Blue Screen really necessary ??

4 replies [Last post]
Mamute
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Joined: Jul 23 1999

Hello !!
Is the blue / green screen really necessary to mix (paste) one scene in the other ..?
Isn't there any way with software to "paint" the scene were the Blue Screen would be , to do the same effect ?
I know it is possible by painting each frame by frame but it gives a lot of work/time..Is there any simple way ??
Tks in advance!!!

Another .. thing ...does a yellow flurescent paper do the same job as a Blue Screen?Because i don't know what they are made of ...TKS!!

Christian Lett
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Joined: Apr 26 1999

Hi,

Of course, you can paint each frame (mask) but this will take absolutely ages! Better to take time setting up the shot with a blue or green screen and retouch the odd frame when needed. Best conditions for shooting these kind of FX are bright but completely overcast days because of natural lights with no shadows (shadows will ruin a bluescreen shot). Unless you're using completely pro lighting gear, it's unlikely you'll get a completely uniform blue but the computer gives you a bit of leeway on this if needed.

Yellow fluorescent paper could work but I wouldn't use it - for a start, anything light yellow in colour on your subject will end up being invisible. Secondly, an area too brightly lit may end up looking overexposed (ie. white) and that won't work either. If you want to use a solid background, paint a board with professional blue/green screen paint (£15 a pot from Stage Electrics). We use a big blue cotton sheet which works okay but we'll be trying other methods soon.

The colour should be as near to pure as possible - go into Paint and draw a block of pure blue or green and this will give some indication.

Hope this helps,

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Christian J. Lett
[email=clett@nationalexpress.co.uk]clett@nationalexpress.co.uk[/email]

Christian Lett After Effects and Maya Artist www.quarterlightpictures.com

Mamute
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Joined: Jul 23 1999

Thank you very much for your reply..i'll try to do what you suggested!!

Bye!

Shaun Tregear
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Joined: Apr 17 1999

There is a way to do this if you are shooting a moving subject against a static background. The camera has to be static with no movement at all, so that the background doesn't change or move at all.

You start by shooting the background on its own as a reference shot.

Then shoot your scenes as normal making sure that you do not move the camera at all from the position that your reference shots were taken from.

When you are in the edit suite you export a single frame of your reference shot for use as a matt.

All of these instructions are for Premiere although you should be able to do this in any good application.

Place your footage on the superimpose video track and choose transparency from the clip menu.

Choose Difference Matt as a Key type. Choose your saved reference frame as the key image. Select the reverse Key option to key out the static background.

Now your Video clip to be used as a background can be placed in one of the normaal video tracks.

Render it and with any luck it should look akay.

Check out page 270 of the Premiere 5 manual for reference to this technique.

Christian Lett
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Joined: Apr 26 1999

Was on the phone to Bristol Paints Ltd. yesterday (0171 624 4370), web address http://www.bristolpaint.com/ about their studio paints, specifically chromakey colours. The guy I spoke to (Glynn - very helpfull) explained that the blue/green screen paints are all very matt finishes for a more even colour. They're quite expensive though (£34.74 for 4.5 litres although this might be cheaper than Stage Electrics - I got the price wrong in my last post!!)

He told me that Chromakey Blue and Video Blue (their equivalent of Ultimatte Blue) are very similar (Ultimatte is a company who specialise in Blue/Green screen compositing) but the differences in the green paint are huge, with Video Green being slightly luminous, and therefore more expensive (£50 for 4 litres I think).

This is the proper stuff to go for. If you're interested, phone them and they'll send you a colour swatch.

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Christian J. Lett
[email=clett@nationalexpress.co.uk]clett@nationalexpress.co.uk[/email]

Christian Lett After Effects and Maya Artist www.quarterlightpictures.com