PDF to PNG

Lossless rendering, and why it matters for documents

Every compression format makes a bargain. JPG's bargain is that it will throw away detail your eye is unlikely to miss in a photograph, in exchange for a dramatically smaller file — a bargain that is excellent for a sunset and terrible for a paragraph. Text is high-contrast, high-frequency detail: sharp black shapes on plain white. That is the exact pattern JPG handles worst, producing a faint grey shimmer known as ringing around each letter. PNG makes the opposite bargain: it never discards a single pixel, accepting a bigger file in return. When you are converting a PDF — a format used overwhelmingly for text documents, contracts, invoices, diagrams and forms — PNG's bargain is the one you want.

Picking a scale for print versus screen

The scale multiplier decides how many pixels are generated per point of the original page. At 1×, a standard A4 page renders to roughly 595 × 842 pixels, which looks fine in a browser and is a sensible size for the web. Printing is far more demanding: print quality is conventionally reckoned at 300 dots per inch, and hitting that for an A4 page needs something closer to 2,480 × 3,508 pixels — which is what 3× to 4× gets you. The simple rule is to render at the smallest scale that still looks sharp at the size it will actually be viewed. Rendering everything at maximum just produces enormous files that are slow to open and no better on screen.