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This module is about the challenges we faced when detecting objects and the solutions to them.

Resolution difference between template and video

In the beginning, we made the template image and the video separately. In our experiment we used the large green breadboard as the object to be tracked. We first took a picture of the breadboard lying on the table using a high-resolution camera. Then, we switched the camera to video mode with a size of only 480×640 and recorded a video with someone moving the board around. We ran the code and the tracking result was disappointing.

Template with high resolution
Tracked result – off target (the “matched” points do not even make sense)

Then we realized that lots of details in the template image could not even be seen on the object in the video. For example, the screws and pinholes were not at all visible. Hence, we decided to crop out the template from a screenshot of the video so as to ensure the same level of detail. And it worked!

Template that is cropped out from the same source video
Tracking result of a video frame

Motion blur and video with lower resolution

Another problem with matching video frames is that when the shutter speed is relatively slow, the image in each frame blurs and the features of the object are no longer distinguishable.

Motion-Blurred Image
Motion-Blurred Image

Clear image
Clear image

To avoid motion blur, we had to slow down our movements when recording the video. Otherwise, the tracked position would be completely off.

However, the overall resolution and quality of the video matter, too. We tried converting one of our video files online because one member’s MATLAB cannot read in a .mov file. But after converting the file, the quality of the tracking result went down dramatically. We believe that it was partially due to the even lower resolution of the converted file. When the resolution is too low, a sharp corner can no longer be distinguished from a round corner. On the other hand, there could also be a problem introduced by the compression method that was used by that website, because clearly we could see non-uniformity in the once uniform white board area. This compression method actually introduced additional features or errors into the video frames.

Before video conversion
Before video conversion

After video conversion (also notice that the ratio of the image is changed)
After video conversion (also notice that the ratio of the image is changed)

Complex background

Since the resolution of our recording devices was not very good, a complex background could also be problematic, because there would be plenty of similar features in the background, but there would not be enough details to fully distinguish them. As a result, we had to use a simple background, such as a wall, and had to avoid wearing shirts full of complex patterns.

Features of template are inaccurately matched to similar features in the background
Features of template are inaccurately matched to similar features in the background

Objects without distinct features

An object that doesn’t have distinct SURF features is extremely problematic. We were experimenting with a blue pencil box. If the pencil box, lying on the table by itself, was used as the template image, OpenSurf would not output any feature descriptor that was above the threshold. Not until we lowered the threshold all the way down to 0.00001 (it was always set to 0.0008 for our project) did we find six features (normally more than a dozen for a small template and more than a hundred for a full video frame), and even those six features were degenerated!

Only six repeated features are found when threshold is set to 0.00001

If we cropped the template in such a way that some background was included, then only the outline or features in the background would be detected, and looking for matching features in the testing image would not make any sense. As is shown below, the matching failed.

All tracking points are attracted to irrelevant edges.
All tracking points are attracted to irrelevant edges.

In order to avoid all of the problems that occurred during our experiments, we decided that for the demo video we would only have one dancer, so as to get a closer shot and a higher resolution. The person would wear plain clothing, act in front of a wall, and move slowly and avoid out-of-plane rotation in order to increase the accuracy of object tracking.

However, because the feature matching is not very robust, and even one or two mismatches would introduce huge error into the orientation of the object, the output angular velocity is extremely noisy. That is why we finally decided to discard the angular velocity data.

Questions & Answers

How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
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
How can I make nanorobot?
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
how can I make nanorobot?
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
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Source:  OpenStax, Dwts - dancing with three-dimensional sound. OpenStax CNX. Dec 14, 2012 Download for free at http://cnx.org/content/col11466/1.1
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