The PNG Image Format

PNG is a relatively new invention compared to GIF or JPEG, although it's been around for a while now. (Sadly some browsers such as IE6 still don't support them fully.) It stands for Portable Network Graphics. It was designed to be an alternative to the GIF file format, but without the licensing issues that were involved in the GIF compression method at the time. There are two types of PNG: PNG-8 format, which holds 8 bits of colour information comparable to GIF), and PNG-24 format, which holds 24 bits of colour (comparable to JPEG).

PNG-8 often compresses images even better than GIF, resulting in smaller file sizes. On the other hand, PNG-24 is often less effective than JPEGs at compressing true-colour images such as photos, resulting in larger file sizes than the equivalent quality JPEGs. However, unlike JPEG, PNG-24 is lossless, meaning that all of the original image's information is preserved.

PNG also supports transparency like GIF, but can have varying degrees of transparency for each pixel, whereas GIFs can only have transparency turned on or off for each pixel. This means that whereas transparent GIFs often have jagged edges when placed on complex or ill-matching backgrounds, transparent PNGs will have nice smooth edges.