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Outputting ALPHA overlook
Hey, having some difficulty rendering out a simple sequence with an alpha channel, I created some particle smoke and outputted over a transparent bg, animation – millions color+ – straight unmatted, like I have many times before, but for whatever reason it is not giving me my alpha channel and giving a black bg and white edging around the smoke with alot of stair-stepping, so I thought weird try again, same thing, so I ran a test of just a red circle over a transparent background, same result, so it is not the particle that is doing it to me, I feel I have been staring at a computer screen for too long and am over-looking something simple, any takers?
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2 Replies
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Ha figured it out, I guess it was working all along, but when I was opening it in quicktime it was giving me the white edging, it was also giving me the same thing when i was doing a quick preview in the OS, so I figured what the heck just drop it in Final Cut and see what happens, and of course it worked no problem, I dont know why it is showing up in quicktime like that though, waste of time, do you have any ideas why it would show up like that? Usually when I preview it in the OS it will give me the transparency, oh well.
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What you’re seeing in QT or the OS is absolutely correct as this is the way a straight alpha is displayed outside of a compositing application. For a great explanation of straight vs. premultiplied alphas take a look at this podcast from Aharon Rabinowitz. It should be able to answer all of your questions:
https://library.creativecow.net/articles/rabinowitz_aharon/straight_vs_premult.php
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