Region render problems 1.5_SP1

[re:FORM]

I've noticed that there differences in lighting when using region render with vray 1.5 sp1.

Is there something wrong with my scene? scale? IR/LC settings? or is this expected behaviour?

p.

edit> Its not just the size of the region that changes the lighting, just moving the region seems to cause problems.

[vlado]

400 subdivs for the light cache are too low to give you a stable GI solution, which is why you get this issue - for the region render, the light cache samples are distributed in a slighly different way, which causes the rendering to be different.

Best regards,
Vlado

[re:FORM]

Ah ok, so this is to be expected...

Thanks for clearing that up

[re:FORM]

I'm trying with higher samples in the LC, but still have discrepancies between region renders. (2000 samples, no prefilter, nearest=20, DMC noise thresh = .005, global subdivs=2, min samples=4, adaptiveDMC 1/16, IR High preset)

Can you suggest some settings that would give me a more stable LC solution to work with?

Thanks again!

[timmatron]

Are you using the SP1 that was released to the public, or an earlier internal build?

There were problems with region renders and light cache samples before, but it seems to be working fine now in the public SP1 build. Here is the thread about the old problem.

http://www.chaosgroup.com/forums/vbu...ight=disparity

[re:FORM]

Hi Tim, Thanks for that, I've been looking over that thread.
I am using the public release sp1, 64-bit with max 2008 if that makes any difference.

Could you have a go with the file above and see if you can recreate the problem (you probably need to increase the LC and IR settings as per vlado's post).

[andrewjohn81]

vlado mentioned this, but maybe you missed it.

Region render distributes the light cache samples in a different way, so you will get slightly different results no matter how many samples you give it. The more samples, however, the less different that should be in most cases.

This is one problem with rendering in strips as well. Each strip is often slightly different from the next with light cache. If you want the region to be the same you could render the light cache and save it to a file. Then reuse that for the region render. Although, for most reasons you would do a region render that would be pointless.

[re:FORM]

I guess the only way to ensure predictable lighting for region renders is to use brute force for primary samples to just deal with the extra noise.

Its a real shame that this happens as its quite common for me to render out a region to drop over a previous render in PS.

I guess its just the nature of the beast!

[andrewjohn81]

sure, I do that as well, but why not just maybe render out a little larger region than you thought you might need, then do some blending in photoshop. That's what I end up doing.

Usually darker things end up pretty damn close, and white ends up a little poor, so i usually blend that a bit more using some erasing/paint mask methods. I prefer painting masks since it's non destructive. Then I "bake it in" (apply mask) later on to save some file space if it's a very large file.

[re:FORM]

Good point...

[^Lele^]

I should mention that it also changes if i render a region or a crop (without actually modifying the region itself).
It did so also in every previous version, though, just it was somewhat less noticeable (tried it with rc5, rQMC sampler, under max 8, so i ASSUME it's always been like this).