In POV-Ray 3.5 antialiasing was done after clipping the color to the range
0...1. In POV-Ray 3.6 this has been changed so that antialiasing is done
before clipping.

Before 3.6 this issue had been discussed here in the groups on several
occasions and there were both quite some people who found the 3.5 behavior
correct and quite some who found it incorrect.

The commonly mentioned advantage of the new 3.6 behavior is that starfields
with sub-pixel sized (but very bright) stars will now show up.

The disadvantage is that all objects or textures with very bright (or
brightly lit) colors will now have jagged edges even though AA is turned on.

This can be demonstrated by this simple scene:
// +w160 +h120 +a0.3
sphere {z, 0.5 pigment {rgb 10} finish {ambient 1 diffuse 0}}

One might argue that the sphere doesn't need to be that bright, but if it's
used as a light-source in a radiosity scene, it might actually need to be
that bright.

One of the advanced sample scenes that comes with both POV-Ray 3.5 and 3.6
"bwstripe.pov" is seriously ill affected by the new behavior, and looks
really bad, since it was highly dependent on the color clipping being done
prior to the antialiasing.

Also, in povray.binaries.images, several people have seen the bad effects of
the new behavior. On an overexposured white table the objects have jagged
edges, and in another picture with some laser beams, those beams are awfully
jagged.

Despite how bad these jagged edges look, some people argue that they are
*desirable* because they are *realistic* since real cameras work the same
way. I don't think this makes sense. In real cameras overexposure makes a
glow that is often much larger than a pixel. This is the job of focal blur
(which *should* be done prior to clipping), not antialiasing.

Anyway, my point is, making a new feature is fine as long as it is optional,
but making it at the cost of braking an old feature is very disrespectful to
those who liked the old feature and found it to be the current behavior.

I hope the new antialiasing behavior will either be changed back or be made
optional very soon...

Rune
-- 
3D images and anims, include files, tutorials and more:
rune|vision:  http://runevision.com
POV-Ray Ring: http://webring.povray.co.uk

Post a reply to this message