Image Tools Group

Part 1.
Other parts:

| 2. The GIF87a and GIF89a standards.
| 3. The creation of the animation.
| 4. The animated GIF-file optimization.

The computer graphics is divided into two categories: bitmap and vector graphics.
The vector graphics operates with segments and curves. A vector graphics image is being drawn up upon vectors, described by means of mathematical tool. A vector graphics image consists of an object, that may be freely translated, resized, recoloured regardless of other objects. There's no quality loss at the same time. The images of this kind never depend on resolution. The vector graphics is widely used in graphic fonts.
The bitmap graphics uses pixels for screening an image. Each pixel has a certain location and color. Because they can use a wide scale of shades and colors, the bitmap images are very popular in "natural" images creation. The bitmap images are bound to a certain resolution, that's why they may loose details or become "ragged" when scaled.

One of the most popular bitmap graphics format is GIF-format (Graphics Interchange Format). It was developed by experts of CompuServe computer net as a simple bitmap format for the network interchange. Because of the CompuServe net's popularity the GIF-format became wide spread and is supported by a majority of computer graphics programs. It is also embedded in a variety of Operating systems (MS DOS, Windows, Macintosh, UNIX, Amiga etc..). The popularity of the format is being increased because of its freely distributed specification and free use. Because the format initially was developed for the data streams, and not for the data storage in the file, its sequential structure perfectly fits the graphic image installation in the WWW-servers.
The positive features of the format include: the possibility of image series storage, addition of the overlapping text, mapping of the sequence of the images with delay period, the previous image recovery mode setting, the input of the entry specific for a certain application.
The negative features of the format include: restricted amount of the colors (not more than 256) from 24-bit color set, lack of the possibility of gray and color correction scaling, lack of data storage in patterns other than RGB (such as CMYK or HSI). Although in most cases 256 colors are quite enough, the storing of the photorealistic images in this format may lead to color gamut degradation.

The GIF-format is widely used in Internet. The most browsers that handle graphics support it. GIF-images are divided into: GIF87a and GIF89a. Both support 8-bit color manipulation and use the LZW (after Lempel-Ziv-Walsh) encoding for lossless compression. As a rule, the file's extension is GIF. The GIF89a-format also enables creation of transparent images and animations.

In Web the GIF-format is used for the creation of buttons and Web-page's complex graphics compound elements. Because of the animation features, the GIF-format is most widely used in Web-servers commercial banners creation.

Image Tools Group 2004.

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