Mtg 17/26: Tue-11-Mar-2025

Outline for Today

Midterm review

Administration

Today

  • Going over the midterm exam

For Next Meeting

Wiki

Link to the UR Courses wiki page for this meeting

Media

Transcript

Audio Transcript

  • So Did everyone see The grade scope? Email? I
  • this is what it looks like. So it'll have a link to view your
  • graded work, and it'll Be from no reply@gradescope.com
  • so what Is sRGB?
  • Stand it up in I
  • Five in the 1990s I
  • so it was defined in the 90s
  • so that
  • we'd Have a standard representation of colors on the
  • web and
  • this is a color space.
  • So what about a gannet? I
  • What is? What do we mean? We're talking about a color gamut for
  • so gamut is just means, like a range. So when we see out of
  • gamut, it just means something's outside the range. So in our
  • case, the color space, so if it's not represented in the
  • color space, it would be out of gamut. Yeah, I
  • so how do we define the gamut for an RGB color space
  • would that just be considered the zero to one or the zero to
  • 255, depending on like, which version you're doing or and then
  • anything above those numbers would be considered, I Guess,
  • out of gamut, or they get truncated normally.
  • So the zero to 255
  • talk about
  • zero to full
  • color? Yeah, I
  • so typically, we're defining a gamut,
  • so we have the tri stimulus theory of colors, so we can
  • represent colors based on red, green and Blue, and the gamut is
  • defined by the particular chromaticity of those three
  • colors.
  • So we can make
  • all the point. All the colors inside the triangle can be
  • represented by the sRGB color space.
  • So how does the gamut for sRGB compare to other gamuts we
  • looked at and that are available now,
  • bigger or smaller?
  • Bigger?
  • No, I remember the diagram. I just don't remember which was
  • labeled what? There's just one that was bigger than all the
  • rest, though. Yeah.
  • SR should be as the smallest gamut in That picture you
  • Does That makes sense. You.
  • No. Sorry about That. I
  • so here's the section of the book
  • from which this question came.
  • So in pbrt, we assume that
  • the geometric, geometric optics is adequate model for late
  • scattering. So we have linear, linearity, okay. Linear
  • linearity, combined effect of two inputs an optical system is
  • always equal to the sum of the effects of each input
  • individually. Energy Conservation, when light
  • scatters from a surface or participating media, the
  • scattering event can never produce more energy than it
  • started With no polarization,
  • no fluorescence or phosphorescence and steady
  • state. So the environment is assumed to have reached
  • equilibrium, so the distribution of radiance is not changing over
  • time. So realistic situations, as happens very, very quickly.
  • So we lose a geometric up with a geometric optics model,
  • diffraction and interference effects and
  • does that make sense?
  • And just to confirm the thing, steady state, that's like, if
  • you were taking, let's say, a picture of the stars at night,
  • and then all of a sudden, a street line turned on beside
  • you. It's assuming nothing like that street mount will appear.
  • You're capturing the light as if it was all steady, so no sudden
  • light turns on.
  • No cars are driving by, therefore causing new lights to
  • appear for just moments and things like that. Consistent
  • luminance, right? I
  • I would say even when you have new lights appearing,
  • their contribution is
  • reaches a steady state almost instantaneously.
  • So it's not
  • that you're avoiding people. You're disallowing people from
  • turning on lights or street lights or
  • driving by a scene,
  • but the way we model it is that
  • we use exposure settings right where there's like a long
  • shutter time or whatever. So in that time you're capturing light
  • as though it was steady or consistent. So if you've had
  • suddenly something turn on midway through, would that would
  • interfere with an actual photography so I assume it has a
  • thing like we're assuming that can happen. That's one of our
  • assumptions with the steady state.
  • I think the steady state, it means that we're not, we're not
  • dealing with a period of time when the light comes On,
  • and seeing the effect of the light coming on
  • over the period of our exposure,
  • that there's A difference in
  • the inner energy from the light. Rather,
  • if the light appears,
  • then we're just we just accept that it's
  • In the steady state, there's a new steady state, And
  • that might be Interesting to To Explore I
  • so what is literate programming, and Do you have examples aside
  • from pbrt?
  • How about Writing Code. I'm
  • I think that's a Good explanation of literary
  • programming. I
  • anyone. What do you mean by the narrative?
  • So describing how code is designed or written? Do
  • you want to create an exposition of the design of the code,
  • and so You're writing it a way that supports the narrative So
  • does anyone have examples of literary programming systems
  • I've done pbrt Do thanks.
  • Yeah, It's pronounced tech. I
  • What do you think about Jupiter Notebooks? Does anyone use those
  • before?
  • So just to clarify, literate programming is not like C Plus
  • Plus, where you have to declare the function at the very top,
  • and then later you can do the function, but you have to do
  • this here and stuff like that, like a very ordered and
  • structured thing. What exactly is literate programming, as far
  • as Like how does it differ?
  • So the documentation I
  • and Then there are Two pieces and
  • so in Python with These Jupiter Notebooks, you can have
  • documentation, and then you have code that runs. So it's not
  • necessarily the same, but it's an
  • so first of all, how many people are familiar with tech and late
  • tech.
  • Cool, so,
  • yes, with a computer notebook example, it's more like, it's a
  • coding environment that
  • also kind of, like allows you to work with the building blocks.
  • It allows you to build up various blocks until you reach
  • the very end. Because, like, that is, I mean, that's kind of
  • nice. Mean,
  • I think with these notebooks, you can intermingle descriptions
  • and and code, and so they're a little bit separate. So you
  • you're including the code in the document, but the document and
  • the code are different, so it's about having a single source
  • that can be parsed into these two different streams. I
  • so it's an interesting discussion. Okay, who's who
  • here. Is familiar with Emacs? Does anyone know what emacs is,
  • what kind of application it is?
  • So editor, I
  • so we can have a continued discussion about this. I'll put
  • some resources online, but it won't be on the final exam. The
  • other things will be on the Final Exam. I
  • it rasterization versus ray tracing. So we talked a little
  • bit about, very little bit about Z buffer and being a
  • rasterization algorithm. We're keeping track of the closer
  • pixel that's closer. We're testing against a Z buffer to
  • see whether the new picture pixel will be computed is closer
  • than the existing one. If it is, we update the pixel. If it's not
  • We discard it. You
  • writing a little bit too small there, I apologize. So
  • rasterization says for each object in the scene, then for
  • each pixel i
  • that is possibly associated with the object as it gets scanned
  • converted. Is it closer than what's stored in the set buffer?
  • Okay, so what does ray tracing do? I
  • to do the same loop, To organize the same way I
  • so who says it's the same loop as rasterization for each object
  • done for each pixel? Anyone?
  • My brain's not working today, but that's how I interpret it.
  • Okay?
  • So actually, we're starting from the pixel,
  • yeah, it comes, it comes towards that Ray, right?
  • The ray comes out of the pixel? Yeah, so the eye, which is the
  • camera, we trace a ray through the Pixel and into the scene.
  • So for each pixel, then
  • so what's as we Go through the scene, what's the closest and
  • then how is the value of the pixel determined? So we're
  • tracing rates. If it's a reflective surface that we
  • bounce the reflection rate, retrace rate in light source,
  • see if it's in shadow and so forth. We're
  • Does That make sense? I
  • so the depth of field is what, what happens
  • in the space? Sorry,
  • I'm really bad headed right now my brain can the best I can give
  • you is This pretty much a second of
  • that. So what's in focus compared to what's out of focus?
  • I
  • so when it's not in focus, the lines don't converge to a point
  • on The film. They convert it comes towards a desk. I
  • boundary of the disc.
  • So as to focus, the larger this disc is the film, the more out
  • of focus the image will be without the image will be or
  • that part that's out of focus,
  • so what are the different court assistance we talked About in
  • pbrt. So
  • the world, the object, the camera, then I also put texture
  • coordinates which I didn't know if it was a Click of
  • one, yeah. World, object, Camera,
  • camera, world, i
  • i also seen a normalized device coordinates discussed in Chapter
  • Five about the projections.
  • So if we need to move between them, we use matrices. So why,
  • when we're doing projections, do we have four by four matrices
  • discusses
  • the classes? Because when we're doing translation, stuff like
  • that, I so we
  • Got homogeneous coordinates and
  • so for registers allow rotation, scaling and translation to be
  • expressed in the same matrix.
  • That's why we
  • a four by four matrix for three dimensional objects is a useful
  • thing. Take A
  • Picture. I
  • it. Somebody asked, where this was mentioned? Does it be the
  • four that we talked
  • about? So we have a square,
  • and then we have
  • an arc, one quarter, one quadrant in a circle. So just
  • imagine that's that's part of a circle. So when we're doing
  • Monte Carlo and
  • and number
  • of the it's basically trying to find The ratio of points that
  • are inside the circle compared to inside the Square.
  • I'll put to the link to that administration and anything
  • clarificational to that as well. Does that make sense? I
  • spherical geometry and
  • why is it important for rendering? I
  • So why can we are we supposed to specifically worried about, or
  • concerned about spherical coordinates vertical Geometry
  • and ray tracing.
  • The so we're dealing with all in coming and outgoing directions.
  • Look at that in terms of these directions are expressed in
  • spheres or hemispheres, depending on the case.
  • We got to translate all of that to be a two dimensional screen
  • at the end, because it's got to be viewable.
  • Yes,
  • you're taking in like every single direction you could
  • possibly go up your day to get all that information.
  • But also, if you did every single direction, you would be
  • there for more than a day. I think,
  • yeah, we do it every day.
  • It just works in nature.
  • It's a simulation that's the hard part, and we're getting
  • more fidelity with our simulation
  • so
  • and if we have
  • a bright light source
  • that makes it easier for having dimly lit space, then it's hard
  • to or to Find the light in the scene.
  • But anyway, so I
  • so what are the three parameterizations for spherical
  • coordinates,
  • octahedral encoding, equal area, mapping spherical coordinates, I
  • so this spherical coordinates gives us an easy representation,
  • easy To convert between this and Cartesian coordinates.
  • Octahedral encoding Is space saving. I
  • so I wrote down E coli mapping some reasonable equilibrium
  • mapping is important, because if you're sampling
  • with spherical coordinates, you might get, we're not going to
  • get a uniform distribution, or we get extra stuff in the poles
  • and some distortion there as well.
  • Okay, Does that make sense? I'm
  • so how do we use bone and glasses to accelerate re
  • intersection tests? You
  • can use it to truncate rays that aren't hitting your object. And
  • rather than checking like the very fine shape of the object,
  • you just search a general area. If you don't hit that general
  • area, well, you're not going to hit the shape. And also, when
  • the ray leaves that general area, if it doesn't hit the
  • shape, well, it's not it's never going to hit
  • the shape unless it bounces. I analysis.
  • So imagine
  • these are two axis aligned bounding boxes.
  • What can I what other improvement can I do in CS
  • having a collection of bounding boxes at the same level, so very
  • shallow tree can
  • have multiple different like levels of it. So you have one
  • boundary box that maybe contains both of those ones. If you don't
  • hit that one, you're not gonna hit any of the ones inside of
  • it, either, right? And you can just keep going outward.
  • So hierarchical, I
  • realize we're in a time here. So Ken,
  • the chapter seven, kind of was about that when you told us
  • to read, yeah, that's making the the data structures for
  • for the hierarchy hierarchical bounding structures. So there's
  • a list of things that are common to Ray tracing systems,
  • cameras and lights and visibility and light scattering
  • and so forth.
  • I'll post A link to that. I
  • so question 11 about the importance of choosing an
  • integrator in the sampler
  • that's from the user guide.
  • That's a guide for the answer anyway, But I
  • tried to be open. I
  • so bi directional distribution functions and
  • the bi directional reflectance function, bi directional
  • transmit distribution function, bi directional surface
  • scattering, reflectance, distribution function. These are
  • the three we've talked about. So why are they bi directional? You
  • equation, incoming direction and not going direction. So we have
  • those pair.
  • Okay, so it seems like we're just at a time since I'm
  • learned about my next meeting.
  • So that makes sense. Okay, so I was generous with marking. So
  • this is an opportunity, so 15 marks for the midterm won't sink
  • you,
  • but if so, be clear about this stuff for the final.
  • Okay. Thank you for today. Now the winters back, stay warm and
  • take care, and we'll see you on Thursday. Oh, have a look at
  • chapter 8.1, section one of chapter eight. Okay, thanks
  • again.
  • again.

Responses

No Responses