Object property node

[stezza]

Should it make a difference when calculating maps for character animation to have an OPN applied to background items first! then calculate the maps. Or just apply it after the maps have been generated.
We do get different results but i thought the OPN would be ignored during calculation of maps if it was applied before calculations.?

S

[Zdravko]

Could you please clarify what do you want to achieve?

[vlado]

Like Zdravko noted, it would be good to clarify a bit. It might be normal to get a difference, depending on the matte settings (in particular, the "No GI on other mattes" option).

Best regards,
Vlado

[stezza]

I simply applied a opn to the background objects as matte with -alpha so i just had the character for comping. I have done what i needed to do but during a test i tried calculating maps with opn applied to the background items (before pre pass) which gave a different result compared to having it not applied (as it should be for calculation).

[Svetlozar Draganov]

Hello Stezza,

We've done some tests here but we didn't get any noticeable differences between render with OPN added before or after.
We would like to have some more information about the setup along with some screen-shots illustrating the issue.
Also, what do you mean by "calculating maps" - are you talking about pre-calculating GI ?
It would be very helpful if you describe in details what and how do you want to achieve - a test scenes will be very welcomed too.

[stezza]

Hi there.
I will supply a scene, though ours are very heavy with references but will strip out. Give me a day or 2 as I need to finish job first.
Thanks for your help.

S

[stezza]

Here is a shot of the two procedures calculating at around %20 complete.
The first image is with the OPN disabled then calculate the prepass. Second image is with OPN enabled and then calculate prepass.
As you can see the results are very different. I know that there isnt a real problem with this as just disableing it at prepass phase is the way to go but I just thought that having OPN enable before prepass should'nt have any effect.

[Svetlozar Draganov]

Could you also post the final render of both versions, and send us a stripped version of the scene - just delete everything without the walls / floor /ceiling .

[stezza]

OK here is a finale render. first is with the opn turned off during prepass and second with it turned on during prepass.
will send scene file via email as i cant seem to upload that here?

s

[Svetlozar Draganov]

We managed to achieve a similar result with our scene.
There is a difference between OPN applied before and after the IM/LC calculation indeed.
The OPN applied after the pre-calculation seams to be the right one - in other case the GI doesn't look correct.

The result in both scenarios is correct!
In OPN there is an option "No GI on other mattes" - and it is ON by default.

Your scene is enclosed and here what is happening when the above option is ON :

Vray shoot ray to your foreground (FG) objects - then this ray bounce from FG object to your background (BG) object (GI first bounce) - then the same ray bounce from the BG-object and try to reach the BG-object again (GI second bounce) - but when the "No GI on other mates" is ON - this ray doesn't reach the BG-object - it reaches the environment instead.

In other words - Having this option enabled with enclosed scene is like calculating GI with only 1 bounce!
That's why the image looks darker than the other one - turn off this option and the scene and both results should be the same.