History of the Portable Network Graphics Format
Internet GIF tax,
PNG to the rescue!
The Portable Network Graphics image format, or PNG for short, is the
first general-purpose image format to achieve wide, cross-platform
since JPEG/JFIF arrived in the early 1990s.
Almost every major feature in PNG exists in other general-purpose
formats--specifically, GIF, JPEG, and TIFF--yet in January 1995, a
group of strangers felt compelled to band together and design another
image format from scratch. To understand why, it is necessary to
delve even further into history.
In 1977 and 1978, Israeli researchers Jacob Ziv and Abraham Lempel
published a pair of papers on a new class of lossless data-compression
algorithms in the journal IEEE Transactions on Information Theory.
These algorithms, now collectively referred to as ``LZ77'' and ``LZ78,''
formed the basis for an entire industry of software, hardware, and
subsequent research papers. One of the follow-up papers was by Terry
Welch and was published in the June 1984 issue of IEEE Computer.
Entitled ``A Technique for High-Performance Data Compression,'' it
described his research at Sperry into a fast, efficient implementation
of LZ78 called LZW.
By 1987, when CompuServe's Bob Berry was busy designing the GIF image
format, LZW was well established in the Unix world in the form of the
compress command, and in the PC world in the form of SEA's ARC.
As a fast algorithm with good compression and relatively low memory
requirements, LZW was ideally suited to the PCs of the day, and it became
Berry's choice for a GIF compression method, too. In turn, GIF became
the image format of choice on the Internet, particularly on the worldwide
discussion forum known as Usenet.
And so things remained largely unchanged until 1994. The introduction
(from a practical standpoint) of JPEG around 1992 or 1993 may have slowed
GIF's rising star slightly, but computational requirements and the
limitations of then-current graphics cards limited JPEG's acceptance for
several years. With the advent of graphical browsers for the World Wide Web
in 1992 and 1993,
GIF's popularity only increased: simple graphics with few colors
were the norm, and those were ideally suited to GIF's palette-based
format. With the release of Netscape Navigator 1.0 in 1994, progressive
rendering of images as they downloaded suddenly became widespread,
and GIF's interlacing scheme worked in its favor once more.
Then, three days after Christmas 1994, CompuServe quietly dropped a small
bombshell on an unsuspecting world: henceforth, all GIF-supporting software
would require royalties. In fact, the announcement was apparently the
culmination of more than a year of legal wrangling with Unisys, which had
inherited the Welch LZW patent in the 1986 merger of Sperry and Burroughs,
and which had by 1993 become considerably more aggressive about enforcing
its patent in software-only applications.
In any case, shortly after the holidays ended, word of the announcement
reached the Internet--specifically, the ever-volatile Usenet community.
As one might expect, the results were spectacular: within days, a full-fledged
conflagration of bluster, whining, flaming, vitriol, and general-purpose
noise had engulfed several of the Usenet newsgroups, among them
comp.compression and comp.graphics. But mixed in with the
noise was the genesis of an informal Internet working group led by Thomas
Its purpose was to design not only a replacement
for the GIF format, but also a successor to it: better, smaller, more extensible,