posting
describing a patent taken out by Apple on alpha compositing.
Looking at patent US5379129
itself, I see that it contains no new intellectual
content. Usually, when I see a claim that Company X has patented
Obvious Technique Y, I'm skeptical. Whether you agree with the patent
system or not, in many cases the actual patent contains claims that
show that Company X has at least used Obvious Technique Y in a new
context, or figured out an implementation trick.
Here, however, the patent really is as dumb as it looks at first
glance. Every person whose name appears on it should be deeply ashamed
of themselves - the inventors, Konstantin Othmer (now a venture capitalist)
and Bruce A. Leak (later a cofounder of WebTV), for being so unaware
of the field that they actually believed it patentable, the Apple
lawyer, Mark Aaker, for not bothering to find out whether it was
patentable, and of course the primary examiner, Bentsu Ro, for letting
the patent go through. And Mr. Ro has been honored on the Patents
Recognition Wall, at that!
At the time that this patent was filed in 1992, the technique of
integral alpha had already been published for about 12 years: Smith,
A.R., Painting Tutorial Notes, SIGGRAPH '79 course on Computer
Animation Techniques, 1979, ACM. Alvy Ray Smith went on to receive an
Academy
Award for this work in 1996. In the interim, this seminal work has
been cited by many, many other researchers, including Bruce Wallace's
1981
SIGGRAPH paper, and the landmark Porter-Duff paper, which added
the additional innovations of premultiplied alpha and an image
algebra:
Porter, T. and T. Duff, Compositing Digital Images. Computer Graphics,
1984. 18(3): p. 253-259.
However, the Apple patent contains no trace of these later
innovations. Everything in it is in the Wallace paper's description of
Alvy Ray Smith's work, and in essentially identical mathematical
terminology to boot.
Thus, this patent can easily serve as a poster child for well
known techniques, widely published in the academic literature, and
then patented.
Apple is kindly agreeing to provide the use of this patent on
"reasonable and non-discriminatory" terms for use in the SVG
standard for vector graphics. Needless to say, the lawyers at Apple
who are involved in this fiasco should also be ashamed of themselves.
Update 2001 Oct 11: Apple has posted an amazingly strong
anti-patent position in
response to the W3C patent controversy.
Update 2001 Nov 20: I missed something important. The main
focus of this patent is per-channel alpha compositing, ie having a
separate alpha channel for each of the color channels. That's
not present in the Porter-Duff work. Claim 1 still suffers from
the ridiculous overbroadness described above. Per-channel transparency
is described in the literature (including Foley, van Dam,
Feiner, and Hughes), but is just a little more work to track down.
Also please see this call for
prior art on the PNG/MNG tools website.
www.levien.com