Jaime Vives Piqueres <jai### [at] ignoranciaorg> wrote:
> Sorry for responding my own post, but I forgot to mention that I was also
> inspired by Clipka "secret" scene, and used these radiosity tests to see if
> that kind of scene could be rendered more realistically with this technique.

One thing that makes your scene much easier to render is that you allow the
light to enter via a straight way. In mine, the profile of the door and frame
is more complex, and the door is almost closed, so much that light cannot enter
straight (well, except through the keyhole).

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> - By setting nearest_count to 10, no additional samples will be taken
> after the 10th pass whatsoever. In fact, many samples will have been
> taken much earlier.

   I should have warned that "I really don't know what I'm doing" is my
second name... but thanks for the pointer.

> - By taking high error_bound samples first, which are low quality, you
> will reduce the number of low error_bound samples taken.

   Well, here I must admit that I thought I knew what I was doing... ;) What
I wanted was to take first the high error_bound samples, to avoid the 
problem of radiosity coming trough the joints... but perhaps it works 
equally the other way: I must try it.

> - The artifacts you see in the 16b image are not due to the quality of
> the radiosity samples used for that shot, but due to the moment they were
> taken: What we see are the results of final-trace sampling, with the new
> samples affecting their surroundings only in successive rows.

   I think I didn't fully understand this explanation... sorry (not your
fault). But the 16b was done apart in one pass, without loading any radiosity...

> I expect that exactly the same quality - if not even better - can be
> achieved within just two frames by using constant settings as currently
> used in the... hm, let me guesstimate... something like the 6th frame.
> 
> You may also want to try using 1/max(image_width,image_height) as
> pretrace_end, and N/max(image_width,image_height) with N being some power
> of 2 as pretrace_start, and render just a single frame. Try a
> nearest_count of 3 or the like.

   Again, I must try these tips...

> Finally, expect 3.7 radiosity to become better anyway.

   I hope so!

> Oh, and finally finally - keep having ideas like these, 'cause even if
> they don't work as you may think they may still be inspiring. And
> inspiration is the thing most needed with POV's radiosity.

   Thanks: I have lots of weird ideas... and not only abut radiosity, but 
many show to be nonsense after the first tests.

  For example, I also tried something similar to what Holger Karsten tried
with MCPov: rendering many frames with random sample sequences (MegaPOV) and
then averaging them with ImageMagick. It sort of works, but needs too many
frames to get ride of the noise.

   Now, if someone is interested, I had the strange idea that a 
fade_distance  for reflections will help making blurred reflections with 
averaged normals... but I'm unable to test on my head if it will work.

--
Jaime

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Warp <war### [at] tagpovrayorg> wrote:
>   I think it also deserves to be considered being implemented as an
> internal feature of POV-Ray. In other words, something which could be
> turned on to make POV-Ray do this automatically, and without the need
> for the save files.

The idea of doing a final pretrace step that does exactly the same as the main
render definitely deserves attention.

However, this would theoretically have to include all the bells & whistles, like
anti-aliasing or focal blur, diffraction etc., as these *may* have an impact.


I was also pondering the idea of avoiding radiosity sampling during the final
render in some other way, but haven't come up with a conclusive idea yet. The
problem is always the same: Once you "slipped off" an existing sample into
no-man's land, you'd need to use *some* other color - but whichever you choose
will possibly be different from that last nearby existing one, and give a
(comparatively) sharp edge - an artifact.

Theoretically it would be possible to just keep using the nearest sample, but
this has drawbacks as well:

- Speed: The sample lookup algorithm is designed around the expected maximum
radius of influence of a particular sample. Searching for samples further away
than their expected radius of influence would be a hassle.

- Artifacts: When moving further away from a sample, there would be a moment
when the closest sample would switch to another one, potentially causing yet
another jump in color.

- Geometry: Some samples just don't fit, e.g. because they're on the other side
of a comparatively thin object.


POV already provides (theoretically) good tools for addressing this issue: The
reuse_count (together with always_sample off), forcing more samples to be
collected during pretrace than will be needed during final render, reducing the
risk of any spot being missed completely, and the low_error_factor, allowing
samples to be re-used at greater distance during final render.

There were a lot of design flaws in 3.6 acting against these mechanisms. Let's
see how things work when these flaws have been eliminated.

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In these discussions it would be nice to know how the "reference
renderer" handles this. Reference being MC-Pov. In 1 hour the result
might be quite good with a path tracer. At least if MC-POV implemented
all known techniques to speed up the convergence.

Severi S.

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Jaime Vives Piqueres <jai### [at] ignoranciaorg> wrote:
>    Well, here I must admit that I thought I knew what I was doing... ;) What
> I wanted was to take first the high error_bound samples, to avoid the
> problem of radiosity coming trough the joints... but perhaps it works
> equally the other way: I must try it.

If you're talking about that light leaking though walls and the like, that's
actually the high error_bound samples, not the low ones.

If you're talking about light leaking through at the hinge side of the door,
that may even be physically correct.


> > - The artifacts you see in the 16b image are not due to the quality of
> > the radiosity samples used for that shot, but due to the moment they were
> > taken: What we see are the results of final-trace sampling, with the new
> > samples affecting their surroundings only in successive rows.
>
>    I think I didn't fully understand this explanation... sorry (not your
> fault). But the 16b was done apart in one pass, without loading any radiosity...

I'll try again, just the basics:

One of the main source of artifacts are radiosity samples which are taken during
the final render. The artifacts seen in the 16b sample look exactly like that
type.

(I'll not go into detail *why* they look that way ;) it's simply a side effect
of final-render-sampling that cannot be avoided)

This happens when the pretrace steps didn't generate enough samples.

If the same samples would be available at the start of the final render already,
you would not get any such artifacts.

They are available *after* that final render, and this is the moment when
radiosity data saving is done. So if you render the whole smash all over again,
this time loading the samples from the previous run, you don't get a different
set of samples - but you get a much better render.


>    Now, if someone is interested, I had the strange idea that a
> fade_distance  for reflections will help making blurred reflections with
> averaged normals... but I'm unable to test on my head if it will work.

Now it's me who understands just half of what you're saying :)

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The amazing JVP back at work, ladies and gentlemen!  Someone please shoot that
damned RL! :D

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> If you're talking about that light leaking though walls and the like, that's
> actually the high error_bound samples, not the low ones.

   Yes, I'm talking about these... but my experience says they appear at low 
error_bound values... ?!?!?

>>    Now, if someone is interested, I had the strange idea that a
>> fade_distance  for reflections will help making blurred reflections with
>> averaged normals... but I'm unable to test on my head if it will work.
> 
> Now it's me who understands just half of what you're saying :)
> 

   Sorry, I was too short on the explanation... what I mean is that when you 
look at blurred reflections in RL, the reflection seems to disappear at some 
distance from the reflected object. I know the reflection is there, but very 
blurred... but in practice it looks like this is just the underlying 
material color.

   Now, if you had a fade_distance keyword on the reflection{} statement, 
which attenuates the reflection until it reaches 0 for objects beyond the 
specified distance, perhaps this would help getting less noisy materials 
with the existing blurring techniques (averaged layers with big normals, 
micronormals,...).

   But as I said, my ideas turn to be nonsense often... and also it seems 
too simple to not have been figured out before.


--
Jaime

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Severi Salminen <sev### [at] NOTTHISsaunalahtifiinvalid> wrote:
> In these discussions it would be nice to know how the "reference
> renderer" handles this. Reference being MC-Pov.

Why would MC-Pov be qualified as a "reference renderer" in this case?

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Jaime Vives Piqueres <jai### [at] ignoranciaorg> wrote:
> > If you're talking about that light leaking though walls and the like, that's
> > actually the high error_bound samples, not the low ones.
>
>    Yes, I'm talking about these... but my experience says they appear at low
> error_bound values... ?!?!?

Huh - that sounds weird to me... I can't imagine why that would be.

Then again, thinking of it: Did you also set minimum_reuse low? Otherwise the
low error_bound might increase the probability of samples being placed very
close to edges, while the comparatively high minimum_reuse might allow for
"cross-talk" with the other side of the wall.

There might also be a connection to some other radiosity flaw I just found,
which explains how light will "leak" into dark corners (still doesn't explain
leaks at edges though). Unfortunately I still lack a good idea to fix it.


>    Now, if you had a fade_distance keyword on the reflection{} statement,
> which attenuates the reflection until it reaches 0 for objects beyond the
> specified distance, perhaps this would help getting less noisy materials
> with the existing blurring techniques (averaged layers with big normals,
> micronormals,...).
>
>    But as I said, my ideas turn to be nonsense often... and also it seems
> too simple to not have been figured out before.

Naaah - that doesn't sound like nonsense to me. It may be somewhat different
from reality, but it may *look* convincing after all.

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> One thing that makes your scene much easier to render is that you allow the
> light to enter via a straight way. In mine, the profile of the door and frame
> is more complex, and the door is almost closed, so much that light cannot enter
> straight (well, except through the keyhole).
> 

   Yes, you're right, but my scene also had the problem with the light 
leaking, which is what I wanted to "solve" with the technique I was testing...

--
Jaime

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