Chroma-Key Lighting

[Ilthigore]

I know it has to be done but I don’t know how. How do you light a surface for chroma keying (either blue or green depending on what I can get hold of for the least money )? I know something has to be done to prevent the actors' shadows messing up the key, but shoving a light each side almost parallel to the screen would surely create a brighter area where both lights meet unless they attenuate pretty quickly. As you can probably tell I am not an LX person, and am a complete amateur video-maker. I'd just like to try this.

[p.k.roberts]

I know it has to be done but I don’t know how. How do you light a surface for chroma keying (either blue or green depending on what I can get hold of for the least money )? I know something has to be done to prevent the actors' shadows messing up the key, but shoving a light each side almost parallel to the screen would surely create a brighter area where both lights meet unless they attenuate pretty quickly. As you can probably tell I am not an LX person, and am a complete amateur video-maker. I'd just like to try this.

<{POST_SNAPBACK}>

 

Avoid the shadow on the background by not having the subject stand too close to it, then light using whatever your usual technique is (hard key, soft fill or whatever). To help with the chroma keying, light the background evenly and it also sometimes helps to avoid 'fringing' if you use a very pale yellow gel (say, quarter CTO or pale straw) on the backlights; this tends to neutralise any blue/green reflections from the background.

[James]

Chroma Key is easy to play with but very hard to do well nowadays since standards keep on rising (unless you want it to look like 1970's Dr Who??).

 

Just a couple of questions if you don't mind...

 

What type of camera are you planning on using? (film/ccd?)

 

Are you planning on performing the keying operation in real time or are you going to do it in post?

 

What is your aim for this key and what alternatives have you thought about?

 

What is this for? (a commercial job, an educational project, something for a theatre production? or just messing arround?)

 

PS, assuming this isn't considered as advertising - may I quote this example

 

http://www.bbcresources.com/images/post/signing_picturebox.jpg

 

This is our signing studio, to quote our websiteThe Signing Studio was built as a dedicated area to allow the addition of an in-vision signer to programmes, either for live transmission or recording back to tape for future use. The studio is equipped with a single fixed camera, lighting rig and a green screen lightbox. A "Magic Dave" vision mixer allows flexible positioning of the signer, who is combined with a reduced image of the original programme to provide the new image. A second, simple vision mixer, and an edit controller allow

 

I don't supose anyone else has noticed that this page appears to be incomplete...

 

As you can see from the picture we use an illuminated screen to get round the problem of having to evenly light the screen. you can just see in shot a couple of DMX soft lights, again soft lights like kinos produce very few shadows on the screen. and as PK roberts said, one of the best tricks is to backlight in a contrasting but acceptable colour to the screen, (usualy an orange shade) you can just see the backlights in the photo. Also, the better the camera the better the results, you want nice large high resoulution CCDs, and a decent keyer, If you have to record it first, please use a recording format with a sensible colour content, this is one instance where 4:1:1 from DV realy shows up compared to 4:2:2 from Digi. (oh and in an ideal world, this would be uncompressed, but I doubt you have access to D1 or you wouldn't be asking this question.)

 

Anyway good luck and if you can explain a little more about what you are trying to do we might be able to supply some more appropriate advice.

 

James

[Ilthigore]

We're just really messing around trying out effects. Obviously, the better it looks the better, but it is lower than low budget (I'll have to try to borrow lamps from here there and everywhere), so '70s Dr Who style really isn't bad. Also, it's in post, not live. I really just want to get a bit of experience trying all these things out, and have some fun.

 

As for recording content, my camera is (prepare to cringe) PAL mini-VHS tapes: that's right! Ye olde analogue. I'll probably have to borrow a decent digital camcorder from a friend for this though, but it's still not going to be professional quality stuff. I'm not aiming to get professional results though - infact it could even be the cheesier the better, but I don't want bits of blue and green floating around on screen. (That's all I need).

[shellshox]

but I don't want bits of blue and green floating around on screen. (That's all I need).

<{POST_SNAPBACK}>

 

My 2 cents worth -

One way to get rid of those bits is to use your editing software to mask out the more obvious bits using mattes or masks. Of course, this takes a bit of work and may get tedious at times. Or you could add effects in post like glow or choke to clean it up a little....

[mac.calder]

We're just really messing around trying out effects. Obviously, the better it looks the better, but it is lower than low budget (I'll have to try to borrow lamps from here there and everywhere), so '70s Dr Who style really isn't bad. Also, it's in post, not live. I really just want to get a bit of experience trying all these things out, and have some fun.

 

As for recording content, my camera is (prepare to cringe) PAL mini-VHS tapes: that's right! Ye olde analogue. I'll probably have to borrow a decent digital camcorder from a friend for this though, but it's still not going to be professional quality stuff. I'm not aiming to get professional results though - infact it could even be the cheesier the better, but I don't want bits of blue and green floating around on screen. (That's all I need).

<{POST_SNAPBACK}>

 

You can do perfectly good chroma work on older cameras. I used to work a bit with an old VHS camera which mum was 'loaned' permanatly from her old work after they bought mini-VHS cams (I loved the camera because it was so easy to do steady work and had a good weight... and it looked cool having a camera on my shoulder... the joys of youth). I was also using a rather cruddy analogue editing station. The trick is to get the tollerance right and a good contrast. If you are doing it digitally, it becomes a hell of a lot easier, as you can also do frame by frame edits (tedious I know) or touch ups.

[paulears]

VHS isn't a major issue - what is worth doing though, especially if you are going to do the keying in post, is shoot some test material, before you waste hours on something with a problem. The background problems are usually due to light dropping off at the edges - so look out for corner problems. Not normally a problem with proper cyc lighting - but if you use a wide source, close in, the drop off at the edges can be considerable. Moving them further away helps tons - but you also have to move the talent forward too, then the camera, so experimentation is required.

[Ilthigore]

Thanks for the advice. I am using digital video editing software (a copy of Premiere I'm borrowing from a freelance pro who had upgraded). I'm using a rather cruddy camera - it turns itself off sometimes, although I have upgraded to a nice new battery which isn't about half an hour long due to various people recharging it too soon.

 

One way to get rid of those bits is to use your editing software to mask out the more obvious bits using mattes or masks.

This really doesn't appeal to me - especially if the bits are directly next to the talent (as it would be if there was a serious shadow problem).

 

Moving them further away helps tons - but you also have to move the talent forward too, then the camera, so experimentation is required.

But presumably this would require an even larger piece of bluescreen - and I'm thinking, the smaller I can get away with the better. I'll try some stuff out over the next week (I haven't actually got a production on at the moment, although I'm starting to plan one).

[paulears]

Moving them further away helps tons - but you also have to move the talent forward too, then the camera, so experimentation is required.

But presumably this would require an even larger piece of bluescreen - and I'm thinking, the smaller I can get away with the better. I'll try some stuff out over the next week (I haven't actually got a production on at the moment, although I'm starting to plan one).

<{POST_SNAPBACK}>

 

yep- that's the catch 22 - having as bigger background as you can does helpif you are trying to do it on tyhe cheap

[p.k.roberts]

Moving them further away helps tons - but you also have to move the talent forward too, then the camera, so experimentation is required.

But presumably this would require an even larger piece of bluescreen - and I'm thinking, the smaller I can get away with the better.

<{POST_SNAPBACK}>

 

Dont't forget that to acheive a given shot size, moving the camera further away and using a 'longer' lens (i.e. zooming in) will show less background.