What is a PNG file?
PNG — lossless image
What is it?
PNG compresses without discarding anything: the image you reopen is exactly identical, pixel for pixel, to the one you saved. No degradation at all, even after a hundred re-saves.
Its other major strength is transparency, and not just an on-off switch: every pixel carries an alpha channel that sets its opacity across 256 levels. That's what lets a drop shadow or a softened edge blend cleanly onto any background.
History & origin
PNG was born in 1996 out of a revolt. The GIF format, universal up to that point, relied on a compression algorithm patented by Unisys, which suddenly decided to start claiming royalties on it.
The web community responded by designing, within a few months, a free format that was technically superior and carried no patents at all. PNG became a W3C recommendation as early as 1996 — a rare case of a standard born from collective pushback.
Why it is useful
No quality loss whatsoever, high-precision transparency, and crisp rendering on text and fine lines.
It's the go-to format for screenshots, logos, icons, diagrams, and anything that needs to stay sharp.
Limits & drawbacks
On photographs, PNG files get very heavy: where a JPEG might weigh 300 KB, the same shot in PNG can weigh 3,000. A lossless compressor simply can't work miracles on millions of subtly different shades.
It doesn't support animation in its standard form, and has never managed to displace GIF on that front.
Practical tips
Use PNG whenever you need transparency or perfect sharpness. For a photo bound for the web, convert it to JPEG, WebP, or AVIF instead: you'll cut its size by a factor of ten with no visible difference.
Be careful when converting a transparent PNG to JPEG: the transparency will disappear, replaced by a solid background — usually black or white, and rarely the one you actually wanted.
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