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Understanding photon mapping

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Understanding photon mapping

Post Wed Jul 31, 2013 1:25 pm

I have almost finished the first part of a complete document in english about photon mapping. You can take a look at:
https://docs.google.com/document/d/1OZF ... sp=sharing

The idea is to complete it with sections about caustics and SPPM.
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Samo
 
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Re: Understanding photon mapping

Post Wed Jul 31, 2013 3:21 pm

:D
Great work Samo.
Very precise and very well written.

I wonder why you didn't talked about the option of using the photon map algo on exteriors with a semi-sphere shooting bg photons and other well proportioned photon sources.
Even on this conditions photon map can achieve the same result as path tracing and have much better times.

I think when vlado introduced the vray "irradiace map and light cache", it was the result of the advantages of the photon map with the necessary tools to make it more "exterior friendly". I think vray abandoned the photon map algo before 1.4 very much because it was reduntant with irradiance and ligh cache.

I talked a bit about this because i think in a future with a few tweaks on the yafaray photon map/ final gather system we can make it more "exterior friendly" because in fact I use it already for exteriors. I just tweak the scene a litle bit more than if i were using path tracing.

To make it a perfect algo and more "tweakable" I would sugest the code masters something like:

Final gather
- a slider with final gather distibution ratio across edges ( irradiance )
- a button for viewing it saying "only show fg samples"
- map samples along camera pixels or along blender units

Photon map
- an option to increase photons size far away from the camera and optimize the visible photons

Do you agree with this?
I went a bit off topic but you got the idea...

Anyway can't wait to see caustics and SPPM on your guide. I never get a good memory use with SPPM. Maybe because of my settings Ram gets a crazy amount and I usually crash the render...
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Arquitecto
 
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Re: Understanding photon mapping

Post Thu Aug 01, 2013 11:58 am

I have tried some solutions for open scenes, like the one you mention.

The problem I see is that we introduce too much human bias and error in a method that otherwise should be phisically correct without using any kind of portal lights, photons lamps or any other trick like the one you mention. In a perfect photon mapper there would not exist portal lights, and that should be the aim of the YafaRay engine, which always have combined biased solutions with physical correctness and simplicity.

The problem of using tricks and portals is that you never known when to stop adding them as there is many cases, and then the engine becomes much more complex. You lose physical correctness because many light or/and photon sources are just duplicated.

I believe importance photons shooting should be the main feature we should add to improve all photon mapping cases at once: diffuse photon mapping in open and semi enclosed scenes, caustic photons and SSS. Restricting the photon emission to areas relevant to the problem at hand.
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Samo
 
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Re: Understanding photon mapping

Post Thu Aug 01, 2013 9:21 pm

Samo wrote:I believe importance photons shooting should be the main feature we should add to improve all photon mapping cases at once: diffuse photon mapping in open and semi enclosed scenes, caustic photons and SSS. Restricting the photon emission to areas relevant to the problem at hand.


Yes you are right.
It's a very dificult path too since simplicity for the user usually costs more time...
And if we make more features lots of users would be lost...and phisically incorrect results may occur more often.
But I must agree on everything you said.
It's always good to know the team's opinion on the subject.
And I would even add that you must optimize any code work to the most important features since there are very few coders available.

And once again, thanks for the docs. :D
I read each one with an enormous pleasure.
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Arquitecto
 
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Re: Understanding photon mapping

Post Wed Aug 07, 2013 6:18 am

People pay, 3D artist to make picture looks realistic (and in short time), not to be "physically correct". 99% of clients (people) do not see and know the difference. Each large, well-known graphic designer will tell you to take a good visualization is the art of deception.
Do not imagine visualization of a hall where we have 4500 spotlights with soft shadows using physical correctness. But You may try ;)

@Samo
A great piece of knowledge, from the ground up for examples many people can learn something from this. And not only put 200 lights and wait for the PC and physically correct engines calculate everything for 400 hours. Please if you finish this book, sell them even 5$ but please people must know to have Yafaray We must support him and people responsible as well.
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blenderman
 
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