Mtg 22/26: Thu-27-Mar-2025

Outline for Today

Reflection Models, Texture Mapping, Area Lights

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Today

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Take quiz before the start of our next meeting

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Audio Transcript

Struggling with it, and then I looked at it.
Okay, so we're at meeting 2226
so
reflection models I'm
textures and materials and
so this is chapter 10.
This is in chapter 12.
I want to mention these other things, because
the assignment that's due and
thinking about what we're going how we're going to finish up The
class. I'm
so meeting
324, 2526 and
so are we shooting to get to chapter 12 by the end of the
course is that this is indicated.
Yeah, I'm wondering if, if we Touch on chapter 11 as Well. I
Bless you. You're
too quick for Me. You
Yeah, I think we'll dabble in chapter 11 as well.
So I suppose Are we just lightly touching on those three
subjects? Do you have another three kind of lectures? Yeah,
11 looks a little bit shorter, Though I
CS, so I would invite your input for questions that would be
final exam questions that would Be a fair assessment of Your
learning this semester. Applause,
so I'm sorry for missing last day's meeting.
Let's go over the quest, The quiz questions From that you
so what are the three major classes of behaviors that come
out of The electromagnetic theory of light.
Semiconductors Do
conductors,
and I guess, insulators. I
The answer you have on the quiz is dielectric, conductor and
semiconductor just has two of them listed. I know I'm just
looking at it right now, since I got that one wrong, but yeah, me
too.
Yeah, I have dialectics, conductors and semiconductors,
because I put semiconductor is one word and you put it as two
words.
It might be because of the order, oh no, I
put mine in the same word.
I put commas in between them, and I have semi and conductors
one word,
okay, I will check my Answer and regrade them. Oh, yeah,
that makes sense. I
I also didn't pluralize or I did pluralize conductors, so
arguably, I have none of those parts.
Yeah, I realized all night.
Okay, let's look at the question. Since there are
questions about the question, I Oh, I
didn't put wild card At the end Here. I
I will check
it right now.
I will check other issues as well.
If you have other quizzes that you think are Right, that got
marked wrong. Let me Know If
what impact does the difference between indices of refraction of
neighboring materials have on reflection? I
Are you asking for? Like, the like mathematical impact, I
wasn't quite sure about what you're exactly asking for on
this one, what I wrote was the differences between indices of
refraction is scaled by the square root of the two indices
of refraction. This is reflection, which I don't know
if that's what you were looking for, necessarily.
I also I had that, plus I had, intuitively, this could be
understood those results, the radiance is differential, solid
angle being compressed or expanded due to transmission.
I was thinking about if there's a greater difference between in
the season refraction neighboring media
to reflect this reflection will be more intense. So diamonds are
more reflective than glass, because there's a greater
difference.
Diamonds are more reflective than glass. I guess you don't
often see a nice diamond mirror like that's not something you
just commonly come across. Diamonds are so small it's hard
to see. I imagine it would be really hard to make a diamond
mirror. I don't think it's impossible, though, with
synthetic diamonds, i i
because otherwise that's really expensive Mirror, mirror on the
wall, who's the fairest of the
Wall? Could use it in like a telescope or something.
You said, the greater the difference, the greater
difference More intense function. I that we Were saying
yes,
what is Snells window?
If you're at like, the bottom of a pool, and you look up, there's
gonna be an area that's clear to you, and then the rest of it
will be, I guess, a little bit occluded. You basically have a
nice little pothole of like vision that is clear that that
actual like frame, that window is Snells window, right? Yeah, I
don't know if that's the most articulate way of saying it, but
it made me want access to a pool.
Can't say I've ever opened
my eyes. Don't you like chlorine in your eyes? Do
where the pain goes away in a few days. I also
don't stand too well.
Less Salt i
So cells window is
when you're underwater, you'd look up, there's a circle.
Inside the circle, you can see the blue sky and the palm trees
or whatever else you have around your pool,
outside that outside of that window, you don't, you don't get
to see out. You see
reflection. What is that last word after Water? Slash, air
interface.
You're welcome. You
What are three important geometric effects to consider
with Micro facet reflection models,
masking, shadowing and inter reflection.
I so I
just shadowing.
I masking happens when?
When the light hits the surface, but You catch you See it? Yeah,
I
How do you like my pictures?
Some of the mountains. I don't know what happened to them. I in
their example, they use three identical mountain ranges. You
got a little bit liberative With your creativity there.
Thanks. Creative license. Exactly.
So why does pbrt use a specialized BS DF for air and
fur? Because
otherwise it would be extremely expensive computationally, but
it also make important sound like difficult for Monte
Carlo, yeah. So there's a lot of parameters that
there's a lot of ways to improve the efficiency of the sampling
for hair and fur, so they have A special one. That's what I was
looking for. I Sorry.
Could you say that again you're looking for
just could you just repeat what you just said? There? Sorry.
So there are
using COVID diffuse materials and
more generic BS df and
we can do the do hair and fur, but it's very computationally
expensive, and I
so it helps to make,
it helps with efficiency, to to create a special BS DF, so it's
more efficient
and produces
better results. And
thank you.
Well, I know how hard it is to resist the urge to just have one
thing work for everything like that, just have one sampling
method that works for everything, and you just try to
do it as much as you can, but then it messes up other things,
and then, like, Oh, yeah. Now hair works really well, but now
all of a sudden, leaves are breaking. You just get a bunch
of like, weird things, as lame as it is, just to Break Your
coat up and create other specialized forms i
What is the purpose of a go Neo photo meter or go Neo, reflect,
Do meter?
So the answer you were looking for was it measures the SDF?
Yeah. I talked about how it had two separate, like, two or more
arms for separating the camera and the light, so you can
measure something from all the different directions. That's
what I wrote. But I suppose that's a very indirect way of
saying the same thing.
I love. So go Neo,
the etymology of that word Gonio is angle do.
So it's the same the same root, and as we see in polygon, so
polygon would be many angles, and
so a couple of those sections had the Don't you can skip this
on your first reading. So I didn't, I wasn't looking for a
great deal of detail. I just thought, Gonio photometer,
photometer. Either
way, I thought, I thought it was cool, and I understood its
intended purpose right away, because there's a lot of value
in not having the camera and the light just actually attached to
each other, especially if you're trying to measure the way light
hits a surface. Well, that's very limiting. And to have all
these separate arms I can picture, you could
computationally have the arms all move around and like, take
it from different angles, and you just record it with record
it, just sort of capture that you can get a lot of data out of
that from any material or whatever.
Yeah,
really good for digitizing new materials, like maybe even,
like, storing them to using, let's say, a game or something,
just storing a texture by capturing lights. That would be
a very interesting way of talking about
You. So I wanted to show you to start of rendering of the manger
sponge was linked from Last Meeting And
it'll be a good problem. No,
I don't think so.
This is
a finished version. I
so this generates a segmentation fault. So I'm not sure how many
millions of triangles are in this. I didn't do the six. I
CS, I did the Fifth Level, not the sixth level. I
so you can see the starting point looks pretty good already.
I
The sponge appears. It's just the spaces that need to be
cleaned up. And you can see on the histogram,
there's a peak
at 1.065
so the value should as we refine the
image that
maximum value will go down and get us to the point of,
ideally, We'll be in the range of zero to one. I
so I want to show that to you because of
the relationship with Sir Pinsky tetrahedron, you
can See it's going down And
so this is
an example that I did with a triangle mesh. So it's really
one triangle, and I put them, I use them twice. So, so first
three values are point one, second, three values are point
two, and the third three values Are the third point, so indices
01, and two and
so you don't Have to have them. I did two triangles back to back
that we could just do 01 and two for The triangle and
so here I've combined
the model with spheres in the gasket, dot, PBR, key file with
the triangle, so The triangle is the same size as the gasket. The
it. So if we're doing for generating the tetrahedron with
a triangle,
well, let's talk about the gasket. If we're doing a
triangle, how do we create more detail in the triangle mesh?
Does that make sense? I
Are you referring to? Like the interior faces, like,
if you were to take the triangle and let's say you slap four
triangles, one of the bottom and the three side ones you would
have, like An empty triangle, is that What you're referring to?
I so if we do it in 3d the tetrahedron. So this is made out
of four triangles, Then the first step would be to make the
and we get four. And then
we get I got you,
but with a triangle, I
We can construct the model by making the triangles so we're
shrinking the triangle
by a half
and bringing it to vertex and
so we can start With The
so we can Take the triangle then we can define three new
triangles and
so we have three triangles. So 00102, that's a new triangle.
And then 011, and one two, that's another triangle. And
then we can do 02122, to make a third triangle. And we can do
that recursively.
Does that make sense? I
What do you observe these two images.
The one on the right looks good.
I I want to vote the one on
the left. Well, the one on the left is trying its best. It's
It's definitely having troubles in figuring out what it wants to
display it looks like.
Yeah. So
the one on the right is filtered. So what do we want to
filter? So this is a texture. It's the same texture, and it's
one sample per pixel.
So we want to filter out
what wet from
our texture And
sorry,
yeah, it's noise,
Maybe even more specific. I
so how do we
how do we know we have a
of enough samples
to reconstruct an image
when it looks less like The left one or more Like the right one.
I two times. Highest frequency,
highest frequency. Thank you.
I so if we're sampling at a rate that isn't
that doesn't encompass all the high fruit, the highest
frequencies in the signal we're trying to reconstruct. I
so we can think the frequencies above the above the sampling
rate will be noise.
Does that make sense? What's the word between we and Two one.
Thank
you. You're welcome. I
so I'm going to filter out I'm
so
done some filtering on The texture, and it looks a lot
better.
And you said anything about that highest frequency is noise. I
Yeah, so the frequency that are above
the samples and
so If we're sampling at a rate, at
rate, r so,
so if we sample the radar, then we can reconstruct frequencies.
That have a maximum the maximum frequency we can reconstruct is
R over two.
So anything above r over two So
so that makes sense. I
I think It would be useful if there were code examples or
input file examples to generate these examples.
That would be good. That's that seems like a really easy quality
of Life thing. Yeah.
So I wanted to jump to talk a bit about area light sources.
Here is the mythical point light source, Deluxe. Illuminating a
dragon like mythical Dragon, mythical Dragon, Yes,
so we have Very sharp shadows and
here's a small disk area, Lake source. Let's compare it to
white light source
so we can see some terrible soft the other word,
let's look At a large disc.
There. You're almost non existent. How
there's still glass in here, guys,
the correct answer would have been way outside and
we're still in Class. Can you guys leave? There's still COVID.
All right? You now, I feel like we should go on for 10 minutes.
We're not done yet. I like,
sorry. So,
what do you want us to read for next week? Yeah,
probably 1011, I think you said,
let's look at What
let's look at chapter 10,
and we'll talk about purlin noise as a way to generate
textures. So if you want to do wood and some other very
realistic textures there are. So we'll look at some details of
that, okay,
thank you for today.
Have a good weekend.
Sorry. Any questions about the assignments, please post into
the class discussions.

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