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Looking for a way to provide alpha channel in parallel with slides for good visual composition

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David Johnson
Looking for a way to provide alpha channel in parallel with slides for good visual composition
on May 18, 2017 at 3:21:11 am

I have a church studio built around a BlackMagic ATEM 1 M/E 4K. Our webcast regularly features powerpoint slides.

We are trying to set something up so that we can present textual slides that are more geared to the webcast needs than the FOH needs. By configuring one of the ATEM upstream keyers as a luma keyer, I have been able to achieve the effect I want.

The current configuration uses a graphic on one of the built-in media players as an alpha channel while the powerpoint is fed into one of the regular inputs.

Is there software which is capable of offering a presenter's view, presenting two different slides on two separate outputs, so I can put the graphic on one slide and the alpha on the other? If so, I can feed the presentation graphic into the regular input and the alpha into input 9 or 10.

Thanks in advance.


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Tom Matthies
Re: Looking for a way to provide alpha channel in parallel with slides for good visual composition
on May 19, 2017 at 2:10:55 pm

Can you post an example-even a mock up of what you need to achieve? PowerPoint shows can be exported as .PNG files that would include an alpha channel and these would work as graphics in your media pool. I believe that this model of ATEM switcher includes a DVE option if you are looking to include a squeezed back PPT over live video.

Basically, are you looking for a way to have an alpha channel as well as a fill channel coming from the computer and into the ATEM switcher? Are you needing to key the PPT over live video, set it back within live video or???
I'm a bit confused over just what you would need the final composite to look like.

Not my monkeys. Not my circus.


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David Johnson
Re: Looking for a way to provide alpha channel in parallel with slides for good visual composition
on May 21, 2017 at 6:22:20 pm

Thank you!

Here is a screenshot of the effect I have today:



To achieve the transparency, I put this image on the ATEM's media player 2, used the media player as the alpha channel for luma keying on Key 1, and then used a powerpoint slide with the colored backdrop for the sermon series and lettering for the for the fill input.



This looks good because the background is dark, so the white words pop out well. However, the platform is not always dark. If you look closely, you will see that the black outline around the lettering disappears when it gets out of the space controlled by the alpha channel (we are luma keying, so it's not really a surprise)

I would like to supply an alpha channel with the slides so that we can achieve the same effect on light backgrounds, and be able to use dark lettering and foregrounds where appropriate.

In order for this to be possible, we would need to create (and manage) distinct alpha backdrops for every slide in the set. I would prefer to keep this load on my key grip, leaving the technical director free to focus on the overall composition of the production.

Does this help?


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David Johnson
Re: Looking for a way to provide alpha channel in parallel with slides for good visual composition
on May 21, 2017 at 6:37:29 pm

We do not have to be limited to Powerpoint. We also have a site license for ProPresenter, for which we can purchase an alpha keying plugin module. Might this be the solution I need to be looking at?


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Tom Matthies
Re: Looking for a way to provide alpha channel in parallel with slides for good visual composition
on May 22, 2017 at 2:02:14 pm

The alpha module for ProPresenter would probably be the best way to go, but it seems to be priced pretty high for what it does. A less expensive, but also less flexible approach is to simply do the graphics in a program like Photoshop and export them as /PNG files into the ATEM switcher media pool. I'm not sure what the capacity is for storing graphics on your particular model, but the .PNG graphics have their own alpha channel and would key perfectly within the switcher.
It would be a little "clunkier" during a live production, however.

Not my monkeys. Not my circus.


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