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Graphic with alpha channel issues
Hey all!
I am seeing an issue with how FCP handles graphics with alpha channels. We are using animated lower 3rds built in After Effects that have thier own alpha channels. When I try to use them in FCP they have a bit of a drop shadow effect happening like it is not dealing with the key properly and leaving some black in.
-The grfx has very fine fades in its design.
– the file is in the Animation codecMy solution to this is building it in Motion where the key looks much cleaner – but this seems like an unessesary step.
Am I doing something wrong? Is this some sort of bug/ limitation of FCP?
Thanks!
Liam Lawyer
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Wee Beastie -
13 Replies
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Check to see how FCP is interpreting the alpha. You may have to tell FCP whether or not it’s premultiplied.
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[Arniepix] “You may have to tell FCP whether or not it’s premultiplied.”
In my experience, FCP ALWAYS guesses wrong. I constantly have to change it to ‘Black’ and FCP wants to use ‘Straight’.
Jeremy
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Well the truth is you want to use straight. Straight will generally produce better results. It pretty much always produces better results. Only thing with straight, is it looks like hell on it’s own. Premulitplied tends to have the fringe effect in my experience. I use straight. Always get the expected results. FCP always guesses right.
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I find just the opposite, but I’m weird so it makes sense.
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I thought the only reason to use premultiplied was for older systems that didn’t support straight, or for when it also needed to be a stand alone graphic. It always seemed odd to premix transparent areas with black (think feathered edges) and that’s where I have had issues with it back in the old media 100 days. I switched to straight and never had a problem again. With straight it appears to premix transparent areas with the same color as that particular part of the animation. That way the alpha for a feathered edge is applied to a solid color, not to a gradient of color to black (premultiplied).
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Hey all! So I switched it to Black and it is perfect!!! Guess it depends on how it is built..
Thanks so much for getting me in the right direction!
Liam Lawyer
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Wee Beastie -
slightly ot, but If one is charging people for their editing services it’s also thier JOB to know these things. I run into things I don’t know all the time that is part of editing. I don’t charge clients for my learning curve. I learn it, then I know it. Then I charge the next guy. 🙂
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It does? It doesn’t say anything at all about FCP. FCP has the ability for you to discern what kind of alpha was rendered and you tell FCP accordingly. That way it really doesn’t matter. I use premultiplied and have great results. Straight mattes always mess up and don’t show all of the information, but again I’m weird and this is how I do things.
Jeremy
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As the video pointed out many programs have trouble discerning just what needs to be transparent in a premultiplied matte, and in turn, leave black fringing around the edge, so when in doubt use a straight matte. FCP is not the best program for dealing with mattes & transparency. So this is probably good advice for FCP.
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[Dave LaRonde] “can you not use what you’ve learned to good use in FCP?”
No, it doesn’t really say anything about FCP specific, or how FCP can handle different mattes and the choices therein. I wouldn’t expect it to as it’s an AE tutorial, not an FCP tutorial. Aharon does a fantastic job (as he does in all of his tutorials) of explaining the difference between straight and alpha but he never says which is best, specifically for FCP. He basically says that you have to figure out what’s best for you and in my little post-production metropolis cave, pre-multiplied always works better for some reason.
Eh, whatever it’s neither here nor there, the original poster turned his alpha to black and he said that all was well.
Jeremy
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