When PNG is better than JPG
JPG compression is designed for photographs. On pages with black text on a white background, it leaves a faint halo around every letter, and the effect gets worse each time the image is saved again. PNG is lossless: text edges, thin table lines and small icons remain exactly as rendered. Choose PNG when you will:
- paste a page into a document, wiki or presentation and zoom in on it;
- crop out a chart, formula or signature from a PDF;
- edit the image further in a graphics editor;
- run text recognition (OCR) on the result.
For pages that are mostly photographs, PDF to JPG will give much smaller files.
Resolution and file size
A PDF stores text as vector shapes, so it can be rendered at any size. At 150 DPI an A4 page becomes 1240 × 1754 pixels — clear on any screen. At 300 DPI it is 2480 × 3508 pixels, suitable for print. PNG files of text pages are usually modest in size; pages full of photos can reach several megabytes.
After conversion
You can crop or resize a page with the image resizer, or turn a set of PNG files back into a document with PNG to PDF.