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Gives the highlights of the projective flow algorithm we used for image registration.

Overview

Superresolution is based on the idea that images with slight shifts can be aligned and combined into a single, higher resolution image. While aligning images with respect to one another may not seem too complex at first, there are a number of technical details that muddy the waters. Additionally, superresolution requires registration results that are accurate to the subpixel level. While an error of one or two pixels sounds just fine, it would lead to a poor quality image after combination.

Motivation

Let's first look at the impact of registration before delving into the details of the algorithm we chose. Consider the following two test images:

Registration test images

Two slightly shifted images (Source: http://lcavwww.epfl.ch/software/superresolution/superresolution_dataset1.tar.gz)

While these two images may appear to be the same, they are actually just slightly different from each other. While we could try to combine the images as they are now, we need to register them first to achieve a better result. Below two difference graphs illustrate the impact of registration, the first showing the difference before registration, and the other after.

Difference graphs

Before registration
After registration

Even though it is hard to see a visible difference when viewing the two images separately, the difference graphs above show how registration can still detect difference and account for them.

Algorithm

While there are a number of different techniques that can be used to register images, many of them are feature-based . They attempt to track the same set of points as they move from image to image. This can work well, but only if the points are detect accurately each time. Instead, we chose to use a featureless algorithm, which avoids feature points by using the flow of all pixels in the image. It improves upon the optical flow concept discussed in a previous module by allowing for changes in translation, rotation, scale, pan, and tilt between each image. The algorithm is detailed below.

  • Calculate the vertical, horizontal, and time derivatives between the two images. This is same process mentioned in Optical Flow .
  • From these spatiotemporal derivatives, estimate an approximate model (q) of the projective parameters. There are several models that can be used, such as bilinear and pseudo-projective. The system used to estimate the bilinear model is shown below.

    Bilinear approximation model

    System of equations that relates derivative to the bilinear approximation model (Source: 1)
  • Using the four corners of the image, calculate their new coordinates from the approximate model. In the formulas for the bilinear model below, u m + x and v m + y denote the new x and y coordinates respectively.

    Bilinear coordinate formulas

    Relates old and new coordinate via approximate (q) parameters (Source: 1)
  • These old and new coordinates now completely determine the projective parameters in the exact model (p).
  • Apply these new parameters (p) to one of the images and iterate until the difference is negligible.

Improving accuracy

To get better results, we can create a multi-resolution pyramid for each image first. This means that we generate several levels of increasingly blurry images. Starting at the blurriest level, we apply several iterations of the algorithm as described above. Then, we move up to a less blurry level and repeat, but we carry over the result from the previous level and use that as our starting point.

Questions & Answers

Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
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
yes that's correct
Professor
I think
Professor
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
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
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
hi
Loga
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Elec 301 projects fall 2006. OpenStax CNX. Sep 27, 2007 Download for free at http://cnx.org/content/col10462/1.2
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