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Warp wrote:
> Unless I understood incorrectly, the "lightcuts" algorithm is not about
> global illumination, but about speeding up illumination from hundreds of
> thousands of point light sources, which is a rather different thing. (Global
> illumination is about light reflecting from surfaces and illuminating other
> surfaces, in turn reflecting from them and illuminating yet other surfaces,
> and so on. "Lightcuts" looked like an algorithm for direct illumination only.)
Yes, I was in doubt too. But in the webpage for the paper they say:
"It handles arbitrary geometry, non-diffuse materials, and illumination
from a wide variety of sources including point lights, area lights,...
and indirect illumination." They couldn't just be plain lying.
So, I did a test using the Blender implementation:
http://img440.imageshack.us/img440/1255/lightcutstestzg0.jpg
Only lightsource is an area light outside and above the window. So,
indeed it handles indirect illumination automatically...
It has a lightcuts panels with quite a few parameters, among them,
number of point lights generated from an area light. The default is
immense, so I fearfully put it down to a modest 128 as well as a
indirect light factor about the same. I think such "low" settings can
be accounted for the splotches and "cuts" seen.
OTOH, it took 44 minutes on a P4 2.66. Not as fast as I had hoped for... :P
Next, I'll try to export to pov and play around with radiosity. I
didn't like the radiosity in Blender, even with quite lots of
subdivision, it still looks quite ugly and not on par with the lightcuts
picture...
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clipka wrote:
> Guess what: HDRI actually *is* in the beta :)
Great! Now only a few more years until mechsim, AOI, displace warps and
some others...
> besides: Who uses standard POV anyway? :))
I never used megapov.
> 4.0 is still at its very basics, and is intended to head for radical changes
> anyway (new SDL and all).
Is it anything other than a hope at this point?
> be feasible in the POV world - would most likely tip the scales. A sub-linearly
> scaling algorithm - and not only that, looks like we're talking about very close
> to logarithmic here - where do you get *that* in 3D rendering, where sometimes
> you'd be happy if things would scale sub-quadratic?!
Well, it does seem to handle indeed a huge amount of point lights
automatically generated from quite a few light sources. But it seems
about as slow as any other GI method. OTOH, there doesn't seem to be
any radiosity count limit. And, I wonder if it'd be more amenable to
multiprocessing than radiosity...
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nemesis <nam### [at] nospamgmail com> wrote:
> Well, it does seem to handle indeed a huge amount of point lights
> automatically generated from quite a few light sources. But it seems
> about as slow as any other GI method. OTOH, there doesn't seem to be
> any radiosity count limit. And, I wonder if it'd be more amenable to
> multiprocessing than radiosity...
I'd guess so. With radiosity, lots of interim results would have to be shared
beteen adjacent pixels. With Lightcuts, theoretically you'd have just the one
light source tree that would be shared, and for each pixel you would calculate
a new cut of the tree anyway, so no need for sharing this information (although
it *could* be shared among pixels calculated in the same thread, in order to
speed up finding the optimal cut. If there is any sense in doing so.)
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nemesis <nam### [at] nospamgmailcom> wrote:
> http://img440.imageshack.us/img440/1255/lightcutstestzg0.jpg
The shadow under the head doesn't make physical sense. Where is it
coming from? That shadow would indicate that there's a strong light
source above the head, but the illumination of the head does not correspond
to this. The bright area on the floor would rather obviously not cause
such a shadow.
--
- Warp
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Warp <war### [at] tagpovrayorg> wrote:
> nemesis <nam### [at] nospamgmailcom> wrote:
> > http://img440.imageshack.us/img440/1255/lightcutstestzg0.jpg
>
> The shadow under the head doesn't make physical sense. Where is it
> coming from? That shadow would indicate that there's a strong light
> source above the head, but the illumination of the head does not correspond
> to this. The bright area on the floor would rather obviously not cause
> such a shadow.
I've put 3 bounces or more. Probably some of the light in the bright area on
the floor under direct illumination bounce to the ceiling, then down again. It
is present in the radiosity version too, though much less sharp:
http://img111.imageshack.us/img111/7218/lightcutstest3radiobm0.jpg
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Warp <war### [at] tagpovrayorg> wrote:
> nemesis <nam### [at] nospamgmailcom> wrote:
> > http://img440.imageshack.us/img440/1255/lightcutstestzg0.jpg
>
> The shadow under the head doesn't make physical sense. Where is it
> coming from? That shadow would indicate that there's a strong light
> source above the head, but the illumination of the head does not correspond
> to this. The bright area on the floor would rather obviously not cause
> such a shadow.
You're forgetting about all the indirect scattered light.
With the head so close to the surface, it is blocking the indirect light from
almost all directions except sideways, so it gets significantly less light
(plus, light of same intensity from sideways is actually weaker at illuminating
a surface).
The indirect lighting in this picture seems quite exaggerated to me, but apart
from that there's nothing wrong with this.
Radiosity will produce a shadow there as well. Or at least it should - if it
doesn't it's off reality.
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clipka <nomail@nomail> wrote:
> With the head so close to the surface, it is blocking the indirect light from
> almost all directions except sideways, so it gets significantly less light
Also directly under the ear? The ear is so small that it's not blocking
almost anything, yet the shadow on the floor produced by the ear is very
pronounced.
--
- Warp
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Warp <war### [at] tagpovrayorg> wrote:
> clipka <nomail@nomail> wrote:
> > With the head so close to the surface, it is blocking the indirect light from
> > almost all directions except sideways, so it gets significantly less light
>
> Also directly under the ear? The ear is so small that it's not blocking
> almost anything, yet the shadow on the floor produced by the ear is very
> pronounced.
I didn't notice in the original, but the blue square on the wall is supposed to
be a window. Assuming the outside to be very bright, I would expect the shadow
under the head. Warp is correct though; without this assumption, the shadow
isn't right.
This makes the colour of the outside completely wrong, of course - it would need
to be hundreds of times brighter to be believable.
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"Bill Pragnell" <bil### [at] hotmailcom> wrote:
> This makes the colour of the outside completely wrong, of course - it would need
> to be hundreds of times brighter to be believable.
Yes, sorry. Blender's default background is that color. I just didn't change
it and it looks dark outside. It has no influence on the lighting, though.
I did provide a link to the radiosity version where I also took the time to
change the background to some more sunny-day look-alike. :)
Yes, the shadows are very sharp and pronounced and I'm not quite sure wether
it's because there's too much brightness, the Blender implementation is still
buggy or whatnot. Don't you guys think it's funny though when we begin
wondering wether a synthetic image is correct or our own assumptions about how
it should work in real life? ;)
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Two more radiosity renderings. Thankfully, after some half-hour of
pre-calculating, taking shots from other angles is a breeze.
http://img377.imageshack.us/img377/7061/lightcutstest4radioxv4.jpg
http://img377.imageshack.us/img377/3884/lightcutstest4radio2dh3.jpg
I increased the mesh resolution of the ground, so the shadow of the ear is more
visible, though still faint. I'd guess it has to do with the fact that sharp
shadows are not really possible with radiosity.
Also, while not seen in none of these scenes, there's quite a bright spot in the
ceiling, no doubt contributing for the shadow below. It is itself illuminated
by some of the ground outside (I put the floor as a plane rather than part of
the cubic room).
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