• Adobe After Effects

  Transparent background – HELP!

  Posted by Dave Forrest on June 27, 2007 at 4:29 pm

  Hi,

  Please forgive my ignorance. I’m fairly new to After Effects and I am still very much feeling my way.

  I have created a series of short intro stings in AE to preceed each clip on a DVD. In the AE composition, the background dissapears before all the other elements do – the idea being that the video clip that is being introduced will become visible through the animation as it runs its course.

  The problem is that after rendering the composition into a movie and dropping it into Premier the background, which should become transparent, shows up as black. I’ve tried a number of different settings in the Output Module but it’s really just trial and error and I’m not having much luck with it. Some research on the web has flung up a lot of stuff about Alpha Channels – could this be something to do with it perhaps?

  Any help or advice would be very much appreciated.

  Many thanks,

  Dave.

  da**@****52.com

  Steve Morris replied 18 years, 10 months ago 4 Members · 4 Replies
• 4 Replies

• 

  Steve Roberts

  June 27, 2007 at 4:52 pm

  To render with alpha channels, you need to render to a codec that supports alpha channels, such as the Animation codec, at millions+ colours and RGB+alpha.

  Then in Premiere, you need to recognize the alpha there.
• 

  Darby Edelen

  June 27, 2007 at 5:00 pm

  [Steve Roberts] “To render with alpha channels, you need to render to a codec that supports alpha channels, such as the Animation codec, at millions+ colours and RGB+alpha.

  Then in Premiere, you need to recognize the alpha there.”

  This becomes slightly complicated by the fact that there are two different ways to save/interpret alpha: premultiplied and straight.

  Premultiplied means that the areas marked as transparent by the alpha channel are filled (‘multiplied’) with a color (usually black) in the RGB channels of the footage. If the program you are importing the footage into doesn’t know how to handle premultiplied footage then you will see a black (or whatever color the footage was premultiplied with) fringe around your footage where the pixels should be semi-transparent. After Effects and many other programs can be told to interpret premultiplied footage as such and remove the black matting from the semi-transparent portions of the RGB channels.

  If you render it Straight then the RGB channels will spill out over the bounds of the alpha and you will not see any fringing, but the footage will look very strange if you view it as RGB without alpha transparency.

  If you’re not familiar with handling Premultiplied footage then I recommend using Straight.

  Darby Edelen
  DVD Menu Artist
  Left Coast Digital
  Aptos, CA
• 

  Steve Roberts

  June 27, 2007 at 5:20 pm

  Indeed.

  https://forums.creativecow.net/cgi-bin/new_page_wrapper.cgi?forumid=2&page=https://www.creativecow.net/articles/rabinowitz_aharon/straight_vs_premult/index.html

  https://www.adobepress.com/articles/article.asp?p=597700&seqNum=3&rl=1

  https://livedocs.adobe.com/en_US/AfterEffects/8.0/help.html?content=WSbaf9cd7d26a2eabf53ab041041081290f-7ff6.html

  https://livedocs.adobe.com/en_US/AfterEffects/8.0/help.html?content=WS3878526689cb91655866c1103906c6dea-7f7e.html

  Many such jouneys are possible. Let the COW (and Google) be your gateway. 🙂
• 

  Steve Morris

  June 27, 2007 at 6:09 pm

  I always use STRAIGHT when importing into Premiere.

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