trying to understand better light cache...

[lukx]

I'm trying to understand better Light cache. I'm not quite get the filter and pre filter section. I'm reading all over help and don't get it.
What Interpolation samples do? Is is good to use pre-filter or not? If I got a lot of glossy reflections in my animation is it good to turn on Use light cache for glossy rays? Also the whole scale thing is magic for me? What is it good for. I always has it set to screen.

I'm looking for setting that will produce very, very good quality for stills (render times up to 24 hours are acceted=) and also for animations (max 1 hour render time).

[jujubee]

I agree- those questions remain even after I've read throught the help and the forum.

Adding to these questions - should 'Use light cache for glossy rays' be disabled when rendering out an Irradiance Map?

[flipside]

Sample size is the size of your samples

Do a test with LC for first and second bounce and turn both filters off, that way you can clearly see the sample size in the render.
Screen is view dependant, far away samples will actually be larger than nearbye samples. (view is divided in equally sized samples).
World scale uses real units for the samples. You'll see the difference very well in a test.

For camera animations it is best to use world scale, because then the samples won't vary in size between two frames as the camera moves closer/further away from objects.

For stills I always use screen size (0.01 or 0.005) with LC only in second bounce. If you use lc also for first you may need to go smaller.

The filter section is easy to understand if you test it. If you use LC in secondary only, you don't need to use any filter, altough it can clear up light leaks sometimes. The interp filter can be quite tricky, if you use wrong settings it can produce very long rendertimes (especially tricky with fixed filter size). I never use it. If I wanna use a filter, I use the pre filter only.

Interpolation is just like in ir map, interpolation means averaging values between surrounding samples to clear out extreme lighting differences.

The settings depend on how you use LC (secondary only? what you use in first bounce? ppt?)

Use LC for glossy is tricky sometimes too. I usually don't use it, because quality is lower than with 'real' glossies. Also in animations this can cause problems. Many posts here report problems that get solved if you turn off the use LC for glossy. I think it should be off by default.

[jujubee]

Thanks Flip for the great explanations. Your Interpolation settings - you have any rough numbers for using it as primary or secondary?

Also, 'Glossies for lightcache' - I understand that this is supposed to speed up scenes with glossies in it but people are getting strange results instead? By checking this, does this automatically override glossies with IR or QMC? I read somewhere that if you have this enabled, that you should always have this map loaded in as a secondary if used with an IRmap. I think some sort of warning should appear as this was causing confusing prepasses...

[flipside]

Because people use low quality LC settings for secondary bouce, with glossy for LC checked. So this means their glossies will also show low quality (sometimes). Especially when using glossy refraction you will notice this.

The lc for glossy vs ir map problem is when you use precalculated LC for camera animation. There's some info about it in the tutorial from vlado about flytrough animations. If you use the option, you must leave LC for secondary bounce on for your final rendering. If you don't use the lc for glossy option, you can turn of secondary bounces because all the lighting info will be stored in the ir map already. (see tutorial, it's very late here so my explanation will not be very clear...)

Interpolation settings: If I use a filter it is the prefilter and usually don't change its default value... If you use LC for first and secondary, turn both filters on and don't use fixed for interp filter type. Default values work pretty well, it also depends a bit on your sample size. Just do a simple test scene with lc in first and secondary, it's pretty straightforward.

[lukx]

thanks flipside. I guess I have to find time to run few test. Anyway I hope vlado will put some examples in future vray help.

[flipside]

There are already examples in the vray help...
http://www.spot3d.com/vray/help/VRay...lightcache.htm

this, together with the normal help and the flytrough tutorial should teach you everything there is to know about lightcache.