"Christopher James Huff" wrote:
> Maybe a smarter algorithm would be possible...if
> there are other high-brightness pixels nearby,
> you are at the edge of a bright object, so clip
> and supersample, otherwise supersample then clip.

I have had similar considerations, but have not managed to get any further
than wondering what method could be used. I don't think it will be trivial,
and there'll always be cases where you get an opposite behavior of what you
want.

If a smart behavior isn't possible, I prefer the current one. The current
method works the same way as if you rendered the image at huge resolution
and then scaled it down.

Rune
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Jan Walzer wrote:
> 
> > This reminds me...are the colors clipped before or after antialiasing?
> > It should be after...a "superbright" object (rgb > 1) should contribute
> > more to a pixel than a dim (rgb 1) one.
> 
> 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 :(


_____________
Kari Kivisalo

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Rune wrote:
>
> It is clipped before AA and there's a good reason.

It's not realistic.


_____________
Kari Kivisalo

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"Kari Kivisalo" wrote:
> Rune wrote:
> >
> > It is clipped before AA and there's a good reason.
>
> It's not realistic.

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

The current AA give the same result as if you rendered the image at a very
large resolution and then scaled it down. I think that's what AA is meant to
do. It gives smooth results. the way you'd like it to work, it wouldn't
always give smooth results, often things would look like they had not been
antialiased at all.

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

Take a picture either with a film or ccd camera of a 10 candela source.
Compare that to picture of a 1000 candela source with same exposure.
You say they would look the same.

We are making _digital_ images. Even digital images of nature have
been subject to aa or lpf at some point. In real life the clipping
occurs at the image detector/film, not before. The aa/lpf operates
on the unclipped intensities. Would be hard to make it work the other
way around :)


_____________
Kari Kivisalo

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Wow. I'm impressed. Your new methods look very good. Can you conduct a few
tests on more complete scenes? It would also be nice if you could explain
how you acheived each one so some more discussion about them can be had.

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Tony[B] wrote:

> Wow. I'm impressed. Your new methods look very good. Can you conduct a few
> tests on more complete scenes? It would also be nice if you could explain
> how you acheived each one so some more discussion about them can be had.

If you have a particular scene that you want to have tested you can send it 
to me and I will test it. I still want to do some modifications to my 
implementations. Once I have finished that I will make a detailed 
explanation how they work.

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"Kari Kivisalo" wrote:
> We are making _digital_ images. Even digital images of
> nature have been subject to aa or lpf at some point.

Photos are not subject to antialiasing I think. They are subject to focal
blur and probably other types of blurring that I don't know about. (Is that
what lpf mean?) But blurring has nothing to do with antialiasing. Blurring
(in nature) is resolution independent and covers many pixels, while
antialiasing is highly resolution dependent and has to do with individual
pixels.

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/
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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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