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[DRAFT] QA Tips - Gif versus PNG

From: Karl Dubost <karl@w3.org>
Date: Thu, 18 Sep 2003 11:54:59 -0400
To: www-qa@w3.org
Message-Id: <75061649-E9F0-11D7-8969-0003934BEBF0@w3.org>

This is a draft Open for comments for future publications               
  http://www.w3.org/2001/06tips/

It's there for a long time, I just have forgotten to announce it. Sorry.


************************
Title: Use Gif or PNG

Draft - PNG vs GIF

    This is a draft "webmaster tip", under work and review by the
    [7]Quality Assurance Team, and shouldn't be considered as an official
    tip from W3C while it remains a draft.

       [7] http://www.w3.org/QA

GIF versus PNG

GIF

    The GIF format is a format which compresses files using an algorithm
    called LZW, which keep traces of the colors and helps to reduce the
    size of the file. The LZW algorithm was protected in USA by a
    [8]patent hold by the company Unisys. The Unisys LZW patent expires 
in
    the USA on June 20, 2003 though LZW patents are still in force in
    Canada, France, Italy, Germany, the United Kingdom, and Japan.

       [8] http://www.delphion.com/details?&pn=US04558302__

PNG

    NG (Portable Network Graphics), an extensible file format for the
    lossless, portable, well-compressed storage of raster images. PNG
    provides a patent-free replacement for GIF and can also replace many
    common uses of TIFF. Indexed-color, grayscale, and truecolor images
    are supported, plus an optional alpha channel. Sample depths range
    from 1 to 16 bits.

    For the Web, PNG really has three main advantages over GIF:
      * alpha channels (variable transparency),
      * gamma correction (cross-platform control of image brightness),
      * two-dimensional interlacing (a method of progressive display).

    PNG also compresses better than GIF in almost every case (5% to 25%).

Further Reading

      * [9]PNG Homepage
      * [10]Benefits of the PNG image format
      * [11]PNG W3C Recommendation

       [9] http://www.libpng.org/pub/png/
      [10] http://www.atalasoft.com/PNG.aspx
      [11] http://www.w3.org/TR/PNG

--
Karl Dubost - http://www.w3.org/People/karl/
W3C Conformance Manager
*** Be Strict To Be Cool ***
Received on Thursday, 18 September 2003 11:55:04 GMT

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