‘Visual effects’ is so many things. It’s art and it’s science, and it covers an incredible range of disciplines, including illustration, photography, lighting, modeling, animation, rendering, compositing, coding…in fact, the list goes on and on.
I think it can be hard as a new filmmaker or film enthusiast to just get your head around VFX (frankly, as someone who came into visual effects journalism not as an artist originally, I am always playing catch-up on what others in the industry might consider basic concepts).
Eran knows his stuff, and he also teaches it. His courses at fxphd were some of the most well-loved (trust me, I was there and saw the incredible feedback). Now he’s distilled a lot of this VFX knowledge into a book designed to be a clear guide for filmmakers about where and how visual effects can fit into their productions.
To give you a taste of what’s in the book, Eran has kindly let me publish an excerpt from a chapter about shooting on set, and specifically shooting with green screens. The rest of the book includes discussion about all the important disciplines in VFX, and as I read each chapter I was silently wishing the book had been written when I got started!
So, check out the excerpt below for The Filmmaker’s Guide to Visual Effects (that link takes you to the book’s Amazon page).
Smoke and Atmospherics
This is where things become a bit tricky. Ideally, green (or blue) screen shots should be kept completely clean. Indeed, it does not make sense to cover the green screen with smoke or fog, as this will make it very hard (or impossible) to extract. Also, all this smoke will be cut out and discarded anyway, so it might seem like a total waste to have it there in the first place. Generally speaking, green screen shots are better off without atmospheric effects like smoke, fog and steam.
There are, however, good reasons to make exceptions to this rule. I have worked, more than once, with DPs who rely heavily on smoke and mist to shape the light, texture, and “feel” of their shots. On such films, and especially if surrounding non-VFX shots all have smoke and fog, a clean shot will feel strangely out of place. While smoke and other atmospheric effects can be added as VFX, it is usually very hard to precisely replicate the look of practical atmospherics. I have found myself more than once in a debate situation with a DP—me, understandably, trying to push toward a clean shoot, while the DP, equally understandably, wanting to preserve the look and feel of the rest of the scene. My reasoning that all the smoke that happens on the green screen will need to be cut out and replaced with CG smoke (and will most likely not be an exact match), is challenged by the DP’s reasoning that the smoke on the subjects will still be retained, at least preserving the right look on the main action.
One parameter that can help the decision in such cases is the size and prominence of the green screen in the shot. If the screen covers only a small portion of the frame (for example, if it is placed in the very back for some minor set extension), then it definitely makes sense to leave the smoke or fog on, as most of the atmospheric effect will be retained and only a small portion will have to be replaced. However, if the frame is predominantly green screen, it is much better to shoot it clean, since large chunks of the smoke will go away with the green screen and will need to be recreated by the VFX team anyway.
An often overlooked aspect of green screens is their reflections in surrounding surfaces like windows, cars, water, mirrors, metallic or glass objects, or even the actor’s sunglasses. It’s important to remember that the green color can usually be easily removed through the usual spill suppression methods. However, if the reflection is sharp and you can see the distinct shape of the screen, some measures must be taken to avoid that, as this will require more elaborate (and often unnecessary) paint-out work. Change the actor’s angle to eliminate the sunglasses reflection, stick a poster on a background window, or dry out those water puddles on the ground.
In the film The Immigrant (which takes place in the 1920s) we had a shot of Joaquin Phoenix and Marion Cotillard walking down a NYC street, in the shadow of the imposing prison known as The Tombs (which no longer exists). During pre-production meetings, we suggested that the best location to shoot the scene would be a place that has a period-accurate cobblestone pavement. The logic behind this was that it would be easier for us to replace and rebuild everything around the actors, but not the ground beneath their feet (because of the interaction and shadows). Bond Street in NYC, which has an old cobblestone surface, was selected as the location, but now the question was how to cover the actors’ long walk down the street with a green screen. Instead of building a costly ultra-long green screen along the street, it was decided that a few grips would carry a smaller portable screen and simply move with it behind the actors. It all worked very well during the shoot, except for a certain “force majeure” that went practically unnoticed by all of us: a couple of hours before the shoot it had rained heavily, leaving the cobblestones wet and shiny. We weren’t really aware of any problem until we received the scans and started working on the shot. Only then we realized that the wet cobblestones acted as a mirror, clearly reflecting the moving green screen (and the guys carrying it). No spill suppression or any cosmetic fix would do the trick here. We had to replace the entire ground, and recreate every contact shadow and subtle interaction between the actors’ feet and the ground. It worked in the end, but, ironically, we had to replace the one surface in the shot that we planned to keep.