For general-use Web graphics, use GIF, JPEG, or PNG.
| Format | Compression | Platforms | Colors | Notes |
| JPEG (Joint Photographic Experts Group) | Lossy | Unix, Win, Mac | 24-bit per pixel; 16.7 million colors. | JPEG is a compression algorithm; the format is actually JFIF (JPEG File Interchange Format) |
| GIF (Graphic Interchange Format) | Lossless | Unix, Win, Mac |
8-bit; 256 colors (216 web palette). |
LZW compression algorithm developed by Compuserve; patent now held by Unisys, which charges for use of the code in graphics programs. Once Unisys began enforcing its patent (in 1995), programs began moving to PNG. |
| BMP (Bitmap graphics) | Uncompressed | Win | 24-bit; 16.7 million colors. | Like all uncompressed formats, these files are very large. |
| PICT | Lossless | Mac | Very little compression; large files | |
| TIFF (Tag Interchange File Format) | Lossless or uncompressed | Unix, Mac, Win | TIFF-LZW uses the propietary LZW compressions (see GIF). | |
| PNG (Portable Network Graphics) | Lossless | Unix, Mac, Win | 48-bit; "true color" plus transparency | Will likely replace GIF. Supported in IE, NN 4 and above. A WC3 specification. |
Lossy formats provide compression by "throwing out" some information. Once a file is saved in one of these formats, the lost information cannot be retrieved. When saving into a lossy format, such as JPEG, the image quality degrades with each save. The amount of loss can be controlled in most graphics editors, but the image quality comes at the cost of file size. If you're editing jpegs, be sure to save at the highest quality setting. Or better yet, edit in a lossless format. (For more on this, see Saving and Exporting Images)
Lossless formats compress but do not lose any information. In lossless formats, image quality remains the same no matter how many times the image is edited and saved. GIF is lossless, but is limited to 256 colors. PICT and TIFF are lossless, but are generally too large for use on the web. PNG is lossless, and supports up to 48 bits of data per pixel (color plus transparency and gamma or brightness values).
Bitmapped: Graphic information is stored as pixels. Uncompressed bitmapped graphics can be very large files, as each pixel has to be described.
Vector: Graphic information is stored as mathematical equations which decribe the areas, color, etc.. Vector graphics are generally smaller files. A new format, Scalable Vector Graphics (SVG), is an XML-based description of graphic content which is rendered by a browser. SVG graphics offer animation, interactivity, and broad compatibility. Currently, most browsers require a plugin to view SVG content. Adobe's SVG viewer is the most popular.More info: http://www.w3.org/Graphics/SVG/Overview.htm8
Stanford Academic Computing graphic file formats info
Yale Library comparison (GIF, JPEG, PNG)
World Wide Web Consortium (W3C) Web Graphic formats