# 0.5 Edge detection

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## Canny edge detector

We use the Canny Edge Detector to (hopefully) obtain sharp edges for our image now that we have “blurred” together the dots which form the cell edges. The Canny edge detector first takes a gradient of the image. A gradient magnitude, as well as the edge direction (which way the gradient is increasing) can then be found. The Canny edge detector does this by using four different filters which can detect horizontal, vertical and diagonal edges. For each pixel, the filter which outputs the largest response can be found and the direction determined.

## Distance matrix

Once we have run our image through the Canny edge detector, a distance filter is used to connect all remaining lines in a cell’s border. The distance function calculates the Euclidean distance between each pixel and the nearest pixel which is on. The output of the distance function is a matrix having the same dimensions as the image matrix. The entries correspond to the distances; for example, if pixel (i,j) was a distance x away from the nearest on pixel, the (i,j) entry in the distance matrix will be x.

After the distance matrix is found, an iterative method is used to go through each entry of the matrix. A threshold distance is determined and every entry of the distance matrix which falls under the threshold is mapped to one, and every entry which falls above is mapped to zero. What exactly is this doing? Well, if a pixel is close enough to an on pixel, then we assume it is part of the cell’s border, and thus must be turned on as well. The distance function and subsequent thresholding is performed multiple times, with the threshold getting small and small each time until the cell borders are completely continuous. The result is shown below.

#### Questions & Answers

I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
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
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
research.net
kanaga
sciencedirect big data base
Ernesto
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.
Bharti
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
Daniel
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
Maciej
characteristics of micro business
Abigail
for teaching engĺish at school how nano technology help us
Anassong
How can I make nanorobot?
Lily
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Detection of cell boundaries in optical fiber probe images. OpenStax CNX. Jan 20, 2008 Download for free at http://cnx.org/content/col10501/1.2
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