Black fringe on render passes

[DPS]

I have a comp that is setup like this:

http://vray.info/tutorials/basiccomping/

The difference being that I have rendered my FG and BG objects separately.

I rendered against a black background and am getting a black fringe where my FG objects are comped over the BG. Beauties look fine when comped together.

Seems to be right at the top of the stack:

Forground: (Diff*RawGI)+(Diff*Raw Light) comped over BG gives black fringe.

[DPS]

The solution was to unpremult exr before comping, then premult.

[svetlozar.draganov]

Yes that would solve the issue.
You can also try to avoid using Raw-elements generated from Vray and create custom Raw-elements by the following formula:
RawGI = Diffuse/GI
RayLight = Diffuse/Light

[DPS]

Thanks for the reply. Is there a problem with the raw passes?

[svetlozar.draganov]

Yes - this is the problem with the Raw passes, and it is better to create custom Raw passes like I explained you in the previous post.

[Donald2B]

Svetlozar bet me to it. I never use the RAW passes and create my own using the formula above. Works great in Nuke!

[DPS]

Would I be right in thinking that the difference between the RawReflection element and a RAWRefl=Reflection/ReflectionFilter is that the Raw element has a premultiplied result regardless of whether you unpremultiply it, where as the divided version doesn't have any AA?

***

Say you're using a Multimatte to selectively adjust parts of the Reflection pass - should I render a non-AA version of the multimatte if I'm grading any unpremultiplied passes including the RawRefl=Refl/Refl Filter? I could use an integer ObjectID element in that case which can hold more objects.

[Donald2B]

Yep, the Raw passes have aa applied so when the passes are added back together, the borders don't add properly.

I typically use the Multimatte straight from the render, but you can get some edge ringing depending on how drastic the changes. Others have mentioned that doing with a deep pixel approach resolves most of those issues. I have not figured out the deep pixel workflow yet between VRay and Nuke. It's definitely on the to-do list.

[DPS]

I tried the deep approach today - it's pretty neat. Render all your lovely teapots separately and bung them all together and it places one in front of the other without any user intervention - not tried with different elements yet.

[Donald2B]

So how did you go about exporting / saving data as deep exrs? I haven't figured that part out. (Note: more like haven't had the time to look into it too much yet.)

[DPS]

Here's a link to the 3.0 thread, I'll add to that if any steps are missed, but better to get info in one place.

http://forums.chaosgroup.com/showthr...p-data-support