I have a problem with a highly detailed cloth texture on a jacket. It looks
good from near but very bad and grainy from far due to an aliasing effect.
(I have pictures but I'm sure you can imagine what I mean - lemme know if
you want the pics.)
How can I solve that problem?
I have done a search here and I have found some postings where people
describe similar problems. The answer they usually got was just "increase
AA".
I have tried rendering the scene with +a0.1 +am2.
The ugly effect was reduced, but not removed, and that small improvement
came at the price of a very washed-out look and an increase in rendering
time from like twenty seconds to about half an hour (!).
C'mon, there must be a better solution!
In 3DS MAX (which I ported the scene and texture from), the thing renders in
three seconds, and it looks excellent from near *and* far.
So what kind of trick is MAX pulling and is there a way to "emulate" it in
POV?

Thanks a lot in advance,
Ansgar

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Ansgar <Tem### [at] gmxde> wrote:
> C'mon, there must be a better solution!

  Decrease the resolution of your texture.

> In 3DS MAX (which I ported the scene and texture from), the thing renders in
> three seconds, and it looks excellent from near *and* far.
> So what kind of trick is MAX pulling

  http://en.wikipedia.org/wiki/Trilinear_filtering

  http://en.wikipedia.org/wiki/Anisotropic_filtering

> and is there a way to "emulate" it in POV?

  Not really.

-- 
                                                          - Warp

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Am Fri, 27 Apr 2007 14:35:46 -0400 schrieb Ansgar:

> I have a problem with a highly detailed cloth texture on a jacket. It
> looks good from near but very bad and grainy from far due to an aliasing
> effect. (I have pictures but I'm sure you can imagine what I mean - lemme
> know if you want the pics.)
> How can I solve that problem?
> I have done a search here and I have found some postings where people
> describe similar problems. The answer they usually got was just "increase
> AA".
> I have tried rendering the scene with +a0.1 +am2. The ugly effect was
> reduced, but not removed, and that small improvement came at the price of
> a very washed-out look and an increase in rendering time from like twenty
> seconds to about half an hour (!). C'mon, there must be a better solution!
> In 3DS MAX (which I ported the scene and texture from), the thing renders
> in three seconds, and it looks excellent from near *and* far. So what kind
> of trick is MAX pulling and is there a way to "emulate" it in POV?
> 
> Thanks a lot in advance,
> Ansgar

I guess MAX uses MIP-mapping to make anti-aliasing of textures that are
far away faster. Anyhow, you could try to render the hole picture at a
higher resolution and decrease your AA settings, then scale it down in a
graphics program. If you want to emulate MIP-mapping you have to try to
measure the distance of the object to the camera and apply a downscaled
picture, if it is very far away. That mayot work, if the object has
parts that are far away and other parts that are very near to the camera
or even if you view the texture at a shallow angle. It would look blurry
in some parts and aliased in others. POV has no real support for any
LOD-techniques (level of detail). That is not so important for raytracers,
but however...

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Lukas Winter <web### [at] removeitgeloeschtnet> wrote:
> POV has no real support for any
> LOD-techniques (level of detail). That is not so important for raytracers,

  What makes you think so? LOD filtering is equally important in raytracing
as it is with any other rendering technique. The problem is that it's more
difficult to implement in raytracing because of all the reflections and
refractions and such.

  The movie Cars was raytraced (instead of scanline-rendered as usual),
and they used mip-mapping and LOD filtering. They used some type of ray
volume algorithms to determine the mipmap levels. It's not trivial, but
possible.

-- 
                                                          - Warp

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Thanks for the answers, guys.
I guess I'll have to craft a simple MIP-mapping algo myself, then.

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Am Fri, 27 Apr 2007 16:54:07 -0400 schrieb Warp:

> Lukas Winter <web### [at] removeitgeloeschtnet> wrote:
>> POV has no real support for any
>> LOD-techniques (level of detail). That is not so important for
>> raytracers,
> 
>   What makes you think so? LOD filtering is equally important in
>   raytracing
> as it is with any other rendering technique. The problem is that it's more
> difficult to implement in raytracing because of all the reflections and
> refractions and such.
> 
>   The movie Cars was raytraced (instead of scanline-rendered as usual),
> and they used mip-mapping and LOD filtering. They used some type of ray
> volume algorithms to determine the mipmap levels. It's not trivial, but
> possible.

With a scanline renderer, the times decrease more trastically when you
lower the polygon count. You can also circumvent LOD-techniques for
textures with a raytraces by doing a lot of supersampling (like depth of
field). If I implemented a raytraces (which I partly dream of and partly
already have done) I would try to include such things (by keeping a cone 
along with each ray or each bundle of rays). But it's not a must, as there
are other features in raytracers that make up for it.

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