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GIF (Graphics Interchange Format) is the most common graphic format on the Web. GIF can be pronounced with a hard or soft "g". Invented in 1987 by Compuserve to allow images to be displayed on its network, GIF is a powerful, useful file format suitable for many types of images. It allows for 256 colors, non-lossy compression, transparency, interlacing, and animation. GIF is most useful for graphics with clear separation of colors such as line art or cartoons.
GIF can do more than displaying pictures one after another, such as:
There are two very important things about GIFs. One is that they are Cross-platform, meaning any kind of computer can view them. Many other file formats cannot be sent from one system to another, but people have been sending GIF files back and forth to each other ober the Internet since 1987. And because all kinds of computers are being used to view web pages, it's critical that we are all able to view the same graphic.
The second important thing about GIFs is that they are compressed. Compression makes a file smaller -- smaller in file size, not in dimensions. For instance, a 2 x 2-inch image in the graphic file format called TIFF might be 900k. The same 2 x 2-inch graphic in the GIF file format might be 5k.
There are two kinds of GIFs, 87a and 89a. The former was developed in 1987 and not used much anymore. The latter was developed in 1989 and is the current standard. The biggest difference between the two is that 89a files can have one color that is transparent.
Transparency is a big deal. It's what lets the background color of a page show through part of an image. You can choose one color in your image to be transparent. Without transparency, most of the graphics on the web would be set in a big white box. The other most common graphic format that is used on the web, JPEG, cannot have any transparent areas.
Another important feature of GIFs is that you can create animations with them. Let's see a GIF animation file without and with transparent background.
A third important advantage of GIFs is interlacing. Have you noticed that some web graphics appear in layers, each layer adding more clarity to the image? That's interlacing. It lets you get an idea of what the graphic is going to be, just in case you might want to skip it and move on to another page. It also allows you to scroll up and down and read any text that appears while waiting for the graphic to fully resolve itself. A JPEG file can be "progressive," which is similar to interlaced.
Animated GIF can be annoying if you are not careful. See this tutorial for how to make animated gif.