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March 21
2018

ISSUE

Web Exclusive

THE LAST JEDI: Previs, Postvis and Techvis Explained

By IAN FAILES

By now, most people are likely familiar with the previs process for big visual effects films. Previs – and its related disciplines of postvis and techvis – helps directors, crew and actors imagine complex scenes months before they are filmed or before visual effects get started. And the process continues as production on the film goes on.

Here’s how previs, postvis and techvis from The Third Floor formed part of the making of Rian Johnson’s Star Wars: The Last Jedi, narrowing in on where it was used for the space battles and the action scenes on Crait.

Space race

The Last Jedi opens with an exciting bombing run against a First Order Dreadnought. It’s a sequence that The Third Floor worked on starting from original storyboards. “The first steps were to create a detailed animatic based on the storyboards and the script,” outlines Previs Supervisor Albert Cheng. “Ian Differ, our Previs Editor on the show from The Third Floor in London, put together an edit using the boards, also temp’ing in sound effects and music from the original trilogy. At this early stage, some ship designs were in progress while others, like the Dreadnought, were still being made. While we didn’t have all of the actual ship designs or models at that point, we were able to work a lot with Rian to complete a very solid pass, including temp dialogue.”

A massing of Star Destroyers formed part of The Third Floor’s previs for scenes in space.

“[Director] Rian [Johnson] wanted to explore what it would look like to push down onto the planet past the rebel ships evacuating and asked our postvis artists to visualize this. … The ideas for most of these shots largely came from Rian during postvis reviews. He typically would go over his ideas verbally, sometimes using objects from around the room to illustrate where the camera would be in relation to the center of interest.”

―Barry Howell, Postvis Supervisor

As the previs evolved, The Third Floor continued discussions with ILM – which led the visual effects effort – as ILM worked to model ships and environments. At the same time, previs artists substituted storyboard frames with their shots and honed the sequence with Johnson. That honing even continued into postvis, where any shot elements were incorporated and where additional previs was also imagined as the sequence evolved.

“The shot that opens the sequence was also conceived in postvis,” says Postvis Supervisor Barry Howell. “Rian wanted to explore what it would look like to push down onto the planet past the rebel ships evacuating and asked our postvis artists to visualize this. These shots, along with the Star Destroyers jumping into orbit and the Dreadnought firing at the planet to destroy the rebel base were all developed early in the postvis phase. The ideas for most of these shots largely came from Rian during postvis reviews. He typically would go over his ideas verbally, sometimes using objects from around the room to illustrate where the camera would be in relation to the center of interest.”

The bombing run was carefully constructed and revised in previs and postvis.

Previs and, of course, postvis offer up the possibility to experiment and determine if certain types of action will work, without the expense of completing final visual effects shots. In fact, a number of elements changed or were added as editing continued on the battle.

“The shot of General Leia on the bridge, where we see Kylo Ren coming around for an attack run on the cruiser, is one example,” notes Howell. “The shot had a hologram, which we added in postvis, but her eye line and the camera motion in the plate required a specific composition to get the effect Rian was looking for. So in the postvis comp, we rotated the ship and changed the scale while also exploring angles to aid the visual effects being created by ILM and to eliminate the need to build a new section of the ship.”

The creation of Crait

The Last Jedi’s final battle scenes take place on Crait, a salt-covered planet with a red crystalline under-surface that makes for a some particularly stunning visuals. Unlike the space shots, some live-action plate photography was possible – this took place on salt flats in Bolivia, where a camera car achieved low shots and a helicopter was used for aerials. Earlier, The Third Floor crafted previs with that in mind although they took advantage of the vast environment and expansive flat surface of Crait to visualize the battle.

The Millennium Falcon makes a run over the salt flats of Crait in this previs frame.

To simulate the [red dust] effects in previs, we created particle instance effects in Maya that we could attach to the speeder blades for both the rooster tail red dust that gets kicked up as well as the trail lines that represented the ground scarring. The red dust and trail were particle emitters that spawned a variety of sizes of red rocks to which we could adjust the density, direction and speed. We also had red mist particle sprites for very fine dust to help sell it.”

―Albert Cheng, Previs Supervisor

“A majority of the shots traveled along with the speeders, sometimes with framing that favored the sky to include tie fighters in the shots,” discusses Cheng. “We were able to depict the action pretty easily, given the planning and the planar environment we knew we were working with.”

One aspect of the battle that featured highly in the previs was the red dust effect kicked up by Resistance fighters and in crashes; it was also an important element to reveal in the scarring of the ground. “To simulate the effects in previs,” says Cheng, “we created particle instance effects in Maya that we could attach to the speeder blades for both the rooster tail red dust that gets kicked up as well as the trail lines that represented the ground scarring. The red dust and trail were particle emitters that spawned a variety of sizes of red rocks to which we could adjust the density, direction and speed.

We also had red mist particle sprites for very fine dust to help sell it,” adds Cheng. “For the ground churn, separate emitters would spawn red rocks onto the ground surface along with larger white rocks to help represent the raking effect and give the trails a bit more visible volume. Overall the effect worked very well and allowed our artists to animate the vehicles the way they wanted during previs while the particle emitters just did their thing.

Techvis rounds out The Third Floor’s work

In addition to previs and postvis, The Third Floor delivered techvis for some sequences. This was designed to aid in visualizing how certain scenes could be captured, how sets were constructed and what the visual effects process might then involve.

A greenscreen plate of Chewbecca and a postvis frame which is a rough composite of the scene. Postvis tends to be used to continue to design final shots and place temporary shots into the edit, while final visual effects are being worked on. Techvis had earlier been delivered to help with shooting some cockpit scenes.

“In addition to accuracy, clarity is really important for techvis. It’s easy to overwhelm with information, so we like to make sure to clearly show what the camera is doing in the shot while providing the most relevant info.”

―Albert Cheng, Previs Supervisor

Techvis was particularly helpful with envisioning cockpit shots for the battles in space and on Crait. Artists at The Third Floor oftentimes even worked from the same art department CAD models that were used to build all of the practical ship cockpits and gun turrets. “We also used models of each designated stage at Pinewood Studios,” says Cheng, “so we knew what the clearance and dimensions were and could help work out the camera placement and movement for each shot confidently.”

A typical techvis delivery included animated Quicktime diagrams, usually in plan view, which encompassed the movement of the camera, lens, frustum and the camera’s visible path, along with the relevant dimensions and speeds. “To provide context,” details Cheng, “we also included picture-in-picture of the previs shot as approved, as well as the view through the techvis camera, which helps validate the techvis.

As is often the case, continues Cheng, “sometimes you need to do camera cranes that are tricky when working with stationary cockpits where there is both camera movement and implied vehicle movement over distance. In addition to accuracy, clarity is really important for techvis. It’s easy to overwhelm with information, so we like to make sure to clearly show what the camera is doing in the shot while providing the most relevant info.”


Read more about the visual effects of Star Wars: The Last Jedi in Crafting New Effects Frontiers in The Last Jedi

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