LED screens are nothing new to filmmaking; so-called "rich mans process" has been used for years to simulate car travel in driving scenes. But their usage in virtual production truly unlocks their potential in the filmmaking process.
However, with great power comes great complexity, and there are a lot of things about shooting LED screens that are counter-intuitive. Unfortunately, these issues aren't easily fixed in post--so it'd important to get them right in-camera. In this post, I'll go over a few of the most critical things to consider when shooting on an LED backdrop.
1. Exposure is critical
Proper exposure is a huge part of making the image feel real, and not artificial. It's best to think of an LED screen (or any screen) as the opposite of a camera--just as a camera "sees" a certain amount of dynamic range, a screen can display a certain amount. This is referred to as the screens contrast ratio. The higher the contrast ratio, the more dynamic range information the screen displays to camera. Make sense?
To that end, it's important to not think of the screen brightness as a "tool" and instead think of the image on screen as "reality." You shouldn't be varying the brightness of the screen to match your exposure, you should be aiming to get the brightness of the image to be as close to reality as possible, and lighting/exposing just as you would in that real situation.
This means that in bright situations, the screen will be very bright--that's fine. Compensate with ND filters just as you would in real life, and that will provide the most realistic image. Remember, cameras don't see light or color linearly, and their particular look and color science is dependent on the intensity of the light hitting the sensor. Trying to aim to empirical reality will trick the camera into thinking that the background is real.
2. Balance of foreground and background
To add onto exposure, it's very important to match the background and your foreground subjects with both color and intensity of light. LED screens can't get as bright as the sun, or as a specular off a car, so it's critical to compensate with that in your exposure. It's very common to see amatuer LED wall footage where the backlight of the subject is brighter than the sun in the background. False color is your best friend in matching highlights/shadows!
The same applies for the shadows as well. An LED wall shoot can be instantly given away by an elevated black level on the screen relative to the foreground subjects. Remember--under studio lighting conditions, an LED wall will only provide about 10 stops of dynamic range information. You must consciously choose where to place that information on the cameras response curve.
A trick for this is to over-rate or under-rate the cameras ISO. If you're shooting a bright outdoor scene for real, most of the information will be above the toe of your cameras response, I.E. most information will be in the highlights. This is where using relative lighting ratios can get you into trouble, as the way the camera sees information in the shoulder is different that how it sees the same information in the toe. Over rating or under rating your camera can push the information more towards the correct place on the exposure curve.
3. LED walls hate dim/low contrast scenes
LED walls are digital, and as such, they have a particular bit depth. Even though most of them will be wired for 10 bit, that still may not be enough to eliminate artifacts on very low contrast or dim scenes--there just aren't enough bits of information available to represent incredibly fine tonalities.
If you're planning on shooting a very low key scene, consider shooting everything a stop over and bringing the image back down in the grade. This will help the LED wall display the best image it can for that scene.
4. Flag your lights!
LED walls are made of plastic, and as such are quite reflective. Even small amounts of ambient light in the room will reflect off the screens and raise their black levels, reducing contrast or creating hot spots. This results in images that feel "thin" and artificial, even if everything is calibrated correctly.
It's absolutely critical to tease, flag, and grid off all ambient light spill from the screens. Your LED stage will have a quick way to black out the screens when asked, allowing you to see exactly where light is hitting the screen. Because LED walls are made of faceted flat tiles, curved screens can be very problematic as shallow angle lights can highlight the faceted nature of the wall.
What tips and tricks have you found to be effective? Comment below!
Recently, I've seen some articles speaking out against ILM's LED Volume technology, saying it is inhibiting creativity by forcing filmmakers to think entirely inside of a 70' diameter space.
The Mandalorian came out in 2019, and I'm honestly surprised it's taken this long for these kinds of articles to come out. Usually when there's some kind of new technology in film--digital, 3D (color and sound as well, I'm sure) there are always people who are quick to naysay. I think LED Volume technology, however, is a little harder to wrap your brain around--so it takes a little longer to fully understand the implications of it.
I work in the virtual production industry, I've been a consultant and VP supervisor for a few years and we're opening a large LED volume in Chicago in just a few weeks. We're already talking with some huge shows about it, and the interest only seems to be picking up speed. However, this technology absolutely does have some pretty major downsides:
Limited physical space
Screens are delicate (rain/pyro/snow/stunts are tricky or impossible)
Calibration of the system takes ages
Off-axis artifacts with DoF and color
Moire pattern when focused on the screen
Absurdly expensive (even for the film industry)
So why, then, has this industry absolutely exploded in popularity over the last couple years?
Is it because it's cheaper? Well, yes and no.
If the alternative is shooting on an actual location, an LED volume will almost certainly be basically the same cost. That is, your bottom line number will be equivalent. Now, obviously, it's cheaper than actually going to the moon for real, so it's not really possible to make a blanket statement on cost.
What is possible to make a statement on, though--is how it affects production.
You've seen articles recently about how overworked the Marvel VFX artists are. You've seen articles about people dying in car crashes from overwork. You've seen articles about the insane hours we all put in. I can tell you, from firsthand experience--this isn't even scratching the surface. The filmmaking process is brutal, there's no nice way to put it.
Sometimes you get to work on something great, and being able to say "I helped make that," is an amazing feeling--but the truth is, this industry has changed. The majority of productions happening are not epic cinematic masterpieces. They're cookie cutter movies and quickly made shows to fill streaming services. Dedicating your life for 9 months to a mediocre project that everyone hates is the fast lane to burnout and depression.
The LED Volume is the answer to this problem. This technology allows shooting days to be shorter, it allows them to be far safer, and it enables this while increasing the creative options available to the crew (if they can accept the limitations.) The ultimate promise of virtual production is not just cost savings; it's life savings.
There is something to be said about shooting on top of a mountain, or the bottom of the ocean. After all, we're in the business of showing audiences things they've never seen before! But at a certain point, the returns diminish--and the audience, frankly, stops caring. I know that sounds depressing, but if 95% of people can't tell the difference, if the crew is happier, and if the studio is able to get their content, it really is a win for everybody.
Now, I do want to mention that literal billions are being poured into R&D for this technology. It's only going to get better, and many of the limitations we face today will be solved in the future. It also will never replace location shoots, as there will always be scenes that simply can't be done in a confined space (car chases etc.) We've really just begun to scratch the surface of what we can do with virtual production.