The Use of "Green Screen"

[S.A.C Martin]

Some of you may be aware I film my model trains for videos I make on youtube (see signature for details). However I have a very confined space with which to work with, and have found it difficult to write stories which are away from the shed area - for the simple reason I don't have a large enough set to work on!

 

This video

- where a film maker uses game footage to create a background, then used for shots with green screen, got me thinking carefully.

 

If I were to set up a straight section of track, ballasted - and set a particular angle for the camera - could I put a green screen behind it and then use still photographs or similar to make a scene look more realistic?

 

By this, I mean the background - the green screen - would take on the still photograph's qualities, while the train itself moves through the "model" landscape as per normal.

 

This would allow me to photograph real locations and then use them within my films (possibly...)

 

Is this possible, purely from a film making point of view?

 

With regards the photography of the piece, it could be that I could go to a location like King's Cross - take some photographs, modify them to look more like 1960s Britain, and then have the model trains running into King's Cross in this way.

 

Green Screen equipment is expensive to indulge in, however my thoughts are that if it takes cost away from building separate sets everytime I want to shoot certain sequences, it must be better in the long run?

 

Thanks in advance for reading my thoughts, gents.

[S.A.C Martin]

A small "bump" in case of interest.

[Pacific231G]

Some of you may be aware I film my model trains for videos I make on youtube (see signature for details). However I have a very confined space with which to work with, and have found it difficult to write stories which are away from the shed area - for the simple reason I don't have a large enough set to work on!

 

This video

- where a film maker uses game footage to create a background, then used for shots with green screen, got me thinking carefully.

 

If I were to set up a straight section of track, ballasted - and set a particular angle for the camera - could I put a green screen behind it and then use still photographs or similar to make a scene look more realistic?

 

By this, I mean the background - the green screen - would take on the still photograph's qualities, while the train itself moves through the "model" landscape as per normal.

 

This would allow me to photograph real locations and then use them within my films (possibly...)

 

Is this possible, purely from a film making point of view?

 

With regards the photography of the piece, it could be that I could go to a location like King's Cross - take some photographs, modify them to look more like 1960s Britain, and then have the model trains running into King's Cross in this way.

 

Green Screen equipment is expensive to indulge in, however my thoughts are that if it takes cost away from building separate sets everytime I want to shoot certain sequences, it must be better in the long run?

 

Thanks in advance for reading my thoughts, gents.

I'm not sure that you need expensive green screen (or perhaps better blue screen) equipment to achieve this so much as having this capability fairly well realised in your video editing sofware.

 

The actual use of a colour as a keying source is mostly about getting fairly even lighting onto a suitable back drop that doesn't spill forward onto the set. I suspect blue (which used to be the norm in television chroma-key before green became more popular) may be better than green as a keying colour for a model railway based scene as our scenery naturally contains a lot of green in the form of grass, vegetation etc.

[S.A.C Martin]

I'm not sure that you need expensive green screen (or perhaps better blue screen) equipment to achieve this so much as having this capability fairly well realised in your video editing sofware.

 

The actual use of a colour as a keying source is mostly about getting fairly even lighting onto a suitable back drop that doesn't spill forward onto the set. I suspect blue (which used to be the norm in television chroma-key before green became more popular) may be better than green as a keying colour for a model railway based scene as our scenery naturally contains a lot of green in the form of grass, vegetation etc.

 

I think I understand - making the light even over the set and onto the backdrop is key. I have been playing around with the Pinnacle Studios green screen formatting, and it hasn't quite come out well on - well - green! Should I be looking at perhaps different software as the scale of filming is perhaps smaller than pinnacle is intended for?

[Mr Lizard]

Ok, I'll have a go at answering this, as a CG artist I have experience of compositing, although usually that entails putting CG on to a live action backplate.

 

Firstly, I would say that it could work, but there many things to consider...

 

Matching the camera:

Avoid moving cameras as it would be close to impossible to match a camera move from one shot to another.

Matching perspective between shots would be difficult, especially considering the difference in scale were you to use model locomotives and real life backdrops.

Also the scale discrepancy would make the depth of field hard to match.

 

Matching the lighting:

Again this would be tricky to get right - perhaps your best chance at an acceptable result would be to shoot in natural daylight on an overcast day, to minimise strong shadows.

 

The reason blue or green screens are used is that these colours are least likely to occur in skin tones. As already mentioned above, with locomotives and stock which may well be green themselves, keying out the green is clearly not going to work. You should choose a key colour which occurs the least in your subject. Also light the scene in such a way that the background is evenly lit and free from highlights and shadows, and try to avoid colour spill, that is reflected light from the background spilling on to the subject.

 

It may be that this is all too much hassle for the effect you want to achieve. Many of these issues could be avoided if you only use shots where there is a clear disconnect between the foreground and background, but that could be too limiting for you. Have you considered the "machinima" approach, perhaps using one of the many train simulators available to create footage?

[S.A.C Martin]

Ok, I'll have a go at answering this, as a CG artist I have experience of compositing, although usually that entails putting CG on to a live action backplate.

 

Firstly, I would say that it could work, but there many things to consider...

 

Matching the camera:

Avoid moving cameras as it would be close to impossible to match a camera move from one shot to another.

Matching perspective between shots would be difficult, especially considering the difference in scale were you to use model locomotives and real life backdrops.

Also the scale discrepancy would make the depth of field hard to match.

 

Matching the lighting:

Again this would be tricky to get right - perhaps your best chance at an acceptable result would be to shoot in natural daylight on an overcast day, to minimise strong shadows.

 

The reason blue or green screens are used is that these colours are least likely to occur in skin tones. As already mentioned above, with locomotives and stock which may well be green themselves, keying out the green is clearly not going to work. You should choose a key colour which occurs the least in your subject. Also light the scene in such a way that the background is evenly lit and free from highlights and shadows, and try to avoid colour spill, that is reflected light from the background spilling on to the subject.

 

Thank you for all of the above - much to think about. I don't use a moving camera in any of my shots, in 4mm scale the movement doesn't scale well. I will do some experiments using your suggestions above and see how it comes out Thank you for taking the time to reply.

 

I must admit, the depth of field was one concern I had not thought about.

 

It may be that this is all too much hassle for the effect you want to achieve. Many of these issues could be avoided if you only use shots where there is a clear disconnect between the foreground and background, but that could be too limiting for you. Have you considered the "machinima" approach, perhaps using one of the many train simulators available to create footage?

 

The problem is that my series has a very definitive style - somewhere in between Thomas and Tugs in terms of how it is filmed and the characters appear. Switching to CGI would lose that part of its appeal, and in any event machinima videos on Youtube are ten a penny (though I thank you kindly for the suggestion, it was a good suggestion).

[LNERandBR]

I did some green screaning as part of my Uni course.

 

The biggest problem we faced was ensuring the screen was lit correctly. It idealy needs to be all the same tone any variations like shadows cause problems when it comes to getting rid of the green screen.

 

Also stuff like smoke from your smoke units like the one in your character Stephen will be impossible to retain when you get rid of the Green background. The main problem we had at this point was hair, getting a natural non hard edge to it.

 

 

I've ofton thought when watching your vid's what happens behind the carrage works. I know the loop of track for the 'mainline' will loop round to come out behind the shed but how much space is there behind there. Could you create a small amount of countyside there for a few mainline shots. I guess it would be very narrow.

[mikesndbs]

Just entering this world today