Page 144 - DCAP303_MULTIMEDIA_SYSTEMS

Multimedia Systems

notes 8.4 animation file formats

8.4.1 adobe flash

Adobe Flash is a multimedia platform used to add animation, video and interactivity to Web
pages. Flash is frequently used for advertisements, games and flash animations for broadcast.
More recently, it has been positioned as a tool for “Rich Internet Applications” (“RIAs”).
Flash manipulates vector and raster graphics to provide animation of text, drawings and still
images. It supports bidirectional streaming of audio and video, and it can capture user input via
mouse, keyboard, microphone and camera. Flash contains an object-oriented language called
ActionScript and supports automation via the Javascript Flash language (JSFL).
Flash content may be displayed on various computer systems and devices, using Adobe Flash
Player, which is available free of charge for common Web browsers, some mobile phones and a
few other electronic devices (using Flash Lite).
file format
Flash files are in the SWF format, traditionally called “ShockWave Flash” movies, “Flash movies,”
or “Flash applications”, usually have a “.swf” file extension, and may be used in the form of a
Web page plug-in, strictly “played” in a standalone Flash Player, or incorporated into a self-
executing projector movie (with the .exe extension in Microsoft Windows). Flash Video files have
an “.flv” file extension and are either used from within .swf files or played through a flv-aware
player, such as VLC, or QuickTime and Windows Media Player with external codecs added.
The use of vector graphics combined with program code allows Flash files to be smaller—and
thus for streams to use less bandwidth—than the corresponding bitmaps or video clips. For
content in a single format (such as just text, video or audio), other alternatives may provide better
performance and consume less CPU power than the corresponding Flash movie, for example
when using transparency or making large screen updates such as photographic or text fades.
In addition to a vector-rendering engine, the Flash Player includes a virtual machine called the
ActionScript Virtual Machine (AVM) for scripting interactivity at run-time, support for video, MP3-
based audio and bitmap graphics. As of Flash Player 8, it offers two video codecs: ON2 Technologies
VP6 and Sorenson Spark, and run-time support for JPEG, Progressive JPEG, PNG and GIF. In the
next version, Flash is slated to use a just-in-time compiler for the ActionScript engine.
Flash Player is a browser plugin, and cannot run within a usual e-mail client, such as Outlook.
Instead, a link must open a browser window. A Gmail labs feature allows playback of YouTube
videos linked in e-mails.
8.4.2 Graphics interchange format (Gif)
The Graphics Interchange Format (GIF) is a bitmap image format that was introduced by
CompuServe in 1987 and has since come into widespread usage on the World Wide Web due
to its wide support and portability.
The format supports up to 8 bits per pixel thus allowing a single image to reference a palette
of up to 256 distinct colours. The colours are chosen from the 24-bit RGB colour space. It also
supports animations and allows a separate palette of 256 colours for each frame. The colour
limitation makes the GIF format unsuitable for reproducing colour photographs and other
images with continuous colour, but it is well-suited for simpler images such as graphics or
logos with solid areas of colour.
The GIF images are compressed using the Lempel Ziv Welch (LZW) lossless data compression
technique to reduce the file size without degrading the visual quality. This compression technique
was patented in 1985. Controversy over the licensing agreement between the patent holder,
Unisys and CompuServe in 1994 spurred the development of the Portable Network Graphics
(PNG) standard; since then all the relevant patents have expired.

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