Multimedia and Human Computer Interfaces

1. Multimedia and Human Computer Interfaces Hao Jiang Computer Science Department Boston College Nov. 20, 2007 CS335 Principles of Multimedia Systems

2. Outline • Human Computer Interface. • Multimedia interfaces and applications. • Vision based interfaces • Systems using vision based interfaces. • Some basic methods in vision interfaces • Background subtraction. • Color blob detection and tracking. • Face detection (Viola and Jones face detector). CS335 Principles of Multimedia Systems

3. Human Computer Interface • Different meanings of HCI • The study of people, computer technology and the ways they interactive with each other. • The design, evaluation and implementation of computer systems for human use. • The research to study how to make computer systems more useable. CS335 Principles of Multimedia Systems

4. Aspects of HCI • Design • Intuition, experiences and design principles. • Human factors • Experiments testing the perception, memory and cognition models of human being. • Devices • Physical devices such as mouse, keyboards and other fancy HCI hardware. • Software and systems • Such as windows GUI, shell commands in Unix etc. CS335 Principles of Multimedia Systems

5. HCI Studies • Computers • What are they good at and bad at? • Input, output, processing, networking, etc. • People • What are people good at? • What is the limitation of human abilities? • Input, output, memory, perception and cognition model. • No average answer. Must accommodate diversities. • Usability • More than the size of widgets, where are the buttons and syntax of commands. • Context • Environment, physical constraints, cognition constraints, task, etc. CS335 Principles of Multimedia Systems

6. The Quality of HCI • There are fives factors that affect the design and implementation of HCI • Time to learn. • Speed of performance. • Rate of errors. • Retention over time. • Subjective satisfaction. CS335 Principles of Multimedia Systems

7. Multimedia Interfaces • Multimedia interface combines different sorts of media modalities to achieve more natural and more efficient human computer communication. • Speech, audio, touch, video input (patterns, posture, gesture) etc. • “Put that there” is an example multimedia HCI that combines speech, gestures and graphics. Put that there, MIT 1981 http://www.media.mit.edu/speech/sig_videos.html CS335 Principles of Multimedia Systems

8. Early and Late Integration Mode 1 Classification Output Features Mode 2 Early integration Mode 1 Classification Features Output Mode 2 Classification Late integration CS335 Principles of Multimedia Systems

9. Advantages of Multimedia Interface • More alternative methods. • The flexibility of combining different schemes. • More efficient for specific tasks. • Greater precision of information. • Help handicapped people to use computers. Virtual Reality Pen gesture interface http://www.youtube.com/watch?v=d7eGypGOlOc&feature=related http://www.youtube.com/watch?v=Gnq-8iaOcXk CS335 Principles of Multimedia Systems

10. Vision Based Interfaces • Vision based interfaces uses computer vision techniques to achieve more effective HCI. • Vision based interfaces are based on techniques such as: Hand tracking, Hand gesture, Arm gesture Hand Pointing Face detection Head tracking Gaze Expression Lip reading Posture, body gesture and action recognition CS335 Principles of Multimedia Systems

11. Example Systems Motion Capturing CS335 Principles of Multimedia Systems

12. Example Systems • The MIT Kidsroom Posture recognition Action detection CS335 Principles of Multimedia Systems

13. Methods in Vision Interfaces • Background subtraction. • Estimating the background B(n) = B(n)*alpha + I(n)*(1-alpha) Foreground Map = |Image – Background|>threshold alpha is a positive floating point number close to 1. CS335 Principles of Multimedia Systems

14. Color Blob Detection We would like to compare the template color histogram with each location in the image. h(x,y) is the color histogram a b (x,y) c d We first convert each image pixel by its bin number. s(x,y) = s(x,y-1) + i(x,y) h(x,y) = h(x-1,y)+ s(x,y) CS335 Principles of Multimedia Systems

15. Blob Tracking (Filtering Scheme) t3 t2 t1 t4 Search window : Predicted location. : detected object. p y : Final estimation. x x = p * alpha + y * (1-alpha) CS335 Principles of Multimedia Systems

16. Blob Tracking (DP Approach) C F B A E D t3 t2 t4 t1 cost(F) + alpha ||2C-B-F|| CF const BC CE AB t DF BD DE CS335 Principles of Multimedia Systems

17. Mean Shift Tracking • Instead of exhaustive search in a window, if object moves slowly, we can use a more efficient location updating scheme – Mean shift. • In the following equation, x(i) are points in the search window and y is the location of object, w(i) are weights. CS335 Principles of Multimedia Systems

18. Mean Shift Tracking Result http://www.caip.rutgers.edu/~comanici/Papers/KernelTracking.pdf CS335 Principles of Multimedia Systems

19. Face Detection • Viola and Jones face detector These features can be computed using integral images similarly to the color histograms discussed before. CS335 Principles of Multimedia Systems

20. Face Detection • It uses boosting scheme to automatically choose the optimal weight for the classifier based on each kind of feature. • To further improve the efficiency, a cascaded classifier is used. CS335 Principles of Multimedia Systems

21. Summary • We only touch the very surface of multimedia interfaces. • Currently, the dominant HCI is still GUI with keyboard and mouse. • Multimedia interfaces are beginning to attract more and more interests. • We need more robust and efficient media recognition schemes to support effective multimedia interfaces. CS335 Principles of Multimedia Systems