Refraction, effect channels not working

[rmaytee]

I'm not sure if this is a new issue with this build (I am using 3.20.03), but for some reason I am not able to have the refraction of my materials affect the alpha channel. I have a view looking off a balcony with a glass railing. On the other side of the railing are some shrubs. I would like to replace the background post render, and the only way I can do that is to set the object's alpha contribution to 0.0. But then I don't have any reflections when I save a PNG. I have the material set to colors + alpha on the effect channels of the refraction, but it is not working like it has in the past.

Any ideas?

[im.thatoneguy]

If the alpha contribution is 0 then PNG won't give you reflections. The "solution" is to set the alpha contribution to the same as the reflectivity contribution. Make sure your "Affect Channels" on reflection is set to color only. Otherwise it'll refract the cold hard black nothingness of the abyss. Then your refraction set to Color+Alpha should work properly. Another option is to render to a file format like EXR or use a compositing application which gives you access to the raw data. My suspicion is that by rendering PNG it's premultiplying the RGB channel by the 0.0 alpha and you're just getting black RGB. Or even if there is data there if you're using something like Photoshop which notoriously is terrible at premult/unpremult problems it's just premultiplying on open and blacking out your RGB channels again. Alternately you could set the alpha contribution to just a generic Fresnel falloff map and that should approximate the reflectivity contribution well enough.

[rmaytee]

Thanks for the reply. I have the glass handrail back with 1.0 alpha contribution and the refraction affect alpha set to color only. I have realized, when it is set to color+alpha (like I used to which always worked fine) it is working the way I had hoped. For some reason, I was not able to see it properly in the VFB. I have rendered high res and all seems to be well. I have wasted your time.