Portable Network Graphics

PNG (Portable Network Graphics, pronounced “ping”) is the lossless image format of the web. Screenshots on Windows, macOS, iPhone and most Android phones are saved as PNG, and so are logos, icons, diagrams and most exports from design tools. Every pixel comes back exactly as it was stored and the image can have a fully graded transparent background. The price is size: for photographs, PNG files are several times larger than JPG.

A format born from a patent dispute

At the turn of 1994 and 1995, Unisys and CompuServe announced licence fees for software that wrote GIF files, because GIF used the patented LZW compression. Within weeks a group of developers on Usenet, started by Thomas Boutell, drafted a free replacement. PNG 1.0 became a W3C Recommendation on 1 October 1996 and was published as RFC 2083 in January 1997. Versions 1.1 (1998) and 1.2 (1999) added colour management and international text, and the format became the international standard ISO/IEC 15948:2004. The third edition, a W3C Recommendation since 24 June 2025, finally brings animated PNG (APNG), HDR colour (cICP chunk, PQ and HLG) and an official chunk for Exif metadata into the specification.

What is inside a PNG

• Chunks. After an 8-byte signature the file is a sequence of chunks: IHDR (dimensions, bit depth), PLTE (palette), IDAT (image data), IEND, plus optional ones for gamma, ICC profile, text, physical resolution or Exif.
• Lossless compression. Each row is first predicted from its neighbours (five filter types), then compressed with DEFLATE, the same algorithm as ZIP. That is why PNG excels at flat colours and sharp edges and struggles with photographic noise.
• Colour types: greyscale, RGB, palette (up to 256 colours), each optionally with alpha. Depth 1 to 16 bits per channel. A 16-bit RGBA image holds 64 bits per pixel.
• Real transparency. The alpha channel has 256 or 65,536 levels, so soft shadows and anti-aliased edges blend into any background.
• No CMYK, no layers. PNG is a screen format. Adobe Fireworks once kept layers in private chunks, but other programs saw only the flat image.

“Lossy PNG” also exists. Tools like pngquant reduce a full-colour image to a 256-colour palette, which cuts size by half or more while staying a valid, lossless-stored PNG.

Opening and editing PNG

PNG opens everywhere: Photos and Paint on Windows, Preview on macOS, every Linux image viewer, every browser and phone gallery. GIMP, Krita, Paint.NET and Photoshop edit it with full transparency. For smaller files without quality loss, the open-source optimisers OxiPNG and optipng recompress the data more thoroughly.

Common PNG problems

PNG file is too big

Usually it is a photo saved as PNG, a screenshot of a video or a phone screenshot of a picture. Photos belong in JPG or WebP; see PNG to JPG. For graphics, try an optimiser or palette reduction first.

PNG has no transparent background

A grey and white checkerboard that will not go away is painted into the pixels. Many images offered as “transparent PNG” on the internet are like that. Only a file with an alpha channel is really transparent; in an editor you can check whether the image mode includes alpha.

Transparent background turns black or white

The receiving program does not support alpha, or the format you converted to cannot store it. JPG and BMP have no transparency at all, so our converter fills the background with white there. WebP, TIFF, TGA and GIF keep transparency, GIF only as on/off.

Print shop rejects PNG

Print needs CMYK and usually PDF or TIFF. PNG is always RGB, so the colour conversion happens at the printer. For logos it is better to deliver a vector file (SVG, PDF).

Converting PNG

PNG is converted to JPG for smaller photos, to PDF for documents, to ICO for website icons and to WebP for the web. Into PNG people convert JPG before editing and SVG where a vector cannot be used. With our converter, PNG output keeps transparency, from animated GIF or APNG only the first frame is used, and photos tagged as rotated are turned upright. Conversion to ICO shrinks the image to at most 256 pixels. PNG to SVG traces the shapes in black and white only; colours are not vectorised. PNG to TXT runs text recognition (OCR).

PNG at a glance

More: the W3C PNG specification, the PNG home site and the Library of Congress format description.