What is PNG?
PNG is a lossless image format: it stores every pixel exactly as it was saved, supports a full alpha transparency channel, and never degrades no matter how many times the file is opened and saved again.
PNG at a glance
- MIME type
- image/png
- File extensions
- .png
- Specification
- ISO/IEC 15948, and W3C PNG Specification
- Compression
- Lossless, DEFLATE with per-row filtering. Compression level changes speed and size, never quality.
- Transparency
- Full 8-bit alpha channel, plus simple index transparency in palette mode.
- Animation
- Not in the base format. The APNG extension adds it and is supported by all major browsers.
- Colour depth
- Up to 16 bits per channel; greyscale, palette and truecolour modes.
- Metadata
- tEXt, iTXt and zTXt chunks. EXIF is possible but far less common than in JPG.
- Support
- Universal in browsers, operating systems and editors.
Strengths and weaknesses
- Exact pixels — the only sensible choice for screenshots, UI assets, charts and line art.
- Real transparency, including soft anti-aliased edges.
- Safe to edit and re-save repeatedly with no cumulative loss.
- Photographs come out several times larger than the equivalent JPG or WebP.
- No support for HDR or wide-gamut workflows in normal use.
- Palette optimisation to reduce size can wreck gradients if applied blindly.
Why a PNG of a photo is so large
Lossless means the encoder must be able to reproduce every pixel, including the compression noise a JPG left behind. A 500 KB JPG photo commonly becomes a 3–5 MB PNG. Nothing is wrong when that happens — you are paying to store detail that JPG had already thrown away, plus its artefacts.
Converting a JPG to PNG does not restore quality. It stops further loss from happening; that is the whole benefit.
Palette compression and when it hurts
The usual way to make a PNG smaller is to reduce it to a 256-colour palette. On flat graphics that is invisible and cuts the file by half or more. On a gradient it produces banding: in our own measurements a palette-quantised gradient scored 0.9892 structural similarity with an average colour error (ΔE) of 3.04, which is visible to a normal viewer.
Our PNG compressor measures the palette version against the original and falls back to plain lossless compression when the similarity drops below 0.995, so a gradient never comes back banded.
Working with PNG files
Convert to PNG
- JPG to PNGConvert JPG images to PNG
- WEBP to PNGConvert WEBP images to PNG
- Compress PNGReduce PNG file size
Convert or edit a PNG file
Formats people compare this with
- JPGJPG (also written JPEG) is a lossy image format that discards visual detail the eye is least likely to notice, which is why photographs stored as JPG are typically 5–15 times smaller than the same image stored losslessly..
- WebPWebP is an image format developed by Google that offers both a lossy and a lossless mode, supports transparency and animation in either mode, and is typically 25–35% smaller than a JPG of comparable quality..
- AVIFAVIF stores a still image using AV1 video compression inside a HEIF container.
- GIFGIF is a lossless image format limited to a 256-colour palette per frame, with frame-based animation and one-bit transparency — obsolete for still images, still universal for short looping clips..