How do?

Though I'd chuck my two-pence into the ambient occlusion struggle with POV.

After looking and playing with radiosity solutions for AO, I found the results
to be lacking something.  It didn't really square up to the proper AO offered by
the more expensive renderers.

So I was thinking that the AO pass is really just white objects that collect
light from a whole load of angles to give a nice approximation of occlusion.
Thus, armed with a trusty dragon model, I tried simply rendering (in this case)
350 frames with one light source rotated about the main object.  I then averaged
these frames using Image Stacker and multiplied the AO output with the textured
render.

Seems to work, but take bleedin' ages!

Standard render
    http://i53.photobucket.com/albums/g69/aspule/DragonNoOcc.jpg

Ambient occlusion pass
    http://i53.photobucket.com/albums/g69/aspule/DragonJustOcc.jpg

Final
    http://i53.photobucket.com/albums/g69/aspule/DragonOcc.jpg

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"arblick spule" <aspule> wrote:
> How do?
>
> Though I'd chuck my two-pence into the ambient occlusion struggle with POV.
>
> After looking and playing with radiosity solutions for AO, I found the results
> to be lacking something.  It didn't really square up to the proper AO offered by
> the more expensive renderers.

AO is nothing more than a fake GI method.  It doesn't take light into
consideration, only how far geometry is from each other to affect occlusion.
This way, it might occlude in shadow some parts even if it was entirely under
direct light.  That means it's truly fake and does not correspond to reality.

May be nice to get some more contrast, but that extra contrast may have no
correspondence in real life.

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"nemesis" <nam### [at] gmailcom> wrote:
> "arblick spule" <aspule> wrote:
> > How do?
> >
> > Though I'd chuck my two-pence into the ambient occlusion struggle with POV.
> >
> > After looking and playing with radiosity solutions for AO, I found the results
> > to be lacking something.  It didn't really square up to the proper AO offered by
> > the more expensive renderers.
>
> AO is nothing more than a fake GI method.  It doesn't take light into
> consideration, only how far geometry is from each other to affect occlusion.
> This way, it might occlude in shadow some parts even if it was entirely under
> direct light.  That means it's truly fake and does not correspond to reality.
>


Indeed, however GI is fake as well.  Let us not forget that math doesn't always
equal real(istic).

All images that come out of all renderers (freeware or otherwise) have
noticeable flaws in them.  For instance the dragon render above, without AO
pass, has a very bright hard-palate despite all three of the lights being
"behind" it and the material having quite a low reflectance value.  Radiosity
was turned on for this render and yielded a, quite frankly, wildly displeasing
picture.  3DSMax's renderer will do exactly the same and I have no doubt that
most of those that exist will too.  What, I opine, AO does is give an obviously
fake image (Dragon sat on checkered disc) some degree of - well - realism for
the eye, or maybe "depth" is a better word.

Hang on.  Ambient occlusion is generated by firing off a load rays from random
points towards the pixels 3D/2D intersection.  If the object/pixel doesn't get
hit directly then it is considered occluded, but only from that angle.  AO takes
a few (generally 40 or so) samples and averages them to get an "occlusion level"
if you like.  At least this is how Mental Ray describes how it does it.  So it
differs from global illumination by not bouncing light from object to object,
but assessing how much ambient light "could" hit the target even if there was no
light at all.  'Tis all theoretical.

The problem I guess here is differing artistic acceptability (if that makes any
sense...). I will trade off technical realism to have an image that looks nice,
to put it simply.


Original render:
    http://i53.photobucket.com/albums/g69/aspule/BoxesNoOcc.jpg

Ambient occlusion pass:
    http://i53.photobucket.com/albums/g69/aspule/BoxesOccPass.jpg

Final image:
    http://i53.photobucket.com/albums/g69/aspule/BoxesOcc.jpg

This is where my method falls down!  Look at the shadows around the base of the
closest box.  Not very good!  This could be corrected by rotating the average
angle towards the real light source, I guess...

.....Hey ho...              ...Peace out!

Post a reply to this message

>
>
> Original render:
>     http://i53.photobucket.com/albums/g69/aspule/BoxesNoOcc.jpg
>
> Ambient occlusion pass:
>     http://i53.photobucket.com/albums/g69/aspule/BoxesOccPass.jpg
>
> Final image:
>     http://i53.photobucket.com/albums/g69/aspule/BoxesOcc.jpg
>
> This is where my method falls down!  Look at the shadows around the base of the
> closest box.  Not very good!  This could be corrected by rotating the average
> angle towards the real light source, I guess...
>
> .....Hey ho...              ...Peace out!

Oh, actually, that shadow would be there if there was sky light going on.  All
that would be needed would be to make the black "sky sphere" white and it would
all look okay!  Oh how fickle art is.

Post a reply to this message

"arblick spule" <aspule> wrote:
> "nemesis" <nam### [at] gmailcom> wrote:
> > "arblick spule" <aspule> wrote:
> > AO is nothing more than a fake GI method.
>
> Indeed, however GI is fake as well.  Let us not forget that math doesn't
> always equal real(istic).

GI is not a technique, but a family of techniques to get very realistic indirect
lighting.  It's fake as in it's an approximation of reality, but a much, much
closer approximation than AO anyway.  Of course, depends on which GI technique
you're using too.

> All images that come out of all renderers (freeware or otherwise) have
> noticeable flaws in them.  For instance the dragon render above, without AO
> pass, has a very bright hard-palate despite all three of the lights being
> "behind" it and the material having quite a low reflectance value.  Radiosity
> was turned on for this render and yielded a, quite frankly, wildly displeasing
> picture.  3DSMax's renderer will do exactly the same and I have no doubt that
> most of those that exist will too.

Radiosity only takes into account diffuse interreflections.  For a reflective
material, you'd probably do better by turning diffuse down a lot in its finish.

I'm also sure photon mapping in 3DSMax's MR would do a much more realistic job
than either AO or radiosity.  And unbiased, physically-based techniques would be
even more accurate.

If that's disgusting, well, blame optics...

> What, I opine, AO does is give an obviously
> fake image (Dragon sat on checkered disc) some degree of - well - realism for
> the eye, or maybe "depth" is a better word.

never heard of statues and checkered floors?

In any case, I'm all for artistic license.

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arblick spule <aspule> wrote:
> Oh, actually, that shadow would be there if there was sky light going on.  All
> that would be needed would be to make the black "sky sphere" white and it would
> all look okay!  Oh how fickle art is.

  The shadows underneath objects produced by the ambient occlusion technique
look realistic in many situations because it simulates what happens in real
life. In real life, even if there is a single bright light source at some
point, light will still bounce from other surfaces, such as walls and
ceilings, and will often cause those darkened areas below and near objects.

  The ambient occlusion technique cuts the middle-man, in this case
calculating how the light coming from the one light source bounces from
walls, ceilings and other objects, and simply assumes that there's light
coming about equally from all directions due to all the reflected light.
The result is not completely unrealistic for most situations, which is why
it works so well.

  (Of course it becomes unrealistic if it's clear that there are no walls
nor ceiling around from where the light could reflect.)

-- 
                                                          - Warp

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Just to add my 2c, I find the easiest way to deal with this is to add a sky 
sphere that radiates light - map an image (ideally HDR) onto it

This then simulates realistic lighting of objects and gives you the proper 
shadow effect

An example can be seen in a short animation I did here: 
http://www.soware.co.uk/POVRay/player.php?id=6
or the original by Paul Debevec here: 
http://www.youtube.com/watch?v=EHBgkeXH9lU
and a very good example similar to PD's but with better shadows here: 
http://www.youtube.com/watch?v=sDAYBG6L8HY

Hope this helped

Regards,

Simon

"arblick spule" <aspule> wrote in message 
news:web.4b2c2ac027e91db9b5d84fdc0@news.povray.org...
>
>>
>>
>> Original render:
>>     http://i53.photobucket.com/albums/g69/aspule/BoxesNoOcc.jpg
>>
>> Ambient occlusion pass:
>>     http://i53.photobucket.com/albums/g69/aspule/BoxesOccPass.jpg
>>
>> Final image:
>>     http://i53.photobucket.com/albums/g69/aspule/BoxesOcc.jpg
>>
>> This is where my method falls down!  Look at the shadows around the base 
>> of the
>> closest box.  Not very good!  This could be corrected by rotating the 
>> average
>> angle towards the real light source, I guess...
>>
>> .....Hey ho...              ...Peace out!
>
> Oh, actually, that shadow would be there if there was sky light going on. 
> All
> that would be needed would be to make the black "sky sphere" white and it 
> would
> all look okay!  Oh how fickle art is.
>
>

Post a reply to this message