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Types of Shots: Gallery of Horrors
We've found that often new customers don't recognize the type of shots they have, or special problems in them, and therefore fail to employ the appropriate techniques. So here we'll give you a quick introduction to different types of shots and various difficulty elements, so you'll know what to look for, and where to start to do something about it. Note that a given shot can be several types simultaneously!
Camera tracking. We are interested in the 3-D path and field of view of the camera with respect to the background, as opposed to that of any independently-moving objects in the scene.
Object tracking shot . We are interested in the 3-D path of one or more moving objects in the 3-D environment, with the camera either locked or also moving. All the trackers on the moving object must be rigidly positioned with respect to one another: the object cannot bend or deflect like a face.
Camera and object tracking shot . The shot contains one or more moving objects, in addition to a camera that is also simultaneously pan/tilt/rolling and translating. When the camera also translates, there are additional relative scaling issues between the camera and objects.
Model-based tracking . Camera or object tracking accompanied by known pre-existing 3D mesh models of the set or moving object. Trackers will be constrained to the corresponding locations on the mesh.
Motion capture shot . Two or more calibrated cameras used to produce individual 3-D trajectories for each pair/triplet/etc of trackers, which all move independent of one another. Typically used to drive animated faces.
Normal shot. The 'ideal' camera-tracking shots handled by SynthEyes, which feature a camera that translates smoothly along some path, with many visible features etc. Mainly, not one of these other types!
Hand-held shot . Typically a hand-held camcorder with much bounce, which will make tracking more difficult. Use the Track/Hand-held: steady prediction mode . Also consider stabilization . Counter-intuitively, hand-held shots are often tripod (nodal) shots, as frequently the shooter is standing still, ie not translating.
Lock-off shot . The camera does not move, typically it is hard-mounted on a tripod. We may be doing object tracking, or we may want to know where the camera is using model-based tracking, or more roughly, using single-frame alignment .
Tripod shot. The camera is panning, tilting, rolling, maybe zooming... but not translating. No 3-D information is present! We will tripod-track the camera motion, but cannot determine the distance to objects in the scene. To position the camera in 3-D, we might use model-based tracking or single-frame alignment .
Nodal shot. Another name for tripod shots.
Nearly-Nodal. Avoid! This is a (camera tracking) shot where there is a small amount of translation, enough that a nodal solution isn't appropriate, but not enough translation for a full 3D solve. Common with amateur hand-held shooters.
Possible rescues require very careful supervised tracking and using a known field of view, or a lidar scan.
Low Perspective (Object) shot. Like Nearly-Nodal, but when an object is being tracked. In bad situations, Inverted Perspective can result. Addressed with Known lenses and Model-based tracking.
Mixed tripod . A shot with bothtranslating and tripod sections: the camera moves down a dolly track, reaches the end, then pans around for a while, for example. Use Hold Mode features.
Low-information tripod shot. Typically a nearly-stationary hand-held shot. The camera moves (reorients) somewhat. There's insufficient information to determine field of view, use a Known lens.
Traveling shot. The camera moves forward continuously for long distances, for example on the front of a car. If the motion is very straight, estimating field of view will be difficult (think of the original Star Trek open). Possible cumulative errors may require external (GPS) survey data to resolve.
Survey shot . The shot is a collection of digital stills, rather than film/video. Typically used to measure out a set from a wide range of vantage points. Special survey shot features simplify handling these.
Zoom shot . The camera zoom was changed during the shot. Turn on zoom processing on the Summary or Solver panel.
Hidden Zoom. Watch out: sometimes shots will have hidden zooms, for example, intentionally to compensate when a dolly runs out of track, or unintentionally, as a result of focus breathing. Turn on zoom processing on the Summary or Solver panel.
Green-screen shot . The background is a big green (or blue) backdrop. It must have trackable features on it, and out in the foreground! Beware situations where the camera movies in to focus on an actor... leaving no markers in sight. The green- screen panel can help auto-track these quickly.
Stereo shot . You're given left-eye and right-eye cameras to track. Some people think stereo should be less than twice as hard, but really it's more like three times as hard, since you must match each camera to the world, plus match the two cameras to each other.
Occluded shot . Typically, actors or cars are moving around in front of the background. The camera must not include any trackers on moving objects like this (if they are to be tracked, they will be tracked separately as moving objects). Delete unwanted trackers or use the roto-masking or alpha facilities to handle these.
Windy shot . The shot contains grass or trees with branches blowing in the wind, or shots with moving water. Such features are not reliable and must not be tracked. Use Zero-weighted trackers to approximately locate them, roto- or alpha- masking, or in an emergency, many short-lived trackers.
Flickery shot . The shot contains rapid changes in overall light level, typically from explosions or emergency lights, possibly from candlelight or torches. Handle using high-pass filtering in the image preprocessor.
Noise Amplifier. All the features being tracked are much further away than the object being inserted. No matter what, physics says the insert will be unstable: there's no information to say what happens up close. Filtering will be required.(An advanced technique is to put a tracker on an up-close inserted object, retrack it, manually adjust that track, then refine the overall solve.)
Fisheye shot . The shot features visible lens distortion (of any kind). These require substantial additional workflow . If at all possible, shoot and calibrate using lens grid autocalibration .
Perfect Push-In. The camera moves forward in a straight line exactly along the optic axis—the direction it is looking. Most likely to occur on vehicle or dolly shots. There is no information available in these shots to estimate field of view. You will need to supply a value manually, from an on-set measurement or a best guess.
Planar Shot. All the trackable features lie on, or nearly on, a single plane in 3-D, typically a flat floor or back wall (especially for green-screen shots). That's a problem, because there is no 3-D in that tracker data, basically the trackers are all redundant: this is actually the underlying mathematics used for planar four- corner pinning. A supplied field of view is helpful. Be sure to track any off-plane features, ie using supervised tracking.
Rolling-shutter shot . A shot from a CMOS camera that contains enough rolling shutter distortion that it must be handled carefully. Rolling shutter is present in all CMOS shots and must frequently be addressed. In very noticable forms, you'll see vertical lines made diagonal, or objects squished or stretched vertically.
Jello shot . A rolling-shutter shot where significant high-frequency vibration is present (say more that 1/10th the frame rate of the shot). Jello shots are unusable.
Note that though we've given you some jumping-off links to look at, working through the manual is going to be necessary. You need to learn the fundamentals that go behind all the shot types; they are not repeated everywhere.
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