Well, Mister POVxar, you did it again it seems! Very smartly done.

I used your ao techniques several times and it added much to my scenes.

Thomas

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"SafePit" <ste### [at] reids4funcom> wrote:
> "Robert McGregor" <rob### [at] mcgregorfineartcom> wrote:
> > "Robert McGregor" <rob### [at] mcgregorfineartcom> wrote:
> > > So, here's an example shot of the "blob with negative strength" from the
> > > pvengine64 "Insert" menu, using five separate render passes.
> >
> > And here's the final SDL composite :)
> >
> > -------------------------------------------------
> > www.McGregorFineArt.com
>
> Wow, just wow!  Sounds promising.  Would it work with media and focal blur?

Yes, that's the beauty of it, it works with anything available in POV-Ray. And
you have the choice of using radiosity and/or standard lighting in a scene;
whichever makes objects/effects look best and render fastest.

And actually these example shots all make use of subtle focal blur using:

camera {
   location Cam_Loc
   look_at  Cam_At
   right x*image_width/image_height
   angle 50
   #if (Use_Focal_Blur)
      aperture 2
      blur_samples 7*Focal_Blur_Factor
      focal_point <10, 0, -2>
      confidence 0.9
      variance 1/200
   #end
}

Cheers,
Rob
-------------------------------------------------
www.McGregorFineArt.com

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Stephen <mcavoys_at@aoldotcom> wrote:
> On 09/03/2011 4:46 AM, Robert McGregor wrote:
> > And here's the Buddha Balls final comp
> >
>
> I really like this one but I wish you had called it Buddha Spheres or
> something. ;-)
>
>
> --
> Regards
>      Stephen

LOL, Stephen!!
"Buddha Balls" just rolls off the tongue better (sorry, couldn't help myself).

-------------------------------------------------
www.McGregorFineArt.com

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"Thomas de Groot" <tDOTdegroot@interDOTnlANOTHERDOTnet> wrote:
> Well, Mister POVxar, you did it again it seems! Very smartly done.
>
> I used your ao techniques several times and it added much to my scenes.
>
> Thomas

Thanks Thomas, I didn't realize that :)

-------------------------------------------------
www.McGregorFineArt.com

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OOC, what exactly is the ambient occlusion pass used for? After all, the 
global illumination effect should already be accounted for by the 
radiosity pass.

AFAIK, in shader-based render engines, AO is used to get self-shadowing 
right, and/or to /fake/ global illumination.

So I guess what you're doing there is actually just deepening the 
shadows for artistic effect, and might better be served by tone mapping.

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clipka <ano### [at] anonymousorg> wrote:
> OOC, what exactly is the ambient occlusion pass used for? After all, the
> global illumination effect should already be accounted for by the
> radiosity pass.
>
> AFAIK, in shader-based render engines, AO is used to get self-shadowing
> right, and/or to /fake/ global illumination.
>
> So I guess what you're doing there is actually just deepening the
> shadows for artistic effect, and might better be served by tone mapping.

AFAIK, Ambient Occlusion is used to gain some render time and flexibility rather
than realism. In Mental Ray for instance, Photon mapping and Final Gather are
helpful to generate faster some color bleed, and global indirect light. Yes in
theory, you get more realistic lighting if you let photon mapping do all the
job, but in practice this makes the render time too long, so it is advised, in
most Mental Ray training material, to use Both (photon mapping + Final Gather)
and Ambient Occlusion together in a synergy, using the final gathering radius to
set up some degree of smoothing that depends on your AO distance: This way,
Photons+FG generate overall lighting, whereas self shadowing which happens at
smaller scales is left out of it thanks to Gather blurring and sparser sampling
but is simulated with Ambient Occlusion, rendered much faster than photons or
gathering would require to reach. So to some it up and anyone correct me if I'm
wrong,

Final Gather (wich in mental ray can also be used without photons) takes on the
widest scale, and Ambient Occlusion takes care of much smaller shadows.

In the process, if some photons are shot, some details can be added locally with
photons targeting from lights, importance, portals, various techniques, to get
also more small scale effects like luminous caustics (whereas AO only emulates
ambient shadows.

Being a pragmatic observation rather than lab approach, I would think of AO as
the opposite approach to unbiased techniques, where instead of calculating
indirect light for unspecified times towards some configuration that is the most
specific to your scene, you start by what is common to almost every scene, and
decide that some part of the light bounces so much that it will end up
contributing to all of a set to some degree and since it can happen all over the
place it's initial directions doesn't actually matter that much, so AO focuses
on shading places where light definitely wouldn't reach, which is contact
between surfaces and very acute angles. The important thing being that you can
tweak overall contribution of that ambient light by intensity of shadows and by
distance at which it extends far from the object casting it. Once it's decided
that this contribution is not zero you switch on AO and tune the frequency and
intensity of your other indirect lighting  features accordingly. This leaves
much more sampling budget for local effects.

It is often said that AO is not phisically correct, but I'd say that for a
uniformly and very thickly overcast sky with no lights around, then only AO
would be correct. Or the light cast by surrounding sky of some clear night.

So when you consider that you actually don't use AO by itself but only to take
care of some part of the light, you realize that this lighting component is to
various degrees present in almost every scene.

There are also other uses of AO like to bake it and use as a basis for dirt
maps, mask to mix different materials and many textures to process further.

Sorry if nothing of the above answers your question or if any of it is wrong, it
mostly comes from memories of CGSociety discussions, and I'm not a hardcore
programmer/scientist.

@Robert McGregor, Even If AO does not get implemented further into POV, I'm much
interested into any tutorial you could make and would love to include pov passes
to our Blender 2.5 to Povray exporter because Blender compositing pipeline is
quite capable and that's an area where both software would best synergize.
Thanks for your efforts.

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"Robert McGregor" <rob### [at] mcgregorfineartcom> schreef in bericht 
news:web.4d7780576b0cef9b94d713cc0@news.povray.org...
> "Thomas de Groot" <tDOTdegroot@interDOTnlANOTHERDOTnet> wrote:
>> Well, Mister POVxar, you did it again it seems! Very smartly done.
>>
>> I used your ao techniques several times and it added much to my scenes.
>>
>> Thomas
>
> Thanks Thomas, I didn't realize that :)

Well... to tell the truth: the latest ones did not...  :-/

Thomas

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"Robert McGregor" <rob### [at] mcgregorfineartcom> wrote:
> "Robert McGregor" <rob### [at] mcgregorfineartcom> wrote:
> > "Robert McGregor" <rob### [at] mcgregorfineartcom> wrote:
> > > So, here's an example shot of the "blob with negative strength" from the
> > > pvengine64 "Insert" menu, using five separate render passes.
> >
> > And here's the final SDL composite :)

awesome.

But really, this is why pov-ray never quite gets much of a foothold:  only
ingenious guys like you, Sam Benge, Jaime Vives Piqueres and a host of others to
imagine such tricks.  And even worse: some tricks that ought to be in the
software are seemingly always reinvented by newcomers, like stacked sky,
micronormals and this one:  it is a well known fact that the multipass approach
is the way to go and that radiosity does not play fine with reflections,
refractions, media and now SSS.

So, how about a multipass switch for povray, devs?  I mean, sure there's the
quality switches going from 1 (plain constant ambient light) to 9 (full with
radiosity), but the numbers going higher only add more effects, don't isolate
them from one another.  I know it's a postprocess to combine the results and it
is outside the scope of a raytracer, but then again, an IDE to write scenes is
also outside the scope of a raytracer.  At the very least, providing scripts for
such...

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"Mr" <nomail@nomail> wrote:
> AFAIK, Ambient Occlusion is used to gain some render time and flexibility
> rather than realism.

Exactly, it's fast and really brings out hidden geometric details that radiosity
doesn't typically reveal, and our brains are fooled into thinking it looks more
realistic even when it's not physically accurate.

> It is often said that AO is not phisically correct, but I'd say that for a
> uniformly and very thickly overcast sky with no lights around, then only AO
> would be correct. Or the light cast by surrounding sky of some clear night.

Yes, and my AO solution is really just that: white materials under a very
thickly overcast sky with no lights around.

> So when you consider that you actually don't use AO by itself but only to take
> care of some part of the light, you realize that this lighting component is to
> various degrees present in almost every scene.

I usually only multiply in 15-50% of the AO pass, depending on the shot.

> There are also other uses of AO like to bake it and use as a basis for dirt
> maps, mask to mix different materials and many textures to process further.

That's something else I'm working on, using the AO pass as an image_pattern mask
to control grime and such in crevices, for an additional dirt/grime pass.

> @Robert McGregor, Even If AO does not get implemented further into POV, I'm much
> interested into any tutorial you could make and would love to include pov passes
> to our Blender 2.5 to Povray exporter because Blender compositing pipeline is
> quite capable and that's an area where both software would best synergize.
> Thanks for your efforts.

Thanks, that sounds great; I'd be very interested to work with you on that!

Cheers,
Rob
-------------------------------------------------
www.McGregorFineArt.com

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On 03/09/2011 12:09 PM, nemesis wrote:
> ingenious guys like you, Sam Benge, Jaime Vives Piqueres and a host of others to
> imagine such tricks.

Tell me about it ... I thought my doily trick was cleaver, but hey
here's the context for you ... I have a tough time drawing a straight
line /even/ when I use a straight edge ;-)

I look at it this way ... If you stay on the porch and never run wid da
big dawgs every now and then, you aren't going to ever learn anything.
What's cool about these guys is that they are willing to share!

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