> It is a clear correction to previously incorrect behavior.  Previously
> POV-Ray was broken, it no longer is.

The previous behavior was correct; the current behavior is broken.

There was one single reason that people complained about the 3.5
antialiasing: the fact that it made objects which were smaller than one
pixel (stars) disappear.

Well, duh. If an object is 1/10000 of the image's width, then of course it
should be nearly invisible! The solution to the problems that these people
were having was to make their stars larger.

The reason people use antialiasing is to remove the jagged edges that are a
result of a finite resolution. The point of antialiasing is to simulate an
image of infinite resolution.

Now, let's say that my monitor had an infinite resolution. If I rendered an
infinite resolution image without antialiasing ('cause it wouldn't be
necessary), and displayed it on my monitor, what would my eyes see? They
would see what looks like the output of a POV-Ray 3.5 image, and not the
output of a POV-Ray 3.6 image.

I recognize that the 3.6 behavior is useful, but that usefulness is limited
to occasional situations, including the creation of stars with very tiny
very bright objects. But that is a misuse of the antialiasing feature. If I
make a little star shaped object (an actual star shape with 5 points), scale
it real tiny, make it bright and put it far away, and the renderer
interprets that as a square of light (a white pixel) on my screen, how is
that correct? Now, a grey pixel caused by the averaging of white samples and
black samples is not a star shape either, but it more accurately reflects
the area that my star shape covers out of the square pixel.

The oversaturation of an entire pixel from a single very bright sample can
be useful in this situation if that's the effect the user wants. However, if
it's usefulness that we're going for, then consider the recent images in
p.b.i.

At least twice now, users have posted images that suffer from bad
antialiasing, one of them even asking what was going wrong. Our answer was,
"you're making things too bright." So now, it seems, the user is required to
make scenes without bright objects if they want them to look good. That
doesn't sound very useful to me at all.

This isn't even restricted to colors like rgb 1000. If I made a sphere with
color rgb 2, the artifacts would show up along the more brightly lit parts
of the sphere. Setting the sphere's color to rgb1 would fix the problem, but
*change the appearance of the sphere* even where the antialiasing was *not*
a problem. The 3.6 antialiasing restricts my artistic freedom in a way I
can't even work around.

The solution to the "antialiasing ruins my stars" problem was always "use
bigger stars." The solution to the new "antialiasing ruins my bright
objects" problem is "POV-Ray 3.6 doesn't allow you to use bright objects."
This is a severe limitation. So if usefulness is the primary concern, then
the 3.5 antialiasing was a much better choice. It can also be pointed out
that the star problem was something that new users tended to be troubled
with, while the bright objects problem is something more likely to affect
experienced users, and therefore it has a much higher chance of ruining
*good* images.

But let's say that correctness is the primary concern. Well, it is difficult
to say what is "correct" in this case. The reason being that antialiasing
has always been a bit of a hack feature (not just in POV-Ray but in
everything); it tries to simulate high resolution where only low resolution
is available, and it does this by altering pixel colors.

I think, however, that there is one thing everyone can agree on: the primary
purpose of antialiasing has always been to remove jagged edges. POV-Ray
3.6's antialiasing does not always do that anymore.

I still argue that the output of an antialiased image should be the same as
if the image was rendered at infinite resolution and then sized down. That
is no longer the case in POV-Ray.

I admit that the new functionality is occasionally useful, which is why I'm
OK with Rune's suggestion to make it optional. But it should not be the
default.

 - Slime
 [ http://www.slimeland.com/ ]

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