Animated Graphics with Transparency and ATEM Switchers

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patrickbk
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Animated Graphics with Transparency and ATEM Switchers

Post by patrickbk » Tue Jun 19, 2018 2:00 pm

Hi there,

I have been doing internet livestreaming for years now, since before periscope and facebook live. I used to rent tricasters with operators, and about 2 years ago purchased an ATEM switcher (and love it).

One of my clients has a project where I need to have animated graphics with transparency on screen for several hours. I tested a solution of exporting ProRes 4444 files (with transparency), saving them to an SD card, and using a blackmagic HyperDeck Studio Mini as an input into the switcher. It worked great, using the hyperdeck as both the fill and key layer.

However, as we got close to the live event, I got the final graphics from the client and they were much darker than what I tested with. And all of the dark parts of the graphics were interpreted by the ATEM as being transparent. So the white text came through very clearly, but the dark background that was supposed to animate in and out did not show up at all. In my tests, I had used a light background, which was interpreted properly.

What is the best way to achieve animation with transparency with an ATEM? Is the correct way to do this using a computer with HD-SDI outputs (decklink or similar), and software like CasparCG or ProPresenter with the alpha plugin to output the animation and the alpha channel as two separate HD-SDI signals? If they wanted multiple animated graphics (they do), do I need a separate computer to drive each of them?

For example, if I need a countdown clock (counting down for 1 hour), as well as informational graphics that animate in and out throughout the hour, will I need two high end computers with a decklink each, and use 4 HD-SDI inputs (fill and alpha for each of 2 graphics)? Is there a simpler solution?

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PID_Stop
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Re: Animated Graphics with Transparency and ATEM Switchers

Post by PID_Stop » Tue Jun 19, 2018 3:06 pm

There are several ways to accomplish this, but since you're familiar with ProPresenter, I would suggest using that with their alpha keyer module. My previous church ran exactly that, using a BlackMagic UltraStudio connected to the Mac's thunderbolt output; the key and fill outputs go to your switcher's key and fill input. You're using an ATEM, which automatically synchronizes all of the inputs; we were using a Ross Crossover, so we had to genlock the UltraStudio to the Ross's reference output (which you don't have to worry about).

Another approach we used at one point was to set the animation background to an unused color (e.g., green) and do a chroma key. Of course, the advantage of using an external key (with separate alpha) is the ability to have graphics with varying degrees of transparency.

ProPresenter can easily handle different graphics like countdowns and other content, so I should expect that would not be a problem. If I remember right (it's been several years since I left as part of a church plant), I think you can set a countdown clock as an independent object that automatically inserts over other ProPresenter-generated graphics internally, so that might also solve part of what you're trying to accomplish.

Regards,

Jeff

patrickbk
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Re: Animated Graphics with Transparency and ATEM Switchers

Post by patrickbk » Mon Jun 25, 2018 1:41 pm

Aha! If anybody else is having this problem, you can adjust the "Clip" level in the downstream key in the ATEM to choose what grey level you want the keyer to ignore.

It defaults to 50% I believe, by sliding it down to 10% I was able to have the graphics appear correctly. No external presenter needed!

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PID_Stop
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Re: Animated Graphics with Transparency and ATEM Switchers

Post by PID_Stop » Thu Jul 12, 2018 6:29 am

What you're doing is actually a luminance key, and the key clip level adjustment is the center of the threshold for enabling the fill video. The key gain adjustment lets you set the threshold range to go from all-on / all-off to a linear key (which is necessary for translucent graphics).

I am assuming that your graphics don't include black or very dark colors -- that's where luminance keys typically fail. Black text over a light grey background, for instance, will give you background video peeking through the text. If you do need graphics like that, one solution is to make the background of the graphics solid green or blue, and have the ATEM do a chroma key. In fact, by varying the intensity of the background color and playing with the key gain, you can have graphics with variable translucency.

Naturally, the ideal case is to have separate key and fill signals (e.g., from a Presenter module) -- that lets you use any colors you like in your graphics.

Jeff

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