Key facts
- MIME type image/png; every file starts with the 8-byte signature 89 50 4E 47 0D 0A 1A 0A.
- Data is stored in chunks (IHDR, IDAT, IEND, ...) each protected by a CRC-32 checksum.
- Compression is lossless DEFLATE, so photos as PNG are much larger than JPEG.
- Supports greyscale, palette (8-bit), truecolor and 8-bit alpha transparency; animated APNG is an extension.
- Created by screenshot tools, design apps (Figma, Photoshop) and image libraries such as libpng and GD.
How to open a .png file
Windows
Double-click to open in Photos; edit in Paint, Paint.NET or GIMP. Any web browser also opens PNG files.
macOS
Opens in Preview and Quick Look (press Space in Finder). Use Tools > Adjust Size in Preview for quick resizing.
Linux
Opens in the default image viewer, GIMP or a browser. Check integrity with pngcheck image.png and inspect it with identify image.png (ImageMagick).
Common problems and fixes
- PNG is corrupted, shows half an image or 'CRC error'
- The file is truncated or damaged, often from an interrupted download or an FTP transfer in ASCII mode. Re-download or re-upload it in binary mode; run pngcheck to see which chunk is broken.
- PNG file is far too large
- PNG is lossless, so photos and big screenshots get heavy. Resize it, run a lossless optimizer (oxipng, optipng) or palette-reduce with pngquant, or convert photos to JPG or WebP.
- Transparent background turns black or white
- The image was converted to a format without alpha (JPG) or the viewer ignores transparency. Keep it as PNG or WebP if you need a transparent background.
- File named .png will not open
- It may really be a JPEG, WebP or HTML error page saved with a .png name. Check with the file command or a hex viewer and rename or re-download accordingly.
Often converted to or from: JPG, WebP, ICO, SVG (by tracing), PDF