Render Mask Fringing

[Dominic_Patel]

Does anyone know why there appears to be a few pixels of fringing around the edges of items rendered using the render mask feature with bucket rendering? I don't seem to the get the issue if you render using RT for production rendering. Is there a way to fix this?

Thanks

Dominic

[VISUALISERA]

Hi, Dominic. I have a similar problem. It's true that the fringe disappears when using RT but since there's no antialiasing it comes with a jagged edge around the objects.
You can use different renderelments to eliminate this in post via a mask. But in my case I have to avoid post since there are several thousand images that will be produced.
I have temporarily solved it by saving to TGA and uncheck Pre-Multiplied Alpha and use the alpha as mask. (I know I said I wanted to avoid post but this I can do using a simple macro i Photoshop.) Using this method, the Advanced-engine does a better job than RT since it doesn't leave the objects with jagged edges...

[Alex_M]

You may get fringing if you render the same object multiple times with Render Mask since by default vray doesn't clear the contents of the previous render (which in most cases is a good thing) and the alpha channel's "semi-transparent" pixels at the objects' edges get overlaid onto each other every time you render making the edges very sharp and aliased. You can prevent this by changing the Previous Render setting to Clear. It's in the Settings tab, just make sure you switch from Default (the little green button) to Advanced. This will clear the contents of the previous render and alpha channel pixels around objects' edges won't overlap anymore.

[VISUALISERA]

Thank you for the tip and I can't speak for Dominic Patel but that is not the case for me. I have already switched the setting to clear. Still getting the fringe/edge...
Another solution I found is to set the other objects alpha contribution in vray properties to -1. In that case I can even save directly to png with good result. But this kind of contradicts the reason why I use render mask in the first place. Using this method I still have to render the whole image even if the saved result, thanks to alpha, is correct. Takes way too long.