This document summarizes the development of a face tracking technique using video processing and the Kalman filter in MATLAB. The author captured a video of their face moving, then developed code to segment the face from each frame, recognize it as a blob, represent it with bounding box coordinates, and track its position over time using Kalman filtering. Key steps included background subtraction segmentation, blob detection recognition, extracting bounding box representation, and implementing Kalman filtering for tracking within MATLAB's tracking framework. The results showed the tracker successfully following the face as it moved in and out of frames.

1. FINAL REPORT OF DIGITAL VIDEO PROCESSING
FACE TRACKING
I.INTRODUCTION
In this report, the work consists of capturing a video with my face moving in and out;
developing a technique to track my face(in video) ;finally I will show the details the
technique I used to do this by showing final results in pictures. To do this some
techniques related to matlab programming language was used as we will see it in details
bellow. The result of this report was obtained with the help of the combination all code
for the tracking in appendences.
II. PROJECT IN DETAILS
II.1.Capturing a video with my face
Although I have mentioned in introduction do my project I used technique related to
matlab programming language, but this step (Capturing a video with my face) is not
related to mat lab programming language. To capture a video, I only used a
camera(digital camera).After capturing this camera ,I saved it in my computer in 3gp
format in file as gashema.
II.2.Playing the captured video in matlab.
To play the captured video in matlab ,matlab function was used as will see it in the
indices of this report. The objective of playing this video in matlab was for testing it
before tracking it. As the original video was in 3gp format and as I used matlab function
to play this video as avi format, before playing it in matlab I first converted it in avi
format by using one of suitable software to tthis work(avi converter).To do it I used
play_video (‘filename.avi’) as function to read this video in matlab.
III.TRACKING MY FACE.
To track my face ,I used technical based on Kalman filter i.e. useful technique for
tracking different types of moving objects which was invented by Rudolf Kalman at
NASA( National Aeronautics and Space Administration) to track the trajectory of
spacecraft. Normally, at its heart, the Kalman filter is a method of combining noisy (and
possibly missing) measurements and predictions of the state of an object to achieve an
estimate of its true current state.As the aim of this project is not to explain or develop this
technique(Kalman filter) applied to track my face. I inserted those few explanations of
Kalman filter in order to allow someone who reads my report can have some ideas of
this technique i.e what this technique is about.
a. Running Kalman filter tracker.
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2. To run the basic Kalman filter tracker for my video,the following matlab function was
used: kalman_tracher(gashema,0.05,50,3);
Matlab code for this function is found in appendices.The code is tittles as matlab code for
combination of all above codes.
When you are tracking the face in matlab, pressing any key while the tracker is running
will pause the tracker until you press another key.
b. Implementation of the project in tetails
To implement this project on tracking, four steps were implemented using matlab
programming language. Figure bellow shows how the process looks like.
The basic processing pipeline for object tracking.
In this section we will describe each of the processing modules and the implementation
provided. First we describe the toplevel function that strings together all processing
modules into a complete tracker.
1 .The toplevel function
A tracker in the practicum software framework consists of:
• A segmenter that segments foreground objects from the background;
• a recognizer that identifies which foreground objects are being (or should be)
tracked;
• a representer that represents each tracked object in terms of some abstract feature
space;
• a tracker that actually does the tracking (i.e. estimates the position of each tracked
target in the current frame); and
• an optional visualizer that displays a visualization of each frame of the tracker.
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3. As I have mentioned at the beginning of this report,a to track my face in video, Matlab
function implementing each of these modules in order to be complete is required .i.e a
tracker (i a collection of processing modules) is modeled in Matlab as structure
containing references to each module (that is the Matlab function implementing the
module). This structure also contains all state variables that must be passed down the
pipeline to other modules. The structure T must contain the following substructures:
1. T.segmenter which must contain a function
reference T.segmenter.segment to a function taking the structure T and the
current frame.
2. T.recognizer which must contain a function
reference T.recognizer.recognize to a function taking the
structure T and the current frame.
3. T.representer which must contain a function
reference T.representer.represent to a function taking the
structure T and the current frame.
4. T.tracker which must contain a function reference T.tracker.track to
a function taking the structure T and the current frame.
5. And optionally T.visualizer which must contain a function
reference T.visualizer.visualize to a function taking the structure T
and the current frame.
For example, you can run the tracker on a video using the run_tracker function.
where T is the structure setup previously with references to all of the tracking modules
and fname is the filename of the video to run the tracker on. Also,you will write a
wrapper function around run_tracker that sets up the processing pipeline and sets
any needed parameters We will see all these matlab functions in matlab codes at the end
of this report in appendices .
2.Segmenter
The segmenter provided performs simple background subtraction based on a rolling-
average background model and temporal differencing. The background model is updated
like this:
where is a learning rate parameter that controls how quickly the background
model incorporates new information and how quickly it forgets older observations. Every
pixel in every frame is classified as either background (0) or foreground (1) using a
simple threshold:
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4. where is a threshold on the difference between a pixel in the current frame and
background model. This threshold controls which pixels are classified as foreground.
Finally, the foreground image is cleaned a little to close small gaps:
where is the morphological closing operation and is a disk of radius .
The Matlab implementation of this segmenter looks like this
(file background_subtractor.m in the framework directory).See matlab code for
this at the end of this report in appandices.
3. The recognizer
The next stage in the pipeline is the recognizer. The basic recognizer provided with the
tracking framework is based on simple blob detection. Connected components are found
in the segmented image, and the whole set of components is retained as the "recognized"
object to be tracked.
By referring to the matlab code of recognizer, you can see how the recognizer assumes
the segmented image from the previous stage is passed in
the T.segmenter.segmentedvariable. This is an example of how state is passed between
processing modules. The recognizer then puts its result in the
variableT.recognizer.blob for subsequent modules to use.
It is important to note that the framework does not enforce any particular protocol for
passing state variables from module to module. You are responsible for establishing how
each module receives its parameters and how it stores its results.
4. The representer
The next module is the representer, which takes the results of recognition and computes
a representation of each recognized object to be tracked. In the basic tracker, the
representer extracts the BoundingBox and size of each blob and only keeps the biggest
one as the single object being tracked. See the matlab code in the appendices.
In a more realistic tracker, the representer module would be responsible for maintaining a
list of objects being tracked and establishing correspondences between recognized objects
and those currently being tracked.
5 The tracker
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5. A simple Kalman filter tracker has been provided in the practicum framework. It uses the
results of the representer to track the position and extent of the object being tracked. The
Kalman filter works by estimating an unobservable state which is updated in time with
alinear state update and additive Gaussian noise. A measurement is provided at each time
step which is assumed to be a linear function of the state plus Gaussian noise. It is the
most complex module in the framework, and receives and stores a large amount of state
information .Matlab code of this step is at the end of this report in appendices.
3.6 The visualizer
The final module in the processing pipeline is the visualizer. It is not mandatory, but it is
always a good idea to provide a minimal visualizer to see how your tracker is performing.
The visualizer provided simply displays the current frame with rectangles indicating the
current detection and current estimate (file visualize_kalman.m in the framework
directory).See matlab codes in appendences.
III.THE RESULT AND DISCUSSIONS ON MY WORK
When my face in the video is tracked,it was shown that the tracker is tracking the
face.When the face is moving,the tracker also will move to where the face moves in
order to track it(the face).When the face is out, the tracker disappears.If the face comes in
again ,immediately the tracker also comes in.If the face is stationary, the tracker stops
moving i.e it track the face without movement.
The result of the work.
a.the face is in and moving
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I
REFERENCE
1. Yao-Jiunn Chen, Yen-Chun Lin, simple Face-detection Algorithm Based on
Minimum Facial Features.
2. Sanjay Kr. Singh1, D. S. Chauhan2, Mayank Vatsa3, Richa Singh3*, A Robust
Skin Color Based Face Detection Algorithm
3. Eli Brookner: Tracking and Kalman Filtering Made Easy. Wiley-Interscience, 1st
edition, 4 1998.
4. http://en.wikipedia.org/wiki/Face_detection
5. http://www.micc.unifi.it/bagdanov/tracking/
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8. V.APPANDENCES
1.Matlab code to read my video
function play_video(fname);
% PLAY_VIDEO - simple function to play a video in a Matlab
figure.
% PLAY_VIDEO(fname) will play the video in the file
specified by 'fname'.
% See also: videoReader, nextFrame, getFrame
vr = videoReader(fname);
while (nextFrame(vr))
img = getFrame(vr);
imshow(img);
pause(0.01);
end
return
2.Matlab for Tracking framework
a.Matlab code for segmenter
function T = background_subtractor(T, frame)
% Do everything in grayscale.
frame_grey = double(rgb2gray(frame));
% Check to see if we're initialized
if ~isfield(T.segmenter, 'background');
T.segmenter.background = frame_grey
end
% Pull local state out.
gamma = T.segmenter.gamma;
tau = T.segmenter.tau;
radius = T.segmenter.radius;
% Rolling average update.
T.segmenter.background = gamma * frame_grey + (1 - gamma) *
...
T.segmenter.background;
% And threshold to get the foreground.
T.segmenter.segmented = abs(T.segmenter.background -
frame_grey) > tau;
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9. T.segmenter.segmented = imclose(T.segmenter.segmented,
strel('disk', radius));
Return
b.Matlab code for recognizer
function T = find_blob(T, frame)
T.recognizer.blobs = bwlabel(T.segmenter.segmented);
return
c.Matlab code for representer
function T = filter_blobs(T, frame)
% Make sure at lease one blob was recognized
if sum(sum(T.recognizer.blobs))
% Extract the BoundingBox and Area of all blobs
R = regionprops(T.recognizer.blobs, 'BoundingBox',
'Area');
% And only keep the biggest one
[I, IX] = max([R.Area]);
T.representer.BoundingBox = R(IX(size(IX,2))).BoundingBox;
end
return
d. Matlab code for tracker
function T = kalman_step(T, frame)
% Get the current filter state.
K = T.tracker;
% Don't do anything unless we're initialized.
if isfield(K, 'm_k1k1') && isfield(T.representer,
'BoundingBox')
% Get the current measurement out of the representer.
z_k = T.representer.BoundingBox';
% Project the state forward m_{k|k-1}.
m_kk1 = K.F * K.m_k1k1;
% Partial state covariance update.
P_kk1 = K.Q + K.F * K.P_k1k1 * K.F';
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10. % Innovation is disparity in actual versus predicted
measurement.
innovation = z_k - K.H * m_kk1;
% The new state covariance.
S_k = K.H * P_kk1 * K.H' + K.R;
% The Kalman gain.
K_k = P_kk1 * K.H' * inv(S_k);
% The new state prediction.
m_kk = m_kk1 + K_k * innovation;
% And the new state covariance.
P_kk = P_kk1 - K_k * K.H * P_kk1;
% Innovation covariance.
K.innovation = 0.2 * sqrt(innovation' * innovation) +
(0.8) ...
* K.innovation;
% And store the current filter state for next iteration.
K.m_k1k1 = m_kk;
K.P_k1k1 = P_kk;
else
if isfield(T.representer, 'BoundingBox');
K.m_k1k1 = T.representer.BoundingBox';
K.P_k1k1 = eye(4);
end
end
% Make sure we stuff the filter state back in.
T.tracker = K;
return
e. Matlab code for Visualizer
function T = visualize_kalman(T, frame)
% Display the current frame.
imshow(frame);
% Draw the current measurement in red.
if isfield(T.representer, 'BoundingBox')
rectangle('Position', T.representer.BoundingBox,
'EdgeColor', 'r');
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11. end
% And the current prediction in green
if isfield(T.tracker, 'm_k1k1');
rectangle('Position', T.tracker.m_k1k1, 'EdgeColor', 'g');
end
drawnow;
return
f. matlab code for combination of all those above codes
function T = kalman_tracker(fname, gamma, tau, radius);
% Initialize background model parameters
Segmenter.gamma = gamma;
Segmenter.tau = tau;
Segmenter.radius = radius;
Segmenter.segment = @background_subtractor;
% Recognizer and representer is a simple blob finder.
Recognizer.recognize = @find_blob;
Representer.represent = @filter_blobs;
% The tracker module.
Tracker.H = eye(4); % System model
Tracker.Q = 0.5 * eye(4); % System noise
Tracker.F = eye(4); % Measurement model
Tracker.R = 5 * eye(4); % Measurement noise
Tracker.innovation = 0;
Tracker.track = @kalman_step;
% A custom visualizer for the Kalman state.
Visualizer.visualize = @visualize_kalman;
% Set up the global tracking system.
T.segmenter = Segmenter;
T.recognizer = Recognizer;
T.representer = Representer;
T.tracker = Tracker;
T.visualizer = Visualizer;
% And run the tracker on the video.
run_tracker(fname, T);
return
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