BLUE /GREEN SCREENS

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ianmak
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WHERE CAN I BUY/OR HOW CAN I MAKE BLUS/GREEN SCREENS

Alan Roberts
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First, there's no need to shout, it's easier to read lower case than upper.

Now, about CSO colours. There's nothing magic about them, so it comes down to how you want to use them. I've seen it done all ways, from entirely painting the studio blue with emulsion paint, through blue cloth cycloramas with 200kW or more of light on it, to glass-bead cloth and coaxial leds on the camera. There are some "industry standard" matte colours, like Ultimatte Blue and Green, but they cost an arm and a leg and are no better than any other way that works. The simplest way I've used is a swathe of blue curtain material draped over a door.

So, give us a clue as to how you intend to shoot with it, and we'll give it a go.

[This message has been edited by Alan Roberts (edited 22 April 2001).]

Get my test cards document, and cards for 625, 525, 720 and 1080. Thanks to Gavin Gration for hosting them.
Camera settings documents are held by Daniel Browning and at the EBU
My book, 'Circles of Confusion' is available here.
Also EBU Tech.3335 tells how to test cameras, and R.118 tells how to use the results.

RayL
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A little off-topic, but there is a type of mousemat made with a soft, fabric surface and a foam backing which comes in a range of colours, including an excellent CSO blue. I always buy this type because it is a great way to demonstrate chroma keying during training sessions. (The mouse is superimposed over an unlikely background).

Now if this material could be bought in large rolls . . . . . .

Ray Liffen

ChrisBitz
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I stand ready to be corrected, but I think the blue/green dependence is largely related to film processing, and although we hear of 3 CCD cameras red/blue/green, with modern NLE systems, any colour can be used as the background, as long as it doesn't occur on the subject.

We recently had some success with filming a black pussy cat (awwww) with an orange plain curtain behind. I'd say that the uniformity of the lighting of the background is far more important than the actual colour.
(the yellow eyes were farily similar to the curtain, so.... we couldn't help putting a bright red mask behind them to make a DEVIL cat!) :)

Give it a try, as long as you have a background that is not patterned...

Chris.

Anonymous

I agree with Chris, as in an evenly lit background is vital to get a good result, the colour is secondary. One last thing as far as the blue/green goes, i have a freind at the Beeb who swears that you get a better quality effect with green, meaning the outline around the subject tends to blend in with the background better (a bit like the feather effect in photoshop), with bluescreen you get a faint blue outline if you look close. I have done experiments with these two colours and i have to agree with may mate at the Beeb. Hope this helps.

Alan Roberts
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The reason for using blue is that it's a colour that rarely occurs naturally in high saturation. It also allows an "excess blue" process, not just detecting the presence of blue at high saturation but of distinguishing it from other similar colours. Green is less successful because it occurs more naturally at high saturation. Orange is less satiusfactory because it's not too far from some skin colours.

None of the choices of colours has anything to do with film properties, or tv properties come to think of it. It's alkl down to the discriminablity of the colour against others in the scene.

Get my test cards document, and cards for 625, 525, 720 and 1080. Thanks to Gavin Gration for hosting them.
Camera settings documents are held by Daniel Browning and at the EBU
My book, 'Circles of Confusion' is available here.
Also EBU Tech.3335 tells how to test cameras, and R.118 tells how to use the results.

Mad_mardy
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apparently with DV green is a better keying colour. because DV is 4.2.0 it chucks away a lot of blue colour imformation but retains more green
This may not be true but the source is normally pretty reliable

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Julian
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The thing I’ve always wondered about Blue screening is this, (if I can explain myself):

Say you have a long shot of a subject in front of your keyed in background, then you cut to a close up or mid shot. Would the background you have keyed in have to cut to a close up or mid shot as well?

Which means you would have to shoot a lode of different background shots and angles.

Have I got that right or am I barking up the wrong tree.

Julian

vega1970
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Joined: Oct 10 2000

Heh...funny you should ask that,
i'm just about to start editing a scene which is shot in front of a blue wall (it's not perfect but I plan on making the bluescreen perfect by importing it to PhotoShop and getting the color right - probably long winded way but using mediastudio I find it's very fussy) then I will be placing the 'background' in place. There are three angles, and I have had to design each angle in PhotoShop for each bit. I'm not entirely sure if this is the best way but i'm new to Chroma-keying and not too hot at using MediaStudio - but it's a lot less confusing then Premiere 6.

So long Suckas !!!

Alan Roberts
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Two points:

1 The comment about green being better than blue in DV is a good observation. Since DV (in PAL lands) has 4:2:0 sampling, the chroma bandwiths is indeed less thah full broadcast 4:2:2. But the comment about retaining more green resolution than blue is definitely valid. I'd hoped this one wouldn't come up for a ling time, but it's to do with the luma and chroma coding equations, which don't observe the principle of "Constant Luminance", this means that some of the luminance you see actually travels via the chroma channel, and the amount depends on luminance. Detail in saturated blue travels over 80% via the chroma channel and so is highly attenuated, while more than 85% of detail in saturated green travels via the luma channel and so looks sharper. One day, I'll go into the maths of this, but it will have to be the longest posting I've made here by far to explain it all.

2 When you shoot with a colour matte (blue, green, whatever), you're using the colour background as the keying colour, and it has no effect on the signal you key into. So, if your foreground moves, zooms etc, the background will not change at all. If you want the background (the colour the key switches to, i.e. it replaces the matte colour) to move with the foreground (the non-matte colours) then you'll have to shoot the material to do that. The keying is only a switch between the two video streams. Getting these streams to match each other is crucial to kidding the viewer that it isn't really keyed.

Get my test cards document, and cards for 625, 525, 720 and 1080. Thanks to Gavin Gration for hosting them.
Camera settings documents are held by Daniel Browning and at the EBU
My book, 'Circles of Confusion' is available here.
Also EBU Tech.3335 tells how to test cameras, and R.118 tells how to use the results.

Julian
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Thanks Alan. Thats what I thoutht. The second point, I mean, not the first. The first went right over my head.

I wish there was a way of logging straight into your head when I have a question.

Although, thats what we're doing on this great board, i suppose.

Julian

Alan Roberts at work
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It's hard to convey the significance of some of the theory in a few words, it's taken me years to fully understand what's going on in the maths, so you'll have to accept that it's a hard topic. But, there is a mathematical explanation for everything you see, and I can provide most of them given time and space. Time is more limited than space at present, successive 15 hour days on location don't leave much time to do anything, let alone the brain power to put it into plain English. But I promise I'll do it one day soon.

Christian Lett
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I bought some blue cloth from a local textile store and had a seamstress turn it into a useable screen that can be hung from rafters, poles, etc. Results have been varied due to difficulty lighting the screen evenly and the tolerances of the software when choosing the colour to remove.

However I came up with an idea that uses the solarise (or posterize as it's called on my TRV900E) digital setting on a camcorder - whose only use otherwise is to create a tacky 80's music video feel. It groups similar colours into one solid colour block and is a useful aide in setting up your blue/green screen shot.

As you're lighting the screen, view it through the camera with the solarise setting switched on (I know Sony cameras have this mode) and adjust your lighting until you get one solid block of colour. Don't forget to switch back to normal mode before shooting! This should allow your editing software to pick out the background much easier.

Christian.

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

jgl
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Joined: Jul 24 1999

When I go to Homebase today I want to buy blue or green paint so that I can make a blue / green screen.

Can anyone who has bought paint in a DIY shop for this purpose tell me what sort they boughtand, specifically, the make and shade and / or reference number.Thanks.John.

DAVE M
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Joined: May 17 1999

This might sound odd but.....

C.V. Mag April 2001 page 20 subscriptions
at the top is a blue square in a black box.
That almost exactly matches the fabric that i use
colour is not too specific as you should be able to tweak it. I use fabric on the walls, and A4 paper (close but not the same) on the floor, as it gets dirty.

It helps if you gel the background lights blue (117) as it helps even out things. use lots of light, bounced if poss. a small backlight helps lift the subject and will show hair etc.

I'd use a flat matt paint as any sheen will become white in the camera's eyes.

Find something at home that you can chroma on, and then take that to the shop.
best of luck

jgl
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thanks for that Dave.

Can anyone who has bought paint tell me exactly what colour and or shade of paint they used and where they got it from?Thanks

mbridge
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I found in an article a brief description of why green is better than blue for chroma keying using the DV format at www.dvcentral.org/DV-Beta.html . The article compares DV with Beta SP, I am far from a mathematicain but after reading the article a couple of times it did begin to make sense, hope this helps.

FerrymanR
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I often use fluorescent lighting on backgrounds to get an even light (I use the double 6' fittings which come with white metal reflector plates along each side, each mounted upright on a stand).
I wonered whether the greenish light from these better matched a green background.
Richard

Alan Roberts at work
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Richard, any greenish tint is very minor in the colorimetric scale of things. It will make only a percent or so difference in light level on a green cloth. Broad-band light is what you need, and lots of it.

jgl
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optek 020 84412199

paint £36.75

collapsable screen £155.00

hope this helps Ianmak !

Alan Roberts at work
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Ian, I know this looks like nitpicking, but the company name is Optex, not Optek.

ianmak
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quote:Originally posted by Alan Roberts at work:
Richard, any greenish tint is very minor in the colorimetric scale of things. It will make only a percent or so difference in light level on a green cloth. Broad-band light is what you need, and lots of it.


what is broadband light
ianmak
jgl
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Thanks for the helpful correction.The firm is Optex not Optek.
Ian can now rest assured that any telephone call he makes to this firm will not result in confusion and disappointment.

Alan Roberts
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I was only trying to be helpful, if you look up http://www.optek.co.uk you'll not find them, but you will find them at http://www.optex.co.uk., or maybe it's .com, can't be sure.

Broadband light is what you get from a tungsten light bulb, a continuous spectrum of light, no humps or bumps or holes in the spectral power distribution. By comparison, some fluorescents are exteremely spiky, with large proportions of the power concentrated in very narrow spectral peaks. Decent fluorescents have broadband phosphors which emit the visible light, converting the UV made from ion discharge, but some of the narrow band emissions get through as spikes in the spectrum.

Discharge lamps in general make very spiky spectra, sodium lamps (the orange street lights) make light over only a few nanometres, which is why it's hard to see colours by them. But they're hugely efficient. And useless for lighting a green cloth.

That's what I meant by broadband light (the sun's a very good broadband emmitter).

Hope that helps more than it confuses.

[This message has been edited by Alan Roberts (edited 09 May 2001).]

Get my test cards document, and cards for 625, 525, 720 and 1080. Thanks to Gavin Gration for hosting them.
Camera settings documents are held by Daniel Browning and at the EBU
My book, 'Circles of Confusion' is available here.
Also EBU Tech.3335 tells how to test cameras, and R.118 tells how to use the results.

Guy Caplin
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quote:Originally posted by jgl:
When I go to Homebase today I want to buy blue or green paint so that I can make a blue / green screen.

Can anyone who has bought paint in a DIY shop for this purpose tell me what sort they boughtand, specifically, the make and shade and / or reference number.Thanks.John.

I set up a TV station abroad and before I left I went to B & Q and using the Dulux colouriser system bought a couple of litres of the brightest and most saturated blue that I could find on their colour charts. It worked perfectly. The actual shade is not critical. In fact many different colours will do for chroma-key - just avoid any colour that will appear in the foreground and yellow is particularly good. The trick to getting good results is even lighting on the CK B/G and AS MUCH BACK LIGHT AS FRONT LIGHT on the object to be keyed.

Guy Caplin

Julian
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Be carful of Optex. They are very expencive (look elcewhere first) and they mucked me around a lot.

julian

jgl
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Joined: Jul 24 1999

Thanks.Incidentally I have found optex ok..but wish I could have done it cheaper!

FerrymanR
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Has anyone used Ultimatte for DV format work? I believe there is a Premiere 5 plugin which may also work with Premiere 6, and also an After Effects 4.1 plugin. In theory chroma key techniques would benefit from a format that samples chroma at the same rate as luminance and PAL DV is half that. I have seen the limitations with normal chroma key but wondered if the very expensive Ultimatte plug-ins suffered as much.
Richard

Alan Roberts at work
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Richard, chroma-key with DV is rarely very successful. Although PAL DV has half-luma bandwidth horizontally, it's also half vertically. NTSC DV has quarter-luma resolution horizontally and full vertically. Broadcast/pro formats have half horizontal and full vertical, and even they can still struggle to get chroma-key to work successfully. The best system is 4:4:4 from the camera, but.....

The biggest problem with using chroma key in DV is the standard of the camera, not the sampling/recording system. If you use a decent camera (JVC700 sort of level) with enough pixels in 3 ccds, then you'll get a decent performance. Try it with a PC100 and you'll not like the results. It's because there isn't enough resolution in the image to get good keying. That, plus the overuse of aperture correction in attempts to compensate for inadequate ccd and/or lens performance.

------------------
alan@mugswellvillage.freeserve.co.uk. Delete village for a spam-free diet.

Hamish
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quote:Originally posted by Julian:
Thanks Alan. ...

I wish there was a way of logging straight into your head when I have a question.

Look out for the new blockbuster movie "Being Alan Roberts" out soon. You get into Alan's head through a portal hidden behind the copies of 'Computer Video' in WHSmith, and after you've done seeing the world through his eyes, you tumble out dazed and confused onto a verge on the M25 near Reigate Hill...

Alan Roberts at work
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Aha, you've found my village on a map. Well done, it's very small and secluded and I'd like to keep it that way. But the way in/out of the head is via the 5-pin XLR just behind my right ear.

nattt
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I pulled a decent key from 3:1:1 HDCAM for a project I worked on for Panavision that was shown at NAB. Panavision also did a demonstration of keying with Ultimatte and 3 different varieties of HD 4:4:4 (recorded onto a big Hard disk array) 4:2:2 and 3:1:1. They just used the standard ultimatte settings with minor tweaking in After Effects on their Mac (the SGI they tried it on initially didn't work very well :) ) The results showed it was very hard to tell the difference between the three versions. Most people, other than die hard techies couldn't tell. The keying included glass and smoke and water, so it was quite a test.

nattress.com - Filters for FCP & Color
red.com - 5k Digital Cinema

Dave Currie
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Regarding Blue v Green discussion.Here's a Transatlantic perspective on the subject courtesy of DV.com's Moderator JJ...

HE WROTE:

Well, I'll tell ya -- I had heard this for a couple of years from reliable sources. Did a couple of tests myself. Didn't see much difference. Looked at the formulas that extract info from YUV into RGB.

Mathematically works out just as good for green or blue. So -- I had about concluded it was a myth, until I discussed it with Arpag Dadourian, the director of R&D for Ultimatte (who knows a bit about this stuff). He says it's true -- that the extraction of the green channel from YUV is slightly more accurate than blue on most systems.

But not lots. Green performs SLIGHTLY better than blue for DV, but it is not the major factor. However, since smooth chroma key is so tough in DV, you can use any edge you can get. For a few tips on DV keying, visit: www.greatdv.com/post/bluescreendv1.htm

By the way, the original color keying process Petro Vlahos invented for Mary Poppins did not use either color. I asked Dick Van Dyke about this a couple of years ago (he's a 3D animation/keying fanatic), and he said they used YELLOW for shooting Mary Poppins. This intrigued me, and I did some research on the camera Vlahos invented, and indeed the filters did split out a BW matte neg based on yellow.

------------------
John Jackman
Comenius Communication, Inc.

mdoragh
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I was glad to find this topic in this forum (albeit buried from a few months ago), as I was about to ask the same question.

Basically I would love to experiment with blue/green screen effects. I have no current project in mind, it is more to play with the concepts, and see what creativity it sparks. I was considering painting my bedroom wall blue or green. I have read all the above comments (thanks for them) and have therefore taken in the point that lighting evenly is far more important than the actual colour.

I have access to borrow up to eight, PAR64 Parkand's (spelling?) and matching dimmer packs and stands. I think each lantern has a 500watt bulb in (or was it 1000W?).
Can I use these effectively to light the blue/green screen? If so, how many would I need, what colour gels in them etc..? Would they need dimming?

What is likely to be the best way to create an effective blue/green screen, with next-to-no budget.... Paint or fabric?

Thanks for your help.

Mike

Ps Sorry for digging up an old thread.... I thought it best to add to this one, than to start again.... it keeps the distilled wisdom from your comments on this subject, all in one place!!!

My Equipment:
+ Panasonic DS15B Camcorder
+ DV500 Editing system
+ Premiere 5.1

PerryMitchell
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Joined: Apr 1 1999

A point going back to the original discussion about changing the background size to match the foreground. When you zoom in on a subject you get less depth of field and thus the background tends to go progressively out of focus.
You can use this fact by digitally zooming in on the background in post, as long as you have an application like After Effects that uses a high quality sizing interpolation.

Further to the mention of the Mary Poppins yellow screen, it is my understanding that this is the only film that used this technique. The point is that it created a seperate matte reel and therefore needed no separation processing, but obviously it was a lot more unwieldy to shoot.

Lastly it is worth noting that the Ultimatte process is fundamentally different to chroma-key or CSO as the BBC used to call it. For many years the Ultimatte Corporation fiercely protected their patents but they have now mostly expired. The differences are such that the Ultimatte process is only able to work properly when done on the R,G,B signals directly from the camera (or from a specially contrived 4:4:4 recorder).

DAVE M
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Joined: May 17 1999

Just a quickie-
The lanterns that you're not sure off are called PAR CANS ( ie a can that holds a PAR lamp)
PARs are given a code number such as 64 which indicates the angle of the output (64 degrees)PAR lamps are more or less mains operated (bright) car headlamps, they're most often used in rock lighting to deliver splodges of light over a stage, from about 20 - 40 feet.

If you have no other source, then bounce them off a large sheet of polystyrene to soften the light. the average bedroom would be better lit by B&Q style flood lights, 150 - 300w rather than 500 or 1k PARs

best off luck

dm

mdoragh
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Joined: Dec 5 2000

Thanks Dave. I thought my speling was off. I had only ever heard the name spoken. I will have to just borrow them and give it a go sometime. That will be the best way to find out what works.

Paint or Fabric? Anyone any suggestions...

Thanks

Mike

DAVE M
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Joined: May 17 1999

I'd go for fabric, as you can drape it over boxes to create levels. you also don't get stuck with a room that will give you a headache.
We use a cheap polyester fabric that's about 30 ft x 9ft. It's a close match to an A4 paper that we use a lot of. We cover the floor in sheets of paper, so if we get footprints, we chuck it out.
I've heard that the proper paint (Rosco) is
felt to be overpriced.

Alan Roberts at work
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Rosco paints are good, but definitely overpriced. A shoot I was on recently did a keying shot using a blue plastic tarpaulin (builder's merchant stuff) that had been serving as a rain-proof cover for the set in the car-park. Apart from some problems with creases wqher it had been folded, it worked well enough (in HD).

cornelius
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Joined: Jul 13 2001

i don´t know whether this is usefull or not, but i´ve had some very good results using Combustion by Discreet for chroma/keying.
Especially the object tracking feature. i´m still getting my head around it.

XL1/FCP/AE5/Combstion user