MPC explains the planning, tank shoot and water sims required.
Early on in episode one of Netflix’s Vikings: Valhalla, a group of Greenlanders battle through a fierce ocean storm on their way to Kattegat.
Here, MPC visual effects supervisor Ben Mossman breaks down for befores & afters how the ocean-going sequence was achieved, all the way from previs, to shooting in a tank set-up, to the final water simulations.
b&a: I know that the team at MR. X and now MPC have done water simulations for the previous Vikings series. How did this one compare?
Ben Mossman: The brief here from the showrunner and the director was, well, we’re on the North Sea, it has to be a big choppy, scary storm, as tense as we could make it. And of course, there’s this big rogue wave in the middle of it that they wanted to come through which is kind of the crux of the whole thing and it’s really meant to show how tough the Greenlanders are. They’re these amazing captains and they can navigate through this when everybody else fails.
With the work that was done on Vikings, and continued in Vikings: Valhalla, it’s very much about focusing on realistic environments and extensions of what they shoot on set. Throughout the series, too, there’s not really a big, magical element to it. It’s always supposed to be a retelling of history. So, even though it’s a huge wave, it still has to feel realistic. It still feels like they could conceivably get over it or that they could get out of the storm. It’s not so insurmountable that it’s this magical thing that they’ve survived. The director, Niels Arden Oplev, was really adamant about it.
b&a: How did you shoot these actors, how did you plan it out?
Ben Mossman: The director did boards with the production storyboard artist and then we took those and previs’d them almost exactly to what he had boarded. We ended up using both of these things on set. We had the boards all printed up and we were using the previs really to guide what the camera was doing. One of the things that we found in the previs, and honestly what Vikings had discovered before, too, was that a lot of times the camera doesn’t work as well when it’s ‘off’ the boat.
That’s why in that sequence you only see a couple shots where we’re not in the boat. It just always looks better. Even in the VFX work, I think it translates better when the boat and the camera are all moving together rather than it being detached and the camera’s just some objective view.
It was also one of those rare instances where the previs was pretty close to what is there in the end. We could probably picture and picture it and then almost all the shots line up, which is good from an editorial standpoint.
b&a: How do you previs ‘simple’ water or is it not simple water at all, even in previs?
Ben Mossman: There’s ways to do it in Maya but here we gave the animators an ocean spectrum from Houdini to use in their previs, although it was a really basic one. It had waves they could move around and they could put a boat on it. Our FX lead did that ocean spectrum, and we actually just mocked up some quick cliffs too in Houdini for the section at the end.
b&a: How did you then shoot the live action? I’m actually really curious about this, because I don’t know whether this is just a bluescreen shoot or whether there’s some sort of open water photography for part of the scene.
Ben Mossman: It’s all on a tank, all 60 or so shots. It’s an exterior tank that they used for Vikings as well. There’s bluescreen maybe 120 degrees around that. We would just reverse it anytime we needed to be behind the boat. Since it’s an exterior tank, we flagged off the whole area to get the sun out of there as this is supposed to be in a storm and we were trying to avoid any shadows or really strong, directional light.
In terms of SFX, we had an actual boat in the tank and then SFX would be agitating the heck out of the water with wind machines, rain towers, dump tanks–just soaking the cast for two days!
b&a: As the VFX supe, do you ever wish that there’s not spray and water and wind and stuff? Is that your enemy or is that actually good because it helps with interaction later on?
Ben Mossman: It definitely depends on the sequence. In this case we wanted it and we asked for it. The agitating of the boat and the wind and everything, it’s just going to give us more motion on the boat, give more wind and rigging movement, moving hair, moving with the actors.
For the rain, well, I used to be a compositor. And I was still surprised that we were able to key a lot of the rain out of this. Our comp team was able to get enough out of the footage where the rain was behind them, against the bluescreen–we were able to extract a lot of it. Obviously we needed to add a lot more, but we started with keeping what was there.
b&a: And then once you’ve got the plates, how is that informing some early work with water sims?
Ben Mossman: It’s a challenge to get it to look real on that scale of the environment.
We’d start off with doing a layout on our ocean, then we would pick a speed to translate everything together at. So, we track the boat plate and then create a new camera where we would move the boat and the camera. We had to pick a good speed where it felt like they were still moving forward, but that the storm was giving them enough resistance that they’re in trouble. Speed was always a really important factor through the whole thing in terms of how much progress they were making and how fast the wave was scooping them up.
And then for the size of the wave – what size wave do we block in and how do we frame it when they turn around? You don’t ever see a huge amount of it, except for that end shot where it crashes the boat into the cliffs. It’s the monster for the sequence, so we don’t ever want to try to frame the whole thing and you just see pieces of it where we can to give it that scale.
b&a: When you approach the final sims, is it more of a shot by shot basis or is there ever any kind of ‘whole of ocean sim’ that you do to place your boat into?
Ben Mossman: We started with an ocean spectrum done in Houdini, especially for the shots not on the wave. Then we start getting into more shot by shot sims to add even just small sims like splashes off the front of the boat. Sometimes that’s a practical splash that we key and keep from the plate, sometimes it’s us adding it hitting the side of the boat, crashing off the front of the boat.
Little bits like that, we rendered a few of them out in caches and then would put them into shots or if it needed to be something more specific, like some of the ones where you see the boat actually making contact with the water, we would have to do a custom FLIP sim for shots like that just to really anchor it into the water since you’re seeing the contact with it.
Everything was all done in Houdini. Including the spray and the rain. For the rain, we had comp elements too that we mix in. Then there was foam, and we had two set-ups for that.
There was one part of it where the foam would just cover the whole ocean. That was part of our base where we’d drop it in and we’d have the ocean already there with the boats in it and then, still within Houdini, we’d bake that in. You’d bake large ocean displacement textures, and HDAs so that we could break it up into grids and actually try to render it on time, just because it was so big. Then, closer to the boat we would render out the foam as particles in Houdini.
b&a: There were so many other pieces of detail, like ropes and rigging and sails as well that I’m assuming weren’t always part of the live action shoot. Tell me about adding in those extra things.
Ben Mossman: Most of the rigging on the boat and the sails blowing around was practical. There’s one shot that’s a POV up to the flag changing direction on top of the mast. That shot was completely digital, added in after.
There were also a couple of shots where we actually see the boat contacting the water. There’s one before they go up the wave where they’re in a tank, so we don’t have full size oars for them to row. They’re half-oars, so they’re sticking out of the boat, maybe a foot and a half. So in a shot like that, where we actually see it going into the water, we have to extend the oars out, but then of course for the speed and where they are in the sequence, now all of a sudden their timing doesn’t work. So now we’re moving the oars completely in CG and re-timing the characters and putting new oars in. And then we didn’t have quite enough to frame the boat in all the way, so we have to create the top part of the boat. So okay, now we’re replacing all the rigging. It almost became full CG by the end.
Another thing that did come up were highlights in the plate. We had to go in and remove some of the stronger highlights or reflections that came up from the shoot. We graded them down a little more aggressively than the DI could with masking or just straight up painted them out and created a new texture for them just to set them in there a bit more.
b&a: You mentioned the direction and speed before, and that was going to be my last question actually. It occurred to me that you’re in this ocean and yes, there’s some cliffs at the end, but how do you make it clear for the audience all the time which way they are going, how the water is moving, all that chaos? I’m curious how tricky that is as editorial builds up a scene and you are also working out the visual effects shots.
Ben Mossman: I felt pretty fortunate with our boards and the previs that we were able to keep the sequence pretty tight and pretty close to where we’d planned it out with the showrunner and the director and then through shooting. When we were shooting it, it was always, ‘Okay, which direction are we looking? Which way do we need to have the actors? Where are they at this point?’ We almost shot it in sequence except for a couple of specific setups when they started going up the wave or we had the front of the boat craned up a bit to get the actors to kind of lean back a bit more.
During post, it was always about looking at how much of the cliffs we saw and if we saw enough of them or too much of them to sell that there was still a large amount of storm in front of them. You’d also see those other boats here and there throughout the sequence, but it’s really about how close they are to the cliffs and then turning around and seeing this silhouette of a giant wave coming at them.
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