John VanSickle <evi### [at] hotmailcom> wrote:
> How long do you have to wait before the graininess has reliably become 
> unnoticeable?

  I wonder if an automatic measurement and then a threshold couldn't be
developed. For example, if a given pixel hasn't changed color for the
last n rays which have affected that pixel, then that pixel is done.
When all the pixels fulfill this requirement, the image is done.

-- 
                                                          - Warp

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nemesis <nam### [at] nospamgmailcom> wrote:
> >   POV-Ray is simply a great tool to create "3D'ish" images like those.
> > It's easy and fast.

> so, pov-ray will end up its days as a 3D button design tool?  Are 
> pov-ray users ok with that evolutionary idea?

  Why are you trolling?

-- 
                                                          - Warp

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Btw, does unbiased rendering support volumetric lighting? I can't find
any example image in this site nor int the indigo gallery.

-- 
                                                          - Warp

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Gilles Tran wrote:
>> The trick is the accurate lighting.  It's not impossible to do in PoV.
> 
> Unfortunately, it is.
> 
> POV can do a lot of things, but there are many common lighting situations 
> that are just out of reach from a practical point of view. It's not just the 
> lighting model, but also the texturing model that is insufficient.

Impossible and impractical are not the same thing.  Impractical is fine 
for us geeks with lots of time to fiddle on our hands.  XD

> Another feature that is sorely missing is 
> efficient blurred reflection. There's a trick to do that in POV but the 
> results are usable in only certain (limited) circumstances. In modern 
> renderers, blurred reflection can be applied to all the materials in the 
> scene, thus allowing correct specularity and (inter-)reflections, and this 
> adds tremendously to realism.

Ah, I missed reading that 'efficient' bit when I hit reply.  The blurred 
reflection that you can do in POV is physically accurate per 
'micronormals are how you get blurred reflections anyhow'.

'course, until the next version of Moray gets released, I'm stuck with 
good old POV 3.5 anyways...

-- 
Tim Cook
http://empyrean.digitalartsuk.com

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"Darren New" <dne### [at] sanrrcom> wrote in message
news:47bca80c$1@news.povray.org...
> Nekar wrote:
> > Do scientist completely understand all the
> > properties of light?
>
> Pretty much, yes. :-)

But not _perfectly_. if they understood light perfectly there wouldn't be
any search for unified field theories, etc. :o]


--
- Nekar X -

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Nekar wrote:
> "Darren New" <dne### [at] sanrrcom> wrote in message
> news:47bca80c$1@news.povray.org...
>> Nekar wrote:
>>> Do scientist completely understand all the
>>> properties of light?
>> Pretty much, yes. :-)
> 
> But not _perfectly_. if they understood light perfectly there wouldn't be
> any search for unified field theories, etc. :o]

They're trying to unify the stuff they understand less (nuclear forces, 
gravity) with their understanding of light. QED's theory matches 
experiment to 15 decimal places.

Of course, the "why does it do that" will (almost certainly) never be 
understood down to the lowest level. But the properties of light? Yeah, 
I don't think there's any inability to predict what light will do under 
various circumstances. Unless, of course, someone comes up with 
experimental evidence that doesn't fit, which is always a possibility.

-- 
   Darren New / San Diego, CA, USA (PST)
     On what day did God create the body thetans?

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> I have to say, I've yet to see any unbaised renders where I instantly look 
> and go "wow! POV-Ray could never do that..."

I don't see much nowadays where I say "wow, a modern GPU could never do that 
in realtime" ;-)

It's just a matter of realism and effort.  At the top you have these 
unbiased renderers that take almost no setting up (apart from the scene 
itself) and give a scientifically perfect result after a few days.  At the 
bottom you have GPU rendering, that takes a lot of effort to code, gives a 
pretty good result and takes a few ms to render.  POV is in between 
somewhere, taking a medium amount of effort to get looking good, and taking 
a few hours (not days or ms) to render.

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scott wrote:
>> I have to say, I've yet to see any unbaised renders where I instantly 
>> look and go "wow! POV-Ray could never do that..."
> 
> I don't see much nowadays where I say "wow, a modern GPU could never do 
> that in realtime" ;-)

How about, say, volumetric fog? ;-)

I have yet to see any GPU of any description get that right...

For that matter, I've yet to see any GPU do physically correct 
reflections [although surely it can't be *that* hard?], nor global 
illumination that isn't pre-computed [and hence won't change when 
objects move around].

-- 
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*

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Warp wrote:

>   I wonder if an automatic measurement and then a threshold couldn't be
> developed. For example, if a given pixel hasn't changed color for the
> last n rays which have affected that pixel, then that pixel is done.
> When all the pixels fulfill this requirement, the image is done.

I don't know about unbaised rendering, but the Fractal Flame algorithm 
is somewhat similar. (You stocastically create an image that starts off 
grainy as hell and eventually progresses to being smooth.)

The author's rendering tool allows you to specify a "quality" setting. 
However, the actual quality of the image isn't real closely related to 
this. It turns out that the quality setting is actually just the average 
number of samples/pixel that must be reached before rendering stops. 
This probably wouldn't be a very good measure for unbiased rendering...

A better measure would seem to be to measure the signal to noise ratio 
of the image - but then you'd need a way to seperate "signal" from 
"noise"...

-- 
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*

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> How about, say, volumetric fog? ;-)
>
> I have yet to see any GPU of any description get that right...

A couple of papers show how to do realistic physics-based smoke/cloud true 
volumetric effects (not just static fog):

http://developer.download.nvidia.com/presentations/2007/gdc/RealTimeFluids.pdf
http://www.markmark.net/dissertation/harrisDissertation.pdf

Also real-time volumetric lighting is no problem, in fact Crysis uses it and 
I'm sure there's an nVidia demo kicking about somewhere.

> For that matter, I've yet to see any GPU do physically correct reflections 
> [although surely it can't be *that* hard?],

The reason there is no effort put into doing this is because doing the 
reflection/environment map method is good enough.  In fact with DX10 and 
recent cards the emphasis has gone into speeding up the generation of the 
environment map.  Doing physically correct reflections is hard because you 
need to write a ray tracer inside the pixel shader - it's *a lot* of work 
for very little improvement in realism, which is why hardly anyone bothers, 
unless you are writing some proof-of-concept demo.

> nor global illumination that isn't pre-computed [and hence won't change 
> when objects move around].

http://realtimeradiosity.com/demos/

Real time ambient is done in the "Cascades" demo from nVidia.  Each voxel on 
the surface traces out (32 IIRC) rays to work out the GI at that point.  OK 
so it's not perfect (other geometry doesn't affect it) but it's certainly 
better than no GI.

What you have to bear in mind with all these things, is that they have to be 
designed to work when a frame takes 15 ms to render.  If reducing the 
accuracy by 10% speeds up rendering by 50%, the speed-up option is taken. 
Always.

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