Render Glass For Multiple Backgrounds

[GDC_0059]

Hi everyone,

I'm having an issue trying to work out the best way to approach rendering an object made of glass, and having a final result that can be composited in Photoshop and have it’s background replaced with any image.

At the moment I have a basic studio lighting set up with no background objects. I render the object and get a transparent alpha which is great, the issue is because there is no background I'm getting heavy black refraction marks on the object. This looks fine in the render view because the background is black, however when I change the background in Photoshop the black refraction marks mean the result does not look realistic.

Am I approaching this entirely the wrong way? I feel like there must be something obvious that I'm missing to get the result I'm looking for. Or is the only solution to use a background/lighting set up that will not produce strong blacks and edit the image in post.

Any help you guys could give me would be great. I've attached my scene file, it's a pretty basic set up and also some screenshots to illustrate what I'm talking about.

Thanks!

[maru]

I may be wrong, but from my quick test it seems that:
- you need better compositing software (that would allow you to perfectly select masks, not some color range or feather substitutes)
- you need Corona 6 with mask propagation enabled

You should then render either the glass against just the background and use a masking element like CMasking_WireColor or render the glass against a background object (e.g. plane, box) so that its mask would be visible in the background.

[maru]

Or here is another idea, in case you only need the glass, reflections of lights in it, and a solid background:
Just render the whole thing against a black background. Use beauty, ignore alpha. Place the beauty on top of a colored solid layer. Set the beauty layer to Add mode (Linear Dodge in PS).