Once production wraps, the work is just beginning for the post-production facilities that conjure the final visual effects. Modern blockbuster films are typically shot in pieces or against green screens so that the backgrounds can be replaced in post. A small army of artists and technicians is required to pull all of these elements together and to add anything that wasn’t captured live.
Post-production can be an extremely expensive process, so filmmakers need to make sure that they know exactly what they are commissioning before they pay for it. The studio also needs to have confidence in the outcome of the final visual effects, yet it is often difficult to judge if a sequence is working until the final visual effects are in place. This is a catch 22 that until the advent of Postvis was somewhat unavoidable.
Postvis is a preemptive visual effects pass in which the previs assets are integrated back into the live-action plates. The first step is to determine where the live-action camera was positioned. A few known set dimensions can be all that a postvis artist needs to align a plate to a 3D virtual set. To mimic the motion of the live-action camera, sophisticated 3D tracking programs are typically used. Once the perspective has been matched, a veteran postvis artist can make it appear as though the previs characters are standing alongside the live-action actors. Digital set extensions and placeholder effects can also be added during the postvis process. Anything that can be manipulated or tweaked quickly at this stage, saves countless hours of wasted effort down the line.
It is increasingly popular among VFX Producers to use postvis as a tool for bidding. They can send an approved postvis sequence out to a myriad of VFX vendors for evaluation. Each VFX studio can review the postvis and see clearly what the challenge is. All of their calculations for manpower and resources can be a lot more accurate. This means that the VFX bids tend to come back a lot leaner. VFX vendors can also breathe a sigh of relief because there is less chance of directors changing their minds after they have signed off a polished postvis edit. In addition, the postvis team can provide their 3D files to help jumpstart the final effects pipeline. If the directors are able to use postvis to further define their vision, a lot more of their budget is guaranteed to end up on screen.