Mtg 10/26: Thu-06-Feb-2025

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

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