Web Graphic
Web browsers can only display graphics saved in special file types. The two main graphics formats used are the GIF and JPEG. It's important to know the differences and choose the best format for each image. The one defining principle that separates web graphics from all other graphics is the importance of file size. Web images have to be downloaded before they are viewed and so keeping the byte count as small as possible is vital.
Graphic Information Format (GIF)
• GIF files can contain up to 256 colors.
• GIF files are best for images with less, flatter colors. Use this for presentation graphics type images: charts, graphs, or text set as graphics. The few colors you use, the more efficient GIF files can give you the effect.
• GIF files can be transparent. This means you can select one color to "not show" causing your browser's background color to show through. This keeps your graphics from looking as if they're in boxes and visually makes them more a part of the page.
Joint Photographic Experts Group (JPEG)
• JPEG files are the best for images with many colors, such as photographs or scanned artwork. JPEG allows for up to 16 million colors.
• JPEG compression is variable. You can apply more or less compression to each individual image.
• JPEG files are not good for graphics with only a few colors, such as text set as graphics or graphics with areas of flat colors. If you use JPEG for these graphics, they will be larger than necessary, and look "mottled."
Progressive Network Graphics (PNG)
• PNG is the newest graphics file format for the Web, but it's only supported by newer browsers. These files will not appear in older browsers, so using this format will cause some of your site visitors to be unable to see your graphics
• PNG files are compact and versatile and can combine the best features of GIF and JPEG, such as the ability to have transparent backgrounds or the ability to contain images with millions of colors.