PDF to image: JPG or PNG? The right choice depends on what the page contains
Turning the pages of a PDF into images is useful in many cases: inserting a page into a presentation or a message, posting an excerpt on social media, sending a document to someone who cannot open PDFs, creating a thumbnail. Two formats are offered, JPG and PNG, and people often pick one at random. We measured both on two very different documents, with FileXvert's exact settings.
How FileXvert draws the pages
Each page is drawn by pdf.js, Firefox's PDF display engine, at 144 pixels per inch, that is two pixels for every point of the document. A Letter-size page therefore becomes a 1224 × 1584-pixel image, and a landscape A4 page a 1683 × 1190-pixel image: enough for comfortable reading on screen and ordinary printing, without oversized files.
The image is then saved as JPEG, at quality 0.9 on a scale from 0 to 1, or as PNG, losslessly. A multi-page PDF gives one image per page, bundled in a ZIP archive. Everything happens in your browser: the document is not sent to any server.
What we measured
First document: a four-page Letter-size report, exported from Word by LibreOffice, with headings, paragraphs, a table and a small illustration on each page. It weighs 75.1 KB. Second document: a landscape A4 page containing a photo, for a 530 KB PDF.
| Document | Original PDF | JPG images | PNG images |
|---|---|---|---|
| Report, page 1 (headings and table) | — | 138 KB | 164 KB |
| Report, page 2 (dense text) | — | 198 KB | 186 KB |
| Report, page 3 (dense text) | — | 199 KB | 188 KB |
| Report, page 4 (half page) | — | 78 KB | 94 KB |
| Report, 4 pages in total | 75.1 KB | 613 KB | 632 KB |
| Page with a photo (landscape A4) | 530 KB | 669 KB | 3.63 MB |
On the report, the two formats are on a par: PNG weighs only 3% more in total, and it is even lighter on the dense text pages. On the photo page, the gap is something else entirely: PNG weighs 5.4 times more than JPG.
Why the result flips from one page to another
A page of text is made of large white areas and characters with sharp edges. PNG's lossless compression excels at this kind of image: it efficiently describes long runs of identical pixels. JPEG, by contrast, cuts the image into 8 × 8-pixel blocks and simplifies sharp variations; around every letter it has to store a lot of information to stay sharp, and it still leaves slight halos you can see when zooming in.
A photo, on the contrary, contains almost no pixel identical to its neighbour. PNG has to keep everything, while JPEG discards the nuances the eye does not perceive. That is where it gains a decisive advantage.
The practical rule is therefore simple: PNG for pages of text, tables and diagrams; JPG for pages dominated by photos. For a mixed document, JPG remains reasonable, but check that small characters stay sharp.
An image weighs more than the PDF
The 75.1 KB report becomes more than 600 KB of images, eight times more. This is not a flaw in the conversion: a PDF describes its text as characters and fonts, very compactly, whereas an image has to record every pixel of every letter. The text is also no longer selectable or searchable in the image.
Converting a PDF to images is therefore only useful when the recipient needs an image. To pass on the document itself, keep the PDF: it is lighter, sharp at any zoom level, and its text remains usable.
Good uses
A few situations where converting to images is the right choice:
- Illustrating a presentation with a page of a report: PNG, for text that stays sharp when projected. FileXvert can also convert a PDF straight to PowerPoint, one slide per page.
- Posting a poster or flyer on social media: JPG, for a light image that the platform will recompress anyway.
- Sending a single page of a long document: first extract the page with the PDF editor (a Premium feature), then convert it.
- Archiving a document: keep the PDF, the image adds nothing and weighs more.