Metropol

I've been on the look out for cheap green screens for a few projects of mine, and I've come across the following two on eBay:

http://cgi.ebay.co.uk/Chroma-Key-Green- ... 240%3A1318
http://cgi.ebay.co.uk/ChromaKey-Green-S ... 240%3A1318

I know green screens don't come cheap, but these surprised me. Okay, they're by no means huge, but it does the job. Are there any hidden downsides about the above two or is it just a good bargain? Many thanks.

Hi Reeves.

Hidden downsides - yes. Being made of vinyl, these screens will reflect light and you'll end up with "hot spots", where the light landing on it will be stronger in some places than others. That will cause you many problems when you come to pull a decent key off your shots.

The best material to use is going to be a fabric - and wool is the most forgiving of all, especially where you don't have a lot of lights to play with.

You can buy chromakey green wool serge fabric, 1.5m (5ft) wide, for about £6.00 per metre from manufacturers such as J&C Joels. Google them for a phone number. They sell direct to the public and will send it out on a carrier like TNT to your house. With wool serge you can staple gun it to a wall, or tack it to a wooden baton and suspend it from hanging points on the ceiling.

You can also buy paint - around £45 for a 3.79L container. Look at rosco.com, and look for your nearest stockist. If you buy from Northern Light, ask for Barclay Dakars and tell him Gavin said you would get a discount

The paint is great. Good coverage, matt finish, and its made from an acrylic base, so it bonds well to any old surface.

You'll get more use out of the fabric though, and it means you can put it up and take it down as required.

Lighting, as you probably know, is fundamental to getting good results. You can pick up halogen floodlights from screwfix direct. Buy some diffusion filter to soften it down, or try bouncing the light off a large flat white surface, like a ceiling.

So - avoid vinyl sheets, as they are cheap but rubbish. For the small amount more, buying fabric will give you much better results.

Any other questions, don't hesitate to ask.

Thank you very much for your advice, Gavin. I'll have a look around afterwards. Much appreciated.

Didn't know Datavideo were making those. I like their kit.

I'd love to have a play with and LED/reflector cloth setup

I should also say about the fabric - or any other chroma screen - getting some distance between the talent and the cloth really helps. It should be 6-8ft if you can do it, but that does dictate the size of chroma screen you'll need.

If you find that a 1.5m wide screen just won't do it, J&C Joel's will stitch a large one up for you. You may be surprised how inexpensive it is to have something "custom made" - and partly that's because non-professionals don't necessarily know what to ask for.

A 3m x 4m chroma wool cloth, sewn flat and hemmed all round (with or without eyelets all round for stretching on a frame) would come in at around £60 more or less, with a tenner for carriage (wool is pretty heavy). Not pocket money, but wouldn't break the bank.

However, all over Youtube there's swathes of people advising that you spend silly money on all kinds of odd methods - like buying up all the green craft paper from a stationers and taping it together. One chap went and had a paint custom mixed to match a fleck of green from a magazine picture of a movie set, and paid more than a real can of chromakey paint would have cost. These vinyl chromakey screens on eBay sound just as dodgy, to me.

Anyhoo, forgive the ramble.

The point is that the real products are not prohibitively expensive as they're priced for the trade - and having worked in it for a long time I know that nearly all suppliers have a "no job too small" approach to enquiries; and wouldn't mind you picking up the phone to them one bit.

Backlighting in magenta can help reduce fringing in some cases if you find the halo effect too much to bear. I've had mixed results with this, but it's worth a try. As other posters have said, the best thing you can do is get the talent as far away from the cloth as you can. Also don't be tempted to over light the cloth, it should be actually appear quite dim in the camera compared to the talent.

<is hoping someone in N10 is reading this>

deejay wrote:Backlighting in magenta can help reduce fringing in some cases if you find the halo effect too much to bear. I've had mixed results with this, but it's worth a try. As other posters have said, the best thing you can do is get the talent as far away from the cloth as you can. Also don't be tempted to over light the cloth, it should be actually appear quite dim in the camera compared to the talent.

Absolutely. Worth pointing out to those who may not realise that magenta is at the opposite end of the colour wheel to green, so using a magenta filter (which you can buy from the stockists on the rosco website) will help to cancel out any green spill.

Similarly, orange filter cancels out blue spill from a blue screen for the same reason - although blue is rarely used for video chromakeying these days.

I presume blue isn't used as much due to it being inferior, if this is the case why was it used originally?

Hymagumba wrote:I presume blue isn't used as much due to it being inferior, if this is the case why was it used originally?

Blue was (and is) the colour of choice for film makers because of how colour film works - its made up of separate layers of emulsion that respond to red, green and blue light.

The blue emulsion layer of unexposed film is more sensitive than the green and red ones; so blue screens work better if you're using that medium.

Blue used to be used for video work too until the advent of digital storage; where the information recorded by the camera is compressed during recording. This is measured, or defined, as chroma subsampling.

In essence, most digital video methods record more green information than red or blue - you may have have heard of 4:2:2 subsamping. Basically, for every 4 parts of green information stored, there are two parts of blue and two parts of red information. By using green as your key colour, you'll get better results, as there is more information for your keyer to deal with.

That said, you can now record 4:4:4 on high-end professional HD video decks (as they did in the Star Wars 3 movie), so using blue for your compositing doesn't pose the same problem with video as it has done over the last decade or so.

While 4:4:4 can refer to RGB, 4:2:2 refers to Y'CbCr or YUV. The reason green is preferred within 4:2:2 is Green has a higher weighting within the YUV signal - R:0.3 G:0.59 B:0.11 for white. With that weighting, it just makes more sense to use the green portion of the signal.

Having said that, it was 10 years that I did my degree and you never use that kind of information in real life, so it could be slightly out!