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overEZ
07-13-2011, 05:37 AM
Sorry if this has been addressed. When I render anything semi-transparent with nothing in the background, it looks different composited on a black background than it did in the Render View.

I have pretty much known about this but it just occurred to me that I don't know why? Shouldn't the render view give us the correct look and transparency when there's nothing behind it?

(it is much more transparent when I take said image into AE or Nuke)

Kakkoii
07-13-2011, 05:44 AM
Perhaps this is due to the render preview being linear, but when you save the file it's usually converted to sRGB? Or something like that.

overEZ
07-13-2011, 10:54 PM
hm I don't know anything about linear data. Does it have to do with gamma? I'm gonna have to read up about that...probably has nothing to do with color space.

Sebastianf
07-18-2011, 03:57 AM
Great a plane and put it behind your glass objects. Turn off primary visibilty, casts shadows and visible in reflections in the shape node. Put a 'Use Background' shader on it and turn 'off' reflectivity and put spec to black that should work get transparency showing. I believe this generally happens if something is refracting through the glass even if it has primary visibility turned off the glass inherits the opacity of the background

overEZ
07-21-2011, 06:07 PM
^thanks for the help...it was a good idea but didn't do anything...

I think turning off primary visibility makes it pointless to bother with a Use Background shader or any other shader. I also tried it without changing Render Stats. No difference in alpha channel.

Greedo
07-21-2011, 10:05 PM
What I suggested is ususally if you are getting no alpha in your glass in mental ray, usually happens when you have an enviroment behind it that you dont want visible. Having primary visibility checked off shouldnt matter, for this, as long as as you have visible in refractions checked on.

Im thinking though that maybe your problem may be more to do with the either gamma or color profile. That Kakoii suggested above.

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