Lens Fare Effect Over Alpha
by Eric Goldstein
on
Aug 6, 2008 at 12:17:02 am
Hi,
I'm trying to run the lens flare effect over an image that is limited to the bottom third of the screen. I'd like the Lens Flare to continue out over the rest of the frame, which is purely alpha channel, no image.
I've tried various approaches to this, but haven't found anything that works. The lens flare extends slightly beyond the image in the bottom third of the frame and then just ends. Any ideas?
Re: Lens Fare Effect Over Alpha by Brendan Coots on Aug 6, 2008 at 2:33:23 am
Apply the lens flare effect to a full screen black solid placed above your lower third element, then put the black solid in Screen or Add blending mode.
Re: Lens Fare Effect Over Alpha by Darby Edelen on Aug 6, 2008 at 5:48:03 am
[Brendan Coots]"Apply the lens flare effect to a full screen black solid placed above your lower third element, then put the black solid in Screen or Add blending mode."
I don't think this will work if you want to render your sequence out with alpha (I couldn't tell if you wanted to). You would need a way to create an alpha from the luminance of the lens flare. You could use a luma matte or the Channel > Set Matte effect for that.
Darby Edelen Lead Designer Left Coast Digital Santa Cruz, CA
Re: Lens Fare Effect Over Alpha by Brendan Coots on Aug 6, 2008 at 3:09:04 pm
Oops, I didn't realize the poster needed to render this out with alpha. I thought he was just trying to get the flare to extend beyond his lower third element!
Apply your flare effect over black, the apply Xmult. It will create an alpha for you where the black was. Works like a charm. You may need to stack a couple of copies of the final flare to give you the intensity necessary to make the flare convincing. That's why you normally would composite the flare with black in Additive mode. It adds the values of the brighter pixels, making the effect more convincing.
Re: Lens Flare Effect Over Alpha by Eric Goldstein on Aug 6, 2008 at 9:14:22 pm
Hi Joe,
Thanks for the information. Xmult so far is the best of the different methods I've tried. It's not perfect, but as you suggest, working with different transfer modes and layers in addition to Xmult seems to be a good solution.
Thanks again,
Eric
Eric Goldstein
Giraffe Film Company
Los Angeles
eric@giraffefilm.com
if you're going to work with flares or light effects a lot, I'd consider investing in Knoll's collection. its way beyond adobes default limitations ( for starters the alpha channel is already figured into the effect =)
