About opencv Optical Flow Example

Learning Objectives

OpenCV is a powerful open-source library for image processing and computer vision. This example demonstrates one particularly common workflow in new-media art: performing optical flow. This is immensely useful for determining movement within the scene!

After studying this example, you'll understand how to:

Obtain video from a camera or stored file
Use that video as the basis for image processing operations with OpenCV, including image arithmetic
Extract optical flow data using cv::Mat and apply that information to move objects around in the scene.

Expected Behavior

When launching this app, you'll see a low resolution, colorized representation of the video. Movement in the video will cause elements in the app to change color, spin or move about the screen.

There are a few user-modifiable settings in this app:

Pressing the space bar will change between the 3 modes.
Pressing the up and down keys will adjust the size of the opencv image that is used for calculating optical flow. The smaller the image, the faster the operation.
Press the left and right arrow keys to change the blur amount.
Mirror the image by pressing the m key.
View the optical flow by pressing the d key.

One more thing. In line 7 of the ofApp.h file, you'll see the following line commented out:

cpp

//#define _USE_LIVE_VIDEO

If you uncomment this line, the app will use your computer's built-in webcam instead of a stored video file! It accomplishes this by swapping out the ofVideoPlayer with an ofVideoGrabber.

Other classes used in this file

This example links against the ofxOpenCv core addon. It uses the following classes from that addon:

In addition, this example uses the following classes to access video from a live camera and/or a pre-stored file: