PNG vs JPEG: Alpha transparency vs lossy size optimization

The decision, as a checklist

Rather than a rule of thumb, walk through what the image actually needs:

1. Does it need transparency? If yes, PNG — JPEG has no alpha channel, full stop.
2. Is it a photograph or continuous-tone image? If yes, JPEG usually wins on file size at visually indistinguishable quality.
3. Does it have sharp edges, text, or flat color regions (a screenshot, logo, UI mockup, diagram)? PNG — JPEG's compression actively produces worse results and often larger files for this content type (see JPEG vs PNG for why).
4. Will it be edited and re-saved multiple times? PNG (or another lossless format) as the working file — JPEG's lossy re-compression degrades further on every save.
5. Is absolute smallest file size the priority and photographic content is involved? Consider WebP first (see PNG vs WebP) — it typically beats both formats' size at equivalent quality.

Why "PNG is always higher quality" is a misleading simplification

PNG is lossless, not automatically "better" — for a genuine photograph, a well-tuned JPEG at high quality is visually indistinguishable from the PNG original to virtually anyone, at a fraction of the file size. "Lossless" only matters when the specific content or workflow benefits from pixel-exact preservation — a photo destined only for final web display, never re-edited, doesn't need that guarantee, and paying the PNG file-size cost for it is often wasted bandwidth.

Why "JPEG is always smaller" is also misleading

For flat-color, sharp-edged content (screenshots, logos, simple graphics), PNG frequently produces a smaller file than an equivalent-quality JPEG, precisely because JPEG's DCT-based compression is poorly suited to that kind of content and needs a higher bitrate to avoid visible artifacts around edges — the "JPEG is always more compact" intuition only holds for genuinely photographic, continuous-tone images.

Common mistakes

• Choosing based on format reputation rather than actual image content. The right choice depends on what's in the image (photo vs. flat graphic, transparency needed or not), not a blanket rule.
• Using PNG for a working master file and separately not realizing JPEG is fine for the final, never-re-edited web export of a genuine photograph.
• Assuming file extension alone tells you enough. A .png screenshot re-saved through a lossy pipeline somewhere can still lose quality — the extension doesn't guarantee lossless handling throughout an entire pipeline.

FAQ

Is PNG always better quality than JPEG?
Not in a meaningful sense for genuine photographs at high JPEG quality settings — "lossless" only matters if you need pixel-exact preservation, which most final photographic web images don't require.

Why does a screenshot saved as JPEG sometimes look worse and end up smaller in file size but ugly?
JPEG's compression targets photographic content; on flat colors and sharp edges (typical of screenshots) it needs a much higher bitrate to look clean, so a "reasonable" JPEG quality setting often looks worse there than the same setting would on a photo.

Should I always convert PNG to JPEG to save space?
Only for genuinely photographic content with no transparency needs — for flat-color graphics or anything requiring an alpha channel, PNG often stays the better (sometimes even smaller) choice.

Convert between formats and compare file sizes directly with the Image Converter — entirely client-side.