Umm. I'm tempted to write a long article here, since nobody yet have given
(no-one yet has given? argh! English is diffucult; you get it.) a thorough
explanation of AA in this thread.

Anti-aliasing is, as you know, a technique for reducing jaggies in the
image, resulting from sloped lines and the fact that the computer-screen is
a discrete medium, allowing only certain positions for your coloured dots.
(Unlike when you write with a plotter, for example.)

When you use the +axx.xx option, you turn on antialiasing. The float after
+a is the tolerance of the AA. Lower, the less tolerant. A value of 0.1 will
cause povray to trigger the AA-method for the pixel in question if the pixel
differ with 10% in colour from one of it's neighbours (to the top and left.)
A higher value will cause Povray to be more nonchalant, that is it lets
bigger differences pass.

The AA method actually shoots another ray; i.e. sample, into the scene
_between_ the two differing pixels. The resulting pixels (both the current
and the previous which differed) are then recalculated with the extra
information provided from the second sample. In that way, the image gets
smoother.

There is also an alternate method of AA; the adaptive. (Am I right here?)
Set the +am2 option, the usual +axx.xx and an additional option +rn, where n
is the recursion level. Povray will now; when it encounters two differing
pixels as before, shoot a new ray as before. But it doesn't stop here! It
does so n times, so that even the in-between "pixel" is re-sampled; giving
an even smoother image as result! Alas, the price is rendering time. Try to
model a refractive sphere over a checkered plane. If the ior is about 1.4,
you should see a "warped" version of the plane in the sphere, and it gets
typically _very_ aliased (that is you get interference patterns in the
sphere.) This effect is also visible in the horizon; where the plane meets
the sky. (!). Now, turn on antialiasing with +a0.0, +am2, +r4 and see what
happens to the render time...

In my experience, a depth (+r) higher than 2 gives almost no difference in
apperance. For high quality renders, I use +a0.1 +am2 +r3 as options. This
gives very nice results, but don't do it on test renders when you have a lot
of reflection and refraction going on in the scene!

This should be _failry_ accurate information; arrest me if I'm wrong on
something! (It's late in the evening too...) This was fun. :)

Regards,
- Simen Kvaal. (wannabe antialiasing expert...)



"25ct" <25c### [at] lineonenet> wrote in message news:39994efd@news.povray.org...
>    Hi all,
>             here is the result of my second project. I'm very pleased with
> this, especially as it is very close to the picture I had in my mind.
>    I still do not understand anti-aliasing, although it was rendered at
> 512x384 AA 0.3. Can anyone enlighten me as to getting it better?
>
>    Hope you like it.
>
>            ~Steve~
>
>
>

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