# TU Wien Rendering #30 - Dispersion and Spectral Rendering ## Метаданные - **Канал:** Two Minute Papers - **YouTube:** https://www.youtube.com/watch?v=UcI-RnWzASk - **Дата:** 29.05.2015 - **Длительность:** 9:18 - **Просмотры:** 7,473 ## Описание Some materials, such as prisms have a non-constant index of refraction, and therefore they reflect and refract different colors of light into different directions, creating rainbow-like effects. Yes, rainbows are also created by dispersion! This also requires a fully spectral renderer that traces rays in the continuum of the visible light frequency domain. Ps: hope you also like The Dark Side of the Moon by Pink Floyd, yoohoo! About the course: This course aims to give an overview of basic and state-of-the-art methods of rendering. Offline methods such as ray and path tracing, photon mapping and many other algorithms are introduced and various refinement are explained. The basics of the involved physics, such as geometric optics, surface and media interaction with light and camera models are outlined. The apparatus of Monte Carlo methods is introduced which is heavily used in several algorithms and its refinement in the form of stratified sampling and the Metropolis-Hastings method is explained. At the end of the course students should be familiar with common techniques in rendering and find their way around the current state-of-the-art of the field. Furthermore the exercises should deepen the attendees' understanding of the basic principles of light transport and enable them to write a simple rendering program themselves. These videos are the recordings of the lectures of 2015 at the Teschnische Universität Wien by Károly Zsolnai and Thomas Auzinger Course website and slides → http://www.cg.tuwien.ac.at/courses/Rendering/ Subscribe → http://www.youtube.com/subscription_center?add_user=keeroyz Web → https://cg.tuwien.ac.at/~zsolnai/ Twitter → https://twitter.com/karoly_zsolnai ## Содержание ### [0:00](https://www.youtube.com/watch?v=UcI-RnWzASk) okay so why don't we get started these i will show you some of the small paint contest assignments from previous years is this visible is this i think i should pull some of the curtains maybe right maybe a bit just thanks how about that so you can see that even with the small paint program you can make incredible scenes so this is the thanks state of the art lecture basically what we are interested in this and the next lecture is starting from the very first algorithm that was ever created to solve the rendering equation a classical path tracer up to the most sophisticated works some of them which came out less than a week ago and i won't go into deep mathematical details for most of these techniques what i would like you to know is the basic idea and the intuition behind the method and why we are doing the things we do so deep mathematical details will also be there in the form of links where you can look behind the curtain and you will see what is exactly going on in there now before we start with the state-of-the-art part there's a few things that we need to discuss one ### [1:36](https://www.youtube.com/watch?v=UcI-RnWzASk&t=96s) Dispersion this person so we have talked about indices of refraction the index of refraction for different materials what was it was a number so in every code in every program in every theory we use numbers well in reality ### [1:53](https://www.youtube.com/watch?v=UcI-RnWzASk&t=113s) Indices of Refraction Are Not Numbers indices of refractions are not numbers they are in fact functions what does it mean they could be functions that depend on the wavelength of incoming light and what it exactly means is that there are materials that refract incoming light of different colors two different directions and that's quite profound because you will see the beautiful effects of the dispersion in a second and there are also some supplementary videos that you should take a look at home this is a good example of it this is a prism so you can see that the incoming light is white and the prism does break down to this white incoming light to all possible colors there are another good example of this is rainbows ### [2:50](https://www.youtube.com/watch?v=UcI-RnWzASk&t=170s) Rainbows so whenever you are on a family trip and they are asking what you're looking at and if you accidentally don't say rainbow you will maybe say this persian and they will put you in an asylum instead so but don't worry you are correct scientifically and that's all that matters you can also see and maybe not so beneficial and not so beautiful effect of this person it is called chromatic aberration this means that we have a camera lens that is possibly not the highest quality and it can introduce artifacts like this because different colors of light are reflected into different directions and you don't get the sharp image that you would be looking for now this is a dispersion rendered inside lux render so you can see that with physically based rendering you can actually capture this effect and you can also render diamonds so if you have a fiance and you would like to buy a ring but you're broke because you're a university student then you can just render one and you can also render one with this person well see if you have a nerd girlfriend because if so then maybe she will be happy about it most people aren't and i speak from experience and you can also see this really beautiful effect in the old pink floyd album cover called the dark side of the moon ### [4:23](https://www.youtube.com/watch?v=UcI-RnWzASk&t=263s) The Dark Side of the Moon there are also some videos about this in the internet rendered with lux render take a look now ### [4:34](https://www.youtube.com/watch?v=UcI-RnWzASk&t=274s) Is the Index of Refraction of Glass Constant the first question is the index of refraction of glass constant well let's look it that obviously we may have glasses that are made and manufactured in different ways there are most of them are not completely clear they are some kind of a mixture so there are different kinds of glass but let's just pick one randomly from a database that gives you indices of refraction and you can see that it is actually not flat it is not a constant there there's something happening in the function so this means that there are glass types that have dispersion effects and even only slightly because you can see that behind between the minimum and the maximum there's not such a large difference but there is something so you could say that at least this kind of glass introduces some degree of dispersion so let's take a look what do you think about this image does this caustic have any kind of dispersion effect or does it not what do you think is it a bit more colorful around the edges or is it completely white looks exactly it looks a bit red okay could be give me one more opinion okay what do you think um yeah it's a little bit rough i don't know like a rainbow or something it might be a rainbow but it may be significantly smaller so maybe you would have to zoom in really close to see the rainbow so this is up for debate we could see that the ior seems to be non-constant and therefore there should be a dispersion effect some artists claim that they can spot the difference between a physically based renderer even for materials like that and simple rgb rendering where you cannot render these dispersion effects correctly this is up for debit whether you can see it but science says that yes there is even if there is a slight difference there is a difference if you would like to more know more about this person there is this wonderful series called cosmos a space time of dc have any of you heard of this before raise your hand okay a few of you so this is this is hosted by the magnificent neil degrasse tyson yeah neil degrasse tyson and you should absolutely watch it so everyone who hasn't watched it yet i'd like to hear your excuse or at least i like to hear that you will go home and watch it so this episode is about that this person mostly and you will know all about this person if you're watching okay now we have another question because we have written an rgb renderer so we if you look up the source code of small paint everywhere you just see rgb rgb how do we write a correct physically based renderer and even before that how do we even represent light in the visible spectrum now a good answer to this is to introduce a function that describes how much light is carried at different wavelengths now this would be a continuous function that we could call ### [8:18](https://www.youtube.com/watch?v=UcI-RnWzASk&t=498s) Spectral Power Distribution spectral power distribution and you can see that at these lower wavelengths there is not too much light carried and on the higher wavelengths there is more so you can put this representation into your render and what you would do is that you would just a naive solution you would pick a randomly chosen wavelength and you would trace array into the scene using this wavelength and if you do this you can actually do another kind of monte carlo integration because you would also add one more dimension of integration and this one more dimension would be over wavelengths because you would also be stochastically taking random samples of the rendering equation for a given wavelength in a given color and then you would need to sum it up somehow to get a sensible solution there is more about this in pbrt chapter 5. --- *Источник: https://ekstraktznaniy.ru/video/14982*