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| Chris beat me to it, so I'll just chime in to say "yeah, what he said". > -----Original Message----- > From: After Effects Mail List [mailto:AE-List@media-motion.tv] On > Behalf Of Chris Meyer > > 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 = 100% has an alpha value of > 100% and does not pass the transparency grid through. > > 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.) > > 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. > > 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. > > hope that helps - > Chris > > > > > On Jul 20, 2012, at 8:31 AM, mylenium@mylenium.de wrote: > > > 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. > > > > Mylenium > > > > [Pour Mylène, ange sur terre] > ----------------------------------------- > www.mylenium.de > > > > > > > "Sébastien" <yenaphe@gmail.com> hat am 20. Juli 2012 um 14:46 > geschrieben: > > > > Hi gang, > > 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. > > 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. > > > 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. > > Any idea how to circumvent this ? Is it intended behavior ? > (i'm quite new to Raytracing) > > Thanks ! > > Cheers, > > Seb > > -- > Sébastien > > L'ebook que Nicolas ne trouve pas très drôle, mais que tout > le monde adore > politikaillera.fr <http://politikaillera.fr/> > > > > |
