What Is a PNG File?

A PNG file is an image saved in the Portable Network Graphics format, with the extension .png. PNG uses lossless compression, so the image keeps every pixel exactly as it was saved, and it supports transparent backgrounds. That makes it the usual choice for screenshots, logos, icons and graphics with text. For ordinary photos it produces much bigger files than JPG.

You can open a PNG on almost any device without extra software. Every web browser, Windows, macOS, iPhone and Android can display one.

What is a PNG file?

PNG stands for Portable Network Graphics. It was created in the mid 1990s as a patent-free replacement for GIF, and it became a W3C Recommendation in 1996. Today it's one of the most common image formats on the web.

Two features define it.

• Lossless compression. PNG shrinks the file with DEFLATE, the same kind of compression used in ZIP files. Nothing is thrown away, so saving a PNG ten times gives you the same image as saving it once.
• Transparency. A PNG can store an alpha channel, which sets how see-through each pixel is. A logo saved as PNG can sit on any background colour without a white box around it.

Because it's lossless, PNG keeps hard edges and small text crisp. JPG blurs those areas slightly and can leave faint speckles around letters.

What is a PNG used for?

PNG is a good fit whenever the image has flat colours, sharp lines or needs a transparent background.

• Screenshots of apps, websites and documents
• Logos and icons, especially ones placed over photos or coloured backgrounds
• Diagrams, charts and illustrations with solid colours
• Images with text, like social media graphics or slides
• Master copies of graphics you plan to edit again

It's a weaker choice for photos. A photo has millions of slightly different colours and fine noise, which lossless compression can't pack down well. The same photo saved as PNG is often much larger than a good-quality JPG, and it looks no better on screen.

PNG vs JPG: which should you use?

Use PNG for graphics and anything that needs transparency. Use JPG for photos.

• Compression: PNG is lossless. JPG is lossy and discards detail you mostly won't notice.
• Transparency: PNG supports it. JPG doesn't, so transparent areas turn white or black.
• File size: PNG is small for flat graphics and large for photos. JPG is small for photos.
• Text and edges: PNG keeps them sharp. JPG can add blur and artefacts around them.
• Re-saving: PNG stays identical. JPG loses a little more each time you edit and save it.

If a site or form only accepts JPG, you can convert a PNG with PNG to JPG. Any transparent area gets filled with a solid colour during the conversion, so check the result if your image has a cut-out background. The image formats guide compares PNG and JPG with WebP, HEIC and SVG.

How to open a PNG file

Double-clicking a PNG usually works straight away. Here's what opens it on each system.

• Windows: the Photos app opens PNG files by default. Paint opens them too if you want to make simple edits.
• Mac: Preview opens PNGs, and you can also press the space bar in Finder for a quick look.
• iPhone and Android: PNGs saved to your photos or downloads open in the gallery or Files app.
• Any computer: drag the file into a Chrome, Edge, Firefox or Safari window.

If a PNG won't open, the file is often incomplete from an interrupted download, or it's a different format with a .png name. Try downloading it again, or open it in a browser, which tends to be forgiving about the extension.

Why is my PNG file so big, and how do I make it smaller?

A large PNG usually means one of three things: it's a photo, it has very large pixel dimensions, or it was saved without much compression effort. Screenshots from high-resolution screens can also be large because they hold a lot of pixels.

Ways to cut the size, from least to most change:

1. Recompress it. A PNG optimiser can repack the data more tightly with no change to the image.
2. Reduce the colours. Graphics with only a few hundred colours can be stored as an indexed PNG, which is much smaller. This works well for logos and diagrams and less well for gradients.
3. Resize it. If the image is 4000 pixels wide but will be shown at 1000, scaling it down removes most of the data.
4. Change the format. For photos, JPG or WebP will be far smaller. WebP also supports transparency, so it can replace PNG for cut-out images on websites.

Compress PNG handles the first two steps in your browser. You set a target size in KB, it tries lossless packing and colour reduction, and transparency is kept. The PNG compression guide explains when colour reduction looks fine and when it causes banding.

How to convert a PNG to another format

PNG converts cleanly to most formats because it starts with full detail. Pick the target based on where the image is going.

• PNG to JPG: for upload forms, email and photo sites that don't accept PNG.
• PNG to WebP: for websites, where smaller files load faster. Transparency carries over.
• PNG to PDF: for documents and forms that ask for a PDF. Several PNGs can become one multi-page file.
• PNG to SVG: for simple logos that need to scale to any size. Tracing works well on flat shapes and poorly on photos.

On Windows, you can also open a PNG in Paint and use Save as to pick JPEG. On a Mac, open it in Preview and use File, then Export, to choose another format.

Frequently asked questions