-
Glass Effect
Here’s a question that’s been bugging me for awhile, and I thought I’d ask it here… I’ve had a hard time finding the answer elsewhere. I’m relatively new to 3d applications, so bear with me. How would I render a transparent object (like glass) in order to use it as an element for overlay onto video in my NLE or for use in a live switching environment? A good example of this is the current graphics package for the Today Show, where the lower thirds will pop up with what looks like a rotating glass cylinder. You can see not only the video behind the effect, but the opposite side of the cylinder as well. I keep seeing this type of effect more and more, and I’d like to know how to go about creating it. Is it simply a matter of rendering only select objects in my 3d environment? I hope my question makes sense, I appreciate any help offered.
-
4 Replies
-
David- If I understand you correctly, you will need to render out your element over black, with an alpha channel. The alpha channel is like an embedded matte so that only the element will show through, and the semi transparent parts will come through as semi transparent.
But since you are using this on an NLE, there’s another step. Some NLEs (like Avid) will have a black line around an object imported with an alpha.
What I do is import the 3d mov into After Effects, and render that out STRAIGHT (not premultiplied). This will add pixels around the edge of your element. This mov will be your fill. You will add on another module. Change the setting to ALPHA. This will be your matte.
Import these two movs into your NLE, and use the matte as a luminance matte.
This way you won’t have any black edges, and your semi transparent areas will be perfectly clean.If you need more technical guidance for AE, let me know, and I’ll go into more specifics.
-
Dave –
The most important part of using a transparent reflective element in your composite (such as glass)is lighting that element, if indeed you plan to use a real piece of glass. You could also create it in a 3D package, but the real thing always looks more convincing.
It’s obvious that glass is transparent; if you use a piece of glass that doesn’t have any reflections in it you don’t see the glass. So the idea is to get reflective highlights that you can control in the glass. I always shoot on a black background, then place white reflective pieces (foam core works great) in front of the glass (behind, or next to the camera), and throw my light onto the reflective pieces. That way the transparent part of the glass is black (or transparent) and the reflections become the opaque part of the image. When you composite, you put your image in Additive mode (in After Effects) and the black disappears.
If you’re using a 3D package (I use 3DStudio Max), you want to use the same lighting process as outlined above, and make your texture map a reflection map, so that the light boxes or planes that you place next to your virtual camera reflect in the shot.
In a way, it’s easier to do this in the real world than in 3D, but you have more control over your alpha settings in 3D. Good luck.
Joe Bourke
Art Director / WMUR-TV -
Thanks for the help you two. I think I’m getting the picture. I think for some reason I was hung up on how the alpha channel would work when you have the camera looking through two transparent (glass) layers, when all the software is doing is calculating less transparency for those areas. Thanks!
-
>but the real thing always looks more convincing. < I'll agree with you on that one! When I first started out 12 years ago, NBC was airing their "Must See TV" campaign. One of their most interesting 3d elements was a frozen TV. When I went in for an interview with that department, I was shocked to see the famous frozen TV prop casually stored over a file cabinet.
Reply to this Discussion! Login or Sign Up