ProRes 4444 - Alpha not working

[Drew Schmidt]

Hey All

Trying to create some transparent videos in AfterEffects. I've set the codec settings as follows:

Pulling the video back into AfterEffects, it's all transparent. But playing it in Qlab makes for a white background. Please. Help me find the error in my ways!

[micpool]

That should work

For some reason premultiplied 4444 doesn't work in QLab but Straight Unmatted works fine for me from AE

Have you tried a simple example e.g a composition containing a solid black layer with a mask drawn on it, rendered to 4444 Straight unmatted?

Mic

[Drew Schmidt]

This is all very interesting. 

So I'm trying to layer a 4444 on top of a 422. In that scenario the 4444 covers the 422, making everything white to the outskirts of the 4444 video. (Scaling the video down, I can see the 422 video beneath).

When I try layering the 4444 video on top of the same 4444 video, I can see everything. However, the top layer removes the color from the bottom layer. I'm sure this is what's actually happening in the ProRes 422 file, that it's removing the RGB data below it, showing the Alpha values as white. This is true with Straight and Premultiplied. 

I should also add ... 

I've been sending this to MadMapper via Syphon. When I use straight Qlab, any 4444 file makes the background of Qlab white. 

Playing the videos in MadMapper do not do this.

When stacking two 4444 videos on top of one another in MadMapper, they behave as expected. Black on back. Transparent video. Transparent video.

So ... what's that all about? 

Thanks for the help everyone!

[micpool]

In that case it could be an OS thing (or AE version). I am on OS10.8.5 and AECS6 (QLab 3.1.16) and 4444 works as expected if straight (Unmatted) but not if pre matted

Do you want to do a 2 sec clip of your 2 videos and post them for me to test on my system. Also a CS6 compatible simplified aep file with 2 second clips of the content for me to render on my system, If that would be helpful?

In return I am attaching a black rectangle  on a 4444 unmatted  for you to have a go with!

Mic

[Drew Schmidt]

Figured it out. 

Its an issue of the order of Effects in AE. There was a Brightness & Contrast effect that came after a Keying effect, thereby making the resulting pixels white. 

Puzzled as to why the error only came up in Qlab. 

Happy we figured it out!

Thanks for journeying with me Mic.

[Drew Schmidt]

Turns out I'm still stumped. 

This file shows up as transparent in all my applications except Qlab. When played in Qlab, 

Some transparent pixels are transparent. Some (the reveal) show up as white.

I've done a Linear Key. I've done a Luma Matte. 

Any advice? 

[micpool]

It's an AV foundation thing by the look of it

The attached screenshot shows your file in QTPlayer  QT Player7 and Mail 6.6

QLab will treat it the same as QTPlayer using AV foundation. MadMapper still uses the QuickTime Engine like QT7 and Mail.  (Safari renders it with grey pixels in the middle but we won't worry about that for now!)

Having said that it should be possible to render out of after effects a version to work in QLab

Can you post a simplified After effects project?

Mic

[micpool]

Rendering your file in AE as premultiplied Millions+ 4444 gives identical results in Qlab and After effects

[micpool]

And finally,

Premultiplied 4444 needs to be pre matted with black in After Effects i.e your composition needs to have a  black background  to work in QLab

I have just made a similar file to yours in AE by cutting a mask in a solid black layer and stroking that mask with a white brush.

My renders both premultiplied with black and straight both work in QLab and look identical

[Drew Schmidt]

As I play around with more of our stock footage, the culprit seems to be a certain set of videos and less about my exporting in AE. 

This works with a Luma Track Matte.

This does not.

They're both PhotoJPEG. Same size. One is 30fps the other 60fps. That's the only difference I can see via quick examination. 

For now I've just created two syphon outputs to MadMapper. A bottom layer and a "Multiplied" layer. I then duplicated all my MM surfaces and made the top set Multiply blending mode. This seems to be functioning just fine, but would much rather figure out what I'm missing in the actual videos. 

[micpool]

I got a 4444 Prematted with black out of AE,  which works in QLab using your second clip without too much trouble

I made a composition out of reveal_02

Duplicated the Layer

Put an Inverted Luma Matte on the bottom Layer

Set the composition background to black

Made a new output composition

Put the reveal_02 comp into it

Used Levels on that layer to peak up the white in the edge

Set the comp background to black

Rendered to 4444 Premult with Black RGB+Alpha Millions+ (Output file called DrewPM as in screenshot above)

Rendering the same  Straight unmatted didn't work in QLab it came up solid white in the middle.

I have also attached the .aep AE file

Hope this helps

Mic

[Drew Schmidt]

Mic for the win

For those playing at home ...

• Continued with the same transparency methods. (Luma Matte, Keylight, etc)
  
• Turned off Transparency Grid (Shows white beneath)
• Changed the Composition Settings. Background to Black
• Exported as ProRes 4444, RGB+Alpha, Premultiplied

Thanks Mic!

-Drew

[Kevin Springer]

Yes.. I was having a similar problem tonight and unfortunately had to figure it out myself before finding this post... I am also using After Effects.  QLab was not reproducing alpha channels correctly when the composition background color was white.  The finder however was reproducing it correctly.

Is this a bug?  Or is it because in a standard alpha matte black is transparent and white is visible?

-Kevin

[micpool]

I don't think it's a bug. It's just that alphas and matted or premultiplied alphas can be interpreted in many different ways. After Effects users think they are straightforward, mainly because AE is absolutely brilliant in how it handles them. 

For a full understanding of most of the issues, work slowly through this page and all the examples and references it contains.

http://www.provideocoalition.com/alpha-channels-premultiplied-vs-straight/

Whenever, I'm doing new footage with embedded alpha for QLab I always do a short test render of a couple of seconds, and try it out  in a workspace before rendering the whole file.

I think premultiplying with a black composition background in AE generally works, and that is probably the one to try first.

Mic

[Joe Fox]

It seems like this is something that should be addressed, if other softwares can handle it appropriately (to Mic's point about AE handling it "brilliantly"). 

Otherwise, we're looking at a lot of folks running into this re-render issue (as I presently am with 90GB of files -- Mic's point about rendering a test file first is taken well).

joe

[Chris Ashworth]

Hi Joe,

I definitely hear the impulse here, but it’s also important to note that Adobe has a 64 billion dollar market cap. They have rather a lot more resources to spend on engineering time for things like decoding files. For us, we have to lean heavily on Apple’s engineers for the decoding, which ends up meaning we support what AVFoundation supports.

Best,

C