Compression is a technique used to make a file or data stream small to achieve faster transmission or to use lesser storage space. The two types of compression generally used in designing web banner are lossless and lossy compression.

GIF animated banners have many advantages when used to advertise a website. Most of the website owners accept animated gif banners with a file size lesser than 12K. A skilled banner designer applies the following tricks to reduce the file size of the animated gif banner.

1-Colors: GIF is the short form of Graphics Interchange Format. As a gif format can store 2-256 different colors, when an animated gif banner design is created the designer works in a 256-color palette. To minimize the file size he/she uses only a few contrasting and complimentary web colors because more colors make the file size larger. Also, the smallest possible color palette enables him/her to use more creative special effects in the animation.

2-Dithering: In order to view a full-color graphic image on a 256-color monitor screen, computers have to simulate the colors they cannot display. They do this by a process called dithering where they combine pixels from a 256-color palette into patterns that approximate other colors. At a distance, for the human eyes, the pixels appear as a single color, while at closer, the graphic image will give a pixilated and speckled look. If dithered images are used in an animated banner, the file size will increase. This dithering happens when photographs with thousands to millions of colors are used in a gif banner. So to minimize dithering, use photos that employ only few colors.

3-Interlacing: Interlacing is a process in which a part of data from a single graphic image is stored in multiple sequences. Here, sets of lines, equally spaced, from the original image are stored together and these sets are seen on one above the other in sequence. First a set of horizontal lines appears before the full image is loaded. In interlacing a part of the image appears on the screen instead of waiting for the entire image to download. With the interlacing the end user knows very well that a graphic image will appear soon rather than viewing a blank space. But the problem is that interlacing increases the loading time of the animated banner. So you have to decide, which is more important-increase in the overall file size or the interlacing effect.

4-Number of Frames: The file size of any animation can be reduced by employing the smallest possible number of frames or rotations. Certain special effects take more time to load than other special effects, both in animated gif banners as well as rich media banners. Some effects like glow effect and fading text effect take longer time to load since the animation usually needs more frames to bring about the effect and glows and fades use larger color palettes. Lossy compression helps to reduce the file size if you want glow and fade text effects in your animated banners