More visualization

Overview

Teaching: 10 min
Exercises: 20 min

Questions

• Some more visualization techniques?

Objectives

• Create motion average images.

• Create motion history videos.

Motion average image

While motiongrams are good for getting a general sense of the spatiotemporal distribution of a video file, a motion average image is good for getting a general sense of the space covered. This may be thought of as similar to an “open shutter” on a camera, since the function just averages (and normalizes) over all the frames. Try:

mgmotionaverage('dance_motion.avi');

If the motion is evenly distributed in the image, the motion average image may not contain much information. But if a person has been standing still in one spot, it will show up very clearly.

It is also possible to run this function on the original video:

mgmotionaverage('dance.avi');

Such an average image may also be useful in combination with the motion average image.

If you only want to look at a particular part, you may choose to identify the start and stop positions of the averaging (in seconds from the start of the file):

mgmotionaverage('dance.avi',0,5);

So here we get the average of the first 5 seconds of the file.

Motion history video

One dynamic visualization technique is that of creating a motion history video, which gives you an idea of how the motion has been unfolding in time. This can be done with the following command:

mgmotionhistory('dance_motion.avi');

It can, in fact, also be run on the original video:

mgmotionhistory('dance.avi');

We have up until now primarily worked with video in greyscales. This is more cpu-friendly, since it only consumes 1/4 of the processing power as that of colour. Sometimes colour may be important, though, so it is possible to run the process on all the video planes like this:

mgmotionhistory('dance.avi',20,'color');

The number 20 here refers to the number of frames of the history. You can try some different settings here too.

Key Points

• A motion average image is a kind of open-shutter technique.

• A motion history video visualizes motion trajectories.

• All functions can be run on any type of video input.