PNG to JPG: How It Works
Converting PNG to JPEG usually cuts a photograph's file size by 70–90%. The decision is not really about format — it is about whether the image is a photograph, and whether it needs transparency, because JPEG has none.
What changes
| PNG | JPEG | |
|---|---|---|
| Compression | Lossless | Lossy |
| Transparency | Yes, with alpha channel | None |
| Colours | Up to 16.7 million plus alpha | 16.7 million |
| Photograph of 2000×1500 | ≈ 4.5 MB | ≈ 400 KB at quality 85 |
| Best for | Graphics, screenshots, transparency | Photographs |
Transparency becomes a solid colour
JPEG cannot store an alpha channel, so transparent areas must be filled. Most converters default to white, which looks correct on a white page and produces an obvious white box on any other background.
If the image will sit on a coloured background, set the fill colour to match before converting. If the transparency is genuinely needed — a logo used across varying backgrounds — do not convert to JPEG at all. Use PNG, or WebP if you want both transparency and smaller files.
Which images benefit
- Photographs — large saving, no visible loss at quality 85. This is what JPEG was designed for.
- Scanned documents with images — usually a worthwhile saving.
- Screenshots of text — a poor choice. JPEG produces visible ringing around sharp edges, and text edges are as sharp as it gets. Keep these as PNG.
- Logos and line art — same problem. Flat colour regions and hard edges are exactly what JPEG handles worst.
The general rule: if the image has large areas of flat colour or sharp edges, PNG will be both smaller and better. If it has smooth continuous tone, JPEG wins decisively.
The conversion is one-way
JPEG discards data permanently. Converting back to PNG recreates a lossless container around already-degraded pixels — the file grows again and the quality does not return. Keep the PNG original if you may need to edit later, and treat the JPEG as an output.
Quality setting
Around 85 is the practical standard: roughly half the size of quality 95 and visually indistinguishable at normal viewing distance. Below 70, artefacts appear in skies, gradients and skin tones — the smooth areas where JPEG's block structure becomes visible.
Consider WebP or AVIF instead
If the destination supports them, both handle this case better than JPEG. WebP supports transparency and lossy compression, so a logo can be small without a background fill. AVIF is smaller still. Browser support for both is now broad, and a JPEG fallback covers the remainder. Convert to JPEG when you need maximum compatibility — email clients, older software, printing services — and to WebP or AVIF when you control the destination.
Conversion here runs in your browser. Nothing is uploaded, which matters for personal photographs and anything unpublished.