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image of a stop sign that has been edge detected, outlines of objects show in white on black background

We first tried to find the border of the sign.  The outside edge of the sign is a region most of the time, so this was a possibility.  However, there is not a good way of determining which region was the sign.  A first guess was to choose the biggest region, however this did not always work as the sign was not always the biggest object in the picture. We then noticed that the O of stop showed up as two regions, the inner ring and the outer ring.  Since these two regions have approximately the same center (fig. 7), it is possible to find regions that have centers close together and then analyze them to see if they are the sign in question.  For example, if the point is on a stop sign, then the point, the point a bit above it, and the point a bit below it will all be red.  If the point is on a do not enter sign, then the point will be white and the points above and below will be red.  

Both the inner and outer ring of the 'O' in a stop sign have the same center

The points above and below were chosen by using the height of the region found.  By choosing points the height of the region above and below the identified center, the points are on the outside of the letter.  This tells the background of the sign itself.  

This method of finding signs is not the most accurate.  It can be fooled by other signs. For example, a sign for a business that had an O on a red background would be considered a stop sign by this algorithm.  This could be helped by checking more points.  Points immediately around the center should also be red and some points in between the center and the currently checked outer points should be white.  This would improve the accuracy, but it could still be fooled. This algorithm also works best for signs with color.  Signs with white backgrounds such as speed limit signs are hard to find because values that are defined as ‘white’ cover a large range of pale colors and therefore many things not signs are identified as signs.  

Despite these drawbacks, this code is advantageous because it does not require large convolutions like the first method. This means that the method is much faster. To find the sign of the correct size with the first approach, it takes about 30 seconds. To find the sign including the size with the second approach, it takes about .5-1 second.

Sign Reference Percentage Above Threshold
Stop Stop 95%
Speed Limit Stop 0%
Do Not Enter Stop 15%
One Way Stop 0%

Approach iii: template matching and edge detection

For our final algorithm we used both template matching and edge detection in an attempt to combine the positive aspects of the two approaches.  The combined algorithm first utilizes edge detection to isolate regions within the image, throwing out all regions of a size below a certain threshold in order not to waste time with extraneous convolutions.  Once the significant regions, usually numbering between twenty and one hundred, have been identified, each is re-sized to a standard small template size and compared to each image in the template library.  Regions with high correlations with a template image are assumed to be the part of the sign that template was created from.

This combined algorithm performed quite well, although it was not error-free.  As was the case with pure template matching, attempting to match pictures of entire signs was prone to error because the background of any given sign can vary, occasionally leading to quite low correlations.  However, we discovered that using this algorithm to match only specific elements of a sign, such as the “S”, “T”, “O”, and “P” in stop (fig. 8), was much more reliable, as the conditions for such sub-sign features are much more consistent than for the overall sign.  In addition, searching for individual sign features and not just the sign itself means that partially obscured signs that would be beyond our first template matching algorithm would present no problems for this modified one. Our template library was expanded so as to contain a number of sub-sign features for both stop signs and speed limit signs, as both of these signs contain changing characteristics (background for the stop sign, speed limit for the speed limit sign) that can thwart conventional template matching.  Again, we found that matching individual letters yielded a high success rate (fig. 9).  Our basic algorithm was also fairly successful in identifying one way signs and do not enter signs, even though no sub-feature library was created for these signs and only the sign itself was used as a template.

pictures of individual letter 'S' 'T' 'O' 'P' and stop signs with white and black backgrounds

graph showing letters have higher correlation values than signs

This algorithm showed significant success in combining the positive aspects of both tablet matching and edge detection.  In comparison to pure template matching, this method performs correlation calculations on much smaller images and size matching is a non-issue because all regions are re-sized to match the templates.  In comparison to pure edge detection, this method is less prone to false positives and can be much more easily expanded to detect new signs simply by adding to the template library.  Overall, the combination of template matching and edge detection yields a more robust, flexible, and reliable method of sign detection than either algorithm used alone.

Sign Reference Percentage Above Threshold
Stop Stop 95%
Speed Limit Stop 15%
Do Not Enter Stop 66%
One Way Stop 33%

Questions & Answers

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
what's the easiest and fastest way to the synthesize AgNP?
Damian 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, Street sign detection with template matching and edge detection methods. OpenStax CNX. Dec 19, 2011 Download for free at http://cnx.org/content/col11387/1.1
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