LZW


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LZW

(Lempel-Ziv-Welch) A data compression method that stems from techniques introduced by Jacob Ziv and Abraham Lempel. LZW has been used in many hardware and software products, including V.42bis modems, GIF, TIF and PDF files and PostScript Level 2. The LZ77 method creates pointers back to repeating data, while LZ78 creates a dictionary of repeating phrases with pointers to those phrases.

The Welch in Lempel-Ziv-Welch is for Terry Welch, the Unisys researcher who created an enhanced version of these methods that was patented by Unisys. Unisys collected royalties from thousands of software publishers whose applications used this algorithm until the patents expired in 2004. This was the most widely licensed data compression patent in history. See PNG.
References in periodicals archive ?
In addition, the bundling of TransForce Model 350 as a subcomponent of Volantis' Mariner Digital Media Server also includes a direct license to Unisys Corporation's LZW patent, enabling users to generate and serve unlimited quantities of the GIF, TIFF, and other file formats that employ the LZW compression/decompression method covered in this patent.
Additionally, TransForce MTS incorporates worldwide licenses to Unisys Corporations' LZW patent (used in GIF and other image formats) and Thomson/Fraunhofer's MP3 patent suite, which enable customers to use the product to generate unlimited quantities of these data files.
SEATTLE -- PictureIQ(TM) Corporation, the image optimization company, today announced that it has directly licensed Unisys Corporation's LZW patent on a worldwide basis for use in PictureIQ TransForce(TM) and other PictureIQ imaging solutions.
More importantly, added Angela Finet, Millstar's Project Leader for EEM '97, "We had to find a new compression technology since Unisys began enforcing their patent on TIFF LZW compression, which is what we used last year.
Enhancements include color imaging support for MPW, CodeWarrior and Symantec compilers featuring color decompression and display, faster scale-to-gray, bilinear interpolation or color pixel smoothing at high zoom factors, fast color palette generation, and additional format support including JPEG, TIFF LZW, DCX, GIF and BMP.
This new release includes 32 bit image compression/decompression and image manipulation for Windows 95 and Windows NT, and supports several new image formats including TIFF Color, LZW, DCX, GIF and BMP.
The need for fingerprint specific compression can be demonstrated by this example: a sample fingerprint with a resolution of 589 pixels by 605 pixels, 8-bit grayscale results in a file size of 325 KB when compressed with the standard lossless compression technology LZW.