Export an architecture diagram from a PDF as a JPG and the arrows grow fuzzy halos before you've even posted it. The fix isn't a higher resolution, it's the right format. The choice between PNG and JPG turns out to be simple once you know what each one does to hard edges, flat colour, and transparent backgrounds. Here's the short version, a side-by-side comparison, and how the PDF to PNG tool handles the details.
Two encoders, two approaches.
JPEG compresses by discarding detail your eye forgives in photographs, which is exactly why it hurts the things diagrams are made of: one-pixel lines, small text, flat colour fields. PNG is lossless; every pixel survives, so a rendered flowchart looks identical to the PDF it came from.
The cost is size. On photographic pages, PNG files grow to several times the JPG equivalent for no visible gain. So the rule: pages that look like documents or diagrams go to PNG, pages that look like photographs or scans go to JPG, and mixed decks usually deserve PNG when accuracy matters more than megabytes.
What the tool actually does.
The PDF to PNG tool draws each page with pdf.js inside your browser and saves it losslessly, with nothing uploaded. The Resolution menu runs from 72 DPI, one pixel per point, through 150 and 300 up to 600 DPI.
Leave the Pages box empty for the whole document, type pages such as 2-4, or click thumbnails. One page downloads as a single PNG; several arrive in a ZIP named by page, such as spec-page-001.png, and each also gets its own Download button. For diagrams headed into documentation, 150 DPI is usually the minimum that keeps thin connectors from stair-stepping.
Same page, different bytes.
Take a single A4 system-architecture page, 595 by 842 points, rendered at 150 DPI into an image about 1240 by 1754 pixels. As a PNG, every box edge and label is exactly as sharp as in the PDF. As a JPG the file is smaller, but zoom into the arrowheads and you'll find the smudged ringing that lossy encoding leaves around high-contrast edges.
Swap the content and the result flips: a full-page photograph makes a much larger PNG than JPG, and the two look the same at normal viewing distance. Neither format is better overall; they're tuned for different kinds of pixels.
The background nobody thinks about until it's white.
PDF pages don't always paint a background; many leave it empty and viewers simply show white. By default the tool draws pages on white too. Tick Transparent background before converting and those unpainted areas stay see-through, because PNG carries an alpha channel.
That's useful for reuse: a logo sheet or a diagram exported this way drops onto a coloured slide or a dark-mode doc without a white rectangle around it. It works on PDFs exported from Word or design tools. Scanned pages are one solid image, so they stay opaque, and JPG can't do this at all.
Big folders and gray fuzz, explained.
The same handful of missteps shows up in every documentation workflow.
Render big once, shrink per destination.
Two small rules cover nearly every export decision.
Line art here, photos and round trips elsewhere.
Keep PDF to PNG for line art, interface documentation, and anything with text a reader will zoom into. PDF to JPG wins on photographic pages and email-friendly sizes. Already holding PNGs that turned out heavy? PNG to JPG Converter changes them after the fact, and Image Compressor shrinks either format further.
For the round trip, PNG to PDF puts exported or annotated images back into a single document your reviewers can page through.
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