| Image Type | Gif | Jpeg | PNG |
|---|---|---|---|
| Pronunciation | Either"Jiff" or with a hard G, like "Give" | Jay-peg | Ping! |
| What it stands for | Graphics Interchange Format | Joint Photographics Expert Group | Portable Network Graphics |
| What it's good for | Images with a few distinct colours, including line art and simple colours. Supports animation. | Images with lots of colours and or shades, such as photos and lifelike images. No animation. | Upcoming format. Combines best features of GIF and JPG. Use sparingly for now, but keep an eye on it for future use. |
| What it' not good for | Photo-realistic images with colours that blend : They'll appear broken and jagged | Pictures - either graphics or photos - with large areas of a single colour | Photographs (size issue only) |
| Colours | 1-bit to 8-bit (256 colours) | 24-bit only (millions of colours | 8-bit, 24-bit or 32 bit |
| Animation | Yes | No | Yes, with MNG |
| Transparency | Yes, a single colour can be transparent | No | Yes. Plus 256 levels of partial transparency |
| Compression | Lossless ( ! ) | Lossy | Lossless ( ! ) |
| File Size | Images can be reduced to truly tiny file sizes, but compression isn't as good as it could be | File size tends to be larger than GIFs, but the target is not the same anyway | Compression is excellent (better than GIF) |
| Advantages | + Tiny Images |
+ Excellent colour retention + Excellent compression + Simple compression process |
+ Excellent compression, with no loss of quality |
| Disadvantages | - Complicated optimisation process - Certain visual effects (glowing light, feathered edges, vertical stripes ... compress poorly) - Not patent free !!! |
- Not much control over compression process - No transparency - No Animation |
- Not yet widely supported |
Source : The Unusually Useful Web Book / Everything we've learned about why sites succeed! by June Cohen / New Riders
A must read : Compression / Optimizing Web Graphics from Webreference.com ( http://webreference.com/dev/graphics/compress.html )