PNG file format
PNG stores every pixel exactly as it was and supports real transparency, which makes it the right format for screenshots, logos and interface graphics — and the wrong one for photographs.
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What is PNG?
PNG appeared in 1996 as a free replacement for GIF, whose LZW compression was covered by a Unisys patent that was suddenly being enforced. The working group designed it to be strictly better: full 24-bit colour instead of 256 shades, an 8-bit alpha channel for smooth transparency instead of one on-or-off transparent colour, and a compression scheme, Deflate, that nobody owned.
Compression in PNG is lossless. Before the data is deflated, each row is passed through a filter that predicts every pixel from its neighbours and stores only the difference, which is why flat colour and repeated patterns collapse to almost nothing. Decode a PNG and you get back the exact pixels that went in — no artefacts, no generation loss no matter how many times the file is edited and saved.
That guarantee is expensive on photographs. A camera image has no repeated pixels for the filters to exploit, so a photo saved as PNG typically weighs five to ten times its JPEG equivalent for no visible benefit. The rule of thumb is simple: photographs go to JPEG, WebP or AVIF, while anything with sharp edges, flat areas or transparency belongs in PNG.
| Extension | .png |
|---|---|
| Category | Image |
| MIME type | image/png |
| Released | 1996 |
| Developed by | PNG Development Group / W3C |
| Compression | Lossless |
| Transparency | Yes |
| Animation | No |
PNG: frequently asked questions
- Why is my PNG so much bigger than a JPEG?
- Because PNG keeps every pixel while JPEG discards detail your eye is unlikely to notice. On a photograph that difference is enormous — often ten times the size. On a screenshot or logo the gap narrows or reverses, and PNG also renders those images correctly instead of smearing their edges.
- What is the difference between PNG-8 and PNG-24?
- PNG-8 uses an indexed palette of at most 256 colours and is very compact, which suits icons and simple graphics. PNG-24 stores full-colour pixels plus an alpha channel and handles gradients and photographs without banding. Most editors label them this way even though the format itself is one specification.
- Does PNG support animation?
- Not in the original specification. APNG is a later extension that adds animation frames and is now supported by all major browsers, but many tools still treat an APNG as a single static image. For animation, WebP or a short MP4 is a more reliable and far smaller choice.
- Does saving a PNG repeatedly degrade it?
- No. The compression is lossless, so decoding and re-encoding returns the same pixels every time. Quality only changes if you actively edit the image, resize it or export it through a lossy format along the way.
- How do I make a PNG file smaller?
- Reduce the dimensions first — nothing else saves as much. After that, quantising to a 256-colour palette often cuts the file by half or more with almost no visible change on graphics, and optimisers like oxipng or pngquant strip metadata and pick better filters without touching the visible image.
- Can I convert PNG to JPG and keep the transparency?
- No. JPEG has no alpha channel, so transparent areas are filled with a solid colour, usually white, and the change is permanent. If you need both transparency and small files, convert to WebP or AVIF instead — both keep the alpha channel and compress far better than PNG.