From: Todd Kopriva <kopriva@adobe.com>
To: After Effects Mail List <AE-List@media-motion.tv>
Date: Fri, 20 Jul 2012 09:24:44 -0700
Subject: RE: [AE] Issue with Transparency in CS6 Raytracing
Thread-Topic: [AE] Issue with Transparency in CS6 Raytracing
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Message-ID: <B006868B2420FA4F88AB29E127AA783D0E85FF11@nambx09.corp.adobe.com>
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Chris beat me to it, so I'll just chime in to say "yeah, what he said".=20

> -----Original Message-----
> From: After Effects Mail List [mailto:AE-List@media-motion.tv] On
> Behalf Of Chris Meyer
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> A subtle but important point in CS6 with ray tracing is to distinguish
> between Opacity and Transparency.
>
> Opacity alters the alpha channel for a layer; Transparency does not. If
> you create some extruded text in an otherwise blank comp, and either
> move the cursor across it while watching the RGBA values in the Info
> panel (or simply toggle on the Transparency Grid), you'll observe that
> a fully-transparent object with Opacity =3D 100% has an alpha value of
> 100% and does not pass the transparency grid through.
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> Now, an admittedly confusing (but often desirable) quirk in CS6 is that
> if you place a 2D layer behind this transparent 3D layer _inside the
> same composition_, you can "look through" the transparent-but-opaque 3D
> layer and see the 2D layer. (It won't be refracted - only 3D layers get
> refracted by other 3D layers - but you'll see it.)
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> So if you want to create a transparent object in AE, and render with an
> alpha that represents this "transparency", you'll need to fake it. What
> I used to do in dedicated 3D programs (which often have the same quirk)
> is render a second alpha-only pass and reduce the opacity of the semi-
> transparent objects just for that pass. You might get a better fake by
> placing a black solid behind, rendering the RGB, and converting that
> RGB pass into a grayscale alpha channel; this will show the effects of
> Transparency Rolloff.
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> But I agree that it would be a nice feature request for AE to allow
> exporting of an alpha channel that matches what it does internally if
> there is a 2D layer behind in the same composition. In the meantime,
> think of it as being like exporting a layer with a blending mode: The
> blending mode only interacts with layers inside the same composition;
> not with layers composited outside the program.
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> hope that helps -
> Chris
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> On Jul 20, 2012, at 8:31 AM, mylenium@mylenium.de wrote:
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> 	Either it's a design feature (set Alpha to opaque to avoid
> degenerate generate colors with premultiplied backgrounds) or a bug
> (premature termination of the ray evaluation). Whatever it is, probably
> nothing you can fix.
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> 	Mylenium
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> 	[Pour Myl=E8ne, ange sur terre]
> 	-----------------------------------------
> 	www.mylenium.de
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> 	"S=E9bastien" <yenaphe@gmail.com> hat am 20. Juli 2012 um 14:46
> geschrieben:
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> 		Hi gang,
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> 		I have to export the alpha channel of my comp, nothing
> really fancy at first, but then I noticed that my semi-transparent
> extruded shape objects are considered opaque.
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> 		You can see here on my screenshot:
> https://www.dropbox.com/s/1f4u9v85d54sw7w/transparency.png The selected
> object is 45% opaque, and I should somehow see the checkboard through
> it, but no, the transparency is filled with some default black
> environment.
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> 		At first I thought it was because my difraction was at 1.5
> but no matter what value I change, it's always looking opaque when I
> put it against a transparent background (when I put an object behind it
> behaves correctly, it's only when the bg is transparent.
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> 		Any idea how to circumvent this ? Is it intended behavior ?
> (i'm quite new to Raytracing)
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> 		Thanks !
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> 		Cheers,
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> 		Seb
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> 		--
> 		S=E9bastien
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> 		L'ebook que Nicolas ne trouve pas tr=E8s dr=F4le, mais que tout
> le monde adore
> 		politikaillera.fr <http://politikaillera.fr/>
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