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Rendering Transparent objects onto alpha

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Benjamin parker
Rendering Transparent objects onto alpha
on Dec 11, 2019 at 9:58:04 am

Hi My apologies if this is already resolved I imagine the answer is very simple but for the life of me I am not sure as to how to amend it.



I have a scene with an extremely simple molecule model.
The scene is lit and uses a white curved background which has seen by cam, refraction and transparency switched off in the composition tag.
One of the beads is using a glass material.
I need to render to a format that uses alpha, such as a PNG or TIFF image sequence.

However as you can see the refraction or reflection is picking up the blackness of the scene but isn't including it into the alpha.

Could someone please explain what is happening here and how I may be able to avoid this.

Many thanks


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Steve Bentley
Re: Rendering Transparent objects onto alpha
on Dec 11, 2019 at 5:33:54 pm

The problem is for something to be transparent there has to be a background to be seen through the glass. You can have that background be "not seen by camera" with a composting tag, and it will still show up inside the glass sphere (with Index of Refraction, if you have that set) but won't show up outside the sphere or in the alpha. Reflections will also be captured in the RGB of the sphere.

You can fake a glass alpha with a fresnel effect in the transparency (or alpha) channel of a material and that can generate an alpha that gives a see through fall-off like a glass ball would but does not generate a background, a background inside the ball or the distortion from index of refraction. But you could then generate all that inside your compositor especially if all you are doing is spheres.



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Benjamin parker
Re: Rendering Transparent objects onto alpha
on Dec 16, 2019 at 11:23:14 am

Great. Thank you


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