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From: kurtz le pirate
Subject: anti-aliasing & hdri
Date: 20 Feb 2005 10:54:06
Message: <kurtzlepirate-571F88.16540520022005@news.povray.org>
hello,

it seems that there is a problem (with megapov under mac os x) when 
using hdri : anti-aliasing is inactive. please have a look at : 
http://louisbel.free.fr/hdri/hdri.html
for more infos.

any one can explain ?

regards


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From: Christoph Hormann
Subject: Re: anti-aliasing & hdri
Date: 21 Feb 2005 09:33:22
Message: <4219F1B8.455EFA87@gmx.de>
kurtz le pirate schrieb:
> 
> hello,
> 
> it seems that there is a problem (with megapov under mac os x) when
> using hdri : anti-aliasing is inactive. please have a look at :
> http://louisbel.free.fr/hdri/hdri.html
> for more infos.
> 
> any one can explain ?

That works as intended and it is also not a speciality of MegaPOV. 
Antialiasing is active but with high intensities in the image you will
see aliasing artefacts with aa thresholds above 0.0 none the less (in
fact you only see them because you clip the color values for
display/writing to the file).

-- Christoph


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From: Warp
Subject: Re: anti-aliasing & hdri
Date: 21 Feb 2005 09:47:57
Message: <4219f49d@news.povray.org>
In povray.unofficial.patches Christoph Hormann <chris_hormann@gmx.de> wrote:
> That works as intended and it is also not a speciality of MegaPOV. 
> Antialiasing is active but with high intensities in the image you will
> see aliasing artefacts with aa thresholds above 0.0 none the less (in
> fact you only see them because you clip the color values for
> display/writing to the file).

  Note that this problem will most probably be fixed in a future version
of POV-Ray.

-- 
plane{-x+y,-1pigment{bozo color_map{[0rgb x][1rgb x+y]}turbulence 1}}
sphere{0,2pigment{rgbt 1}interior{media{emission 1density{spherical
density_map{[0rgb 0][.5rgb<1,.5>][1rgb 1]}turbulence.9}}}scale
<1,1,3>hollow}text{ttf"timrom""Warp".1,0translate<-1,-.1,2>}//  - Warp -


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From: Zeger Knaepen
Subject: Re: anti-aliasing & hdri
Date: 21 Feb 2005 13:20:55
Message: <421a2687@news.povray.org>
"Warp" <war### [at] tagpovrayorg> wrote in message news:4219f49d@news.povray.org...
> In povray.unofficial.patches Christoph Hormann <chris_hormann@gmx.de> wrote:
> > That works as intended and it is also not a speciality of MegaPOV.
> > Antialiasing is active but with high intensities in the image you will
> > see aliasing artefacts with aa thresholds above 0.0 none the less (in
> > fact you only see them because you clip the color values for
> > display/writing to the file).
>
>   Note that this problem will most probably be fixed in a future version
> of POV-Ray.

how?  I hope you don't reintroduce the clipping-before-averaging, because I see
this as a feature, not a bug.

cu!
--
camera{location-z*3}#macro G(b,e)b+(e-b)*(C/50)#end#macro L(b,e,k,l)#local C=0
;#while(C<50)sphere{G(b,e),.1pigment{rgb G(k,l)}finish{ambient 1}}#local C=C+1
;#end#end L(y-x,y,x,x+y)L(y,-x-y,x+y,y)L(-x-y,-y,y,y+z)L(-y,y,y+z,x+y)L(0,x+y,
<.5,1,.5>,x)L(0,x-y,<.5,1,.5>,x)               // ZK http://www.povplace.be.tf


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From: Arne Kleinophorst
Subject: Re: anti-aliasing & hdri
Date: 22 Feb 2005 06:11:37
Message: <421b1369$1@news.povray.org>
Sorry, but could someone explain me the advantage of the new clipping 
system as i can see none?

Arne

Zeger Knaepen schrieb:
> "Warp" <war### [at] tagpovrayorg> wrote in message news:4219f49d@news.povray.org...
> 
>>In povray.unofficial.patches Christoph Hormann <chris_hormann@gmx.de> wrote:
>>
>>>That works as intended and it is also not a speciality of MegaPOV.
>>>Antialiasing is active but with high intensities in the image you will
>>>see aliasing artefacts with aa thresholds above 0.0 none the less (in
>>>fact you only see them because you clip the color values for
>>>display/writing to the file).
>>
>>  Note that this problem will most probably be fixed in a future version
>>of POV-Ray.
> 
> 
> how?  I hope you don't reintroduce the clipping-before-averaging, because I see
> this as a feature, not a bug.
> 
> cu!
> --
> camera{location-z*3}#macro G(b,e)b+(e-b)*(C/50)#end#macro L(b,e,k,l)#local C=0
> ;#while(C<50)sphere{G(b,e),.1pigment{rgb G(k,l)}finish{ambient 1}}#local C=C+1
> ;#end#end L(y-x,y,x,x+y)L(y,-x-y,x+y,y)L(-x-y,-y,y,y+z)L(-y,y,y+z,x+y)L(0,x+y,
> <.5,1,.5>,x)L(0,x-y,<.5,1,.5>,x)               // ZK http://www.povplace.be.tf
> 
>


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From: Zeger Knaepen
Subject: Re: anti-aliasing & hdri
Date: 22 Feb 2005 08:47:25
Message: <421b37ed@news.povray.org>
"Arne Kleinophorst" <kle### [at] spamdebitelnet> wrote in message
news:421b1369$1@news.povray.org...
> Sorry, but could someone explain me the advantage of the new clipping
> system as i can see none?

small bright objects don't disappear in AA and focal blur looks more realistic.
In general, the new clipping system is a more realistic and a more logical
approach.

cu!
--
camera{location-z*3}#macro G(b,e)b+(e-b)*(C/50)#end#macro L(b,e,k,l)#local C=0
;#while(C<50)sphere{G(b,e),.1pigment{rgb G(k,l)}finish{ambient 1}}#local C=C+1
;#end#end L(y-x,y,x,x+y)L(y,-x-y,x+y,y)L(-x-y,-y,y,y+z)L(-y,y,y+z,x+y)L(0,x+y,
<.5,1,.5>,x)L(0,x-y,<.5,1,.5>,x)               // ZK http://www.povplace.be.tf


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From: Warp
Subject: Re: anti-aliasing & hdri
Date: 22 Feb 2005 09:49:34
Message: <421b467d@news.povray.org>
In povray.unofficial.patches Zeger Knaepen <zeger.knaepen@student.kuleuven.ac.be>
wrote:
> small bright objects don't disappear in AA and focal blur looks more realistic.
> In general, the new clipping system is a more realistic and a more logical
> approach.

  You are wrong.

  Firstly, antialiasing and focal blur are two different things.
Focal blur can keep the post-clipping, but with antialiasing post-clipping
is not a good solution.

  Secondly, post-clipping antialiasing is not more correct than the
pre-clipping version. Basically both are wrong. However, post-clipping
is more problematic than pre-clipping.

  Pre-clipped antialiasing causes some little annoyances in a few cases
(eg. if you try to make a subpixel-sized bright star) but in general it
gives high-quality smooth non-pixelated images. While it can be as an
annoyance, the resulting images have good visual quality (with regard
to antialiasing).
  Post-clipped antialiasing causes problems in a multitude of images
very frequently. You only have to have a surface which is much brighter
than 1 and a sharp edge adjacent to a dimmer surface (which is quite
a common situation) to get ugly pixelation of the edge. Pixels much
brighter than 1 are completely normal, not modelling flaws.
  Just look at The Kitchen image carefully to see the ugly post-clipping
artifacts (these were not taken into account in judging because it
was decided that these artifacts can be got ridden of in future
versions of POV-Ray).
  There are cases were post-clipping causes horrible artifacts which
basically destroy the image, while pre-clipping results in a smooth
and extremely nice-looking image (one such image I have seen is a
scene with wine glasses which have lots of small bright sparkles
due to how the glasses reflect and refract light; the result with
the pov3.6 was completely horrible while the result with pov3.5
was very nice and photorealistic).

  Note however, once again, that I'm not saying pre-clipping is *correct*.
I'm just saying that it gives much better results in the vast majority
of cases while post-clipping gives horrible results in many.

  What would be the most physically correct interpretation of
higher-than-1 pixels?
  Think about what happens in photography: Having areas of the image
which are much brighter than what the film can register is completely
normal. There's nothing abnormal there and this effect is in fact
used very frequently in photography: Just think about a nature photo
with the Sun visible: The Sun will be much brighter than what the film
can register, specially if the exposure time has been set so that the
rest of the photograph will have a good illumination.

  So what happens with these ultrabright areas?
  Answer: Color bleeding.

  In photography ultrabright areas will bleed their brightness to
surrounding areas of the film. In the above example the Sun will
look bigger than it really is and its brightness will usually fade
gradually (instead of getting a sharp edge).
  This is exactly what happens with all spots in the image which are
brighter than what can be registered: They will bleed their brightness
and look bigger on film than what they really are.
  Thus if you photograph for example a very small source of light in
an otherwise normal lighting and exposure conditions, it will look
like a much bigger light than it really is.

  Now, *that* would be the most physically correct solution for
brighter-than-1 pixels.

  It is still to be decided what kind of solution future versions of
POV-Ray will have, but even if a color-bleeding algorithm is not yet
implemented, pre-clipped antialiasing is still a much better solution
than the post-clipped one.

-- 
plane{-x+y,-1pigment{bozo color_map{[0rgb x][1rgb x+y]}turbulence 1}}
sphere{0,2pigment{rgbt 1}interior{media{emission 1density{spherical
density_map{[0rgb 0][.5rgb<1,.5>][1rgb 1]}turbulence.9}}}scale
<1,1,3>hollow}text{ttf"timrom""Warp".1,0translate<-1,-.1,2>}//  - Warp -


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From: Christoph Hormann
Subject: Re: anti-aliasing & hdri
Date: 22 Feb 2005 10:05:34
Message: <421B4AC5.34261D77@gmx.de>
Zeger Knaepen schrieb:
> 
> > Sorry, but could someone explain me the advantage of the new clipping
> > system as i can see none?
> 
> small bright objects don't disappear in AA and focal blur looks more realistic.
> In general, the new clipping system is a more realistic and a more logical
> approach.

It would be advisable not to start up this whole discussion again - it
won't have any influence on what is changed and what is not changed in
future POV-Ray development.

Or in other words: you are either both right or both wrong - choose
whatever pleases you more...

-- Christoph


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From: Jaime Vives Piqueres
Subject: Re: anti-aliasing & hdri
Date: 22 Feb 2005 13:35:57
Message: <421b7b8d@news.povray.org>
Warp wrote:
>   Just look at The Kitchen image carefully to see the ugly post-clipping
> artifacts (these were not taken into account in judging because it
> was decided that these artifacts can be got ridden of in future
> versions of POV-Ray).

   Yes, they are specially ugly on the fridge handles... :( In fact, I 
was going to use 3.5 due to this, but it was a bit slower and the 
lighting needed to be tweaked again, so I rendered finally with 3.6.1.

>   It is still to be decided what kind of solution future versions of
> POV-Ray will have, but even if a color-bleeding algorithm is not yet
> implemented, pre-clipped antialiasing is still a much better solution
> than the post-clipped one.

   I'm not technically qualified to say which is the best solution, but 
I certainly like more the results of pre-clipped aa, and the balance of 
pros/cons seems better as you say. In the case of focal blur is 
difficult to say what I like most, but pre-clipped focal blur seems a 
bit faster.

   Indeed, the color-bleeding you described so well seems very 
appropriate for photorealistic images (and I'm now dreaming with it 
implemented into POV), but it will be nice to have also the option to 
turn it off for other type of images.

--
Jaime


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From: Warp
Subject: Re: anti-aliasing & hdri
Date: 22 Feb 2005 14:04:14
Message: <421b822e@news.povray.org>
In povray.unofficial.patches Jaime Vives Piqueres <jaimevives@ignorancia.org> wrote:
>    Indeed, the color-bleeding you described so well seems very 
> appropriate for photorealistic images (and I'm now dreaming with it 
> implemented into POV), but it will be nice to have also the option to 
> turn it off for other type of images.

  Well, optimally pre-clipping, post-clipping and color-bleeding
algorithms will all co-exist as antialiasing options.

-- 
#macro M(A,N,D,L)plane{-z,-9pigment{mandel L*9translate N color_map{[0rgb x]
[1rgb 9]}scale<D,D*3D>*1e3}rotate y*A*8}#end M(-3<1.206434.28623>70,7)M(
-1<.7438.1795>1,20)M(1<.77595.13699>30,20)M(3<.75923.07145>80,99)// - Warp -


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