Phase unwrapping, Wavelet transform profilometry (WTP), and MEtrology GUided RAdioTHerapy (MEGURATH)

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Phase unwrapping, Wavelet transform
profilometry (WTP), andMEtrology GUided
RAdioTHerapy(MEGURATH)

• Munther Gdeisat

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Phase unwrapping
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Phase unwrapping

• Problem statement
• 2D phase unwrapping
• 3D phase unwrapping
• Publicityfree source code

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What is phase unwrapping?

• Suppose that you have a signal, an image or a
  video.
• The required information is embedded in the phase
  of the signal, image or video
• To extract the phase information you need an
  algorithm
• Fourier transform
• Wavelet transform
• Etc
• Normally, these algorithms produce complex data.
• The phase can be extracted using the arctangent
  function that operates on these complex data.

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What is phase unwrapping?

• The arctangent function extracts the required
  phase information.
• But this information cannot exceed the range -?
  and ?.
• If the original information exceeds the 2? range,
  then
• The extracted phase is wrapped
• And an unwrapping algorithm is required.

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1D phase unwrapping- example 1

• Phase unwrapping appears simple at the first
  glance but in reality it is a very difficult
  problem.

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1D phase unwrapping
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1D phase unwrapping
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2D phase unwrapping-example 2
Unwrapping using basic algorithm
An image
Unwrapping using our algorithm
The image is wrapped
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Unwrapping using our algorithm
Unwrapping using LP algorithm
Unwrapping using Flynn algorithm
The image
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Example 3

• Doris Mannequin
• Information encoded in the phase of the fringe
  pattern
• The phase information are extracted using the
  Fourier transform. The resultant image is wrapped
• Unwrapping the image to get the required height
  information.

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2D phase unwrapping

• Hundreds of algorithms already proposed in the
  literature
• The robust phase unwrapping techniques are time
  consuming (10 seconds or more to process an image
  with the size of 512 ? 512 pixels)
• Our algorithm is robust and requires 0.25 seconds
  to process an image with the size of 512 ? 512
  pixels
• It is easy to understand-but hard to program
• The C language source code is available to
  download for free from GERI website.

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How the algorithm does work?

• The quality of each pixel is calculated using its
  8 direct neighbours
• Horizontal and vertical edges are constructed.
• Edges connect two pixels together.
• The quality of the edges are calculated
• Search for the edge with the highest quality
• Unwrap the two pixels that it connects or
• Unwrap a pixel and a region that it connects or
• Unwrap the two regions that it connects
• Search for the next unprocessed edge with the
  highest quality
• Unwrap the two..
• And so on for the rest of edges

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3D phase unwrapping

• Sometimes we are required to unwrap a sequence of
  images (i.e., video data)
• The existing algorithms are very time consuming
• The famous prelude 3D phase unwrapper requires
  five days to process a volume of 512 ? 512 ? 50
  voxels.
• Other unwrappers require few minutes to unwrap
  such data volume but they are not robust.
• Our 3D phase unwrapper is fast, robust and free
  to download
• It requires less than a minute to process this
  data volume.
• Our 3D phase unwrapper is more robust than any
  other existing 3D phase unwrappers.
• We have published three journal papers and two
  conference papers about 2D and 3D phase
  unwrapping.
• One of these journal papers is very famous and it
  has been cited 19 times.

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Phase unwrapping

• We got many customers to our phase unwrappers
• 1. The Christie Hospital, Manchester, UK.
  http//www.christie.nhs.uk/
• 2. EADS Astrium, Germany. This is a multinational
  aerospace manufacturer of satellite systems. Its
  website is http//www.astrium.eads.net/
• 3. The European Southern Observatory based in
  Australia. Their website is http//www.eso.org/pub
  lic/
• 4. The Helen Wills Neuroscience Institute at the
  University of California, Berkeley, Their website
  is http//neuroscience.berkeley.edu/.
• 5. Our phase unwrappers have been integrated in
  SciPy free open-source mathematical library. The
  website for the library is http//www.scipy.org/.
  
• 6.Microgravity Research Centre  Universite Libre
  de Bruxelles
• And many we do not know!!!

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Phase unwrapping

• Just search in Google the words phase unwrapping.
  This search will produce around 100,000 pages.
• Search for the phrase phase unwrapping This
  will produce around 50,000 pages approximately.
• We are number four after in both searches
• Wikipedia
• Stanford university (just a tutorial)
• An Italian university (just a tutorial)

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Wavelet transform profilometry
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Wavelet transform profilometry

• Wavelet transform profilometry means the
  utilisation of the continuous wavelet transform
  to extract the phase information from a fringe
  pattern.
• There are two methods to perform this task
• One-dimensional continuous wavelet transform
• Already exists in the literature
• Two-dimensional continuous wavelet transform
• Has been developed in GERI

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Wavelet transform profilometry

• This algorithm has many advantages over the
  Fourier transform method
• little edge distortion
• The extracted phase is more accurate
• No limit on the number of fringes in an image
• Better noise performance

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Example 1 a fringe analysed using wavelet and
Fourier methods
Fringe pattern
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Wrapped phase maps using
Fourier transform
Wavelet transform
Fourier transform
Wavelet transform
Fourier transform
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Unwrapped phase map using
Wavelet transform
Fourier transform
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A fringe pattern with two fringes only analysed
using the wavelet method
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The wavelet method can deal with holes in a
fringe pattern image
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Wavelet software

• We (Munther and Abdul-Basit) have developed a
  software in C that is capable of extracting the
  required phase information from a fringe pattern
  using the wavelet method.
• I will publish this software on GERI website and
  make it available to download for free
• Repeating the phase unwrapping good experience

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Wavelet software

• We have spent over one year in writing this
  wavelet software.
• The execution time required to analyse a 512 X
  512 pixels fringe pattern in Matlab using the
  wavelet method is approximately five minutes.
• The same operation requires less than one second
  using our software.
• We have been invited to write a tutorial paper
  about this topic to the Optics and Lasers in
  Engineering Journal.
• We have published three journal papers and three
  conference papers about this topic

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MEtrology GUided RAdioTHerapy(MEGURATH)
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Headlines

• Introduction
• Specifications
• Components
• Processing Pipeline
• Future Work

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MEGURATH

• This system is designed and built to enable the
  medics to measure the height map of human bodies.
• This is an important step in cancer radiotherapy
  treatment

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Introduction

• A state-of-the-art 3D body measurement system
  using fringe analysis
• A catalogue of fringes analysis, phase unwrapping
  and fringes calibration methods were employed
• User preferences of speed and robustness
• System currently uses only one sensor unit (CCD
  camera and LCOS projector)

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3D measurement System Block Diagram

• Monochrome cameras
• Optical filters to get three channels
• XB08 (Blue)
• XB21 (Green)
• XB24 (Red)

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Specifications

• Field-of-view 40cm x 40cm x 40cm
• Measurement speeds
• From 5 to 14 fps depending on pre-adjusted
  settings
• Phase stepping
• Fourier
• Wavelet
• Maximum error 0.5 mm

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Components
1/4

• System simply consists of projector, camera,
  processing station and processing software

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Components
2/4

• Projector Canon XEED SX60

• LCoS technology
• Advantages
• Low pixelisation
• High brightness (2500 lumens)

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Components
3/4

• Camera Prosilica GE1380

• GigE technology
• Monochrome
• Progressive scan CCD
• Sensitive Camera
• 20 fps _at_ 1360 1024
• 35 fps _at_ 512 x 512
• Direct image registration to the system memory
  via a compatible Gigabit port

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Components
4/4

• Processing software

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Processing Pipeline

• Multithreaded processing framework

• Input Thread Project and grab frames
• Processing thread Apply measurement, unwrapping
  and calibration techniques
• Output thread Save/display results

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Thank you for listening.Any questions or
suggestions?