Shooting Greenscreens (and Bluescreens)

                                                                                                  

By Steve Wright.                                               

The entire point in shooting a good greenscreen (or bluescreen) is to get a good composite in post. Fussing over the lighting of the fleshtones at the expense of good lighting of the greenscreen is a very poor trade. With modern digital compositing tools and heroic rescue efforts even a poorly shot greenscreen can be made into a reasonably good composite, but it will take more time (schedule) and more money (budget) and the results will still not be as good as when starting with a well-shot greenscreen. The fleshtones can always be restored in post with color correction. The entire photographic objective of the backing region (whether green, blue or red) is purity of color (saturation), sufficient brightness, and uniformity so that the digital keyer can pull a good key. Following are tips from a compositor for shooting greenscreens for the best possible composite.

Blue vs Green

The choice of backing color may be dictated by the colors in the objects being filmed. If the foreground objects contain a lot of green then you must use bluescreen. If the foreground objects have a lot of blue then you must use greenscreen.
Skin tones work equally well with green or blue backings when using modern digital keyers.
Green is easier to light brightly than blue, requiring less light on the set.
Bluescreens lit by natural sunlight work well. Throw up a large diffusion silk to kill shadows if needed, or schedule an overcast sky for the day of the shoot.
Blue spill is less of a problem than green spill due to both its less offensive hue and its lower intensity. However, digital keyers have excellent despill tools that render this point moot.
The blue channels of both film and video have by far the most noise, so a bluescreen produces mattes with the noisiest matte edges.
The green channels of both film and video have low noise content so it produces the smoothest matte edges. However, in a greenscreen the grain from the blue channel can show up in skin tones from the despill operation.

Lighting & Backing

The number one issue is uniformity of lighting – within 1/2 stop of uniformity all over.
The number two issue is purity of the backing color. The photographed backing must be as close to 100% of its primary color with 0% of the other two colors as is technically possible. Of course, this is not technically possible. On a video waveform monitor in parade mode values of around 70% green and 20% each for blue and red would be excellent.
The brightness level should be about one stop under the key light. Two bad things happen with too much light on the backing. The backing looses purity (saturation) and it throws more spill onto the talent.
The careful lighting is only needed in the regions behind the talent. If they don’t go near an edge then don’t worry about the lighting there even if it is in frame. It can easily be garbage matted in post.
Tungsten lights on a properly colored backing can produce very good results.
Colored gels improve the purity of the backing color, but can be dangerous. They lower the light levels of the light sources and if they shine on the talent they add hideous spill problems.
Don’t use dimmers. They shift the color temperature of the lights towards red which reduces the purity of the backing.

Lighting &  Talent

Light the talent for the intended background they are to be composited into – dark interior, sunny outdoors, high contrast, whatever. The talent lighting is independent of the backing lighting.
To set up the lighting for the talent, turn off the backing lighting. After the lighting is set up for the talent, turn the backing lights back on and re-meter.
Keep the talent 8 to 10 feet from the backing. The closer they get to the backing the more spill light lands on them.
Make sure the talent lighting does not hit the backing. Make sure the backing light does not hit the talent.
Watch out for reflective objects on the talent such as rings, belt buckles, etc. They will reflect the backing color and make that part of the key transparent punching a hole in the talent.
Never counter-light the edges of the talent with a complementary color of the backing (yellow for bluescreen and magenta for greenscreen). This is an out-of-date trick that is actually harmful with today’s digital keyers.
Do place small lights out of frame and slightly behind the talent to subtly rim light them. Having all the lights in the front quadrant introduces unnatural dark edges to the outline of the talent.
If a cove (cyclorama) is used then the talent will have to be lit with the same lights as the backing. Since the backing must be lit evenly that means that the talent will be lit bright and flat.

The Backing.


The backing might be made by painting a wall with special paint or the use of special colored fabric.
If paint is used it needs to be a specialty paint made for keying, not just any blue or green paint. More than one coat will probably be necessary to get uniform coverage. Watch out for glare spots on the paint.
If fabric is used it needs to be a specialty fabric made for keying, not just any blue or green fabric. It should not have any wrinkles, seams, or folds. If several panels must be used then they must be the same color and joined with matching colored tape.
The backing need not fill the frame, just the area behind the talent. It can be easily fixed in post with a garbage matte. Make certain that the talent does not go off the backing, of course, or you will endure some extra costs for rotoscoping.

Floors.

Green screen floors are often necessary to key the talent all they way to their feet, but they introduce two problems:
1) A great deal of green light will bounce from the floor up to the talent causing spill problems for the key.
2) Walking on the painted surface scuffs and discolors it making the key more difficult to pull in post. Care must be taken on set to keep the floor as clean as possible.
A reflective mirror (such as Mylar) on the floor that reflects the backing will create a green floor without any “up-spill” onto the talent. However, the trade-off is that the talent’s reflection will have to be removed in post.

Film Issues.

The finest grain film stock possible should be used. Grain becomes exaggerated in the keying process and can introduce noise problems in the matte edges or in the despilled regions.
Never use a filter on the camera as it will degrade the quality of the digital matte. Filtering can always be applied to the finished composite.
It’s expensive, but Kodak’s SFX 200 film stock is made specifically for greenscreen and bluescreen photography and produces superior results.
16mm is not pin registered and has gate weave which is bad for compositing as the layer will drift around when composited. However, this can be solved in post using an image stabilizing program.
16mm has much larger grain structure than 35mm film which can create mattes with noisy edges.

Video Issues.

Video cameras all have an “edge enhancement” feature to artificially sharpen the picture. This introduces edge ringing artifacts that flummox the keyer. Turn off all edge enhancement in the camera. If the picture needs sharpening it can be added during compositing.
Do not shoot greenscreens with DVCAM. They have both low sampling in chrominance (the very basis of a good key) plus they compress the video data heavily which adds compression artifacts that further insults the keyer.
Shoot greenscreens with 4:4:4 or 4:2:2 video cameras with as little compression as possible, preferably none.

Photography.

Shooting a clean plate of the backing screen is very helpful to the compositors in post. If the camera is moving this is not practical. However, if the camera is locked off or it is a motion control shot then it should be done.
For motion tracking shots make sure that there are at least 3 tracking markers visible in frame at all times, preferably more. Watch out for the talent covering up too many of the markers.
Tracking Markers:
1) Make tracking markers shaped like a “+” (plus sign). This gives strong vertical and horizontal edge for the motion tracker to lock onto.
2) Don’t let them get too small in frame. You should still be able to see that their shape in the final photography, rather than just a fuzzy blob.
3) Their color is not important as they will most likely be painted out anyway. If they are to be keyed out, then make them either green or blue, whichever is not the backing color.

Useful Links.

Steve Wright’s web site: www.swdfx.com
Steve’s digital compositing books on Amazon.com:
Compositing Visual Effects: http://www.amazon.com/exec/obidos/ASIN/0240809637/wwwswdfxcom-20
Digital Compositing for Film and Video: http://www.amazon.com/exec/obidos/ASIN/024080760X/wwwswdfxcom-20

The Indian Exodus

This Article help you to understand the real  situations of VFX industry in India.

by Steve Wright

There is much concern in the VFX industry about our jobs being outsourced to India, and even China. Indeed, India is rapidly booting up a visual effects industry and has a vast pool of low cost artists to staff it with. Since I have been to India five times to conduct VFX training (the most recent being a two-month visit to two different facilities) I am often asked about the “lay of the land” there. While India has much potential, they do have some systemic problems to overcome.
In the Indian culture, education is highly prized as the road to financial success. Teachers and instructors are honored and admired. As a result, training institutes are big business in India. The problem is that many of them are less than stellar. Their focus is on blasting the student through as many different apps as possible so that their education is “well rounded.” The problem is that the graduate has not spent enough time with any particular app to become truly proficient. The Indian digital artists may have learned the “button pushing” but they usually lack the depth of knowledge to put together a real visual effects shot. Knowing how to operate Maya does not make you a character animator.
Part of this is due to the teaching philosophy of the training institutes and part of it is due to the instructors. Most of the training institute instructors are themselves simply graduates of other training institutes and do not have any real production experience so they cannot pass it on to their students. Further, when the digital artist gets a job most of the artists around him are similarly trained and short of real-world experience. In America, if you are not sure how to approach a problem you can always turn to the guy next to you for advice. Not so much in India.
This emphasis on operating the app also causes them to neglect the artistic side of visual effects. I remember at Cinesite, when we were looking through resumes for new-hires, one of the things we looked for was an artistic interest. Any artistic interest - sculpting, photography, drawing, anything. We knew that an artistic eye was just as important as knowing your tools and craft. A technically well assembled visual effects shot that is poorly composed, badly lit with inept color correction is still a bad visual effects shot.
Of course, the obvious advantage of the Indian talent pool is their low cost. You may be interested to hear that they are rapidly losing that advantage. Here’s why; since setting up visual effects in India has become the “hot new thing,” everybody is setting up a visual effects operation there because there is no shortage of investors. There are now more VFX studio workstations than artists. As a result, they are poaching each others’ staff.
In order to poach staff from another company, they have to offer more money. In some cases, artists can double their salary by jumping to the new venture. You can see that it will not take very many doublings to inflate salaries to the point of
non-competitiveness. There are actually some senior compositors in India now making $60,000 per year. That would be like earning $250,000 a year in the USA.
Where the Indian talent pool can obviously be very effective is the low-end production tasks - roto, wire removal, and the like. These are things that a recent grad from the training institute can do reasonably well right out of the box and with the lower pay grades it can be quite competitive. As you move up the VFX food chain, however, the talent gets thinner and the salaries rise disproportionately.
Another difficulty with Indian talent is the tendency for young people to get into it because that is where the money is. As a result, many of them don’t have the “fire in the belly” that most of the digital artists that I know have. Like most of my colleagues, I got into VFX because I loved it. I was willing to work the long hours and weekends that it took to make deadline. Less so in India.
The influence of Bollywood on their visual effects industry is less than you might expect. In theory, the Indian VFX industry could build up their muscles on Bollywood films then take on Hollywood films. The thing to understand about Bollywood is that they are not big on visual effects. There are two reasons for this. The first is financial. Bollywood films are notoriously low budget. Second, is the type of films they make. They are highly formulaic romance films - boy meets girl, boy loves girl, family hates boy, sing, dance, fight, dance, sing. There are exactly five dance numbers in a movie. Not four, not six. Five. They will even shoot two or three movies at the same time utilizing the same crew and talent. Hopefully, with at least a costume change.
However, there have been a few Bollywood VFX films and they have done well at the box office. These have given the local talent real feature film experience so over time I would expect the budgets to get bigger and the VFX to get better. Eventually they will gain the experience and artistic skill required to take on a Hollywood film. My guess is they will offer a serious alternative in about 10 years.
So what does all this mean to the worried domestic VFX artist? If I were a junior artist with only roto or paint skill I would be worried. The lower the skill and artistic requirements for a job the more vulnerable it will be to taking the exodus to India. To keep our well-paying domestic jobs we will need to continually upgrade our technical and artistic skills. Don’t just be a compositor. Be a lighter-compositor. Be the “shot finisher” with superb color correction skills. Get into stereo. Take some art classes and have an artistic hobby to show a potential employer. Bottom line - the higher up the VFX food chain you are the more secure your job is.