The format supports up to 8 bits per pixel allowing a single image to reference a palette of up to 256 distinct colors chosen from the 24-bit RGB color space. It also supports animations and allows a separate palette of 256 colors for each frame. The color limitation makes the GIF format unsuitable for reproducing color photographs and other images with continuous color, but it is well-suited for simpler images such as graphics or logos with solid areas of color. GIF images are compressed using the Lempel-Ziv-Welch (LZW) lossless data compression technique to reduce the file size without degrading the visual quality.

History of GIF

CompuServe introduced the GIF format in 1987 to provide a color image format for their file downloading areas, replacing their earlier run-length encoding (RLE) format, which was black and white only. GIF became popular because it used LZW data compression, which was more efficient than the run-length encoding that formats such as PCX and MacPaint used, and fairly large images could therefore be downloaded in a reasonably short time, even with very slow modems.

The original version of the GIF format was called 87a. In 1989, CompuServe devised an enhanced version, called 89a, that added support for animation delays (multiple images in a stream were already supported in 87a), transparent background colors, and storage of application-specific metadata. The two versions can be distinguished by looking at the first six bytes of the file (the "magic number" or "signature"), which, when interpreted as ASCII, read "GIF87a" and "GIF89a", respectively.

GIF was one of the first two image formats commonly used on Web sites, the other being the black and white XBM. JPEG came later with the Mosaic browser. The feature of storing multiple images in one file, accompanied by control data, is used extensively on the Web to produce simple animations. The optional interlacing feature, which stores image scan lines out of order in such a fashion that even a partially downloaded image was somewhat recognizable, also helped GIF's popularity, as a user could abort the download if it was not what was required.

How To Make Smaller GIFs

  1. The smaller your Web images are, the faster your site will load and the happier your visitors will be. In addition, many Web sites have restictions on the size of ad banners. These tips will help you make your GIFs as small as possible.
  2. Crop away any extra space around the image. Reducing the pixel dimensions of your image is the single most effective way to reduce the file size. If you use Photoshop, the Trim command works well for this.
  3. Reduce the number of colors in the image. For animated GIFs, reduce the number of frames in the image.
  4. Avoid dithering. Dithering may make some images look better, but it will increase the file size. If your software allows it, use a lower level of dithering to save extra bytes.
  5. Some software has a "lossy" option for saving GIFs. This option can significantly reduce the file size, but it also reduces image quality.
  6. Don't use interlacing. Interlacing usually increases the file size.
Tips To Make GIFs files:

  1. Avoid useless animation. Excessive animation not only adds to your Web page's download time, but many users find it distracting.
  2. GIF images with large blocks of solid color and horizontal patterns compress better than images with color gradations, soft shadows, and vertical patterns.
  3. When reducing colors in GIFs, you'll get the best compression when the number colors is set to the smallest possible of these options: 2, 4, 8, 16, 32, 64, 128, or 256.

What's the difference between GIF, JPG and PNG files?

The GIF Format: The GIF format is one of the most popular formats on the Internet. Not only is the format excellent at compressing areas of images with large areas of the same color, but it is also the only option for putting animation online. The GIF89a format also supports transparency, and interlacing. GIF files support a maximum of 256 colors, which makes them practical for almost all graphics except photographs. The GIF format supports transparency. This allows a graphic designer to designate the background of the image transparent. This means that if you place a transparent GIF in a yellow table cell, the background color of that image will turn yellow. The interlacing feature in a GIF file creates the illusion of faster loading graphics. What happens is that an image is presented in a browser in several steps. At first it will be fuzzy and blurry, but as more information is downloaded from the server, the image becomes more and more defined until the entire image has been downloaded.

Generally, GIF files should be used for logos, line drawings and icons. Avoid using it for photographic images, and graphics which have long stretches of continuous-tone in them. When you're designing GIF files, avoid using gradients and turn off anti-aliasing where possible to minimize the file size.

The JPEG Format: The JPEG format, with its support for 16.7 million colors, is primarily intended for photographic images. The internal compression algorithm of the JPEG format, unlike the GIF format, actually throws out information. Depending on what settings you use, the thrown out data may or may not be visible to the eye. Once you lower the quality of an image, and save it, the extra data cannot be regained so be sure to save the original. Any JPEG file can be saved as a Progressive JPEG. This is very similar to the interlaced GIF. As with GIF, this presents a low-quality image to your visitor at first, and over several passes improves the quality of it. Some graphic editing tools allow you to specify the number of passes before the image downloads completely. As a rule, the JPEG format should be used on photographic images, and images which do not look as good with only 256 colors.

The PNG format: The third, and newest, file format that's widely supported by the Web is PNG (pronounced Ping). PNG was developed to surpass the limitations of GIFs, and as a means by which developers can avoid having to worry about the patent licenses associated with other formats. PNG was designed to offer the main features of the GIF format, including streaming and progressive file formats. It also provides greater depth of color, catering to images up to 24 bit in color. It's expected that support for PNG will be widespread in the near future, although it will never completely replace GIF, as it doesn't support animation.


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