Tracking Feature Points in Videos
The Track page
in the Main Window is used for marking subsequent
frames based
on points marked in an initial frame. Without this component
users would have to mark feature points in every frame
which would be time consuming and tedious.
When feature points stand out, Photo4D can
automatically track them in
videos.
The following explains the basic steps for tracking marks:
- Mark feature points in a frame. Make sure to mark
them accurately using the MagGlass since
they will be used as reference to detect the feature points in other
frames.
- Select the marks to be tracked, by either dragging the Shift-left
mouse button over the marks or by using the menu command
[Mark|Select all] to select all the marks in the image.
All the selected points become highlighted in green.
- Set tracking mode and parameters:
- Mode: "Fast" mode uses unnormalized template matching. It should
be used when the shading of the feature points does not change much.
"Normalized" mode can compensate for the change in lighting but
tracks at a slower rate than Fast mode.
- Mask size: Change this value to reflect
the size of feature points appearing in the videos.
- Range: An estimation of the maximum number of pixels the marks
move in two consecutive frames.
- Score T: Tracking stops for a mark whose detection score is lower
than this value.
- Overlap T: Tracking stops when the distance between two marks is
less than this value (in pixels).
- Start tracking: Using the control buttons, you can track the marks to
the next or previous frame, or track continuously until the stop button
is pressed.
Tracking feature points in videos is an iterative process. Users should
work with one video at a time. Other Image windows
and windows such
as Camera Param window or Preview window, should be closed. This can
significantly increase tracking speed since Photo4D does not need to
spend time updating the other windows. It is best to start with just a few
marks (between two and six) so that it is easier to monitor, detect and
correct errors.
When subjects are well tagged and the feature points
appear very distinctive in videos, Photo4D can track marks fairly well.
Still manual editing is required to connect
different sections of marks, or
to merge marks in different videos.
When the feature points are not obvious in videos, tracking may not work
in some frames at all. In this case, manual editing becomes the only
choice.