This week we looked at 3D motion tracking, its comparison to 2D motion tracking and how we were able to use this in difference ways within one video. For convenience I will shorten this to ‘3DMT’.

What is 3D motion tracking?

3D motion tracking has very similar properties to 2D motion tracking, except that it is more complex and can be used for a wider variety of visual effects. It works almost exactly like 2DMT works except that is able to perceive the Z axis as well as the X and Y. 3DMT can be used to replace and alter images that move within a shot, or to include additional visuals. In the example video below 3DMT is displayed in terms of a ‘sky replacement’- showing how motion tracking can be used to alter an environment.

This video was created by using a high shutter speed footage of a road on a normal, bright day. 3DMT was used to replace the sky with an image that changes the overall tone and feel to the video. In simple terms, motion trackers were applied to two key objects on opposite sides of the frame (using Adobe After Effects) so that the image of the evening sky could be applied onto them. This meant that the image would move in proportion to how the camera moved during the shot. Effects were also applied so that the video footage and sky replacement would match in terms of realistic settings (i.e. colour correction and lens flare for sunlight).

This video above uses the same original road footage, however a different element of 3D motion tracking has been applied. This type of motion tracking (called ‘track camera’) uses ‘targets’ in Adobe After Effects to calculate points within the shot that can be easily traceable. In this video the markers that were used were stones and pebbles on the ground, this was then used as an area in which to edit the hole onto. The hole was originally a still image with its background removed- this meant it could be manipulated onto moving footage easily. As 3DMT is able to utilise the X, Y and Z axis this meant that the hole would remain in its position when the camera changed angles, unlike with 2D. Due to the flatness of the image, duplicate layers had to be reproduced and edited so that there was some depth to the inside of the hole (the laws of parallax here dictating that more of the hole should be revealed as the camera moves closer to it). Colour correction and other texturing effects were also applied so that the image looked a little more realistic and blended in appropriately with its environment. If this video were to be improved the hole itself could be edited so that the texture looks more photo-realistic, as well as the lighting being correct in relation to the light source. Other elements could also be included such as fire, damage and burn marks to enhance the overall look of the video.

Benefits and uses

3D motion tracking is more effective than 2D in the way that it utilises multiple aspects of perspective and rotation of an image in a shot. It can be used to replace images as a whole, to add effects or to display information within video footage that would not necessarily be possible with 2D motion tracking. This could be very beneficial in cinema during post-production to alter elements within the film, e.g. a mythical creature in a fantasy story. I could use this concept for my own personal project if I wanted to change the weather in a shot for example, or to add in images that relate to my personality and creative ideas.

Disadvantages

In a similar way that 2DMT cannot track objects which are obstructed, 3DMT is not very effective at this either. Only high-contrast objects work well when choosing a place to apply the tracking target, which can be a problem depending on the contrast and quality of the overall footage. Unwanted motion blur is also a possible risk if the footage is shot using a slow shutter speed.