What is: PNG?

A PNG is a bitmap image file format. PNG stands for portable network graphics.

The PNG format was developed as a patent-free replacement to the GIF format created by CompuServ in 1989 (as in the ‘GIF 89A’ export function in early versions of Photoshop).

Features of the PNG file format

The new standard supports a range of features not available in the GIF format:

– alpha transparency: allowing ‘clean’ matting against colour backgrounds and image-wide opacity

– gamma and chromaticity correction: information about the originating platform is stored in the image file allowing it to compensate for a range of displays

– metadata: the file can contain text information on the image title, author, description and copyright

– smaller file size: PNG files average 30% smaller than their index colour GIF counterparts, and 30-40% than the equivalent RGB TIFF

– quicker display: due to an advanced interlacing scheme a preview of a PNG image is available after downloading on 1/64th of the image data compared with 1/8th for GIF files

The PNG format is best suited for images containing large areas of flat colour. It is not suitable as a file type for photographic images. (For photographic images prefer the use of the JPEG format.)