<< Chapter < Page Chapter >> Page >


Modified viola-jones face detection

First we detect the face using a Viola-Jones based algorithm. The exact algorithm we used is outlined by Lienhart, et al. [3] . This algorithm uses an extended set of Haar Features to determine where a face is in an image.

Figure 1 : Extended set of Haar-like features used in the algorithm we applied. The Intensity values for each feature will be the sum of the white region minus the sum of the black region. [3]

When a Haar-like wavelet passes over an image, edges become intensified as edges will have a large difference between the white and black regions of the wavelets (Fig. 2 ) By setting a high enough intensity threshold, the points above the threshold will likely be edges. An image of a face will exhibit many edges at different facial landmarks. In order to ascertain if a windowed region of the image is a face, several sweeps of different Haar features are done in order to ensure high enough accuracy of detecting a face. Detection of a face should also be attempted with several window sizes as face size within an image can vary.

This method would be very time-consuming and computationally expensive if all Haar features were swept over all possible windows of the entire image. In order to speed this up, a cascade of feature classifiers is used (Fig. 3 ). At each stage of the cascade, less and less common Haar features with more strict rules are added in order quickly throw out windows that do not contain a face. If the image passes one stage of the cascade, this will weakly indicate the presence of a face. However, if it passes all classifiers, there will be a high confidence level that a face is present.

Figure 2 : Cascade of feature classifiers. [2]

A nice demonstration of how using a cascade of Haar wavelets for face detection works is hosted by the University of St. Andrews ( Haar Wavelet Face Detection Demo ). This example illustrates very clearly how a weak classifier cascade drastically speeds up computation time.

Shi-tomasi corner detection

Shi-Tomasi corner detection is based upon Harris-Stephens corner detection, just with different threshold parameters. Therefore, we start explaining the algorithm by defining the Harris corner detector operator[1] :

  • E - Sum of squared differences between the original and moved window
  • u - x direction window displacement
  • v - y direction window displacement
  • w ( x , y ) - Weighting function of the window, either a gaussian or a window of ones.
  • I ( x + u, y + v ) - intensity of the moved window
  • I ( x , y ) - intensity of the original window

The detector essentially scans the image with a window of size x by y , for places where there is a large change in intensity in both the x and y directions.

In order to simplify the above expression, we use a first order Taylor series approximation of

I ( x + u, y + v ) – I ( x , y ) :

Then changing to a matrix representation gives:

Then defining M as the structure tensor from above:

The determination of R , which is the parameter that indicates the importance of the point as a corner is done by taking the minimum of the two eigenvalues of this matrix.


are eigenvalues of M.

This is the Shi-Tomasi modification of the Harris and Stephens corner detection algorithm[5] . While the Harris and Stephens algorithm was more computationally efficient, the Shi-Tomasi algorithm was found to be more accurate. Since the original Harris and Stephens paper, the computational cost of computing eigenvalues has become less and less significant, so the Shi-Tomasi algorithm is now more commonly used.

Mouth curvature detection

Using the corners detected using the Shi-Tomasi algorithm, we use a least squares method to fit a second-order polynomial to the edge points detected [4] . From the second order term we get a measure of the curvature of the points detected in the mouth region.

Questions & Answers

Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get the best Algebra and trigonometry course in your pocket!

Source:  OpenStax, Smile identification via feature recognition and corner detection. OpenStax CNX. Dec 17, 2012 Download for free at http://cnx.org/content/col11469/1.1
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Smile identification via feature recognition and corner detection' conversation and receive update notifications?