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شغل Matchmover

نوشته شده توسط Sajad Jahangiri. Posted in Book

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Matchmover

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Match Moving or Camera Tracking is a technique that allows the integration of computer generated (CGI) VFX into live action footage. The process allows for the correct position, scale, orientation, and motion of the CGI relative to the real world captured in the shot.

Although Match Moving is traditionally an entry level job into 3D VFX, it is a crucial part of the 3D/CGI pipeline. Matchmoving describing the world inside a computer in 3D, what the original live action camera saw.

What’s it like?

The job is associated in many people’s minds, who have either seen or worked on a film set, with ‘tracking markers’ on green screens – these often being + (varying shapes is better though) shapes made with coloured tape or red LEDs. Any movement on any set needs to be matchmoved, if it is to have cgi added or complex rig removal operations carried out in post production.

A Matchmover, does three things:

• Using specialist software Match Moving converts a 2D Image sequence into a 3D scene and virtual camera inside the computer software. This involves first tracking points in 2D through the film sequence, by finding suitable pixels then computing with the given cameras film back, the software calculates where the object is in 3D space.
• object tracking, using computers to map movement in a scene so that 3D Artists can create or add objects. By using 3D geometry, Matchmovers/Camera TDs ‘match’ the movement of items in the original shot by working with proxy geometry to ensure it accurately ‘sticks to’ moving vehicles, body parts, faces and stand in props in the plate, for example.
• Roto Animation (sometimes called Body Tracking). You use a basic rigged model of a figure and keyframe (or hand) animate it to accurately follow the movement of an actor or animal in the plate. This is then used to ‘drive’, or interact with FX animation. For example a model of a character casting a spell is roto animated to match the original live action actors performance, so that when magic swirls are added they appear to move around the actors body in 3D space. The effect would then also need then to be lit, rendered and composited into the live action plate.

The work of a Matchmover needs to be pixel accurate to ensure that the moving camera or object (often both together) remains in position in the plate. When finished, Matchmoved test geometry inside a Maya 3D scene will be passed into the 3D/CGI pipeline. In VFX animation, matchmoving will have done the same job of scene ‘layout’ that is done in feature animation, except in VFX, the background is a 3D copy of the photographed plate rather than being free form CGI. For FX, any object tracking has also been carried out to create any ‘collision geometry’, used to drive effects simulation. If effects happen around or are ‘caused by’ actors, full roto animation (also called body tracking), will need to have been match animated to the actor in the plate as well. Think of roto animation/body tracking as ‘object tracking’ for people.

Often VFX shots contain both camera and object movement together and some shots require days of trial and error testing to get accurate solves. Zoom lenses and hand held cameras present particular challenges. Matchmoving is painstaking work and needs to be pixel perfect, so that anything else that is built and animated into the ‘scene’ fits without slipping and sliding.

In smaller companies, or on lower spend projects, Senior Matchmovers can be called upon to go on set to survey for camera tracking and put up tracking markers. This involves taking on set measurements, reference still photographs and camera data to provide the software back in the studio, with the information needed to produce accurate camera or object solves (or both). In larger companies or on bigger budget productions, this on set role may be performed by a Data Wrangler.

مهارت ها

• Understanding of the CGI/3D VFX pipeline
• Knowledge of the relevant software (see below)
• Understanding trigonometry will help with problem solving
• Understanding the relationship between the lens focal length and the cameras’ sensor size (still often called the camera back) and image aspect ratio
• Understanding how nodal, non-nodal, mixed camera movement and parallax works
• Ability to be methodical
• To be solution-driven, goal-oriented and problem-solving
• Strong attention to detail – a meticulous quality is needed to achieve pixel perfection
• Ability to communicate with colleagues and work as part of a team
• Ability to take direction and willingness to address comments and make changes to improve the camera/object solve or Roto Animation
• Ability to deliver on schedule, working under pressure if required
• Respect for the requirements of a particular studio, production or pipeline and ability to input tidy, optimised 3D scenes into the process
• Enthusiasm to learn and develop professionally
• Adaptable

نرم افزار

A range of software exists for matchmoving. It has moved out of it’s once very specialist and very expensive VFX niche to have more general application in the computer graphics and post production industries. Packages such as Sytheyes and the 3D tracker in After Effects aren’t usually considered to have the control and enable nuance needed for high end photorealistic VFX, however it’s useful that the basic workflow is the same in any matchmoving software and using Sytheyes or After Effects give you enough foundation knowledge to ‘trade up’ if you want to, to learn match moving in higher end tools.

In high end VFX, 3D Equalizer is the tool of choice. It is the best nuts and bolts package to understand the theory of photogrammetry (the core of matchmoving). Other specialist, more automated, packages such as PFTrack and Boujou are also used. The camera tracker in Nuke 8, is now a reasonable alternative for studios, colleges and individuals who have purchased a Nuke X license. Nuke doesn’t currently support object tracking though. Maya will also be used to set up the scene in terms of ‘layout’ ready for further cgi work (such as animation or FX) to take place in. Maya will also be used for roto animation work.

Matchmovers will need to re-train in software as it develops and new applications become available.

Getting In

Matchmover/Camera TD is a junior level job that is entry level to 3D VFX. Typically Matchmovers have decided on a career in 3D and the job represents the first rung on the ladder. They come via VFX courses and may enter the Matchmover department directly or via the Runner route. Other possible routes to Matchmover are via professions that have strong technical ability and require highly developed spatial awareness, eg surveyors and architects.

In most case example outputs of test geometry sticking solidly within a plate needs to be robustly demonstrated as part of a showreel. Some people demostate a wider skill set of matchmoving with CGI/3D generalism, others focus purely on camera tracking, object tracking and sometimes roto animation. Both approaches can be used to apply for jobs as a match mover. Employers are looking for evidence of pixel perfect camera/object and roto animation that fits to the object without slipping.

Getting On

The role of Matchmover is the foundation for all 3D/CGI VFX work and can develop into senior level roles within its own specialism as Lead Matchmover or act as a good grounding before moving on to work as a 3D/CGI generalist or in modelling, texturing, lighting, animation and FX work.

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