ITK  4.13.0
Insight Segmentation and Registration Toolkit
WikiExamples/ImageSegmentation/ExtractContourWithSnakes.cxx
#include "itkImage.h"
#include "vnl/vnl_math.h"
#include <vnl/vnl_matrix.h>
#include "vnl/algo/vnl_determinant.h"
#include "vnl/algo/vnl_matrix_inverse.h"
#include <vnl/vnl_vector.h>
#include <iostream>
namespace
{
typedef itk::Image< float, 2 > FloatImageType;
typedef itk::CovariantVector< float, 2 > OutputPixelType;
typedef itk::Image< OutputPixelType, 2 > OutputImageType;
FloatImageType, OutputImageType> FilterType;
ImageType, FloatImageType > GradMagfilterType;
}
vnl_vector<double> generateCircle(double cx, double cy,
double rx, double ry, int n);
void createImage(ImageType::Pointer image,
int w, int h, double cx, double cy, double rx, double ry);
vnl_matrix<double> computeP(double alpha, double beta, double gamma,
double N) throw (int);
vnl_vector<double> sampleImage(vnl_vector<double> x, vnl_vector<double> y,
OutputImageType::Pointer gradient,
int position);
int main( int argc, char* argv[] )
{
//Image dimensions
int w = 300;
int h = 300;
ImageType::Pointer image;
if (argc < 7)
{
std::cout << "Usage " << argv[0]
<< " points alpha beta gamma sigma iterations [image]"
<< std::endl;
return EXIT_SUCCESS;;
}
else if (argc < 8)
{
//Synthesize the image
image = ImageType::New();
createImage(image, w, h, 150, 150, 50, 50);
}
else if (argc == 8)
{
//Open the image
ReaderType::Pointer reader = ReaderType::New();
reader->SetFileName( argv[7] );
try
{
reader->Update();
image = reader->GetOutput();
w = image->GetLargestPossibleRegion().GetSize()[0];
h = image->GetLargestPossibleRegion().GetSize()[1];
}
catch( itk::ExceptionObject & err )
{
std::cerr << "Caught unexpected exception " << err;
return EXIT_FAILURE;
}
}
//Snake parameters
double alpha = 0.001;
double beta = 0.4;
double gamma = 100;
double iterations = 1;
int nPoints = 20;
double sigma;
nPoints = atoi(argv[1]);
alpha = atof(argv[2]);
beta = atof(argv[3]);
gamma = atof(argv[4]);
sigma = atof(argv[5]);
iterations = atoi(argv[6]);
//Temporal variables
vnl_matrix<double> P;
vnl_vector<double> v;
double N;
//Generate initial snake circle
v = generateCircle(130, 130, 50, 50, nPoints);
//Computes P matrix.
N = v.size()/2;
try
{
P = computeP(alpha, beta, gamma, N);
}
catch (int n)
{
return EXIT_FAILURE;;
}
//Computes the magnitude gradient
GradMagfilterType::Pointer gradientMagnitudeFilter =
GradMagfilterType::New();
gradientMagnitudeFilter->SetInput( image );
gradientMagnitudeFilter->Update();
//Computes the gradient of the gradient magnitude
FilterType::Pointer gradientFilter = FilterType::New();
gradientFilter->SetInput( gradientMagnitudeFilter->GetOutput() );
gradientFilter->SetSigma( sigma );
gradientFilter->Update();
//Loop
vnl_vector<double> x(N);
vnl_vector<double> y(N);
std::cout << "Initial snake" << std::endl;
for (int i = 0; i < N; i++)
{
x[i] = v[2*i];
y[i] = v[2*i+1];
std::cout << "(" << x[i] << ", " << y[i] << ")" << std::endl;
}
for (int i = 0; i < iterations; i++)
{
vnl_vector<double> fex;
vnl_vector<double> fey;
fex = sampleImage(x, y, gradientFilter->GetOutput(), 0);
fey = sampleImage(x, y, gradientFilter->GetOutput(), 1);
x = (x+gamma*fex).post_multiply(P);
y = (y+gamma*fey).post_multiply(P);
}
//Display the answer
std::cout << "Final snake after " << iterations << " iterations" << std::endl;
vnl_vector<double> v2(2*N);
for (int i=0; i<N; i++)
{
v2[2*i] = x[i];
v2[2*i+1] = y[i];
std::cout << "(" << x[i] << ", " << y[i] << ")" << std::endl;
}
return EXIT_SUCCESS;;
}
vnl_vector<double> generateCircle(
double cx, double cy, double rx, double ry, int n)
{
vnl_vector<double> v(2*(n+1));
for (int i=0; i<n; i++)
{
v[2*i] = cx + rx*cos(2*vnl_math::pi*i/n);
v[2*i+1] = cy + ry*sin(2*vnl_math::pi*i/n);
}
v[2*n]=v[0];
v[2*n+1]=v[1];
return v;
}
void createImage(ImageType::Pointer image,
int w, int h, double cx, double cy, double rx, double ry)
{
size[0] = w;
size[1] = h;
randomImageSource->SetNumberOfThreads(1); // to produce non-random results
randomImageSource->SetSize(size);
randomImageSource->SetMin(200);
randomImageSource->SetMax(255);
randomImageSource->Update();
image->SetRegions(randomImageSource->GetOutput()->GetLargestPossibleRegion());
image->Allocate();
IndexType index;
//Draw oval.
for (int i=0; i<w; i++)
{
for (int j=0; j<h; j++)
{
index[0] = i; index[1] = j;
if ( ((i-cx)*(i-cx)/(rx*rx) + (j-cy)*(j-cy)/(ry*ry) ) < 1)
{
image->SetPixel(index, randomImageSource->GetOutput()->GetPixel(index)-100);
}
else
{
image->SetPixel(index, randomImageSource->GetOutput()->GetPixel(index));
}
}
}
}
vnl_matrix<double> computeP(double alpha, double beta, double gamma, double N) throw (int)
{
double a = gamma*(2*alpha+6*beta)+1;
double b = gamma*(-alpha-4*beta);
double c = gamma*beta;
vnl_matrix<double> P(N,N);
P.fill(0);
//fill diagonal
P.fill_diagonal(a);
//fill next two diagonals
for (int i=0; i<(N-1); i++)
{
P(i+1,i) = b;
P(i,i+1) = b;
}
//Moreover
P(0, N-1)=b;
P(N-1, 0)=b;
//fill next two diagonals
for (int i=0; i<(N-2); i++)
{
P(i+2,i) = c;
P(i,i+2) = c;
}
//Moreover
P(0, N-2)=c;
P(1, N-1)=c;
P(N-2, 0)=c;
P(N-1, 1)=c;
if ( vnl_determinant(P) == 0.0 )
{
std::cerr << "Singular matrix. Determinant is 0." << std::endl;
throw 2;
}
//Compute the inverse of the matrix P
vnl_matrix< double > Pinv;
Pinv = vnl_matrix_inverse< double >(P);
return Pinv.transpose();
}
vnl_vector<double> sampleImage(vnl_vector<double> x, vnl_vector<double> y, OutputImageType::Pointer gradient, int position)
{
int size;
size = x.size();
vnl_vector<double> ans(size);
IndexType index;
for (int i=0; i<size; i++)
{
index[0] = x[i];
index[1] = y[i];
ans[i] = gradient->GetPixel(index)[position];
}
return ans;
}