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Image processing--calibration and canny edge detection

For each snapshot taken from the video, the processing returns the coordinates of the drum stick position relative to the paper boundary.

Since we are only using a part of the screen (only the part of white paper). We need to calibrate a new coordinate system for our later position detection. Therefore, we first took a snapshot of the whole system to detect the edge of the paper and then chose a corner as the new origin.

Intro to canny edge detection

To detect the edge of the paper, we used canny edge detector. To better understand the method, instead of using the MATLAB command, we implemented the method on our own.

Basic steps for canny edge detector

  • Smooth with Gaussian Filter
  • Compute Horizontal/Vertical Gradient
  • Compute magnitude of gradient
  • Non-Maximal Suppression
  • Perform Hysteresis Threshold
We have our codes attached at the bottom.

The image we implemented canny edge detection

After canny edge detection

The edge of the pater has been detected fairly accurately.


Before doing any image processing techniques on an image, we usually first smooth the image to get rid of most noise. To do this, we apply a Gaussian smoothing filter to the image.

Image gradient

An image gradient is a directional change in the intensity or color in an image. Edge detection utilized image gradient a lot since edges usually are places with discontinuity.

Gradient calculations

% The filter that reduces noise f = 1/159*[2 4 5 4 2;4 9 12 9 4;5 12 15 12 5;4 9 12 9 4;2 4 5 4 2]; n = imfilter(mg,f,'same');%Gradient Magnitude and Angle %x direction partial derivativemg = double(mg); Dx = [-1 0 1;-2 0 2;-1 0 1]; % y direction partial derivativeDy = [1 2 1;0 0 0;-1 -2 -1];% Compute the gradient magnitude and the angle of the gradient n1 = imfilter(mg,Dx);n2 = imfilter(mg,Dy); % initializations = [];theta = [];theta1= [];n1 = double(n1); n2 = double(n2);for i = 1:size(m,1)for j = 1:size(m,1) % calculate the gradient magnitudes(i,j) = sqrt((n1(i,j))^2+(n2(i,j))^2); theta(i,j) = 360*(atan(n1(i,j)/n2(i,j)))/3.14;% round anglesif (22.5&lt;theta(i,j)&amp;&amp;theta(i,j)&lt;=67.5) theta1(i,j) = 45;elseif (67.5<theta(i,j)&&theta(i,j)<=112.5) theta1(i,j) = 90;elseif (112.5<theta(i,j)&&theta(i,j)<=157.5) theta1(i,j) = 135;elseif (157.5<theta(i,j)&&theta(i,j)<=202.5)||(0<theta(i,j)&&... theta(i,j)<=22.5)||(337.5<theta(i,j)&&theta(i,j)<=360) theta1(i,j) = 0;elseif (202.5<theta(i,j)&&theta(i,j)<=247.5) theta1(i,j) = 45;elseif (247.5<theta(i,j)&&theta(i,j)<=292.5) theta1(i,j) = 90;else theta1(i,j) = 135;end endend

Non-maximum suppression

This method returns a single pixel width edge of the image. Basic algorithm is as follows: If pixel (x; y) has the highest gradient magnitude of the three pixels examined, it is kept as an edge. If one of the other two pixels has a higher gradient magnitude,then pixel (x; y) is not on the center of the edge and should not be classified as an edge pixel.In this way we could get a clear and thin edge of the image.

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
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Source:  OpenStax, Virtual drum kit. OpenStax CNX. Dec 19, 2013 Download for free at http://cnx.org/content/col11607/1.1
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