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Okay, I
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so I said assignment one would
be six marks
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And then two and three would be
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12 marks each.
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This. I was wondering, well,
let's not make any more of it. I
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looks like the network is
connected. There we go.
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I we go. Oh. Now it's
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undecided.
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Look like You took the click I
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so they would look at the Zoom
transcript. No, it just came as
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a lot of text.
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So I have my phone recording
here, so if the other ones are
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back To the standard
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the regular appearance of the
transcript.
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So Well, I guess I'll switch to
my hot spot.
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I don't need to do anything
there. I
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man, even the cell phone, Even
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the cellular network is Slow.
You
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switch to i
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I'm going to run it for my
laptop,
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See if That helps. If
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Okay, so assignments appears on
the web page, and if you're ever
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able to access the web page,
you'll see it here. So I'm going
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to put some more details here,
but I'm going to fill in the
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rubric. So I have the file on
Dropbox. It's also on the I
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should put the link there the
version four file format page.
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So I want you to take that
change the Image Size to 1280,
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by Oh, type, Oh. 720, I,
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So change the image size of
1280, by 720, and add and place
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two more spheres in the scene,
each with a different material.
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So we run it with the specified
integrator, and also use the
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wavefront integrator and use
different values of samples per
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pixel.
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Okay, so that will and then I
want you to fully document your
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pbrt file with comments in line
that describe all the statements
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used along with all parameters
specified and default values for
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those parameters not specified.
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So lot of writing and lot of
comments into the PBR file, pbrt
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file.
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So I propose that three marks
for describing, documenting the
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input file that's your you.
Using, and then to run and
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analyze the results
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at a three marks, and that'll be
due on February 25 so it's the
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Tuesday back from the break You
said
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to me chairs on that Thursday.
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Yes. Thank
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Okay, do
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Is it blue and black?
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Blue and black, or one color
looks the same as another under
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certain conditions, under
different completely different
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dress? I'm somewhat familiar
with that example.
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How To summarize, I'm two
distinct pairings of like
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spectra that they're they're
different, but they can look the
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same depending on like when you
convert them to like spectra,
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like spectra to like color and
stuff like that, they look
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identical. It's kind of what I
interpreted as pairs of spectra
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was substantially different
distributions that have very
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similar X, Y and Z values, and
thus the human observer appear
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to be the same. Yeah,
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so it's a white or gold or gold
block, is the real question?
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So I have to do more research.
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I'm not sure that
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the dress example
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might be, it might be off his
metamer. The idea is, so if we
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look at the Wikipedia page for
metamer, they say, Here's a
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monochromatic light,
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and then here's
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an RGB. I
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instead of me drawing
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up the picture, I
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so on the right in column one,
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We have a yellow light,
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and then we can also express the
yellow light as a combination of
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red, green and blue in column
two. So the the images one at
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the top of columns one and two
are perceived to be the same,
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but the luminance is has a very
different spectral power
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distribution.
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So going down,
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we have
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so S, M and L and
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anyone know what SM and l
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are when you Don't cook your
chicken enough you get sick?
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Yes, I not
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sound enough, isn't
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it spectral? I
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learning management
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doesn't the stand for spectrum,
no camera, stand for material,
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no light. Getting cold. Short,
reading cold. Short, medium
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long, yeah, but
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That's right. Should I Get
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Good so
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you Just
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take a Picture. CS manager,
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still. So if you use it,
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so the
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our eyes can perceive short,
medium and long
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wavelength. And
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so there's a correspondence with
red, green and blue. What
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else did I ask? Do
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what else do I
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ask? Was A characteristic of A,
C, E, s2, 064,
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so that's a color space.
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So it seems to extend past the
visual light spectrum we can't
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see like they're what was it
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theoretical colors or imaginary
uses primaries that correspond
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To imaginary colors? Yeah, I
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it. So the idea is that it
allows All possible colors to be
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represented. So I
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so it's a benefit for archival
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purposes that
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we can
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we're not limited to sRGB, for
example, which is a standard for
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the web. Does
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that just mean it avoids data
loss? If you just stored in RGB,
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you technically are losing the
data of those imaginary colors.
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So is that why we use it for
archival purposes? Do
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to preserve it historically, in
case the values of our GPS
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change over time.
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Yeah, I
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I'm open to
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doing your own research on this
as well, but I feel, my feeling
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is that, because we're not, I
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the gamut
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made available with picking
primaries that are outside
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the range of
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visible Colors, so that we
capture the whole horseshoe of
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visible colors.
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That gives us
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more flexibility in
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terms of
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keeping a reference to
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and as we Get
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as technology improves, we have
wider Color gamuts and
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are you Looking for your last
question? I I
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just want to get back to my
teacher
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today. So what's the
relationship between x y z
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coordinates and visible colors?
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Not all values of x y z
coordinates correspond to the
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sizeable spectrum,
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realizable spectrum, yeah. So we
can have values of x, y and z
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that don't correspond to
realizable colors. But on the
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other hand, all the realizable
colors I have coordinates in x,
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y and z. So that was a true and
false question. Not true and
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false, True or False. I
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so pbrt is dealing with spectral
rendering, So we have to
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be able to do
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so we have to deal with
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spectral power distributions and
colors and
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So this is physics, physical.
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This perception, perceptual.
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There are two issues. I
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So we want to I
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want to specify the spectrum,
maybe By piece wise. But then We
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also need to, I
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so we need to work with RGB in
some cases, And then we also
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this is part of the other
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so the idea is, first of all, we
have to do input, whether we
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specify
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spectra to
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begin with, that's input to the
renderer, or whether we specify
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things in terms of RGB, then we
need to convert the spectra to
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do the processing. And then we
also need to think about for
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output, converting the spectra
to RGB
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for storage you
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it. So this is this diagram. Is
the horseshoe that I started
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with or ended with last day. So
we could see the wavelengths of
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visible light around the edge,
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so blue is 380
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and red is at 700 and
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so the chromaticity is
independent
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of illumination and
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so we can talk about i
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So, X, Y, Y and
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has anyone heard of y, u, v as a
color space?
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Does it sound for ultraviolet?
By any chance? No,
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u and v are the coordinates.
Perhaps. Parameterization.
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This is what it was called when
I was familiar, when I was
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learning these things that For
the first time, I
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it so now, more generally, We
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talk about why CR, CB,
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so illuminance, of
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course. Corresponds roughly to
the green. And then we can
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specify Chroma differences in
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red and blue and
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So has anyone watched a black
and white TV lately?
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No, there are some movies that
were made in black and white
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that I kept watching color.
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Yes, except for Ted Turner's
wonderful the
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show called one division that
was in black and white for the
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first half of it. Yeah,
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it's a wonderful Street.
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Yeah? Chris, the
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old black and white don't
convert well to color in today's
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world.
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Yeah. Well, this a little bit
different.
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Let's see. I
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i blame Ted Turner for this. Is
that justified?
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So the original black and white
with Alistair sim is that called
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A Christmas Carol, and it gets
called Scrooge, I can verify
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that changed the name. So,
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Miracle on 34th Street. It's a
Wonderful Life. It's very
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knowledgeable.
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Yeah, so I'm
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the point I was getting or
losing towards was,
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well, okay, talking about one
division and different. It's a
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Wonderful Life and so on.
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Unless we
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so the source material is black
and white, Unless we mess with
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it. I
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so TV signals. I
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So the black And white y'all,
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so
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it's like, where should we have
the black and white inside the
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color transmission? So we're
just using part of the data to
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create the black and white
images. I or the black and white
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TV. If it doesn't have Chroma,
it's just using the
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luminance to display the image.
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Does that make sense?
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Yeah. Did the original like
cameras that were used to film
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these things, were they able to
perceive the red and the blue?
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But we just didn't have a way of
like capturing them, like, like
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putting them on screen. Like,
for instance, if we went to an
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old black and white thing and we
had the original tape, could we
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then convert that to IE, to use
Chroma, for instance. That's
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part of what they did with the
colorizing. Is trying to do
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that.
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I mean, a lot of colorizing just
algorithms to just
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read like do it. But
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if you had the original tape,
would you be able to just have
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it? I don't believe that the
systems were able to record that
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data
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at the time. That's the
question.
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Yeah. So there was no tape, it
was film,
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and that was stuck in black and
white. Yeah. I think the
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machines that it was recorded
on, I don't believe that they
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had capabilities
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for life. Yeah, I will look into
the history.
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There was color film at the
cameras. Like, if you put
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colored film in those cameras,
they would still, like, accept
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it. It's just that the film
itself, it was way too expensive
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to actually do any kind of
color, so black and white, just
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black and white was very Cheap.
I
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If anyone's Interested in Very
cones.
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I So Talking about gametes. This
is the range of colors that we
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can represent. So we have the
blue, green and red primaries.
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So based on the particular
quantities of those primaries
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that defines the range of colors
that we can represent the
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So here are some
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other gamuts. So SRGB, that's
the web Standard, and D 65 and
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So the White Point The
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so it's a perceptual quantity,
but
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so the white point is when, if
we're Talking about red, green
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and blue,
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that we have
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full full red, Full green, full
blue.
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So here's the Plot of the
spectral distribution for D 65
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So the nanometers are along the
bottom.
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Pardon, me, I said daylight, but
noontime daylight at European
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latitudes. I
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so F is F series illuminance,
and that corresponds to
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fluorescent lights. And it.
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So earlier in the text had
mentioned
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about a lemon skin,
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not just a skin, but a lemon
with its skin on, and the
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behavior of that under lighting
conditions. And so this is the
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spectra for reflection from a
lip from a lemon
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skin.
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Seems funny to say, lemon skin,
right?
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That feels like you're talking
about the inside of the skin,
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Anyway,
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so we can have different kinds
of spectra and
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we can have a piecewise Linear
spectrum, defining a
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distribution Using a set of
values for
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And then we can sample and
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so the tri stimulus theory of
color,
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I'll do a dramatic reading here.
Of this paragraph
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says that all visible spectral
distributions can be accurately
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represented for human observers
using three scalar values. Its
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basis is that there are three
types of photoreceptive cone
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cells in the eye, each sensitive
to different wavelengths of
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light. This theory, which has
been tested in numerous
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experiments since its
introduction in the 1800s has
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led the development of spectral
matching functions, which are
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functions of wavelength that can
be used to compute a tri
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stimulus representation of a
spectral distribution I
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so these are the color matching
curves for X, Y and Z, a given
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spectral distribution can be
converted to x, y and z by
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multiplying each of the three
matching by multiplying it by
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each of the three matching
curves, and integrating the
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result To compute the values of
x, y and z so,
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here's a representation that I
hadn't seen before. Plot of x,
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y, z, color coefficients for the
wavelengths of light in the
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visible range. Curve is shaded
with the RGB color associated
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with each wavelength, so,
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blue here, red
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here, Green and
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how did I do? I
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so when we're studying, we don't
need to worry about, like their
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process of how they're doing it
in the program. We just need to
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worry about the confidence, like
when
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we're reading the textbook and
stuff. I
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formulas or anything like that,
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in the textbook, yeah, I would
say I
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the details of the mathematics,
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really going to focus on that,
because we're not focusing on
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that in our discussions
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it's about, How do we get
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how are we
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able to
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experiment or access these
physical simulations in pbrt,
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so
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the details of the integrals and
so forth
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won't be our focus.
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Maybe, if you think about the
figures in
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the text.
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That might be a good way to
think about
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does that seem helpful?
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Thanks that formula is pretty,
pretty easy and useful. It's
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really just a percentage like
and then the last one, even even
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show at z is equal to one minus
x minus y, which is just saying
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to all the one in reality,
dividing one wavelength by the
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like, the total of the
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other three, the three of them
combined,
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just what percentage of your
lights, x, what percentage of y,
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what percentage Z? Well,
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then just saying, the kids in a
lot of the choppers and stuff,
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they go into details, show the
lines of code and from different
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functions and stuff. Do we need
to going into that much detail
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about that stuff, or is it more
mainly about the concepts that
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they're
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they're dealing with?
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If we want to change from a gold
sphere to lose fear. What do we
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need to do with the
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code? So it's about using pbrt
So
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the implementation details might
be helpful to look At,
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or maybe not. I
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I don't
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find these controls particularly
helpful because
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it's jumping around.
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But anyway, yeah, I
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the kinds of questions maybe
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that may come up would be and
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you can give your feedback about
this. Why do we use a certain i
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Why do we have Three different
parameterizations of spherical
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coordinates used in pbrt? Do
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just to confirm we're only going
up to Chapter Five for the New
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Jersey, chapter six,
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yes,
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Sorry. I'm throwing all these
random questions at you. I
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I'm sorry. Don't have to be
sorry. These are good questions.
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I
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CS. So here's the overlap of the
gametes for the different color
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spaces that pbrt supports. The
smallest one is the sRGB
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and DCI, p3,
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rec, 2020,
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that's for
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Ultra High Definition, Standard
i
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So here's The color gamut and
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for the rec 2020, color space,
and
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then we See the 65 there. I
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so for next day,
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look at 5.1
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and 5.2 and
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then we'll cover three or 5.3
and 5.4 next Thursday.
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Okay. I
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on Chapter Six will be after the
break.
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Yes, maybe we can
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Yeah, well after a break, I
think,
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thanks for today. Have a good
weekend. Stay warm. See you on
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Tuesday.
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