Digital correction of lens distortion or camera angle artifacts — removes trapezoid and wide-angle warping. Critical when matching CG elements to live-action footage.
You're sitting in the compositing suite and immediately notice: the CGI component doesn't fit the plate. The camera filmed from an extreme angle, the lens distorted trapezoidally — your 3D elements, in contrast, stand orthogonally, perfectly right-angled in space. This is the moment when perspective compensation becomes a fundamental task. It's not about cosmetic retouching, but about restoring a consistent spatial logic between captured and generated reality.
The camera itself causes two major categories of distortion: Firstly, keystoning, when you film from bottom to top and parallel lines (walls, building edges) converge upwards. Secondly, radial distortion from the wide-angle lens — lines at the edge of the frame curve, the geometry is distorted in a "kissing-barrel" fashion. In compositing, you need to undo these errors before adding CGI objects, otherwise your models will be in an optically impossible world.
In practice, this is done via lens distortion modules in your compositing package (Nuke, After Effects, Fusion). You calibrate the lens — focal length, sensor size, specific lens characteristics — and calculate out the distortion. Some projects require you to photograph a color checker and a grid reference chart on set beforehand; this helps you find the exact correction later. With green or blue screen, this is less critical — you can correct while already compensating. It becomes more difficult with plate-based shots: mountain landscapes, city scenes in a live-action background. Here, you must remain geometrically consistent.
An important point: perspective compensation is not just a VFX task. The focus puller on set needs to know that extreme wide-angles require a deeper depth of field — and this influences how accurately the correction will work later. The camera assistant should also take notes: lens information, tilt angle, whether teleconverters were used. This data is gold for the compositor.
The most common pitfall: overcorrection. You set the parameters too aggressively and break the plate itself — it looks artificial, unnaturally hardened. Subtlety is the craft here. You only align as much as is necessary for your CGI integration to work smoothly, no more. And always coordinate with the matte painter and roto artist — their masking work builds upon this corrected geometry.