[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:00.13,0:00:03.55,Default,,0000,0000,0000,,I simply made up the anisotropic function out of my head. However, there's
Dialogue: 0,0:00:03.55,0:00:06.49,Default,,0000,0000,0000,,considerable research about how to capture BRDFs from materials, and how to
Dialogue: 0,0:00:06.49,0:00:11.65,Default,,0000,0000,0000,,make functions to compactly represent them. BRDFs are just the start. There's
Dialogue: 0,0:00:11.65,0:00:15.87,Default,,0000,0000,0000,,also the BSDF, the Beet Sugar Development Foundation. We're more interested in
Dialogue: 0,0:00:15.87,0:00:19.41,Default,,0000,0000,0000,,the Bi-Directional Scattering Distribution Function. This type of function
Dialogue: 0,0:00:19.41,0:00:23.23,Default,,0000,0000,0000,,captures both how light reflects from and transmits through material. There's
Dialogue: 0,0:00:23.23,0:00:27.44,Default,,0000,0000,0000,,also the BSSRDFs which stands for Bidirectional Surface Scattering Reflectance
Dialogue: 0,0:00:27.44,0:00:32.19,Default,,0000,0000,0000,,Distribution Function. Say that one three times fast. This function is
Dialogue: 0,0:00:32.19,0:00:35.36,Default,,0000,0000,0000,,important for materials like marble and milk. For these materials in
Dialogue: 0,0:00:35.36,0:00:38.49,Default,,0000,0000,0000,,particular, the light enters one location on the surface, bounces around inside
Dialogue: 0,0:00:38.49,0:00:42.81,Default,,0000,0000,0000,,the material, and comes out somewhere nearby. One other extremely important
Dialogue: 0,0:00:42.81,0:00:46.63,Default,,0000,0000,0000,,material that has this sort of scattering is skin. Getting skin to look good
Dialogue: 0,0:00:46.63,0:00:50.13,Default,,0000,0000,0000,,for interactive rendering can be quite involved. But the results are more
Dialogue: 0,0:00:50.13,0:00:53.55,Default,,0000,0000,0000,,convincing than using some simple reflection model. See the additional course
Dialogue: 0,0:00:53.55,0:00:57.76,Default,,0000,0000,0000,,materials for more information. That said, the key factor here is scale. The
Dialogue: 0,0:00:57.76,0:01:00.79,Default,,0000,0000,0000,,effect of subsurface scattering lessens as the viewer's distance from the
Dialogue: 0,0:01:00.79,0:01:04.75,Default,,0000,0000,0000,,object increases. Close up, a photon might exit at a location that's a fair
Dialogue: 0,0:01:04.75,0:01:08.79,Default,,0000,0000,0000,,number of pixels away from where it entered the surface. From farther away,
Dialogue: 0,0:01:08.79,0:01:12.88,Default,,0000,0000,0000,,they may be no change in pixel location. In fact the diffuse component for all
Dialogue: 0,0:01:12.88,0:01:16.79,Default,,0000,0000,0000,,non-metallic materials comes from subsurface scattering. It's just that in many
Dialogue: 0,0:01:16.79,0:01:21.22,Default,,0000,0000,0000,,cases this scattering is over an imperceptably small distance. Metals
Dialogue: 0,0:01:21.22,0:01:24.84,Default,,0000,0000,0000,,themselves are essentially all specular. Let me say that again, because all
Dialogue: 0,0:01:24.84,0:01:29.42,Default,,0000,0000,0000,,this time we've been living a lie. Metallic objects have no lambertian diffuse
Dialogue: 0,0:01:29.42,0:01:33.90,Default,,0000,0000,0000,,term. Well, not a lie, I just like being dramatic. Really, diffuse is simply an
Dialogue: 0,0:01:33.90,0:01:37.67,Default,,0000,0000,0000,,approximation of which we should be aware. Using it's fine, even high-quality
Dialogue: 0,0:01:37.67,0:01:42.19,Default,,0000,0000,0000,,applications do so. It's quick to compute and looks plausible. In reality,
Dialogue: 0,0:01:42.19,0:01:45.09,Default,,0000,0000,0000,,metals can indeed be given a roughened surface to give them a glossier, diffuse
Dialogue: 0,0:01:45.09,0:01:49.98,Default,,0000,0000,0000,,look. So, a diffuse term is fine. However, on a an atomic level, metallic
Dialogue: 0,0:01:49.98,0:01:53.75,Default,,0000,0000,0000,,objects have a free floating soup of electrons on the surface which absorbs and
Dialogue: 0,0:01:53.75,0:01:57.100,Default,,0000,0000,0000,,reemits incoming photons. If your surface represents a shiny metal, you
Dialogue: 0,0:01:57.100,0:02:01.59,Default,,0000,0000,0000,,probably don't want a diffuse term. Insulators have a diffuse term because the
Dialogue: 0,0:02:01.59,0:02:05.06,Default,,0000,0000,0000,,photons undergo subsurface scattering. Most of the time the entry and exit
Dialogue: 0,0:02:05.06,0:02:08.97,Default,,0000,0000,0000,,points are so close together it doesn't matter. But the direction of exit
Dialogue: 0,0:02:08.97,0:02:12.44,Default,,0000,0000,0000,,certainly does. Materials such as that in an unglazed clay pot, concrete, and
Dialogue: 0,0:02:12.44,0:02:15.64,Default,,0000,0000,0000,,even the moon itself, are rough enough that the lambertian reflection model
Dialogue: 0,0:02:15.64,0:02:19.97,Default,,0000,0000,0000,,doesn't capture them fully. This again turns out to be a matter of scale,
Dialogue: 0,0:02:19.97,0:02:22.90,Default,,0000,0000,0000,,having to do with the relationship of surface roughness with subsurface
Dialogue: 0,0:02:22.90,0:02:27.65,Default,,0000,0000,0000,,scattering. Admittedly, trying to capture all of these effects leads to a lot
Dialogue: 0,0:02:27.65,0:02:31.62,Default,,0000,0000,0000,,of work and possibly inefficient shaders. These subsurface scattering
Dialogue: 0,0:02:31.62,0:02:34.84,Default,,0000,0000,0000,,renderings are from 3D Studio Max and rendered offline, not at interactive
Dialogue: 0,0:02:34.84,0:02:39.04,Default,,0000,0000,0000,,rates. The main thing is to realize we don't have to stick with illumination
Dialogue: 0,0:02:39.04,0:02:43.60,Default,,0000,0000,0000,,models from the 1970's because of inertia or ignorance. Using reflection models
Dialogue: 0,0:02:43.60,0:02:47.06,Default,,0000,0000,0000,,based on how the real world works has a number of advantages. First and
Dialogue: 0,0:02:47.06,0:02:50.03,Default,,0000,0000,0000,,foremost, if everything is properly modeled, your virtual world acts like the
Dialogue: 0,0:02:50.03,0:02:53.86,Default,,0000,0000,0000,,real world. Change lighting conditions, and you don't have to tweak material
Dialogue: 0,0:02:53.86,0:02:57.50,Default,,0000,0000,0000,,settings to look good. For design software, this assurance can mean that you
Dialogue: 0,0:02:57.50,0:03:00.08,Default,,0000,0000,0000,,can trust what you see on the screen to have some relationship to what you
Dialogue: 0,0:03:00.08,0:03:04.77,Default,,0000,0000,0000,,manufacture. Physically based rendering is also a great help to virtual world
Dialogue: 0,0:03:04.77,0:03:08.37,Default,,0000,0000,0000,,content creators, such as game and film makers. It's a time saver to have
Dialogue: 0,0:03:08.37,0:03:11.60,Default,,0000,0000,0000,,predictable illumination models, as the artist does not have to learn obscure
Dialogue: 0,0:03:11.60,0:03:16.12,Default,,0000,0000,0000,,sliders that have no real world counterparts. It's vastly reassuring, knowing
Dialogue: 0,0:03:16.12,0:03:19.06,Default,,0000,0000,0000,,that materials won't show some glitch from a certain angle, and knowing that
Dialogue: 0,0:03:19.06,0:03:23.41,Default,,0000,0000,0000,,lighting can be changed without destroying the sense of realism. Rather than
Dialogue: 0,0:03:23.41,0:03:26.32,Default,,0000,0000,0000,,limit creativity, a well-designed system makes for a more productive and
Dialogue: 0,0:03:26.32,0:03:28.19,Default,,0000,0000,0000,,unrestrictive environment.