LC and the subdiv count

[Micha_cg]

(I think, it's good to start an own thread for that topic, that start's at the bottom of this wish thread here.)

Thanks for the explanations Damien. I thought, if at the end of the LC pass the image look free of black noise, enough subdivs are shot in the scene.
If the displayed pixels of the LC pass can not be used to get an impression of the quality, how can I know, how much I need? Or could be a rule, that a 800x600 image must be free of black noise and if a bigger image is rendered, than it will be good too?
If I would use to less subdivs, what error would it cause?

I understand now, if the displayed subdiv noise is no criterion for the quality and the image size don't matter too, than my wish makes no sense.

From what is the needed subdiv count dependent? When do I need more and than less, by the same image size? I could imagine me, that an interior need more subdivs than an exterior. But what could be a rule to find the right count? :-\

[dalomar_cg]

Re: LC and the subdiv count

I thought, if at the end of the LC pass the image look free of black noise, enough subdivs are shot in the scene.

This is a rule of thumb that I have used in the past, but in the end it really only works for certain resolutions (btw 640x480 and 800x600). Below that range, you may be able to get a result that is free of black pixels, but is still not a very good solution. Above that range, it will take alot of subdivisions to make all of those black dots go away. So in the end we find that this is really not a good means of determining the final quality of our LC solution.

Because LC simply works by dividing the image based on number of subdivisions and then tracing that number of rays directly from the camera, the resolution has for the most part doesn't play a part in the actual quality.

The only real quality control is subdivisions, and like all other places for subdivisions in V-Ray there is no way to say what is a good setting and what is a bad one. But here are some general guidelines as far as LC subd go. First off, the importance of the LC solution to your rendered result is going to be based on the importance of your secondary bounces (I'm assuming your using LC for secondaries...just thought I would make that known). So for exterior scenes or studio shots, you might find that there is a decreased importance of secondaries due to the amount of direct light and the primary bounces. For previews and quick renders subd values <1000 are generally okay, with lower subds being faster and of lower quality. Between 1000 and 2000 are generally well suited for most final quality situations. Higher then 2000 is really only needed for intricate interior scenes that have allot of complex (glossy) materials. These settings are resolution independent

As far as speed increases go there are two big helpers. Store Direct Light is a no brainer and should really be active all the time. The other one (as I know you know Micha) is the Use for Glossy Rays option. This can greatly increase the calculation of glossy materials, but when you use this you must keep in mind that the quality/speed of this increase will be tied to the number of subdivisions that are used for LC. For final quality renders this should not be an issue because a good number of LC subdivisions will be used, but keep in mind that your glossy materials may not look as good as they could in your previews (but thats why the call it previews...right).

I hope this answers more of your (and other's) questions. And you are correct...your "wish" doesn't really make too much sense, but now you know.

[Micha_cg]

Re: LC and the subdiv count

Thank you Damien.