Another couple renderings of the Alabama Welcome Center building, one
showing it late in the day. I've about got it put together right, less some
minor details, so this is basically how the place actually looks. Unlike my
previous renders of it, which weren't very accurate, this now has the upper
front (or facade) as it should be.

I came across some trouble with reflection exponent causing blacked out
areas. At least, that's what I'm thinking must be part of the problem.
Radiosity exaggerates the problem to the point of obliterating most of the
building entrance area. Perhaps something I'm not doing right, just not sure
yet. Anyone reading this seen such a thing happen themselves? I'm guessing
adc_bailout or max_trace_level, or both, could be the solution/problem.

The blank, or black, artifacting is so severe with the introduction of, e.g.
'exponent 0.8', into the reflection statements that I thought it unusual,
having not noticed anything this bad before.

Bob H.

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Attachments:
Download 'awc1_night-day.jpg' (66 KB)

Preview of image 'awc1_night-day.jpg'

Hi !

Glad to see you're still working on it. (One of my own problems is I give up
projects before they are finished). Well, I'm quite interested in realistic
lighting and such, so maybe I can help.

I haven't used the "reflection exponent" keyword for a long time. It doesn't
seem to be necessary anymore. You have exposure control (at least in
MegaPOV1.0) that compresses the dynamic upper range of an entire rendering.
This means you can setup light_sources with realistic (high) light-emission.
That's why reflections will finally show up properly without the need of a
reflection exponent!

In this particular scene I sort of wonder, why you're putting such
importance into reflections. The materials of the building suggest that
reflection (mirror-like reflection anyway, accessed with the 'reflection'
keyword in POV-Ray) are just the top of the iceberg, meaning, they are
important only when we take a closer look. Most materials here are rough
stone-like (hence gives a very diffuse reflection). If you're talking about
the glassy entrance, it's another story. Well, I don't see any radiosity in
the daylight rendering (shadows are black) so I can't say if it messes up
with the entrance. Assuming you did render this with radiosity, try to
increase "brightness" in radiosity, just to see what's going on... You're
lucky though, with this scene radiosity can do a nice and quick job.

Regards,
Hugo

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"Hugo Asm" <hua### [at] post3teledk> wrote in message
news:4114bd49@news.povray.org...
>
> I haven't used the "reflection exponent" keyword for a long time. It
doesn't
> seem to be necessary anymore. You have exposure control (at least in
> MegaPOV1.0) that compresses the dynamic upper range of an entire
rendering.
> This means you can setup light_sources with realistic (high)
light-emission.
> That's why reflections will finally show up properly without the need of a
> reflection exponent!

And it's been a long time since I used Mega. Hm. But does this work for any
and all objects reflected? My intent was to diminish darker areas and
enhance brighter ones, so I can imagine that would work for lit places but
not shadowed places. Maybe I'm not thinking of the whole raytraced image as
being completely light-controlled.

> In this particular scene I sort of wonder, why you're putting such
> importance into reflections. ---8<--- Most materials here are rough
> stone-like (hence gives a very diffuse reflection). If you're talking
about
> the glassy entrance, it's another story.

Yes, its really the glass entrance part that really must have the
reflection. The marble panels, roof and steps paint is glossy (yep, painted
steps, ugh! not marble) and makes those parts reflective at shallow angles
so I added a little. Not sure if I'll ever get it into MegaPOV. Awaiting to
see what all the next version of it has included, like a lot of people are.

> Well, I don't see any radiosity in
> the daylight rendering (shadows are black) so I can't say if it messes up
> with the entrance. Assuming you did render this with radiosity, try to
> increase "brightness" in radiosity, just to see what's going on...

Been using brightness 0.9, actually. :-)

I should have shown an actual image of the artifacting before it was too
late. By that, I mean, I rerendered again today and couldn't get it to
happen. A good thing I guess, but turns it into more of a mystery. I was
trying to get a short test scene to do the same last night and couldn't,
even though I could go back and run a small rendering of this buidling and
still see it happening. I'm attaching a hand-drawn artifact to show what I
was seeing yesterday and what it looks like without radiosity.

Bob H.

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Attachments:
Download 'awc_no-rad.jpg' (23 KB) Download 'awc_ref-exp.jpg' (24 KB)

Preview of image 'awc_no-rad.jpg'

Preview of image 'awc_ref-exp.jpg'

Hi again,

Thanks for posting the extra renders. Is it true that both the daylight
rendering that you posted yesterday, and the no_rad version you posted
today, are without radiosity? Because they look the same to me.

The entrance-artifact that you mention could be due to a wrong value in
reflection_exponent (for example, if you wanted to write .8 you might have
written 8 ... it was late at night you said) or max_trace_level was set too
low. Usually, radiosity will not have much effect on glassy surfaces because
they provide very little diffuse reflection. They are mirror-like, and
refracts the light, both of which are independant calculations from
radiosity.

> it's been a long time since I used Mega.

Yeah but I've found the exposure control is addictive.  :-)  Anyway it takes
a bit of practice because one must think about light in a more realistic
manner. I think most of us are still used to think directly about, what we
see on the screen (or what we see on photos ... all of which are images
limited/compressed to a low dynamic scale). Real world is different.

I could try to give some suggestions but they would involve changing all
texture values and strength of light_source's, along with using exposure ...
maybe the simplest solution for now, is to further increase the radiosity -
brightness value. Remember you can go above 1.0 and I would recommend 1.3 or
1.6... I've had fairly good results with that, and the results were at
least, that the shadows weren't black anymore. (It may pick up too much
light from the walls then, but anyway ... you could add a blue fill-light to
compensate a little for that)

Regards,
Hugo

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"Hugo Asm" <hua### [at] post3teledk> wrote in message
news:41155258$1@news.povray.org...
>
> Thanks for posting the extra renders. Is it true that both the daylight
> rendering that you posted yesterday, and the no_rad version you posted
> today, are without radiosity? Because they look the same to me.

The first did have radiosity. It's just not plainly obvious because I tried
a brightness of 0.8 and gray_threshold 0.4 to lessen the color bleeds. Maybe
if you were to examine the upper middle roof edge, where it crosses over the
lower roof, you might see it is whiter toward the right side due to the
diffusion effect between the two roof levels. It changed drastically from
yellow-white to pure white if I left those values as default.

> The entrance-artifact that you mention could be due to a wrong value in
> reflection_exponent (for example, if you wanted to write .8 you might have
> written 8 ... it was late at night you said) or max_trace_level was set
too
> low. Usually, radiosity will not have much effect on glassy surfaces
because
> they provide very little diffuse reflection. They are mirror-like, and
> refracts the light, both of which are independant calculations from
> radiosity.

Good point. Nope, not the case, unfortunately. Now I've managed to see the
artifacting again so I attached another image. Both renders are subjected to
the problem, the top one has radiosity and the lower does not (merely
speckles by comparison). This happened after adding back in 'exponent' to
every reflection statement, all but the brick has at least some reflection.
I better speak up about the reflection_exponent no longer being used, it's
only 'exponent' now in 3.6, even though the Editor still recognizes the old
keyword. I had thought it was removed until you mentioned it. #version
directive has no affect.

> Yeah but I've found the exposure control is addictive.  :-)  Anyway it
takes
> a bit of practice because one must think about light in a more realistic
> manner. I think most of us are still used to think directly about, what we
> see on the screen (or what we see on photos ... all of which are images
> limited/compressed to a low dynamic scale). Real world is different.

Yep. I'd like doing some of that, too, just haven't gotten around to
MegaPOVing again.

> I could try to give some suggestions but they would involve changing all
> texture values and strength of light_source's, along with using exposure
...
> maybe the simplest solution for now, is to further increase the
radiosity -
> brightness value. Remember you can go above 1.0 and I would recommend 1.3
or
> 1.6... I've had fairly good results with that, and the results were at
> least, that the shadows weren't black anymore. (It may pick up too much
> light from the walls then, but anyway ... you could add a blue fill-light
to
> compensate a little for that)

Probably... probably... Although, I would like more contrast for night and I
think dark shadows in daytime is a good thing if in the right places. Most
likely I've used too extreme a diffuse on everything while I tried to get
the nighttime lighting. Afterall the roof is diffuse 0.9 (bricks are 0.5 and
mortar 0.67) and so is as bright as fresh snow when in reality it's less
white. That's what happens from a tendancy to use any number that seems to
fit at the moment.
:-)
Thanks for the suggestion to try MP's exposure with this scene. I'll be
thinking about it.

Bob H.

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Attachments:
Download 'awc_reflect-exp.jpg' (48 KB)

Preview of image 'awc_reflect-exp.jpg'

> Now I've managed to see the artifacting again
> so I attached another image.

That's strange. Never seen anything quite like it. Reminds me a little of
two coinciding surfaces, both located between the light_source and the
building, resulting in strange shadows.. Or the recent blob & torus accuracy
problem which is obviously not the case here.. So I don't know what it is.

> This happened after adding back in 'exponent' to every
> reflection statement, all but the brick has at least some reflection.

Strange.

> I better speak up about the reflection_exponent no longer
> being used, it's only 'exponent' now in 3.6

Oh, thanks for the info. I hadn't noticed, and I must confess that I haven't
even started using 3.6 yet... MegaPOV is my preferred choice.

Regards,
Hugo

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