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Chroma key with S16


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I'll be shooting a small art film in a few weeks which juxtaposes the environments of city and nature. The opening shot will start as a view of mountains where we get a chance to breathe in the environment before we zoom out to reveal that what we're seeing is a reflection onto a shard of mirror held by a girl standing on a rooftop in an urban environment.

 

The question is if it makes more sense to cover a piece of glass with a chroma key sheet of paper or just to spray paint it black (or green for that matter) and add some tracking marks?

 

We'll be shooting super 16 on the Aaton XTR. Is there anything else we should keep in mind?

 

I've attached a reference shot!

 

Thanks in advance!

post-64329-0-24520700-1551776971_thumb.jpg

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Its probably possible to track without any colour but I guess you could risk loosing the edges - if it reflects something of similar density to background.

 

Covering it with a colour thats distinct enough from the surroundings would make life easier. It also depends where the actors fingers are, if they don't go in front of the mirror then a simple corner pin track would work and its simple. If the edges of the shard are crisply in focus they can serve as their own tracking marks if contrast is good.

 

Otherwise its Keying or Roto of some combination of to cut round the fingers- might get tricky if the hands cast a shadow on the glass.

 

Also Super 16 can be less good for comping if your using faster stocks. So use the slowest stock you can get away with to give you as much detail and small amount of grain to work with.

 

The issue in your reference shot is the shard of glass is out of focus - that may make comping difficult. But it might look weird if the reflected mountains are in focus and your shard is in focus at the same time - it would be two points of focus unless you settled for very deep DOF.

 

If you want the soft edges of the shard like the photo. It might be a case of shooting the glass in focus and digitally defocusing it after the comp - leaving the mountains sharp.

 

Are you going to do a focus pull - e.g from the infinity of the mountains to the hand and the shard? Again I'd do that in post - It won't work as well in camera - if the shard is out of focus, you have to guess at where the edges are to insert the comp. Deep DOF may be the answer. -

 

Considering your plane of focus is important.

 

test test test.. easily done digitally to see what works prior to burning film stock

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I'd almost suggest doing it live with a big photo blow-up of the mountains on posterboard to reflect into the mirror, that way you'd have the correct focus rack from reflection to mirror. As the reference shows, when you focus on the reflection you are also focusing on the deep background behind the mirror though a photo blow-up won't be as far away.

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Its probably possible to track without any colour but I guess you could risk loosing the edges - if it reflects something of similar density to background.

 

Covering it with a colour thats distinct enough from the surroundings would make life easier. It also depends where the actors fingers are, if they don't go in front of the mirror then a simple corner pin track would work and it simple. If the edges of the shard are crisply in focus they can serve as their own tracking marks if contrast is good.

 

Otherwise its Keying or Roto of some combination of to cut round the fingers- might get tricky if the hands cast a shadow on the glass.

 

Also Super 16 can be less good for comping if your using faster stocks. So use the slowest stock you can get away with to give you as much detail and small amount of grain to work with.

 

The issue in your reference shot is the shard of glass is out of focus - that may make comping difficult. But it might look weird if the reflected mountains are in focus and your shard is in focus at the same time - it would be two points of focus unless you settled for very deep DOP.

 

If you want the soft edges of the shard like the photo. It might be a case of shooting the glass in focus and digitally defocusing it after the comp - leaving the mountains sharp.

 

Are you going to do a focus pull - e.g from the infinity of the mountains to the hand and the shard? Again I'd do that in post - It won't work as well in camera - if the shard is out of focus, you have to guess at where the edges are to insert the comp. Deep DOF may be the answer. -

 

Considering your plane of focus is important.

 

test test test.. easily done digitally to see what works prior to burning film stock

 

Great advice! Thank you, Phil! Changed my film order to a few rolls of 50D in order to get a slower stock.

Edited by Kaspar Kamu
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I'd almost suggest doing it live with a big photo blow-up of the mountains on posterboard to reflect into the mirror, that way you'd have the correct focus rack from reflection to mirror. As the reference shows, when you focus on the reflection you are also focusing on the deep background behind the mirror though a photo blow-up won't be as far away.

I'm just scared that that would compromise the realism of the shot. We're not sure if we're going to have the mountains or the city in the reflection. Or both separately. If it's the city we could get away with it with sound design, etc. But with the mountains I'd like to see trees moving, birds flying, clouds changing and so on.

 

Not a bad idea though.

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OK but if you want realism, your vfx compositor will have to be really good to add the imperfections of reflecting something in glass, racking focus, etc. I would suggest shooting this shot on a digital camera or 35mm because a chattering matte edge from 16mm grain is going to detract from the realism. I guess you have no choice but to composite if you want to start full frame inside the mirror on the view before pulling back and revealing that it is a reflection, and adding the surface imperfections of the glass, etc. Also, it would help if the mirror was as rigid as possible rather than actually being handheld.

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I'd almost suggest doing it live with a big photo blow-up of the mountains on posterboard to reflect into the mirror, that way you'd have the correct focus rack from reflection to mirror. As the reference shows, when you focus on the reflection you are also focusing on the deep background behind the mirror though a photo blow-up won't be as far away.

I did also think "Big LCD TV" and do the shot in camera. If the mirror was held at 45 degrees pointing down the screen could be placed horizontally - in a "peppers ghost" arraignment. The trick would be to make the mirror not look like its held at an angle, I guess if the DOF was shallow enough it would be soft enough.

 

I guess their is more flexibility to adjust the shot in post and you could decide how sharp the mirror is and retime and rack focuses - but that would need some skill on the compositors part.

 

The other thing I would do in this situation is ask the compositor what would they prefer. They will be happy to tell you what elements they need.

 

If your comping it yourself - then I'd spend sometime practising in AE prior to the shoot to see what results your able to get.

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  • 2 weeks later...

I love you idea David. My experience is anything you can shoot on the set is better than dealing with it later. You will also have to transfer without any gate weave, or duplicate it in the matte. Shooting the effect live on set you won't have to worry about that.

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12 hours ago, Tim Smyth said:

I love you idea David. My experience is anything you can shoot on the set is better than dealing with it later. You will also have to transfer without any gate weave, or duplicate it in the matte. Shooting the effect live on set you won't have to worry about that.

Yes, for sure! We decided to go for Mr. Mullen's idea in the end! 

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