[Insight-users] OnePlusOne Optimizer - results are always 0

[itkvtk123 at gmx.net]

Hi!

I'm trying to register two 2d images using the OnePlusOne optimizer (global optimization).
I wanted to give it a try because gradient descent got stuck in local minima all the time.

However, the result of the OnePlusOne is always Rotation=0, TranslationX=0, TranslationY=0.
(Same during entire process -> I monitored it using the observer).

I'm using the NormalizedCorrelationMetric.
Am I doing something wrong or is something missing? (see code)

Take also a look at

http://img3.imageshack.us/img3/1552/unbenannttnb.jpg

for a screenshot of my program (lower left = image 1, lower right = image 2, upper left = subtraction image after registration).

Source:

const Image2DType::Pointer ImageRegistration::registerImagesXYR(const Image2DType::Pointer fixedImage, const Image2DType::Pointer movingImage)
{
	typedef itk::CenteredRigid2DTransform<double> RigidTransformType;
	typedef itk::CenteredTransformInitializer<RigidTransformType, Image2DType, Image2DType>  TransformInitializerType;
	typedef itk::NormalizedCorrelationImageToImageMetric<Image2DType, Image2DType> MetricType;
	typedef itk::OnePlusOneEvolutionaryOptimizer OptimizerType;
	typedef itk::Statistics::NormalVariateGenerator GeneratorType;
	typedef itk::LinearInterpolateImageFunction<Image2DType, double> InterpolatorType;
	typedef itk::ImageRegistrationMethod<Image2DType, Image2DType> RegistrationType;



	//initialize needed objects
	MetricType::Pointer metric = MetricType::New();
	RigidTransformType::Pointer transform = RigidTransformType::New();
	OptimizerType::Pointer optimizer = OptimizerType::New();
	InterpolatorType::Pointer interpolator = InterpolatorType::New();
	RegistrationType::Pointer registration = RegistrationType::New();

	//connect objects to registration
	registration->SetMetric(metric);
	registration->SetOptimizer(optimizer);
	registration->SetTransform(transform);
	registration->SetInterpolator(interpolator);

	TransformInitializerType::Pointer initializer = TransformInitializerType::New();

	initializer->SetTransform(transform);

	initializer->SetFixedImage(fixedImage);
	initializer->SetMovingImage(movingImage);
	initializer->GeometryOn();
	initializer->InitializeTransform();


	transform->SetAngle(0.0);

	registration->SetInitialTransformParameters(transform->GetParameters());

	//we want to register movingImage against fixedImage
	registration->SetFixedImage(fixedImage);
	registration->SetMovingImage(movingImage);

	//we want to register the entire image
	registration->SetFixedImageRegion(fixedImage->GetLargestPossibleRegion());

	//now registration is ready
	typedef OptimizerType::ScalesType OptimizerScalesType;
	OptimizerScalesType optimizerScales(transform->GetNumberOfParameters());

	const Image2DType::SpacingType fixedSpacing = fixedImage->GetSpacing();
	const Image2DType::SizeType fixedSize = fixedImage->GetLargestPossibleRegion().GetSize();

	const double translationScale = 1.0 / (fixedSize[0] * fixedSpacing[0] * sqrt(2.0));

	optimizerScales[0] = 1.0;
	optimizerScales[1] = translationScale;
	optimizerScales[2] = translationScale;
	optimizerScales[3] = translationScale;
	optimizerScales[4] = translationScale;

	optimizer->SetScales(optimizerScales);

	GeneratorType::Pointer generator = GeneratorType::New();
	generator->Initialize(12345);
	optimizer->MaximizeOff();

	optimizer->SetNormalVariateGenerator(generator);
	optimizer->Initialize(10);
	optimizer->SetEpsilon(1.0);
	optimizer->SetMaximumIteration(400); //4000

	//add observer pattern to monitor evolution of optimization / registration process
	CommandIterationUpdate::Pointer	observer = CommandIterationUpdate::New();
	optimizer->AddObserver(itk::IterationEvent(), observer);

	try
	{
		registration->StartRegistration();
	}
	catch(itk::ExceptionObject & err)
	{
		std::cerr << "ExceptionObject caught !" << std::endl;
		std::cerr << err << std::endl;
		exit(EXIT_FAILURE);
	}
	
	// get the registration parameters
	typedef RegistrationType::ParametersType ParametersType;
	ParametersType finalParameters = registration->GetLastTransformParameters();

	std::cout << -finalParameters[0] * 180.0 / vnl_math::pi << " " << finalParameters[3] << finalParameters[4] << std::endl;
	//final Output: 0 0 0 (same during entire process)
}

Thank you.
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