples the number of pixels (both width and height double). The relationship is roughly:
| DPI change | Pixel count | Approximate size impact |
| 72 → 150 | ~4.3x more pixels | ~3-4x larger |
| 150 → 300 | ~4x more pixels | ~3-4x larger |
| 72 → 300 | ~17x more pixels | ~10-15x larger |
Actual file size depends on JPEG compression, but the pixel count is the primary driver.
PulpPDF Preset Defaults
| Preset | DPI | Behavior |
| None | — | No change |
| High Quality | 300 | Cap: images above 300 DPI are downscaled |
| Balanced | 150 | Cap: images above 150 DPI are downscaled |
| Maximum | 72 | Cap: images above 72 DPI are downscaled |
| Ultra | 72-300 (selectable) | Render: entire page rasterized at chosen DPI |
Recommendations
| Scenario | Recommended DPI |
| Email attachments | 72-96 |
| On-screen reading | 150 |
| Presentations | 150 |
| Archiving scanned documents | 200-300 |
| Professional printing | 300 |
| OCR processing | 300 (automatic in PulpPDF) |
