On Wed, 20 Feb 2008 17:01:25 -0300, nemesis wrote:

> Jim Henderson wrote:
>> On Wed, 20 Feb 2008 16:44:59 -0300, nemesis wrote:
>>> like I said, photorealism is not a matter of opinion.
>> 
>> Sure it is.  It all depends on one's perception of the image.  You
>> might look at an image and say "gee, that looks really photorealistic",
>> and I might respond "are you on drugs?  Look at that shadow, that's
>> clearly not right".  You might disagree about that particular shadow
>> (whatever it is).
> 
> if I saw at a sharp shadow and said it was photorealistic, I'd sure be
> on drugs. ;)

Now I didn't necessarily say a sharp shadow, did I?

>> Have you ever been to a movie with someone who thinks the CG effects
>> are outstanding and "the most realistic effects they'd ever seen", only
>> to tell them that they were crap effects?
> 
> People's opinions on whether something is photorealistic is irrelevant
> as to whether it is or not.  The only way to test it out would be to
> take a photo, model a scene similar to it and render.  Then diff the
> render and the photo.

I've seen photos that don't look photorealistic to me.  It most certainly 
is a matter of opinion.

You might opt to take a - shall we say - religious view towards your 
correctness; that doesn't mean you're right. ;-)

Jim

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Jim Henderson wrote:
> On Wed, 20 Feb 2008 17:01:25 -0300, nemesis wrote:
>> People's opinions on whether something is photorealistic is irrelevant
>> as to whether it is or not.  The only way to test it out would be to
>> take a photo, model a scene similar to it and render.  Then diff the
>> render and the photo.
> You might opt to take a - shall we say - religious view towards your 
> correctness; that doesn't mean you're right. ;-)

I'd say that's a technical stance.

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On Wed, 20 Feb 2008 17:17:04 -0300, nemesis wrote:

> Jim Henderson wrote:
>> On Wed, 20 Feb 2008 17:01:25 -0300, nemesis wrote:
>>> People's opinions on whether something is photorealistic is irrelevant
>>> as to whether it is or not.  The only way to test it out would be to
>>> take a photo, model a scene similar to it and render.  Then diff the
>>> render and the photo.
>> You might opt to take a - shall we say - religious view towards your
>> correctness; that doesn't mean you're right. ;-)
> 
> I'd say that's a technical stance.

You measure photorealism in one way - and that's fine.  Doesn't mean 
that's the way everyone measures it.

For one thing, your view of photorealism depends on the scene actually 
being able to be photographed.  So, for example, how would you do a 
photorealism check on, say, Battlestar Pegasus?

Jim

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Warp <war### [at] tagpovrayorg> wrote:
>   Am I incorrect if I get the impression that these unbiased renderers
> offer nothing else than unbiased rendering? In other words, even the
> simplest of scenes will take hours to look ungrainy, no matter what
> you do?

I know of at least one (Kerkythea) that supports unbiased rendering as well as
other methods; you select the rendering algorithm you want to use from a list,
which includes conventional raytracing. You can't mix methods within the same
render, of course.

I don't find it surprising that most of these apps focus on one particular
rendering algorithm, though, considering the effort it takes to get even one of
them right, with features that make such apps useful.

Tom

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nemesis wrote:
> Or you can just buy top hardware, model, texture and drop accurate 
> lighting in your scene and let an unbiased rendering method handle it 
> overnight.

If you buy top hardware, model, texture, and drop accurate lighting in 
your scene, PoV can do it, too.

The trick is the accurate lighting.  It's not impossible to do in PoV.

And sometimes, you want something that's intentionally inaccurate. 
(Ever put a diffuse value of, say, 1000 on a texture in a radiosity 
scene?  How about negative-intensity light sources?  Negative value for 
fade power?)

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

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Severi Salminen wrote:
> Mike Raiford wrote:
> 
>> You didn't answer his question. I'm also curious about render times, but
>> you completely dodged the question.
> 
> See the indigo site gallery. Some captions include render time. Of
> course that tells you nothing about how good/bad the image looked in
> less time. Remember that with brute force you see a lot even after 1 minute.

How long do you have to wait before the graininess has reliably become 
unnoticeable?  That's a question I need an answer to before I can use 
any unbiased renderer for animation work.  I need a renderer that won't 
give me a picture unless the quality is consistent from one frame to the 
next.

With scanline and ray-tracing renderers, there comes a specific point at 
which the renderer is *done* with the image and is ready to render the 
next image.  Unbiased renderers are never really done; they just go 
until the user decides the quality is good enough.  Sure, the user may 
be able to set the renderer to go only a certain amount of time, but 
except for a very short clip, and only after rendering a couple of 
frames in that clip, can the time required for each frame be predicted 
with any meaningful reliability.

Regards,
John

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> With scanline and ray-tracing renderers, there comes a specific point at 
> which the renderer is *done* with the image and is ready to render the 
> next image.  Unbiased renderers are never really done; they just go 
> until the user decides the quality is good enough.  Sure, the user may 
> be able to set the renderer to go only a certain amount of time, but 
> except for a very short clip, and only after rendering a couple of 
> frames in that clip, can the time required for each frame be predicted 
> with any meaningful reliability.

On the only unbiased renderer I used, it uses passes. Being *based* on 
random numbers (shooting rays in random directions), of course the time 
each pass takes is non-deterministic, but you surely could render the 
same number of passes for all frames (instead of leaving it the same 
amount of time), and you would get approximately the same amount of 
noise on all.

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Nekar wrote:
> Do scientist completely understand all the
> properties of light?

Pretty much, yes. :-)

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

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news: 47bc9dbf$1@news.povray.org...
> How long do you have to wait before the graininess has reliably become 
> unnoticeable?  That's a question I need an answer to before I can use any 
> unbiased renderer for animation work.  I need a renderer that won't give 
> me a picture unless the quality is consistent from one frame to the next.

I saw a commercial (an animation of course) rendered with MaxwellRender the 
other day on TV so whatever theoretical problems exist with unbiased 
renderers and animation seem to be have been solved in production (perhaps 
with the help of a large render farm, but that another issue...). IIRC 
there's a page about animation in the Maxwell manual, you can look it up 
(it's free for download).

G.

-- 
**********************
http://www.oyonale.com
**********************
- Graphic experiments
- POV-Ray and Poser computer images
- Posters

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47bc9c10$1@news.povray.org...

> If you buy top hardware, model, texture, and drop accurate lighting in 
> your scene, PoV can do it, too.
> 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.

When I was busy playing with POV, the key to get good images was to 
precisely to avoid these kind of lighting/texturing situations. There are 
things that POV sucks at rendering unless one spends a lot of time trying to 
find workarounds (or brushing off artifacts...).

The area_illumination feature that Warp introduced in the latest 3.7 beta is 
one of those things that the previous versions couldn't do: of course one 
could simulate it with grids of point lights, but it was just too 
impractical for common usage. 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.
The beauty of using more advanced renderers (biased or unbiased) is that 
those blocks no longer exist, either because the results are accurate from 
the start (unbiased) or because they are lots of optimisations for speed 
(biased). Just describe accurately your lights and materials, and the system 
works out of the box.

G.


-- 
**********************
http://www.oyonale.com
**********************
- Graphic experiments
- POV-Ray and Poser computer images
- Posters

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