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Export with alpha problem

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Kees Fluitman
Export with alpha problem
on Feb 27, 2019 at 11:20:02 pm
Last Edited By Kees Fluitman on Feb 27, 2019 at 11:22:06 pm

Hello guys,

I am new to making animated overlays with a transparent background for streamers. So I ran into a problem.
I have an animation but when I export it as Quicktime Animation or any other encoder, it turns out terrible, not how I want it to be....

I am searching how the alpha export works, but cant really find anything just yet. Is a part of my background noise too "small" to be transparent? There is grain on a solid with a high contrasted fractal noise as trkmat to create a line effect which evolves over time by a wiggle.

Is the fractal noise not contrasted enough? It seems completely transparant to me..?
Also, the glow/blur is terrible.

https://ibb.co/pfpKJqt
https://ibb.co/mbrJPRx

thnx in advance, ill keep looking myself.


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Steve Bentley
Re: Export with alpha problem
on Feb 28, 2019 at 2:24:28 am

I can't see the images (I get a "bad gateway" and they aren't showing up under your profile) so I'll take a guess.
Do you have a background solid in your comp? If so that will obliterate the alpha layer - basically making it a full frame white alpha which doesn't help to key out your elements.
Depending on how you are generating your fractals (effect applied to a solid?) this might also not generate an alpha and you only get an alpha of the whole opaque solid. You may need a fractal generator that adds the fractal into the alpha channel too.

If you are getting an alph of some sort but just too closed in, you could try using another type of alpha. Make sure to set your output settings to RGB +alpha and millions+ (if using quicktime) and I personally prefer Straight instead of Premultiplied but it really depends on the content and your pipeline.
Keep in mind too that many of these QT formats are no longer allowed in AE 2017 and above.
Finally you could generate your fractal in black and white (or feed the fractal with a gray scale grad) and use that element as a luma matte and then run another pass with the fractal in color for the RGB element.

Re post the pics and we can help more.



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Kees Fluitman
Re: Export with alpha problem
on Feb 28, 2019 at 6:46:55 am

sorry. guess sth went wrong with that website.

I have no solid BG.

[img=3840,2160,,,"alpha"]https://tweakers.net/ext/f/HiJiq5RkGTQjZ2LgLCn81FkC/full.png[/img]
[img=3840,2160,,,"alpha"]https://tweakers.net/ext/f/VcFtyqAWY0N1T6iQCRJaD7AV/full.png[/img]


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Steve Bentley
Re: Export with alpha problem
on Feb 28, 2019 at 7:21:41 am

To me that first image (that looks obviously wrong) may in fact be correct. All those wild aritfacts are only in the RGB channels. If you put that in AE and it has an alpha aroudn the letters the alpha will cut off all that crazy stuff and leave you with what you probably want. If there is no alpha then either AE is not seeing it and you have to "interpret" the footage - right click and choose interpret footage - then choose either premult or straight alpha. If those choices aren't there then this image has not been rendered with an alpha or the alpha is full frame white (as is the case here).
So this is either because the program that rendered the image can't make PNG's with alphas properly or the settings when rendered weren't correct.

So that the alpha doesn't cut off the edges of objects that are on black, a straight alpha will render pixels extending out past the edges of the objects in what seem like crazy colors but all make sense once the alpha cookie-cutters the extra junk away. If you did this with a pumultiplied alpha you would get a clean alpha as you expect in the alpha channel but the text would be clean and on black in the RGB channels too. The problem is that the premult alpha will now let some of the black at the edges of thergb's antialiasing peek through in the alpha's antialiasing and everything will have a fringe around it (see bad blue screen from the early 1980s).
(if a premult has been set up properly this doesn't happen)
Here's what that frame should look like (give or take) Sorry we can't make PNG's anymore in AE so this is a pshop file. Open it in pshop and look at the RGB channel and then the alpha channel (the one below the blue channel). When you bring this into AE and tell it that the alpha is straight it will look correct.

13159_671536withalpha.psd.zip



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Kees Fluitman
Re: Export with alpha problem
on Feb 28, 2019 at 11:46:07 am

Dude, you're my hero. It is actually true. It all looks weird in the wmp player, but it looks fine if I use it in OBS or After Effects.


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Steve Bentley
Re: Export with alpha problem
on Feb 28, 2019 at 4:22:56 pm

ya wmp doesn't know what an alpha is so it just displays whats in the rgb channel. And with glowy effects that can be psychedelic.



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