Lighjting a greenscreen for a "touchscreen tabletop" from below? / problems...

[Luis Reggiardo]

Lighjting a greenscreen for a "touchscreen tabletop" from below? / problems...

Hi!
I have to light a greenscreen on a table, simulating a touchscreen tabletop (like the one in the Control Room of MI-6 at Quantum of Solace).

5 actors will be around the table interacting with it. The greenscreen should be lit from below to have a nice and even lighting level.

Problem is that what happens with the "green" light (coming from below) that will cast all over the actors faces as they face the table? On shots where both the table and actors are seen, will the greenlight interfere with a good keying on post?

Also, I would like to use the lighting coming from the chroma as a "practical" so the actors are illuminated with light "coming from the screen". I was thinking about doing that with fluorescent tubes aligned around the borders of the table from below, next to the virtual screen.

My main problem is the interfering green-light coming from the greenscreen backlight... any help?

Thanks!
Luis

 

[M Most]

Hi!
I have to light a greenscreen on a table, simulating a touchscreen tabletop (like the one in the Control Room of MI-6 at Quantum of Solace).

5 actors will be around the table interacting with it. The greenscreen should be lit from below to have a nice and even lighting level.

What was done on the Bond picture, and what you should probably consider, was to use a translucent table top and light it from below with soft, even light. The matte extraction will need to be via a combination of luminance keying and roto. The amount of light will need to be sufficient to separate from the hands on the table (not difficult to achieve), but not so strong as to provide an unnatural amount of rim light on the hands themselves. The table top can then be replaced in post. Testing, as always, is the answer.

 

[Luis Reggiardo]

The matte extraction will need to be via a combination of luminance keying and roto.

Thanks! problem is there's no budget for rotoscopy... is there any solution using green/blue screen or only luminance keying and still get nice results lighting from below (without compromising actors' faces)? Probably those will be statics shots (no 3D tracking needed).

thanks
Luis

 

[DCC Erickson]

Keying easy but sloppy, roto painful but nice. Could you slap a lcd screen under the table and show the graphics live? Still a lighting problem, but maybe more manageable.

 

[Luis Reggiardo]

Keying easy but sloppy, roto painful but nice.

Hi!, going with keying... how do I stop the keying light from interfering with actor's faces that will be looking straight at it?

Thanks

 

[Charles Angus]

You could use a green cloth instead of backlit green. You'll still get green spill on the hands, but maybe your de-spiller will be able to handle it.

There was an extensive thread about this on CML - you might want to look it up. IIRC, the DP from Quantum chimed in on the subject.

In no scenario, however, do I foresee needing NO roto work. Roto is your friend...

 

[M Most]

Hi!, going with keying... how do I stop the keying light from interfering with actor's faces that will be looking straight at it?

That would require a combination of production design, shot composition, and testing different levels of table light to find the minimum necessary to accomplish the effect. I would say, though, that if this were a real device, it would likely be backlit (since it would likely be LCD technology, at least at this point in time) and therefore would be a light source anyway. If it's justifiable, you could play down the room lighting and use the screen as a presumed primary light source, but only if low angle light works for the story and the scene.

In any case, I would stay away from the notion of using color on the table screen unless you can design the graphics in a way that justifies the color. On a show I did around the late 90's, we used green, but we justified it by designing screens that were primarily green as well. That allowed the green spill on both the hands (the "operator" was using a light pen) and faces to be appropriate. Appropriate in the 90's, probably inappropriate today.

 

[David Mullen ASC]

I agree with Mike, either go with a white glowing light box, or project video graphics from below, but don't use a greenscreen.

The only time I'd use greenscreen is perhaps a tight shot of the table looking straight down at it with hands moving against it. But even then, a white screen and a luminence key would probably be better.

 

[Luis Reggiardo]

But even then, a white screen and a luminence key would probably be better.

Thanks Mr. Mullen!, know any good reference source/tips for doing a good luminance-key only?

I will use greenscreen on closeup shots of the hands "interacting" with the content on the touchscreen, and leave the luminance key for mixed shots of actors+panel.

 

[David Mullen ASC]

Design the light box so that it's simple to gel the source to turn it into a greenscreen, just make sure you don't overexpose it. I'd shoot the insert of the hands both ways in case the compositor prefers the white screen.

As far as the particulars of making a good key, I'd talk to someone who makes keys for a living...

 

[Wayne Beck]

David is right! The light box is a great idea.

To the original question on green screening you have to overcome several issues. I have used green screening and faced them all, but as of yet only had limited success.

Use greenscreen material not green light.

Your set lighting is going to spill, bounce, onto talent if talent is at short distances from screen and walls with green casting from bouncing light.

Use a magenta jel to create a halo light on talent, red and green makes a dirty brown which helps in keying and separating talent from screen.

If the studio has white walls, I think mine may be the only one of those, you may want to mix some low wattage red light onto walls so that green isn't being projected onto talent from walls. Black walls is great.

The color sample of your camera will help termendously. It should be at a minimum 4:2:2 but best of course 4:4:4.

The keying application is also important. They are not created equal. I have had some success with AE and light factory.

 

[Charles Angus]

Magenta backlight is often recommended, but there's one big problem with it - it doesn't look good/believable in most scenarios. No sense in getting a cleaner key if the talent no longer looks good and doesn't match the bg plate. Also, where could you put the backlight in this tabletop screen setup?

 

[Casey Green]

Another thought, if you do not have much of a budget for this, is to refrain from motion in the shots that feature the screen.

This would allow you to not need to rotoscope and only do a chroma or lumakey in post. (Also, you may not even need green, blue, or white, just have borders of the screen to track depending on the software you are using)

One disadvantage to using cloth rather than a screen is that you may lose natural reflections off the screen (faces, hands, etc.), which sometimes help sell the key. This is easier if you don't have anything in the foreground, but can still be done with software by maintaining a layer in the comp for reflections. Again, this is accomplished much easier on locked down shots.

 

[MiguelOrtega]

use a reflecmedia system, OR use a larger LCD, CRT monitor and have that project a green color. unless its very dark i would be able to pull a key from it even if it were not perfectly lit, even with a green piece of paper so long as you have enough exposure on it. use Nukes IBK

 

[Jim Geduldick]

I would stay away from Reflectmedia system for the fact that anything off axis or not locked off goes to shit with this system. I would stick to the lighting box table set up .You can make this pretty easy with a local hardware store and Ikea . Also you might want to listen to Casey he has more experience then most of us on this subject.

 

[M Most]

Another thought, if you do not have much of a budget for this, is to refrain from motion in the shots that feature the screen.

This would allow you to not need to rotoscope and only do a chroma or lumakey in post.

That's what camera people often think, but the reality is that it's almost impossible to do clean composites - especially with luminance keys - without a degree of roto. It's an inescapable step in almost every high quality composite ever done.

And I say this as someone who's had to do an awful lot of them.

 

[MiguelOrtega]

Also you might want to listen to Casey he has more experience then most of us on this subject.

really? ive done a film or two.

 

[Casey Green]

... Also you might want to listen to Casey he has more experience then most of us on this subject.

Heheh - while that's very kind of you, I'm sure that is not the case, as there are many many REDUsers with a wealth of knowledge and experience in this area.

As far as Roto goes...

I can see needing it more for Film based compositing on locked down shots, since you also are dealing with the registration and weave issues, but for locked down digitally acquired shots, with no foreground objects, in many cases, I have not seen as much of a need for it personally as well as through other professionals I have worked with.

There, of course are many exceptions...

Also, keying/comp software now has become so advanced, that for a good amount of these types of shots, the plugins literally require just a few clicks to set edge detection and auto-tracking, tweak a few settings, and you are on your way... just depending on the complexity of the shot. (There are other cases, however, when frame by frame is still required, even on what might seem the simplest of comps.)

 

[M Most]

As far as Roto goes...

I can see needing it more for Film based compositing on locked down shots, since you also are dealing with the registration and weave issues, but for locked down digitally acquired shots, with no foreground objects, in many cases, I have not seen as much of a need for it personally as well as through other professionals I have worked with.

There, of course are many exceptions...

Also, keying/comp software now has become so advanced, that for a good amount of these types of shots, the plugins literally require just a few clicks to set edge detection and auto-tracking, tweak a few settings, and you are on your way... just depending on the complexity of the shot. (There are other cases, however, when frame by frame is still required, even on what might seem the simplest of comps.)

Casey, I think you really need to spend more time in post - particularly with visual effects compositors - before making such pronouncements. Roto has nothing to do with tracking issues, it has to do with the fact that to get proper edges on keys, compromises have to be made - so the parts of the matte that the key (or, in most cases, combination of keys) doesn't properly handle need to be done by hand. There is also the issue of garbage mattes, which become pretty involved when using things like luminance keys. As an example, if you use a luma key to extract a hand from a backlit table, any hot spots on the hand - and there will almost always be some, it's human skin - will become transparent, so they have to be garbage matted out. Not to mention any overly hot areas on the hand edges that will also tend to go transparent, or at least partially transparent. The bottom line is that there will definitely be some areas that will need to be cleaned up, no matter how perfectly it's shot, and no matter what matting software you're using. In almost every case, a professional result is only obtained by using multiple key passes, garbage mattes, roto, and occasionally some hand painting. The notion that "perfect" mattes can be created with "a few clicks" is really naive. The only mattes that can be created that way are amateurish ones, regardless of the software. Acceptable under some circumstances, but not at the professional level I think we're talking about. If you think it's so easy to do great mattes, you should work in post for a while and show me how to do it.

I never said that this would become a full on, frame by frame rotoscoping job. But it will involve some roto work, just as almost every composite does.

 

[Casey Green]

Casey, I think you really need to spend more time in post - particularly with visual effects compositors - before making such pronouncements. Roto has nothing to do with tracking issues, it has to do with the fact that to get proper edges on keys, compromises have to be made - so the parts of the matte that the key (or, in most cases, combination of keys) doesn't properly handle need to be done by hand.

See what I mean? Plenty of much more experienced folks here in this area. While I've spent some time with a few FX folks and have done some of my own comps, obviously it hasn't been enough to fully grasp it's complexities. I appreciate the insight.

There is also the issue of garbage mattes, which become pretty involved when using things like luminance keys. As an example, if you use a luma key to extract a hand from a backlit table, any hot spots on the hand - and there will almost always be some, it's human skin - will become transparent, so they have to be garbage matted out. Not to mention any overly hot areas on the hand edges that will also tend to go transparent, or at least partially transparent.

While your example is no doubt true, and you obviously have much more experience in this area, I was simply trying to offer a basic solution for what sounded to be a very low budget job, even if it may come at the expense of not being an academy award winning solution.

The bottom line is that there will definitely be some areas that will need to be cleaned up, no matter how perfectly it's shot, and no matter what matting software you're using. In almost every case, a professional result is only obtained by using multiple key passes, garbage mattes, roto, and occasionally some hand painting. The notion that "perfect" mattes can be created with "a few clicks" is really naive. The only mattes that can be created that way are amateurish ones, regardless of the software. Acceptable under some circumstances, but not at the professional level I think we're talking about. If you think it's so easy to do great mattes, you should work in post for a while and show me how to do it.

I certainly did not mean to say that all compositing work is now as easy as 3 mouse clicks with the right software. I'm sorry it came off that way (and also quite sorry if you felt insulted). I realize each professional spends years learning the intricacies of their crafts and there is much more to it than can meet the eye. Compositing and Keying being no exception.

At the same time, I have also witnessed some incredible software apps in the last couple of years (while extremely expensive) which can work wonders in the hands of a skilled artist with what used to take several compositors days to do. It's just the nature of the industry.

I never said that this would become a full on, frame by frame rotoscoping job. But it will involve some roto work, just as almost every composite does.

I don't doubt it. (now) Thanks again for your input.