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Physically based rendering from first principles

imadr.me

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Re: Physically based rendering from first principles

#31

Post by godelski »

MangoToupe wrote: post #16
godelski wrote: post #9

I'm not a fan of how people talk about "first principles" as I think it just leads to lots of confusion. It's a phrase common in computer science that makes many other scientific communities cringe. First principles are things that cannot be reduced and you have to have very good justifications for these axioms. The reason the other scientific communities cringe is because either (most likely case) it's being used im…

I think Musk was the first person I noticed to really abuse this phrase. Not that it's not a useful phrase—of course it is. But it seems like it's an abuse of what should be called "core agreed assumptions" or something.

Yeah he abuses a lot of phrases... He does provide a master class on psuedointellectualism though. Drops enough vernacular that layman think he's smart and even enough that experts might think they're in good company if they don't pay too close attention. But I think the biggest clue that it's fake is how dismissive he is of nuance and detail. It's such a classic defense from psuedointellectuals because they know if they venture into depth then the gig is up. Meanwhile, look at any two nerds arguing. It's always nuanced and over minute things that they'll always insist are very important (because often it is, but only at that level).

Re: Physically based rendering from first principles

#32

Post by imadr »

godelski wrote: post #27
imadr wrote: post #12

Earlier quoted context omitted.

Thanks for the constructive criticism! A few points I'd like to discuss: Let's suppose the aim of the article was indeed to learn PBR from first principles, what would it look like? Quantum electrodynamics? I think there is merit in exploring different physical models for fun and scientific curiosity (like I mentioned in the first chapter). I (personally) feel that it's boring to just dump equations like Snell's law…

Sure! And I appreciate the response. I hope I didn't come off as too mean, it can be hard to find that balance in text, especially while criticizing. I really do not want to discourage you, and I think you should keep going. Don't let mistakes stop you. > Let's suppose the aim of the article was indeed to learn PBR from first principles, what would it look like? I think you shouldn't go that route, but the most hones…

Again, thanks for the thorough and constructive answer, it doesn't come off as mean, on the contrary I appreciate it :)

I strongly agree that teaching is absolutely the best tool for learning. I wrote this article in part because I got inspired by the "What I cannot create, I do not understand" quote by Feynman.

I agree that the article is disorganized, and it's not only a feeling: it literally is! I had to shuffle around parts of the chapter about radiometry because I couldn't find the right place for it. I was kind of in a rush because I submitted this article as part of 3blue1brown's summer of math exposition.

I find it interesting that between the 3rd and 4th edition of pbr book, chapters have been reorganized too. Monte Carlo Integration has been moved to an earlier chapter before radiometry, reflection models..etc which I found confusing, but I suppose the authors had a good reason to do that. So I have a lot to learn on how to improve my writing and how to organize ideas into something coherent.

[0] https://some.3b1b.co/

Re: Physically based rendering from first principles

#33

Post by godelski »

taeric wrote: post #17
godelski wrote: post #9

I'm not a fan of how people talk about "first principles" as I think it just leads to lots of confusion. It's a phrase common in computer science that makes many other scientific communities cringe. First principles are things that cannot be reduced and you have to have very good justifications for these axioms. The reason the other scientific communities cringe is because either (most likely case) it's being used im…

It isn't just computer science people that do this, either. My gut is it was a common thing in MBA style classes as a way to approach a topic in a field you are not expert in. Specifically, it is common among management talkers, from my experience. I think the idea is supposed to be to go back to the "first principals [that you would have been taught]." Which, yes, sometimes you will learn things that show these earl…

I think >90% of the time I hear the phrase "first principles" mentioned I'm safe in expecting something that is very high level to follow. I'm glad nerds have (kinda) been pushed into celebrity status but I also think there's a lot of cargo culting that has followed. Unsurprising I guess, since one is much easier than the other. I just wish there was more pushback, especially in tech (not because the only abuser of this, but we're definitely the ones with the most weight)

  > you can get far more mileage out of the naive models than people want to admit.
All models are wrong, but some models are useful, right? I'm a big fan of this phrase so much because I think it helps us remember that it's okay to be wrong.

I feel like the biggest problem of first principles is that this is almost never where you start. Rather it is something you work towards. Where it then becomes an iterative process expanding/extrapolating out, then coming back in and refining. Low level knowledge is so beneficial, but also very difficult to obtain. It's even more difficult to see how much room is below you without ever having gone down.

Re: Physically based rendering from first principles

#34

Post by imadr »

magicalhippo wrote: post #25
imadr wrote: post #12

Earlier quoted context omitted.

Thanks for the constructive criticism! A few points I'd like to discuss: Let's suppose the aim of the article was indeed to learn PBR from first principles, what would it look like? Quantum electrodynamics? I think there is merit in exploring different physical models for fun and scientific curiosity (like I mentioned in the first chapter). I (personally) feel that it's boring to just dump equations like Snell's law…

> Let's suppose the aim of the article was indeed to learn PBR from first principles, what would it look like? Well given the title I at least expected the article to explain or derive things like why and how metals and their alloys have the color (wavelenght-dependent complex index of refraction) that they do, why and how say quartz crystals have different colors, birefringence, fluorescence (makes T-shirts appear e…

Yes I didn't have time to write a chapter about camera sensors, the human retina, and the whole image formation process. I'll definitely expand on this later on.

Re: Physically based rendering from first principles

#35

Post by godelski »

imadr wrote: post #32
godelski wrote: post #27

Earlier quoted context omitted.

Sure! And I appreciate the response. I hope I didn't come off as too mean, it can be hard to find that balance in text, especially while criticizing. I really do not want to discourage you, and I think you should keep going. Don't let mistakes stop you. > Let's suppose the aim of the article was indeed to learn PBR from first principles, what would it look like? I think you shouldn't go that route, but the most hones…

Again, thanks for the thorough and constructive answer, it doesn't come off as mean, on the contrary I appreciate it :) I strongly agree that teaching is absolutely the best tool for learning. I wrote this article in part because I got inspired by the "What I cannot create, I do not understand" quote by Feynman. I agree that the article is disorganized, and it's not only a feeling: it literally is! I had to shuffle a…

Keep with it! And that reorganization between editions is a good reminder that things don't have to be perfect and can always be improved upon. We call these things "soft skills" but I think we've made a terrible mistake in implying that communicating is easy lol. Often it can be harder than the work itself! I think you got a good attitude and it'll take you far. So good luck on your submission! And FWIW, Monte Carlo Integration confused the hell out of me until I figured out how beautifully simplistic it is. If it hasn't clicked, keep with it. It eventually will.

Re: Physically based rendering from first principles

#36

Post by kelseyfrog »

Are there any data driven approaches to physically based rendering?

Can't we measure micro-facet depth and angle distribution of real world materials using laser speckle and use it to inform the normal distribution function? Deriving ideals from first principles is great and all, but verifying them against real world measurements seems like the bare minimum.

Re: Physically based rendering from first principles

#37

Post by godelski »

delta_p_delta_x wrote: post #20
godelski wrote: post #9

I'm not a fan of how people talk about "first principles" as I think it just leads to lots of confusion. It's a phrase common in computer science that makes many other scientific communities cringe. First principles are things that cannot be reduced and you have to have very good justifications for these axioms. The reason the other scientific communities cringe is because either (most likely case) it's being used im…

> By the end of an undergraduate degree every physicist should end up feeling like they know nothing about physics. You couldn't have been any closer. I emerged feeling extremely stupid after doing physics at uni. My rather mediocre marks didn't help...

LOL to be honest I'm more scared of the people that it doesn't happen to. At first I feared them because I thought they knew so much more and it meant I was so far behind. But later I feared them because I recognized we were at not too dissimilar levels and the main difference was recognizing how far left we have to go.

I don't fear the man who knows more than me, I admire them and only have something to gain by admitting my ignorance to them. But I do fear the man who believes he knows more while in reality he doesn't. Nothing productive comes from them as they don't even recognize the journey we are both on.

Re: Physically based rendering from first principles

#38

Post by imadr »

kelseyfrog wrote: post #36

Are there any data driven approaches to physically based rendering? Can't we measure micro-facet depth and angle distribution of real world materials using laser speckle and use it to inform the normal distribution function? Deriving ideals from first principles is great and all, but verifying them against real world measurements seems like the bare minimum.

If i’m not mistaken that’s in part how they came up with micro facet models, or at least to verify their accuracy. Take this paper for example https://www.cs.cornell.edu/~srm/publications/EGSR07-btdf.pdf

Real life measures are also useful for inverse rendering.

Re: Physically based rendering from first principles

#39

Post by kelseyfrog »

imadr wrote: post #38
kelseyfrog wrote: post #36

Are there any data driven approaches to physically based rendering? Can't we measure micro-facet depth and angle distribution of real world materials using laser speckle and use it to inform the normal distribution function? Deriving ideals from first principles is great and all, but verifying them against real world measurements seems like the bare minimum.

If i’m not mistaken that’s in part how they came up with micro facet models, or at least to verify their accuracy. Take this paper for example https://www.cs.cornell.edu/~srm/publications/EGSR07-btdf.pdf Real life measures are also useful for inverse rendering.

Interesting link, thank you!

It looks like a good model for lower incident angles but begins to diverse at higher angles. There's also one huge caveat - it relates the GGX model to real world ground glass. Obviously it's important to compare like to like. However, very few materials in the real world are ground glass.

Looking around my surroundings, I see painted drywall, wood, paper, plastics, and textiles. It would seemingly be a mistake to assume each of these materials behaved optically like ground glass. I hope that similar measurements are carried out on other materials.

Re: Physically based rendering from first principles

#40

Post by corysama »

kelseyfrog wrote: post #36

Are there any data driven approaches to physically based rendering? Can't we measure micro-facet depth and angle distribution of real world materials using laser speckle and use it to inform the normal distribution function? Deriving ideals from first principles is great and all, but verifying them against real world measurements seems like the bare minimum.

There have been decades of research into generalized BRDF measurement of real materials. Usually it starts with capturing calibrated images of the combination of all camera angles and all lighting angles on the hemisphere.

https://www.researchgate.net/figure/Picture-of-the-BRDF-meas...

https://www.iosb.fraunhofer.de/en/projects-and-products/sig_...

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