OK. Cool. I'll see if I can find anything. I didn't have any specific one in
mind, I was just wondering how different a given scene would look.

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In article <3c78cad6$1@news.povray.org>,
 "Rune" <run### [at] mobilixnetdk> wrote:

> You can't talk about realistic. AA doesn't happen in nature... ;)

But it is intended to calculate a specific thing (the color over the 
entire pixel), and clipping makes that less accurate. And it apparently 
also happens with focal blur...not good!
I'd gladly take having unantialiased edges on superbright objects to 
have them work properly in other cases...I can work around the first 
problem by adding information to the scene, I can't work around the 
second (currently existing) problem. :-(
It also seems unintuitive to me: you have a bunch of small stars, and 
antialiasing wipes them out because they don't cover whole pixels. You 
make them brighter to compensate...nothing happens?!?
And with focal blur, the problem is worse...you simply will get a less 
realistic image.
Maybe some flag to limit the max value of a sample...radiosity uses 
similar tricks.


> The current AA give the same result as if you rendered the image at a 
> very large resolution and then scaled it down.

Not really...you could render to a format with a larger dynamic range, 
like RGBE, and process with tools that can handle it. ;-)

-- 
Christopher James Huff <chr### [at] maccom>
POV-Ray TAG e-mail: chr### [at] tagpovrayorg
TAG web site: http://tag.povray.org/

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In article <3c782656@news.povray.org>, Micha Riser <mri### [at] gmxnet> 
wrote:

> I do not like the idea of antialiasing only at objects frontiers.. as 
> textures are certainly one of the most important thing with POV-Ray.

I wasn't suggesting that this be done. I was talking about a way of 
specifying different parameters for edge and texture AA.

-- 
Christopher James Huff <chr### [at] maccom>
POV-Ray TAG e-mail: chr### [at] tagpovrayorg
TAG web site: http://tag.povray.org/

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"Christopher James Huff" wrote:
> Rune wrote:
> > You can't talk about realistic.
> > AA doesn't happen in nature... ;)
>
> But it is intended to calculate a specific thing
> (the color over the entire pixel), and clipping
> makes that less accurate.

No, it's a definition issue. The current definition of AA in POV-Ray is that
it is intended to calculate the average clipped color over the entire pixel
and it does that 100% accurately according to the definition.

If you want to change the definition, that can be discussed, but the current
behavior is not flawed or inaccurate in any way as it does exactly what it's
intended to do.

> And it apparently also happens with focal blur...not good!

I agree there. Focal blur is a completely different issue, and it should
take the unclipped colors as input. (And then we could get cool lens effects
without "cheating"!)

BTW, as I see AA and focal blur as two separate things, I think it should be
possible to use both at the same time (though it would be slow). I have
never understood why it's not possible.

> I'd gladly take having unantialiased edges on superbright
> objects to have them work properly in other cases...

But I wouldn't. I want my AA to smooth edges without exception. That's what
AA is for. To average colors is not the goal, it's just a mean to reach the
goal. The goal is smooth edges.

> It also seems unintuitive to me: you have a bunch of
> small stars, and antialiasing wipes them out because
> they don't cover whole pixels. You make them brighter
> to compensate...nothing happens?!?

Exactly what would happen if you rendered the image at a large resolution
and then scaled it down. You get smooth results. If your very bright stars
covered several pixels each, they would be completely jaggy using your
method. To me that's not intuitive when I have turned on AA to get smooth
results.

> And with focal blur, the problem is worse...you simply will
> get a less realistic image.

I agree.

> Maybe some flag to limit the max value of a sample...

You mean that the user should be able to change the value that samples are
clipped to, which is currently one? I wouldn't mind as long as the current
behavior keeps being the default.

Rune
--
3D images and anims, include files, tutorials and more:
Rune's World:    http://rsj.mobilixnet.dk (updated Feb 16)
POV-Ray Users:   http://rsj.mobilixnet.dk/povrayusers/
POV-Ray Webring: http://webring.povray.co.uk

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Rune <run### [at] mobilixnetdk> wrote:
> BTW, as I see AA and focal blur as two separate things, I think it should be
> possible to use both at the same time (though it would be slow). I have
> never understood why it's not possible.

  It's probably possible, but thought to be unnecessary.
  (However, it might give a better result if the focal blur is giving a
grainy result no matter what variance values you are giving.)

-- 
#macro N(D)#if(D>99)cylinder{M()#local D=div(D,104);M().5,2pigment{rgb M()}}
N(D)#end#end#macro M()<mod(D,13)-6mod(div(D,13)8)-3,10>#end blob{
N(11117333955)N(4254934330)N(3900569407)N(7382340)N(3358)N(970)}//  - Warp -

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>> Jan Walzer wrote:
>> IMHO it would be a _MAJOR_ design-flaw, if it wouldn't be this way ...

> In beta 11 ambient sphere of rgb 1 and rgb 100 produce the exact same
> image when rendered with +am2 +a0.0 +j0.0. Also DOF produces
> same image for both cases. The colors are clipped before aa
> and DOF calculations :(

/me doesn't like this ...

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"Warp" wrote:
>   It's probably possible, but thought to be unnecessary.

Yet it's a known fact that things very close to the focal point are jaggy.

And thinking about it, just like normally, the AA would only kick in where
necessary, so using normal AA settings together with focal blur would
probably only activate the AA on small amounts of the pixels, thus meaning
that it wouldn't even be much slower. (It's logical, I just didn't realize
it before.) I think it should be allowed. This is a feature request!

Rune
--
3D images and anims, include files, tutorials and more:
Rune's World:    http://rsj.mobilixnet.dk (updated Feb 16)
POV-Ray Users:   http://rsj.mobilixnet.dk/povrayusers/
POV-Ray Webring: http://webring.povray.co.uk

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Jan Walzer <jan### [at] lzernet> wrote:
>> In beta 11 ambient sphere of rgb 1 and rgb 100 produce the exact same
>> image when rendered with +am2 +a0.0 +j0.0. Also DOF produces
>> same image for both cases. The colors are clipped before aa
>> and DOF calculations :(

> /me doesn't like this ...

  So you prefer to have a white sphere which doesn't look antialiased at all?

-- 
#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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Rune wrote:
>
> Photos are not subject to antialiasing I think.

Digital (sampled) photos are. To sample correctly a signal
the sampling frequency must be at least twice the maximum
signal frequency. The signal must be Low Pass Filtered before
sampling or the high frequncy components will be aliased or
mirrored around 0.5*sampling frequency and appear as low
frequency interference in the sampled signal. The term aliasing
comes from this. High frequency components appear as low
frequency components.

> But blurring has nothing to do with antialiasing.

In ccd cameras the obvious choice for LPF would be to defocus
the lens. This blurring limits the spatial frequency and
prevents aliasing. So blurring _is_ antialiasing and operates
on the unclipped signal. The blurred signal is then sampled and
clipped at the detector.


_____________
Kari Kivisalo

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In article <3c7924be@news.povray.org>, Warp <war### [at] tagpovrayorg> 
wrote:

>   So you prefer to have a white sphere which doesn't look antialiased at all?

Yes.
Well, not precisely...a plain rgb 1 sphere with normal levels of 
lighting will render fine. But an object twice as bright should 
influence a pixel twice as much. You can work around a rgb 10 sphere not 
looking antialiased, you can't work around the values being clipped.

-- 
Christopher James Huff <chr### [at] maccom>
POV-Ray TAG e-mail: chr### [at] tagpovrayorg
TAG web site: http://tag.povray.org/

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