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How to get the alpha channel of the object and give it to BlackMagic output?

How to get the alpha channel of the object and give it to BlackMagic output?

I have only one object in a scene and want to give this object with alpha channel to an output signal in BlackMagic card?

Maybe make output 2 signals. Fill and key? how to compose this like did it The Weather channel?

Product Version: UE 4.21
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asked Mar 04 '19 at 12:29 PM in Using UE4

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RomanNikitin
16 1

avatar image Lunchbox Mar 23 '19 at 02:18 AM

I'm also trying to figure this out.

From what I can find you need two output's one for color and one for alpha/mask. You'll need to composite those yourself using hardware like Blackmagic Ultimatte or a software solution that can use a second feed as a mask.

For my setup, I've got two BlackMagic DeckLink Duo 2's and I'm trying to send an Unreal Fill&Key to StreamlabsOBS. I have two SDI outputs from the Unreal PC connected to two inputs on the StreamlabsOBS PC. I can see the color channel on the receiving StreamlabsOBS PC, but nothing in the alpha. This is b/c I don;t know how to send or assign the alpha.

I have two issues currently:

1 - How do I set the alpha output channel? When I set the BlackmagicMediaOutput to Fill&Key my Key Source only has one option: (Single Source 0). What SDI Output is that? I have 1 - 4 but no 0.

2 - The second issue is how do I setup an actors alpha? I've seen in other posts using AJA products, they enabled alphas in the project settings under rendering, which I've done and set to "Allow through tonemapper" as I don't believe SDI sends linear information. Though, I don't know how flag actors to be included/excluded.

Any input is appreciated. This tech is super cool and can;t wait to get it functioning.

Thanks you in advance!

avatar image RomanNikitin Apr 01 '19 at 02:38 PM

I have solved this question. My Black Magic card has 4 input and 4 output SDI.

The setting parameters of BM card set to 3D ( Like a stereo movie). And then input "Panel" sees and starts to receive two signals. The Color (Fill) and Black&White silhouette (Alpha). Two signals Should multiply in the input Reciever (We use Kayenne Video Production Center from Grass Valley)

In Unreal should delete all geometry in the background include Clouds in the sky.

avatar image Lunchbox Apr 01 '19 at 10:44 PM

Oh I see. The alpha takes the all actors into account, I hadn't tried removing the sky dome. I am using a Render Target to selectively choose the actors that get rendered. It would be nice to send the alpha from the render target using the Key & Fill option.

Thanks for posting your results, they are very helpful.

avatar image Lunchbox Apr 01 '19 at 11:28 PM

If it's not too much trouble could you share your BlackMagic settings for both the card and in unreal? I can't seem to get the alpha feed to show up.

You mention "The setting parameters of BM card set to 3D ( Like a stereo movie)." I'm not sure where that is. It may also be a difference in the card we are using as it sounds like you have the quad setup. Is this something you set in the Blackmagic Desktop Video Setup Utility? Or somewhere else?

Here are my Blackmagic Desktop Video Setup Utility settings alt text alt text

Here are my BlackmagicMediaOutput settins in unreal: alt text

Thanks again.

bmdvs-ss-001.jpg (43.4 kB)
bmdvs-ss-002.jpg (13.7 kB)
bmmo-ss-001.jpg (14.6 kB)
avatar image Lunchbox Mar 30 '19 at 11:00 PM

Anyone from epic have more information?! We've seen this done multiple times, but without an explanation. Other than setting the BlackMagicMedia configuration to Key&Fill, what steps are needed to assign the key and fill channels?

Any help is appreciated.

avatar image RomanNikitin Apr 01 '19 at 02:38 PM

I have solved this question. My Black Magic card has 4 input and 4 output SDI.

The setting parameters of BM card set to 3D ( Like a stereo movie). And then input "Panel" sees and starts to receive two signals. The Color (Fill) and Black&White silhouette (Alpha). Two signals Should multiply in the input Reciever (We use Kayenne Video Production Center from Grass Valley)

In Unreal should delete all geometry in the background include Clouds in the sky.

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1 answer: sort voted first

I have solved this question. My Black Magic card has 4 input and 4 output SDI.

The setting parameters of BM card set to 3D ( Like a stereo movie). And then input "Panel" sees and starts to receive two signals. The Color (Fill) and Black&White silhouette (Alpha). Two signals Should multiply in the input Reciever (We use Kayenne Video Production Center from Grass Valley)

In Unreal should delete all geometry in the background include Clouds in the sky.

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answered Apr 01 '19 at 02:41 PM

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RomanNikitin
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