Most image formats use some type of compression to make the files smaller in size. Many scanners are set to save the scanned images using the TIFF format by default. Even though the TIFF format supports compression, TIFF files still tend to be quite large. However, most image editing programs will let you convert TIFF files to other smaller formats.
If you are going to be using your images mostly on the Web, you will want to use a format that is well supported by the most popular web browsers. Currently, the most well supported image formats on the web are GIF and JPEG. Both of these formats support compression to produce smaller files that can be quickly downloaded from the Web.
The GIF (Graphic Interchange Format) can support a maximum of 256 colors. As a general rule, GIFs are better suited for graphics with areas of solid or flat color such as illustrations and logos. Other advantages to the GIF format are that it lets you create transparencies, interlacing, and animations.
A transparent GIF allows one color to be set as transparent, usually a background color. All Web graphics are square or rectangular and transparencies are a way to create the illusion of irregularly shaped images. Interlaced images display a rough version of the entire image quickly and then gradually fill in the details. This affords the viewers a sense of the image before it fully downloads, which helps those with slow dial-up connections. Animated GIFs are files that contain multiple images set to display like a slide show. They work on all major browsers and require no plug-ins.
The JPEG format (Joint Photographic Experts Group) was especially designed for images of photographic quality. JPEG images can contain up to 16 million colors. As a result, JPEGs are ideal for photographs, drawings, and any image with complex or subtle color gradations. Unlike GIFs, the standard JPEG file is not interlaced, a problem addressed by the Progressive JPEG. JPEG also does not support animation.
The PNG (Portable Network Graphic) was created an as alternative to GIF. GIF is a proprietary format, while PNG is an open source format that does not require the manufacturers of imaging software to pay royalties when they use the PNG format. PNG supports improved compression, but unfortunately it is not as widely supported as GIF and JPEG.