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Compositing: How to fly!

Posted: Tue, 15th Apr 2008, 4:02pm

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Simon K Jones

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Rating: +12


Introduction

Minimum requirements:

1 hero
1 greenscreen
1 armless/backless seat
1 cloudy background video
1 powerful fan
FXhome CompositeLab Pro


Recommended requirements:

1 superhero
2+ greenscreens
1 stool
1 cloudy background video
1 large, powerful fan
1 greenscreen suit + operator with no self esteem issues
FXhome VisionLab Studio


Flying has always been the holy grail of visual effects shots, with hundreds of different techniques designed and refined over the years. Peaking for a while with complex front projection systems in the late 70s, as employed in the Superman films, it wasn’t until the advent of digital compositing that convincing flying was possible for low-budget indie filmmakers.

These days, all you need is a decent greenscreen and a compositing program such as FXhome VisionLab Studio. For this tutorial we’ll be looking at an ambitious 'Supergirl' clip:

Supergirl flying!

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It’s always vital to plan an effects shot in advance. For the Supergirl clip we knew we wanted the girl to fly towards the camera, approaching from a distance, move around the screen and then fly off and past.

Given that our budget didn’t allow for an aerial shoot and our schedule didn’t leave us enough time to create a CG shot, we instead opted to buy a piece of stock footage to use as the sky background. If you need to save funds and have the required skills you can use various 3D packages to create similar results.

Here’s the background plate we selected:

Original background plate

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We first reversed the clip, which is easy in VisionLab – simply click the clip’s name on the timeline to display its properties in the toolbox, then activate the ‘Reverse’ option.


The movement of the superhero would determine the nature of the live action shoot and we wanted to have a firmer idea of what would be needed. To achieve this an extremely basic animatic was created in VisionLab using the neon light engine. With some amusingly simple animation a general sense of the final shot’s appearance was decided upon:

Animatic

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From the animatic it was then possible to work out how the camera needed to move in the greenscreen studio. When the animatic’s blue stand-in moves to the right of the frame, for example, the camera would need to move to the left in order to create the correct perspective shift.

The shoot

The first rule of greenscreen is: You can never have enough. Even if you think you’ve got enough, you’ll always want more. The more you have, the more angles you can shoot from. However, even if you only have a small greenscreen you can still create amazing visual effects with careful planning.

The second rule of greenscreen is: Check your lighting. You want a smooth, vivid green with no shadows, creases or bright highlights. The better your greenscreen set-up, the easier the compositing will be later.


Because we like a challenge our greenscreen is actually lit quite poorly – there’s a huge variation of shades and lots of folds and creases. It’s nothing that VisionLab can’t handle, but as the old saying goes: Do as we say, not as we do!

Our studio consisted of three greenscreens, comprising two walls and one floor. The stands and fabric were supplied by Tubetape.com, who offer some pretty cool deals. This arrangement gave us a large amount of green real estate while still allowing for easy camera access. We also used a couple of powerful fans to blow the actress’ hair and costume about as if she was moving quickly through the air.

Originally we had hoped to film it in one shot, with the actress standing and looking up while the camera moved around her. This soon proved impractical due to the low ceiling and a lack of any kind of steadicam system. The backup option was to film the shot in several individual pieces that would be stitched together in VisionLab.

The fly-in

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This was the easiest part of the entire effect. Filming the girl standing still in the ‘Supergirl’ pose enabled us to then rotate and shrink her down to create the illusion of her flying in from the side.

The approach

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After the fly-in, we switch to a completely new angle for the approach. The actress lay on a chair which was also covered in greenscreen material. Particular care has to be taken with the lighting around this area, which can easily become far too dark.

This shot continues until she disappears behind clouds near the end. An additional piece was filmed to help blend the ‘fly-in’ and the ‘approach’ shots together. This was by far the most complex of the shots, with the camera moving in different directions to create the required perspective that would match the background plate.

In an ideal world both the greenscreen element and the background plate could be custom creations, which would make syncing them together far easier and provide a greater degree of control.

The exit

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Similar to the ‘approach’ shot, this provided a slightly different angle for the emergence from the clouds and the final exit from the frame.

Keying

After importing the various media files to VisionLab, the next step is to lay them out on the timeline. You can tighten up the edit at a later stage, as the effects shot evolves.


The result is a rough sequence of the clips without any real sense of what the finished shot will look like.

The greenscreen now needs to be removed. This is easiest using VisionLab’s auto-colour difference key. A spot of key grading and an erode white filter was used to improve the final key:

Final key

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A simple, square garbage matte was used to remove the unwanted areas of the set.


Finally the ever-useful light spill filter was applied, enabling the brightness of the clouds to interact with the greenscreen layer.



Animation

Once all the clips are fully keyed, it’s time for some animation. Convincing animation is the most important element of a shot like this.

The fly-in
As with the shoot, this was pretty easy. The shot needed to be scaled down to about 10% of its normal size, rotated 90 degrees and then positioned to fly in from the left. The only challenge here was determining the speed of the fly-in, when seen in conjunction with the moving backdrop.

Seguing from the fly-in to the approach was trickier than expected due to the different camera angles involved. In retrospect we really needed a more suitable ‘in-between’ segment to use as a bridge.

Instead, we blended three separate pieces together to create the illusion of the girl turning towards the camera, fading from one to another using the transparency filter and carefully rotating each piece as required.

A close look at the turn, blending several elements together

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The approach
This should have been an easy section, essentially only requiring a gradual scaling up of the girl while moving from right to left. Unfortunately the angle of the actress’ arm didn’t match up as intended with the direction of flight.

With a re-shoot not possible, instead we created a second copy of the greenscreen clip on the VisionLab timeline, then isolated the girl’s arm using an animated mask. We then had a floating arm that we could manipulate as required.


After also masking out the arm on the original clip, we were able to apply the new arm in any position we required. Some subtle rotation soon had the arm pointing forwards convincingly. When the girl reaches the foreground of the shot, the fake arm then blends seamlessly back into the real arm.

This example neatly highlights the importance of planning: if we’d known with more accuracy the angle of approach, we would have identified this problem on set and thus removed the need for a time-consuming post-production ‘fix’.

On the other hand, it does show how VisionLab’s tools can come to the rescue. smile

The exit
The last two pieces were blended together loosely, with the switch covered mostly in cloud. The details of creating convincing cloud interaction will be covered later in this article.

Overall the shot required some very precise animation, but this need not be the case. Design the shot to suit your own abilities and the time scale and budget of your production.

Motion blur

Any shot involving digitally animated elements is likely to need artificial motion blur. It’s a vital part of making composited elements feel natural as it blends elements together and introduces imperfections that we subconsciously expect to see.


VisionLab’s ‘blur: angle’ filter was used in this case to create varying amounts of directional blur, dependent on the animation. It’s a subtle effect but really helps to sell the shot.

Clouds

Any effects shot lives and dies on the interaction of its various elements. In this case, the girl needed to appear to be moving through the clouds, not just composited on top. Creating a particle effect that exactly matched the clouds’ appearance and movement wasn’t going to happen, so instead this was achieved using a combination of particle effects and a specific type of masking called an ‘object mask’.

The technique of object masking involves taking the transparency information from one object and applying it to another - in this case we would take the transparency of a particle effect and apply it to the greenscreen layer.

The first step was to create a particle effect that approximated the movement and density of the clouds. It didn’t have to be precise or realistic in actual appearance, which made thing a lot easier! As long as the emitter was pushing out the particles in the right place and at the right kind of density to simulate what was in the background plate it would work. Here’s what the raw particle effect actually looked like:

The raw particle effect - not particularly convincing (yet!)

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An object mask now needed to be applied to the greenscreen layer. This can be done using the ‘Mask’ toolset, by selecting the ‘object mask’ shape. The object mask then needs to be linked to the appropriate object, which in this case was the particle effect. The result is that the transparency of the particles makes the girl become semi-transparent as they flow over her.

With the particles turned off, it is possible to see how the object mask is affecting the girl.

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Once everything was linked up, the particle effect object itself was turned off. This meant the actual particles would be invisible, and we’d only see them indirectly through the effect they had on the greenscreen clip, revealing the clouds underneath and creating the illusion of the clouds passing over and around her.

Simple when you know how, right?

More fun stuff

For the Coalition of Heroes flying shot (which you probably noticed re-used the same stock background!) we had some problems with our fans, which proved to be vastly under-powered when it came to blowing the actor’s hair and shirt about convincingly.

The impromptu solution was simple and extremely amusing: we put a member of the crew into a greenscreen suit, positioned him behind the actor and got him to physically move the guy’s shirt with his hands. In terms of compositing, it was no more complicated to key out the suit than it was the general greenscreen background.

One of the main benefits of this technique is that it's extremely, extremely funny on the set:

There's nothing funnier than a man in a greenscreen suit, other than that same man wiggling another man's shirt.

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The finished shot can be seen at the end of the Coalition of Heroes short film (note: features scenes of slightly rude comedy and mild peril):


While greenscreen suits are most often used for ‘invisibility’ effects, they can also be used for more subtle purposes such as this. You never know when you might need a greenscreen suit to come to the rescue!

Hope you enjoyed this tutorial.

Last edited Wed, 4th Jun 2008, 12:32pm; edited 1 times in total.

Posted: Tue, 15th Apr 2008, 4:22pm

Post 2 of 19

Ste

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Hey, great tutorial, would never of thought of the object mask and loved the mixing of the girl from different angles. *****
Posted: Tue, 15th Apr 2008, 4:53pm

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Redhawksrymmer

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SuperUser

Really cool stuff, great incorporation of the small films in the tutorial smile
Posted: Tue, 15th Apr 2008, 7:09pm

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Qbeck

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i have a really small, quick shot of me flying, using a tiny green screen and a chair turned sideways, not even a fan, as this was mainly just a chroma keying test. The part that I'm really proud of is I simulated the cloud 's mask's opacity getting smaller so i went through the cloud. I DO realize my garbage matte was a bit rushed.

http://youtube.com/watch?v=zbVn2SeiaJk&fmt=18
Posted: Tue, 15th Apr 2008, 9:04pm

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rudemen

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Absolutely well done!
After nearly guessing fxh´s becoming an "Asing the the same questions again"-forum, I´m impressed.
Should help asking the same questions again.

Indeed great implementation of the moving little pieces.

Great educational value.

Well done!
Posted: Wed, 16th Apr 2008, 2:39am

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Rockfilmers

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Gret tutorial! The object mask was a great idea for this case. I would would have put the cloud layer on top of the all the layers and set it to screen and made a basic mask around the girl, but your way was probaly better. Is there a way that we could down load the video clips so we can follow the tutorial?

btw, the flash clips on the page only show up in half the window box, the rest is just grey
Posted: Wed, 16th Apr 2008, 8:11am

Post 7 of 19

Simon K Jones

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Rockfilmers wrote:

Gret tutorial! The object mask was a great idea for this case. I would would have put the cloud layer on top of the all the layers and set it to screen and made a basic mask around the girl, but your way was probaly better. Is there a way that we could down load the video clips so we can follow the tutorial?
That'll be tricky for this particular tutorial, due to the number of (HD) clips, and we don't have the rights to distribute the cloud background in original form. However, for future tutorials I'll try to make sure that there's downloadable stuff you can play with. smile

btw, the flash clips on the page only show up in half the window box, the rest is just grey
Odd, what browser are you using?
Posted: Wed, 16th Apr 2008, 2:53pm

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TubeTape

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Awesome tutorial Tarn. Seems like a lot of folks want to be able to do this type of an effect. The clips and images make it easy to understand the multiple techniques used.
Posted: Wed, 16th Apr 2008, 10:10pm

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Videoace123

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Great tutorial, and Ive always wondered how you did that, so the tutorial was very helpful!
Posted: Thu, 17th Apr 2008, 1:47pm

Post 10 of 19

Rockfilmers

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That'll be tricky for this particular tutorial, due to the number of (HD) clips, and we don't have the rights to distribute the cloud background in original form. However, for future tutorials I'll try to make sure that there's downloadable stuff you can play with.
OK, that's easy to understand. About the wierd video half box thing, it was just that onr time, it's fine now. just a little weird thing that happens every now and then.
Posted: Thu, 17th Apr 2008, 3:05pm

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MetroCityMayor

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thanks for this EXCELLENT posting. Just in time too as I am planning a flying scene. You must be a mind reader!

many thanks,
The Mayor, your humble servant.
Posted: Sun, 11th May 2008, 10:17am

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v3rlon

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Excellent tutorial. Mind sharing where you found that backdrop? I haven't had much luck finding anything so useful for flight.
Posted: Wed, 14th May 2008, 1:05pm

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Simon K Jones

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We got the background from iStockPhoto.com.
Posted: Thu, 5th Jun 2008, 1:17pm

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Menehune Jedi

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love this tutorial will be doing our Mandolorian jetpack flight soon!
Posted: Mon, 1st Sep 2008, 3:35pm

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Wares007

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Can i download that cloudy background video of your tutorial?
Posted: Mon, 1st Sep 2008, 4:18pm

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Axeman

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SuperUser

You can buy the cloudy background from iStockphoto.com, which is where they bought it from.
Posted: Tue, 9th Dec 2008, 11:01am

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DVStudio

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Great tutorial Tarn! Thanks.
Posted: Tue, 9th Dec 2008, 10:45pm

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AwesomeFist

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DVStudio wrote:

Great tutorial Tarn! Thanks.
agreed. biggrin
Posted: Sat, 10th Jan 2009, 3:10pm

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cavickers

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OK, that's easy to understand. About the wierd video half box thing, it was just that onr time, it's fine now. just a little weird thing that happens every now and then.
i agree