Re: Apple's SVG patent

> From: Les Barstow <lbarstow@vr1.com>

> >    result=((1-mask)*source)+(mask*destination).
> >
> >So this is an example of the worst kind of patent: a patent on a mathematical
> >expression.  Furthermore, a particularly obvious one that many, including
> >myself, have been using for years prior to the date of Apple's patent.
> 
> Oh, my.  They claim they've patented the bitmask?!?!?!?!?!

Go read the patent, please. They have patented using a pair of color
images as alpha channels. This might or might not have prior art (it
might well, and I would encourage people to report it) but it is not the
same as 'patenting bitbasks'


> Bitmasks were being used back in the early 1980's in commercial games.
> This patent wasn't requested until 1992.  APPLE THEMSELVES WERE USING
> THIS IN 1984!  Must be a leftover from the "let's patent the icon" days
> when they were fighting MS.

I agree with your general point about bitmasks or more generally alpha
channels (where the transparency  is not a one bit, on or off state but
represents variable opacity) being extremely well documented and
predating the Apple patent by a considerable time. Alpha channels area
well understood technlogy and are freely implemented in thousands of
software products.

The Apple patent, on the other hand describes taking a pair of color
images, call them A and B, and then using the *color* in B as the alpha
for A when compositing over some destination.

So to expand the equation

Redresult=((1-RedB)*RedA)+(RedB*Reddestination)
Greenresult=((1-GreenB)*GreenA)+(GreenB*Greendestination)
Blueresult=((1-BlueB)*BlueA)+(BlueB*Bluedestination)

Notice that 'alpha' does not occur anywhere in this system of equations.

You will not find that this system of equations is used in the SVG
specification and you are not required to use this system of equations
to implement SVG. Thus, the patent does not apply to SVG - it is not
"essential technology".

Of course, you should make up your own mind by reading the patent to
verify this conclusion for yourself, but it seems very clear cut to me.

-- 
Chris

Received on Thursday, 4 October 2001 08:11:33 UTC