Thread: Could use some insight from those who do VFX

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  1. #1 Could use some insight from those who do VFX 
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    Hello,

    I have 3 live action shots with 3 different characters played by the same actor that was shot (single camera) with the intention of combining them via "seamless" split screens into a wide shot.

    You've seen this before where one actor plays multiple roles in the same frame
    https://www.youtube.com/watch?v=jFoUWFmM-NU


    Thankfully it was shot with a locked off camera but unfortunately they varied the angles a bit, so it's not as simple as just split screening the 3 shots into 1 and calling it a day. By doing that there would be noticeable seams at those points like a wall clashing into a table.

    2 of the angles are close enough that I think with some reframing I can get those to match close enough that a simple split screen may work; but the other angle is almost a 30 degree difference and the elements that all the shots share like a wall/table are a different perspective.

    I almost imagine I may need to do something akin to those photo panoramas where they stitch multiple shots together (albeit this is with video) or maybe rototscoping/masking (using after effects) one character from their angle and insert it into the other shot?

    Are there any tutorials one can recommend to tackle such a problem or if you have some general advice on how best to accomplish this?


    Thank you
    Last edited by Joe Riggs; 09-25-2019 at 04:24 PM.
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  2. #2  
    If the perspective is off between takes. Then you might need to roto out the person from all but one take which you use a your back layer and then composite in the other layers with tight mattes.

    If the camera is in the same nodal point then you can use ptgui or similar ap to merge the different plates into the same canvas.
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  3. #3  
    Senior Member Zack Birlew's Avatar
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    Without seeing the shot, it sounds like it was indeed filmed improperly. The camera would have to be locked off like you say but if furniture is being moved around, bedsheets/curtains/tablecloth/etc. being ruffled around by action in the scene or crew in between takes, time of day changes too drastically, anything like that that won't match from the first take, then you're looking at either a big compositing job of rotoscoping every altered object or doing a reshoot of the scene. The effect is simple, yes, but there's a practical and technical aspect to it depending on what you're doing, even the big studios struggle with this, look at the "Paranormal Activity" series which is loaded with shots like this and some even with continuity mistakes and errors too.

    There should be no different angles, that's a whole new shot if the camera had to be moved or putting on a different lens or zooming in, there is no "going back to one" if the image is altered despite being locked down on a tripod.

    Now, if you're talking about the eye line being off with the performer then that's a performance and staging issue that you can only solve by rotoscoping the actor as best you can and adjusting them in frame, if possible, otherwise, again, it's a reshoot. I know the pain of this as we have some shots in my first feature that I'm editing right now that has some greenscreen shots that simply won't work because of small continuity mistakes and staging problems so we had to improvise and adjust things for the reshoots we did a few weeks ago. Thankfully, those turned out great and now things work but, yeah, VFX like this can be really tricky so don't feel bad if you do ultimately have to do a reshoot.
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  4. #4  
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    Quote Originally Posted by Joe Riggs View Post
    Hello,

    I have 3 live action shots with 3 different characters played by the same actor that was shot (single camera) with the intention of combining them via "seamless" split screens into a wide shot.

    You've seen this before where one actor plays multiple roles in the same frame
    https://www.youtube.com/watch?v=jFoUWFmM-NU


    Thankfully it was shot with a locked off camera but unfortunately they varied the angles a bit, so it's not as simple as just split screening the 3 shots into 1 and calling a day. By doing that there would be noticeable seams at those points like a wall clashing into a table.

    2 of the angles are close enough that I think with some reframing I can get those to match close enough that a simple split screen may work; but the other angle is almost a 30 degree difference and the elements that all the shots share like a wall/table are a different perspective.

    I almost imagine I may need to do something akin to those photo panoramas where they stitch multiple shots together (albeit this is with video) or maybe rototscoping/masking (using after effects) one character from their angle and insert it into the other shot?

    Are there any tutorials one can recommend to tackle such a problem or if you have some general advice on how best to accomplish this?


    Thank you
    Hey Joe,

    I'll agree with Zack that without seeing the shot it's hard to discern how salvageable it is, however, if the shot is locked off you can build a clean plate from various frames and use that to build a difference matte for the FG character. That can save you time for generating full body articulate roto. Depending on the alpha it can be crude or could be more usable than you think. All depends on the difference in color/contrast/detail of the BG that the FG character is traveling over. My suggestion would be to generate that difference matte of the character that's the farthest off from the other plates, and once he's extracted repo him back into place and see if it works. Sometimes its easier to fake perspective with people than with furniture depending on how extreme the perspective is. Another quick approach is to look into rotobot for nuke. There's a license but you may be able to rent it for a couple of days to just generate an AI generated garbage matte. Sometimes it's more usable than you would think. FXPHD has some tutorials as well as I'm sure youtube does as well for generating difference mattes in Nuke. However that is just to generate the alpha for the character. If the BG is really far off and you're able to get away with the difference in perspective, the next challenge will be in the edge work after you are able to generate a good alpha/roto/diff key. If the FG character is going over say a bright box or couch in the plate thats off in perspective, you might see that in the edge of the character when you put them over the new plate and the BG doesnt line up. That you can fix with a combination of good edge exend tools/techniques, color correction and paint. I hope this helps and good luck!
    Last edited by John Brennick; 09-25-2019 at 04:16 PM.


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  5. #5  
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    Quote Originally Posted by Björn Benckert View Post
    If the perspective is off between takes. Then you might need to roto out the person from all but one take which you use a your back layer and then composite in the other layers with tight mattes.

    If the camera is in the same nodal point then you can use ptgui or similar ap to merge the different plates into the same canvas.

    Interesting, I'm not familiar with the nodal point I'll have to look into that.

    To respect the client's privacy I don't want to upload full frames but you can see the difference in the angles from this section of the table below. One is more head on, the other comes into the camera (please ignore the color).

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    Senior Member Zack Birlew's Avatar
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    And this is all in one shot? If it's just the table moved between plates and not the camera, then you would definitely have to do some compositing and decide which table image you want to separate the clones and, again, if that chosen furniture position works for all the clones in the shot. If it's trying to cut two or more shots together (ie. one clone in the middle talking to a clone on the right and one on the left but VFX combined all in one shot, yet filmed at three different angles) then I would imagine that's not going to work just based on eye lines and would have to be partially reshot, in this example, with the middle clone looking left and right in the same perspective and not as two side angles. If it's an editing thing, then you could use a clone as a foreground/background object (ie. One clone talking while another is standing in front of him in a post zoomed OTS shot and blurred in the foreground). Again, without knowing the context and layout of the shot or shots, it's hard to offer a gameplan.
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  7. #7  
    reshoot
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  8. #8  
    REDuser Sponsor Gunleik Groven's Avatar
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    Quote Originally Posted by Remington Chase View Post
    reshoot
    If possible, this is probably what will make it happen.

    A camera is either locked off, or it is not.

    If not: Add tons of competence and time
    If locked off and controlled lighting: Ah, you just hit the happy-hour
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  9. #9  
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    Reshoot or not, seems like you have your hands full. Where you present during the shoot?
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  10. #10  
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    Quote Originally Posted by Gunleik Groven View Post
    If possible, this is probably what will make it happen. A camera is either locked off, or it is not.
    If not: Add tons of competence and time
    If locked off and controlled lighting: Ah, you just hit the happy-hour
    I agree with Gunleik. When I've been involved with VFX projects with complex split-screens and so on, they either had the camera locked off with heavy sandbags and weights, or they had a motion-controlled rig that could repeat the moves effortlessly all day. It still needed some roto to fix shadows, small lighting issues, and so on, but a piece of furniture moved that far out of position... that's not gonna work.
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