Whats the truth behind light portals?

[demmi]

Who can explain me what is the truth behind light portals? i mean do we have light portals in real world? i it physically correct to light an interior with it? my thought about a real world lighting is only as main source the sun and its bounces considering daylight setup =)

[Captain Obvious]

Portals are used to manually guide the render engine into focusing its attention into a particular area, to reduce noise. It shouldn't affect the look or anything. It's just that if you're rendering an interior with small windows, it's going to be hard for the engine to find the window with random sampling. By putting a portal in it to guide it, it should clean things up better.

[maru]

i mean do we have light portals in real world?

It makes little sense to compare rendering engine features with real world. Do we have light samples multiplier in real world? Do we have max ray depth? :) It's just a trick designed to make rendering better/faster. It has no impact on "physical corectness". You would get the same image with and without portals, only in different time.

[Juraj]

You don't have to use them, they're not necessity. Obviously it would be great if sampling algorithm could decide adaptively where to sample prioritively light (bidirectional sort of does) but it already does good job,
and portals often help best when the scenario is quite unique is size of the windows to room ratio being very small.

Also Corona's approach to portal light is simple and logical, it's just ray 'emitter', it does not become actual light source so you still get your realistic sun bouncing around without visual alteration, but you will get noise-free image faster.
I rarely use it (almost never) and I am doing just fine.

[demmi]

thnks for the comments now i know a little bit then before about it and i know that you all are the best one here tnks

[Ondra]

Juraj said it the best: you will get the same image in the end, just faster.

[AnubisMe]

This cleared my question about it as well. It seems its like AO, light portals are no longer really needed anymore.

[Juraj]

This cleared my question about it as well. It seems its like AO, light portals are no longer really needed anymore.

They do have their purpose in the right scene, they're just not "must".

So is AO extremely helpful, but only as mask for effects, not direct overlay ala 2004 :- ) Pathtracing creates nice contact shadows that are natural and only where applicable.

[maru]

And light portals are needed when you have a small window and you want your image to be rendered in reasonable time...

[Hamburger]

I don't have much to contribute but it is refreshing to work with Corona on interiors, even in Corona for Maya I am seeing very nice GI and some extremely heavy scenes with small windows, it is a very good renderer and the most natural GI I've ever seen. It is nice to use.