Motion Vectors Mapping

A motion vectors map represents the position, velocity and acceleration of objects in a scene.

Motion vector information can come from two sources:

• An external motion analysis. This analysis can be a motion vector output from another Action node, or from a Motion Analysis Batch node. This approach allows for the pre-caching of the analysis, and should result in better interactivity within Action. It also allows you to use the same motion analysis in multiple Action nodes.
• An internal motion analysis. This analysis is performed within Action by the Motion Vectors node. While this method can decrease Action interactivity, it makes it up by allowing for on-demand analysis. And the Motion Vector node also has its own caching mechanism.

Typically, Motion Vectors can be used to deform a GMask or projector to track points on a surface, and stablize a surface.

Using an Internal Motion Analysis

You can generate motion vectors directly from the Motion Vector Map objects by using the Analysis mode. In this mode, the expected input is a regular RGB image sequence, similar to what is used in the Motion Analysis node in Batch. You modify the motion estimation results the settings Resolution, Smoothness, Edge Preserve and Colour weights.

To add a motion vectors map to a surface:

1. In the schematic, select the surface to which you want to apply the motion vectors.
2. Right-click the surface, and select Add Map > Motion Vectors Map.

   A new Motion Vectors map, with its axis, gets parented to the surface.

3. Double-click the Motion Vectors map to display its menu.
4. In the Controls tab, set the Motion box to Analysis.

To specify the media to analyse:

1. In the schematic, select the Motion Vectors map.
2. Right-click the Motion Vectors map, and select Assign Media > Your Media.

   You usually want to assign the same media as the parent surface, but you can create interesting effects by assigning a different media.

When the Result (F4) view is displayed, Action computes the motion vectors for every motion vectors map set to Analysis. Every new frame displayed requires a new analysis. This analysis is cached as the frames are displayed. But you can cache the analysis on-demand.

To cache the motion vectors analysis:

1. Double-click the Motion Vectors map to display its menu.
2. Display in the Motion Vectors menu, display the Analysis tab.
3. Set the Start and End fields to bound the analysis.

   If you do not need to track the whole length of a scene, use these fields to constrain it in time: the shorter the track, the less time the caching will take.

4. Click Cache Range.

In cases where you know that the tracking is to be performed in a very localized area of a scene, you can use the ROI contraint to minimize the area to analyse.

To analyse only an area of a scene:

1. Double-click the Motion Vectors map to display its menu.
2. Display in the Motion Vectors menu, display the Analysis tab.
3. Enable ROI.
4. Press F8 to display the Motion Vectors map in Object View.
5. In Object View, resize the area to frame the area to track.
6. Close Object View when complete.

Using an External Motion Analysis

The Motion Vector map can receive Forward and Backward motion vector input, but you need to specify this using the Motion Vector map's Controls > Motion box. When feeding both type of motion vectors to the media input node, Flame expects the Forward Vectors to be connected to the Front input and the Backward Vectors to the Matte input.

You can enable Controls > Motion Vector to provide to Action's Output Motion Vector render pass the information from the Surface's Motion Vector: this ensures you are no longer limited to having only a single motion data for the whole surface.

To add a motion vectors map:

1. In the schematic, select the surface to which you want to apply the motion vectors.
2. Click Media.
3. In the Media menu, select the motion vector media to use.
4. Do one of the following:
   • Drag the Motion Vectors Map node from the node bin and place it in the schematic.
   • Double-click the Motion Vectors Map node. You do not need to be in Schematic view to add a node in this manner.

   The motion vectors object is added to the schematic with its own parent axis. The new axis is the child of the selected surface or geometry. In Schematic view, the number in brackets next to the name of the Motion Vectors node indicates the media used for the motion vectors.

   To specify different media as the source, select the media in the Media menu, then click Apply, or use the Read File tab to manage the texture media (see Working With Textures in Map Nodes).

   Note: If you accessed Action as a Timeline FX, you are limited to one front/matte media, and therefore may not get the desired result. In this case, you can access Action from Batch or Batch FX, or from the Tools tab.
5. Double-click the Motion Vectors node in the schematic, or follow the tab population rules for the Object menu (see Populating Menu Tabs of Selected Objects).

   The Motion Vectors menu appears.