New web site owners frequently do not understand which image types to use with a web site. Once you understand the characteristics of each type of image, the choice becomes much clearer.
At this point we are not addressing multimedia images, such as Flash. We are reviewing standard static (non-animated) image types. There are currently only three image types that should be used on a web site: JPG (pronounced jay-peg), GIF (pronounced giff or jiff) and PNG (pronounced ping). JPG and GIF image types have been around since images were first introduced to the Internet in the 1990s. PNG is a newer type of image that shares many of the best characteristics of both JPG and GIF images.
You can use any of these image types on a web site, but you should select the best type for your needs. Never use other images, such as BMP (Windows bitmap) or TIFF (tagged image file format). The file sizes for these types of images are huge and they cannot be optimized properly for better performance. Most browsers will display them, but the web pages will load very slowly, even with high speed Internet access.
When to use GIF images
GIF images use the .gif file extension. GIF stands for Graphics Interchange Format. GIF images are limited to a maximum of 256 colors, which means that they should never be used for images with fine color gradiations, such as photographs. GIF images are best suited for line drawings, such as maps, cartoons, images with text, simple logos, icons, etc. Basically, they should be used for images that do not require a lot of color combinations. The GIF image format allows for transparent backgrounds, which make them useful for logos and icons. GIF files are a lossy format, which means that when GIF files are optimized using color reduction techniques, the lost data is non-recoverable.
When to use JPG images
JPG images use the .jpg or sometimes the .jpeg. JPEG stands for Joint Photographic Experts Group, but the acronym was shortened to JPG accommodate previous limitations with Windows PCs. JPG images support 16 million colors, which makes them ideal for photographs and images with fine gradiations. Transparency is not possible with JPG images, which is one limitation with this image type. JPG is a lossy file type, which means file details are lost when JPG images are optimized using compression.
When to use PNG images
PNG files are fairly new, but are increasingly being used on the web. PNG stands for Portable Network Graphics. The PNG image type can use up to 16.7 million colors and has transparency characteristics. It does, however, have some problems displaying colors correctly with Internet Explorer 6, but it appears that Microsoft corrected the problem with IE 7.
PNG images are a lossless file type, which means that they do not lose data when optimized. The PNG file type is the most flexible of the three, but due to the lossless nature of the file, the file sizes are frequently larger than with JPG or GIF files. However, if you need a file format that can be used with photographic quality images and has transparency capabilities, PNG is the best choice.