HowtoconvertaPDFtoJPG

How a page becomes an image

The page is rendered — the same drawing operation your PDF reader performs to show it — onto a canvas at whatever size you ask for, and that canvas is saved as an image. Resolution is therefore something you choose, not something the PDF has.

This is why a converted page can look sharper than a screenshot of the same document: you are asking for the page to be drawn at high resolution rather than copying pixels off a screen.

Choosing DPI

• 72 DPI — a quick preview or a thumbnail. Small files, visibly soft type.
• 150 DPI — the default for anything read on a screen. Text is comfortable, files stay sensible.
• 300 DPI — print, or anything that will be cropped into and zoomed. An A4 page at 300 DPI is around 8.7 million pixels, so expect large files and a slower conversion.

Higher is not automatically better. A 600 DPI conversion of a page destined for a slide costs you time and megabytes for detail no one will see.

JPG or PNG

JPG uses lossy compression tuned for photographs. It is the right answer for scanned pages and anything with photographic content, and it produces far smaller files.

PNG is lossless and keeps hard edges clean. Pages that are mostly type, tables, diagrams or screenshots look noticeably better as PNG, because JPG's compression puts a faint fuzz around sharp black-on-white edges.

The short rule: photographs and scans go to JPG, documents and diagrams go to PNG.

Converting one page rather than all of them

A multi-page conversion arrives as a zip, because browsers block a page from starting a dozen downloads. If you only want page seven, extract that page first and convert the one-page file — you get a single image straight away.