Green screen background

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BrockleyAndrew
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Green screen background

Postby BrockleyAndrew » Tue Feb 02, 2021 12:46 am

I was just wondering about the background to a railway scene and thought about the theatrics of the H Potter Experience (having endured two offspring visits involving waiting for the shuttle bus - one enlivened by a standoff between a Drunk and an Anti-witch evangelist, not pleasant for my 8yo but entertaining in retrospect) and thought how the green screen is available for movies and for paying punters in the HP experience. Would we as modellers be keen on an adaptive background?

Thoughts about lighting recently in The Burford Branch topic set me thinking. I'm also thinking about lighting a seaside branchline backscene.

Could also be idle speculation.

Has anyone done film style back projection for layouts?

Andrew

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Guy Rixon
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Re: Green screen background

Postby Guy Rixon » Tue Feb 02, 2021 10:50 am

If one were to do this successfully, two problems must be overcome.

First, the movement in the background should not call attention to the fact that the foreground is frozen apart from the moving trains. One might enhance an empty, static scene --- perhaps the fells around the S&C or Dungeness marshes --- with a moody, churning sky. People moving in the back of street scenes seems unlikely to work if the figures in the front are pillars of salt; which is a pity, as I have some serious street-scenes in prospect.

Second, the back projection has to work properly, and this doesn't "just happen". It depends on the relative brightness of the projection and the foreground, on the geometry, and on buying worthwhile kit. "Worthwhile" here doesn't mean expensive; you can't automatically sort it with more money. At work, we used to have a back-projected screen in a meeting room. Despite being very expensive, and built in by specialist contractors, it was too faint for the room lighting and refused to go at all every second meeting. It got replaced with a big telly.

All of which is not to say that one shouldn't try and I would love to see a layout with a projected background, or even an old-school cyclorama. But I think whoever does try this should first borrow some equipment to try it out.

BrockleyAndrew
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Re: Green screen background

Postby BrockleyAndrew » Tue Feb 02, 2021 12:27 pm

Thanks Guy, I looked up Cyclorama which I had a vague knowledge of and now also have sidetracked to reading on infinity screens and the use of such in studio photography/video. Interesting to read that early Cyclorama use 17th/18th C in theatre was to depict skies. I can see that competing lighting for the layout and ambient light would be a problem interfering with projected backscene and that it would probably work best from a limited viewpoint only.

Moody coastal skies would be great. I'm thinking of something simpler though and possibly using backlit translucent material, maybe tissue paper, to represent coastal haze.

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Guy Rixon
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Re: Green screen background

Postby Guy Rixon » Tue Feb 02, 2021 2:27 pm

Cycloramas in theatre are a potent source of headaches. One was used very occasionally in the theatre where my late father used to manage the technical aspects, usually for sky effects, but at least once, IIRC, for a kind of moving comic as illustration of a monologue; a little like a moving Bayeux tapestry. Bringing it into service after a long rest was fraught. They work best in theatres with very deep stages, where the cyc can be left set up and where it's not picking up shadows from the main lights. On a stage with not much back-to-front space it's harder.

Lighting effects for background haze sounds interesting. You might care to investigate painted, transparent plastic as the filter rather than tissue paper; much stronger.

If back projection could be made to work well it would be interesting to see a tramway scene with the track along the front of the layout and all the street-life behind projected.

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Guy Rixon
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Re: Green screen background

Postby Guy Rixon » Tue Feb 02, 2021 2:43 pm

BTW, one of the distinguishing features of scenery in a large and traditional theatre is it's all flown in. The backcloths drop in from flying space above the stage, as do the flats for the middle-ground scenery. Very little is actually standing on the stage. This approach makes scene changes extremely fast and easy, given enough stage hands skilled in flying. C.f. modern arrangements for small theatres where there's little vertical space, not much depth and not enough hands to fly everything at once. This leads to single-set (or single-set per act) productions and fixed scenery, sometimes made not of canvas flats but of solid wood.

So ... extrapolating those ramblings to our models: has anybody tried flying in alternative backdrops on a layout? Vertical space is abundant, and two operators could do it if the rig is well designed. One could have different cloths for day and night, or for different periods. Since weight is not a problem, one could fly in complete sets of half-relief buildings --- or even more elaborate structures. Imagine P4 New Street if the concrete sarcophagus could be flown off and the roof from the 1950s put in place. (I know, they changed the track layout before they wired and buried New Street, but you see the principle.)


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