ART is a proprietary compression scheme designed and promoted by Johnson-Grace, a software development firm founded in 1992 by Steve Johnson and Chris Grace. Johnson-Grace develops software tools such as Web browsers for online services and end users.
As with JPEG, the degree of compression in ART is adjustable, and higher compression ratios are lossy. There is also a lossless mode. Johnson-Grace is marketing ART as a multi-purpose compressor to the online market and expects to adapt it to support audio, animation, and full-motion video in the future. As such, it will compete directly with codecs such as Intel's Indeo and the encoder/decoder packages from Cinepak and Microsoft. Johnson-Grace also plans to support the interleaving of text, graphics, audio, and video in the future.
Johnson-Grace claims that ART provides compression ratios that are typically three times smaller than either JPEG or GIF. This would, of course, be a boon to the online community if decompression were comparable to that of GIF, for example. Documentation from Johnson-Grace suggests that America Online's TurboWeb browser supports ART-compressed images.
Although the details of the algorithm are kept secret, Johnson-Grace has released some descriptive information. The algorithm seeks to analyze an image and identify a number of key features, such as color, noise, edges, and repetitive features, which are then prioritized by the relative contribution of each feature to the quality of the image. The prioritizing engine uses what Johnson-Grace calls fuzzy logic to classify and prioritize features of the image that is being compressed. Repetitive features are identified and linked in the image using a proprietary method. Image components are quantized, and low-priority features are ignored. As with JPEG, the degree of information loss increases with the degree of compression and is offset by the degree of redundancy for a particular compression ratio.
ART apparently uses a variety of known compression methods, including wavelet compression, to optimize compression of data. Presumably, the compression algorithm used is matched to the pixel depth of the image being compressed, because Johnson-Grace claims to compete with both GIF (256-color) and JPEG (24-bit color). Johnson-Grace states that ART-compressed images are typically less than 10K in size, which enhances what they call "speed-to-screen."
ART-compressed images may be layered, which means that they can be transmitted in stages over low-bandwidth modem lines, and can provide nearly immediate, though low-quality, display on the client's display device. The display quality then improves as the rest of the information is received and is progressively rendered.
Images are compressed with an ART toolkit called ART Press (MAC ART Tools on the Macintosh). Johnson-Grace was distributing the ART toolkit free of charge until the end of 1995. Pricing had not been set as of the time of this writing.
Technologically, the ART compression scheme represents a step forward in intelligence and bodes well for the future of compression. Superior results are obtained by matching the appropriate compression technology to the image being compressed. It remains to be seen whether Johnson-Grace will be able to popularize their system in their targeted online community.
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