Help with screen replacement overlay

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happytappin

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Help with screen replacement overlay

PostFri Jul 30, 2021 1:00 am

Screen Shot 2021-07-29 at 7.54.10 PM.png
Screen Shot 2021-07-29 at 7.54.10 PM.png (605.12 KiB) Viewed 537 times
Screen Shot 2021-07-29 at 7.54.10 PM.png
Screen Shot 2021-07-29 at 7.54.10 PM.png (605.12 KiB) Viewed 537 times
So I did a screen overlay with an old commercial and it came out fantastic , looks like its coming from the TV and everything, but now when i walk in front of the TV you can see the obvious problem. How do I solve this?
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Screen Shot 2021-07-29 at 7.54.24 PM.png
Screen Shot 2021-07-29 at 7.54.24 PM.png (527.04 KiB) Viewed 537 times
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bounceHouse

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Re: Help with screen replacement overlay

PostFri Jul 30, 2021 2:12 am

There are multiple options; look up (in Youtube or the Davinci Resolve tutorials) on rotoscoping. There are multiple techniques (all manual, some tracking, etc.).

One approach is on the Color page, having selected the "tv video" clip from the list of clips you can apply correction to:
* turn on a power window (the one that looks like a "pen tool"), which you'll use to draw around your body as it moves across the TV,
* click the 'invert' the mask button next to it so that only the video that is NOT where your body is shows.
Go frame by frame adjusting the window, until you've passed the TV completely (at which point drag the whole mask off completely off the view - before you arrive and after you depart - for the rest of the video.

Early on, in the nodes area, right click to "add alpha output" and connecting the blue output (of your node that has the power window) to the alpha output that appears. Back on the Edit page, you'll be able to see the effect of the masked area.

Given the motion blur I see on the snapshot you provided, you'll likely want to soften the edges of your mask so that it blends well.

Have fun!
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Jason Conrad

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Re: Help with screen replacement overlay

PostFri Jul 30, 2021 3:26 pm

Try Mocha. It’s pretty much the only game in town for rotoscoping, unfortunately.


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Jim Simon

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Re: Help with screen replacement overlay

PostFri Jul 30, 2021 3:30 pm

happytappin wrote:How do I solve this?

The simplest is don't walk in front of the TV.

That can be achieved with a reshoot, or cutting before you cross.
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Gary Hango

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Re: Help with screen replacement overlay

PostFri Jul 30, 2021 4:07 pm

If you reshoot, play a solid green or blue image on the tv while filming, then use a chroma key effect to “underlay” the image on the screen. Your arm will occlude the image.
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Hendrik Proosa

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Re: Help with screen replacement overlay

PostFri Jul 30, 2021 7:37 pm

Just roto the person. Roto isn't rocket science, it is just tedious. Fusion page is good enough, no need for mocha or whatnot. Why mocha is always suggested for simple roto is beyond me, it does roto just the same as everything else, only edge it has to Fu is better planar tracking which is just a helper for quicker roto. Professional roto artists use mostly Silhouette but no-one suggests that for some reason.
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Sander de Regt

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Re: Help with screen replacement overlay

PostFri Jul 30, 2021 8:02 pm

Gary Hango wrote:If you reshoot, play a solid green or blue image on the tv while filming, then use a chroma key effect to “underlay” the image on the screen. Your arm will occlude the image.


PSA: Do not do this. What you gain from the ability to key (if it even works, because usually stuff passing in front of a TV will be motion blurry and out of focus so not that easy to key to begin with) you will lose on the realism front. If the TV is off you can use lumakeying to bring back the original reflections making it easier to make a realistic composit.

If it's on with blue or green, the reflections will be lost and blue/green will reflect all over your scene. It's not worth it compared to doing a quick roto like Hendrik already mentioned.
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Marc Wielage

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Re: Help with screen replacement overlay

PostSat Jul 31, 2021 1:43 am

Hendrik Proosa wrote:Just roto the person. Roto isn't rocket science, it is just tedious. Fusion page is good enough, no need for mocha or whatnot. Why mocha is always suggested for simple roto is beyond me, it does roto just the same as everything else, only edge it has to Fu is better planar tracking which is just a helper for quicker roto. Professional roto artists use mostly Silhouette but no-one suggests that for some reason.

I think this is the best suggestion. I actually can and have done very effective rotos within Resolve, and the key (no pun intended) is to break up the human shape into multiple parts. Don't try to roto out the entire human body with a single mask: do one for the arm, one for the trunk, one for the neck, one for one leg, another one for the other leg, and so on, track them all separately, and then use all of them combined in one node as an "occluded mask" to cover up the TV set image when necessary. If it's a five-second shot, it doesn't take that long to do. If it's a long, complicated, moving shot, I'd just send it out to a VFX artist, let them create an external mask, and use that. If it involves really complex issues like transparency a change in 3D depth (like a camera that moves to the side), I'd give up and hire a VFX specialist. The alternative is learning Fusion, which can be done -- it's just a matter of time and patience.

Details for using external masks are in the manual. So are dealing with masks during composites on the color page, in the section on chromakeying in Chapter 144: "Channel Splitting and Image Compositing," starting on p. 2838 of the Resolve 17.2 manual. There's also a bunch of YouTube videos out there that discuss it.
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Uli Plank

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Re: Help with screen replacement overlay

PostSat Jul 31, 2021 6:17 am

I second that Silhouette is the best tool for rotoscoping, but I'd hesitate to suggest such an expensive tool for this project.
Don't approach Resolve with your expectations from other NLEs! They are all different.
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Hendrik Proosa

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Re: Help with screen replacement overlay

PostSat Jul 31, 2021 8:50 am

Sander de Regt wrote:If the TV is off you can use lumakeying to bring back the original reflections making it easier to make a realistic composit.

There is an easier way too, simply add (plus) the screen graphics. Since screen is emissive, emit light is added to all the reflections and plussing keeps the original strength of reflected light.

Both Silhouette and Mocha are unneeded for simple roto, thus the analogy I brought up. I'd suggest to not grab for compicated solutions for solving simple problems.
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