Explainer
PDF to Image Quality: Resolution, DPI and Format Explained
Converted PDF pages sometimes look blurry, and sometimes the files are far bigger than expected. Both come down to three choices: resolution, image format and the quality of the original PDF. This guide explains each one in plain terms.
Quick answer: for viewing on screens and sharing online, about 150 DPI is enough (roughly 1240 × 1754 pixels for an A4 page). For high-quality printing, use 300 DPI. Choose PNG for text and diagrams, JPG for scans and photos, and remember that no setting can make a blurry scanned PDF sharper than the original.
Pixels, DPI and why they matter
A PDF page usually describes text and shapes mathematically (as vectors), so it looks sharp at any zoom. An image is a fixed grid of pixels. Converting a page to an image means choosing how many pixels each page gets.
DPI (dots per inch, often used interchangeably with PPI, pixels per inch) links pixels to physical size:
pixels = page size in inches × DPI
An A4 page is 8.27 × 11.69 inches, so at 150 DPI it becomes about 1240 × 1754 pixels. Double the DPI and you get four times as many pixels, and much larger files.
Common page sizes in pixels
| DPI | A4 (8.27 × 11.69 in) | US Letter (8.5 × 11 in) | Typical use |
|---|---|---|---|
| 72 | 595 × 842 | 612 × 792 | Thumbnails, previews |
| 144 | 1191 × 1684 | 1224 × 1584 | Screens, sharing, everyday printing |
| 150 | 1240 × 1754 | 1275 × 1650 | Screens, web, documents |
| 300 | 2480 × 3508 | 2550 × 3300 | High-quality printing, archiving |
What resolution does MyImageNinja use?
MyImageNinja renders each page at up to twice its original size, which is about 144 DPI for standard A4 and US Letter pages (the 144 row above). Larger pages, such as A3 posters or drawings, are rendered at a lower scale so their longest side ends up around 2048 pixels (very large sheets stay at their original size), which keeps memory use manageable on phones and laptops.
That is a good balance for screens, presentations, websites, upload forms and everyday printing. If you need true 300 DPI output for professional print or archiving, a desktop tool such as Poppler's pdftoppm -r 300 (see our PDF to PNG guide) is the better choice.
How the image format affects quality
- PNG is lossless: once a page is rendered, saving it as PNG keeps every pixel. Best for text, tables, charts, diagrams and slides. Files are larger, especially for photo-heavy pages.
- JPG is lossy: it discards detail the eye is unlikely to notice to make files much smaller. At high quality (MyImageNinja uses about 90%) the difference is hard to see; at low quality, edges around small text get smudgy. Best for scans, photos and sharing.
The full comparison is in JPG vs PNG for PDF pages.
Why do my converted images look blurry?
- The PDF is a low-resolution scan. If the PDF itself contains a blurry image of the page, converting it can't add detail. Zoom into the original PDF: if it's blurry there, the source is the limit.
- The image is shown larger than its pixel size. Stretching a 1200-pixel-wide image across a 4K screen or a large print makes it soft. Use a higher resolution for large displays.
- Heavy JPG compression. Very low JPG quality creates blocky artefacts. Use PNG or a higher JPG quality.
- The image was resized again later. Apps and social networks often shrink and recompress uploads. Upload at the size the platform recommends.
Why are my image files so large?
- PNG for photo-heavy pages. Brochures and magazines can produce PNG files several times larger than JPG. Switch to JPG for those.
- Very high DPI. 300 DPI images have four times the pixels of 150 DPI images. Only use it when you need print quality.
- Too many pages. Delete pages you don't need before exporting.
Quality checklist before you convert
- Check the original PDF is sharp when zoomed in.
- Decide where the images will be used: screen, web, upload form or print.
- Pick PNG for text and graphics, JPG for scans and photos.
- Rotate sideways pages and remove unwanted ones first.
- Spot-check a couple of exported images at 100% zoom before sharing the whole batch.