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

CS335 Principles of Multimedia Systems 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 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 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 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 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 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

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

CS335 Principles of Multimedia Systems 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. Pen gesture interface Virtual Reality

CS335 Principles of Multimedia Systems 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 Example Systems Motion Capturing

CS335 Principles of Multimedia Systems Example Systems  The MIT Kidsroom Posture recognition Action detection

CS335 Principles of Multimedia Systems 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 Color Blob Detection We would like to compare the template color histogram with each location in the image. 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) (x,y) h(x,y) is the color histogram ab cd

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

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

CS335 Principles of Multimedia Systems 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 Mean Shift Tracking Result

CS335 Principles of Multimedia Systems 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 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 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.