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| ==Introduction==
| | {{warning|1=The media wiki content on this page is no longer maintained. The examples presented on the https://itk.org/Wiki/* pages likely require ITK version 4.13 or earlier releases. In many cases, the examples on this page no longer conform to the best practices for modern ITK versions.}} |
| This is my ITK implementation of Snakes by following the [http://www.cb.uu.se/~cris/ Cris Luengo] Matlab [http://www.cb.uu.se/~cris/blog/index.php/archives/217/comment-page-1 tutorial].
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| Invoke using '''./ExtractContourWithSnakesSnakes 100 0.01 0.4 0.07 4 6000'''
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| [[File:Snakes.png]]
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| ==ExtractContourWithSnakes.cxx==
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| <source lang="cpp">
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| #include "itkImage.h"
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| #include "itkRandomImageSource.h"
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| #include "itkGradientRecursiveGaussianImageFilter.h"
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| #include "itkGradientMagnitudeImageFilter.h"
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| #include "itkImageFileReader.h"
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|
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| #include <vnl/vnl_matrix.h>
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| #include "vnl/algo/vnl_determinant.h"
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| #include "vnl/algo/vnl_matrix_inverse.h"
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| #include <vnl/vnl_vector.h>
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|
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| #include <iostream>
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|
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| typedef itk::Image< unsigned char, 2 > ImageType;
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| typedef itk::Image< float, 2 > FloatImageType;
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| typedef ImageType::IndexType IndexType;
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| typedef itk::CovariantVector< float, 2 > OutputPixelType;
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| typedef itk::Image< OutputPixelType, 2 > OutputImageType;
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| typedef itk::GradientRecursiveGaussianImageFilter<
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| FloatImageType, OutputImageType> FilterType;
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| typedef itk::GradientMagnitudeImageFilter<
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| ImageType, FloatImageType > GradMagfilterType;
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| typedef itk::ImageFileReader< ImageType > ReaderType;
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|
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| vnl_vector<double> generateCircle(double cx, double cy,
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| double rx, double ry, int n);
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| void createImage(ImageType::Pointer image,
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| int w, int h, double cx, double cy, double rx, double ry);
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| vnl_matrix<double> computeP(double alpha, double beta, double gamma,
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| double N) throw (int);
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| vnl_vector<double> sampleImage(vnl_vector<double> x, vnl_vector<double> y,
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| OutputImageType::Pointer gradient,
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| int position);
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|
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| int main( int argc, char* argv[] )
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| {
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| //Image dimensions
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| int w = 300;
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| int h = 300;
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| ImageType::Pointer image;
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| if (argc < 7)
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| {
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| std::cout << "Usage " << argv[0]
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| << " points alpha beta gamma sigma iterations [image]"
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| << std::endl;
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| return EXIT_SUCCESS;;
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| }
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| else if (argc < 8)
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| {
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| //Synthesize the image
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| image = ImageType::New();
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| createImage(image, w, h, 150, 150, 50, 50);
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| }
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| else if (argc == 8)
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| {
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| //Open the image
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| ReaderType::Pointer reader = ReaderType::New();
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| reader->SetFileName( argv[7] );
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| try
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| {
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| reader->Update();
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| image = reader->GetOutput();
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| w = image->GetLargestPossibleRegion().GetSize()[0];
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| h = image->GetLargestPossibleRegion().GetSize()[1];
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| }
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| catch( itk::ExceptionObject & err )
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| {
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| std::cerr << "Caught unexpected exception " << err;
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| return EXIT_FAILURE;
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| }
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| }
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|
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| //Snake parameters
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| double alpha = 0.001;
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| double beta = 0.4;
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| double gamma = 100;
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| double iterations = 1;
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| int nPoints = 20;
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| double sigma;
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|
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| nPoints = atoi(argv[1]);
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| alpha = atof(argv[2]);
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| beta = atof(argv[3]);
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| gamma = atof(argv[4]);
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| sigma = atof(argv[5]);
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| iterations = atoi(argv[6]);
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|
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| //Temporal variables
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| vnl_matrix<double> P;
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| vnl_vector<double> v;
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| double N;
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|
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| //Generate initial snake circle
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| v = generateCircle(130, 130, 50, 50, nPoints);
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| //Computes P matrix.
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| N = v.size()/2;
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| try
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| {
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| P = computeP(alpha, beta, gamma, N);
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| }
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| catch (int n)
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| {
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| return EXIT_FAILURE;;
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| }
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| //Computes the magnitude gradient
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| GradMagfilterType::Pointer gradientMagnitudeFilter =
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| GradMagfilterType::New();
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| gradientMagnitudeFilter->SetInput( image );
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| gradientMagnitudeFilter->Update();
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|
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| //Computes the gradient of the gradient magnitude
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| FilterType::Pointer gradientFilter = FilterType::New();
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| gradientFilter->SetInput( gradientMagnitudeFilter->GetOutput() );
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| gradientFilter->SetSigma( sigma );
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| gradientFilter->Update();
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|
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| //Loop
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| vnl_vector<double> x(N);
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| vnl_vector<double> y(N);
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|
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| std::cout << "Initial snake" << std::endl;
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| for (int i = 0; i < N; i++)
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| {
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| x[i] = v[2*i];
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| y[i] = v[2*i+1];
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| std::cout << "(" << x[i] << ", " << y[i] << ")" << std::endl;
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| }
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|
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| for (int i = 0; i < iterations; i++)
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| {
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| vnl_vector<double> fex;
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| vnl_vector<double> fey;
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| fex = sampleImage(x, y, gradientFilter->GetOutput(), 0);
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| fey = sampleImage(x, y, gradientFilter->GetOutput(), 1);
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|
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| x = (x+gamma*fex).post_multiply(P);
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| y = (y+gamma*fey).post_multiply(P);
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| }
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|
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| //Display the answer
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| std::cout << "Final snake after " << iterations << " iterations" << std::endl;
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| vnl_vector<double> v2(2*N);
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| for (int i=0; i<N; i++)
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| {
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| v2[2*i] = x[i];
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| v2[2*i+1] = y[i];
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| std::cout << "(" << x[i] << ", " << y[i] << ")" << std::endl;
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| }
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|
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| return EXIT_SUCCESS;;
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| }
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|
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| vnl_vector<double> generateCircle(
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| double cx, double cy, double rx, double ry, int n)
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| {
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| vnl_vector<double> v(2*(n+1));
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|
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| for (int i=0; i<n; i++)
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| {
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| v[2*i] = cx + rx*cos(2*M_PI*i/n);
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| v[2*i+1] = cy + ry*sin(2*M_PI*i/n);
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| }
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| v[2*n]=v[0];
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| v[2*n+1]=v[1];
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| return v;
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| }
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| void createImage(ImageType::Pointer image,
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| int w, int h, double cx, double cy, double rx, double ry)
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| {
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|
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| itk::Size<2> size;
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| size[0] = w;
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| size[1] = h;
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|
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| itk::RandomImageSource<ImageType>::Pointer randomImageSource = itk::RandomImageSource<ImageType>::New();
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| randomImageSource->SetNumberOfThreads(1); // to produce non-random results
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| randomImageSource->SetSize(size);
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| randomImageSource->SetMin(200);
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| randomImageSource->SetMax(255);
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| randomImageSource->Update();
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|
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| image->SetRegions(randomImageSource->GetOutput()->GetLargestPossibleRegion());
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| image->Allocate();
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|
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| IndexType index;
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|
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| //Draw oval.
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| for (int i=0; i<w; i++)
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| {
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| for (int j=0; j<h; j++)
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| {
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| index[0] = i; index[1] = j;
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| if ( ((i-cx)*(i-cx)/(rx*rx) + (j-cy)*(j-cy)/(ry*ry) ) < 1)
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| {
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| image->SetPixel(index, randomImageSource->GetOutput()->GetPixel(index)-100);
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| }
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| else
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| {
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| image->SetPixel(index, randomImageSource->GetOutput()->GetPixel(index));
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| }
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|
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| }
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| }
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| }
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| vnl_matrix<double> computeP(double alpha, double beta, double gamma, double N) throw (int)
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| {
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|
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| double a = gamma*(2*alpha+6*beta)+1;
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| double b = gamma*(-alpha-4*beta);
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| double c = gamma*beta;
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|
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| vnl_matrix<double> P(N,N);
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|
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| P.fill(0);
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|
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| //fill diagonal
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| P.fill_diagonal(a);
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|
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| //fill next two diagonals | |
| for (int i=0; i<(N-1); i++)
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| {
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| P(i+1,i) = b;
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| P(i,i+1) = b;
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| }
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| //Moreover
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| P(0, N-1)=b;
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| P(N-1, 0)=b;
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|
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| //fill next two diagonals
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| for (int i=0; i<(N-2); i++)
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| {
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| P(i+2,i) = c;
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| P(i,i+2) = c;
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| }
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| //Moreover
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| P(0, N-2)=c;
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| P(1, N-1)=c;
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| P(N-2, 0)=c;
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| P(N-1, 1)=c;
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|
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| if ( vnl_determinant(P) == 0.0 )
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| {
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| std::cerr << "Singular matrix. Determinant is 0." << std::endl;
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| throw 2;
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| }
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|
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| //Compute the inverse of the matrix P
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| vnl_matrix< double > Pinv;
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| Pinv = vnl_matrix_inverse< double >(P);
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|
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| return Pinv;
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| }
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|
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| vnl_vector<double> sampleImage(vnl_vector<double> x, vnl_vector<double> y, OutputImageType::Pointer gradient, int position)
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| {
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| int size;
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| size = x.size();
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| vnl_vector<double> ans(size);
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|
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| IndexType index;
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| for (int i=0; i<size; i++)
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| {
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| index[0] = x[i];
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| index[1] = y[i];
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| ans[i] = gradient->GetPixel(index)[position];
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| }
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| return ans;
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| }
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| </source>
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| {{ITKCMakeLists|{{SUBPAGENAME}}}}
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