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ENH: Add support for multiple metrics and regularization #1437

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11 changes: 11 additions & 0 deletions ...s/Registrations/MultiMetricMultiResolutionRegistration/itkCombinationImageToImageMetric.h
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Original file line number Diff line number Diff line change
Expand Up @@ -18,6 +18,7 @@
#ifndef itkCombinationImageToImageMetric_h
#define itkCombinationImageToImageMetric_h

#include "itkTransformPenaltyTerm.h"
#include "itkAdvancedImageToImageMetric.h"
#include "itkSingleValuedPointSetToPointSetMetric.h"

Expand Down Expand Up @@ -131,6 +132,10 @@ class ITK_TEMPLATE_EXPORT CombinationImageToImageMetric : public AdvancedImageTo
using MovingImageRegionType = typename MovingImageType::RegionType;
using MovingImageDerivativeScalesType = FixedArray<double, Self::MovingImageDimension>;

/** Typedef for transform penalty metrics. */
typedef TransformPenaltyTerm<TFixedImage> TransformMetricType;

@N-Dekker N-Dekker May 15, 2026

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Nowadays, we are using using, instead of typedef. But a coding style issue like that is not a show-stopper. I can adjust it afterwards. Also, I think I would move the definition of TransformMetricType into the function body of CombinationImageToImageMetric::SetMetric, as that seems to be the only place where it is needed.

typedef typename TransformMetricType::Pointer TransformMetricPointer;

@N-Dekker N-Dekker May 15, 2026

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TransformMetricPointer is never used, so I think I would remove it. (No show-stopper for now.)


/** Typedef for the PointSetMetric. */
using FixedPointSetType = PointSet<CoordinateRepresentationType,
TFixedImage::ImageDimension,
Expand Down Expand Up @@ -163,6 +168,9 @@ class ITK_TEMPLATE_EXPORT CombinationImageToImageMetric : public AdvancedImageTo

/** Get the number of metrics to combine. */
itkGetConstMacro(NumberOfMetrics, unsigned int);
itkGetConstMacro(NumberOfImageMetrics, unsigned int);
itkGetConstMacro(NumberOfTransformMetrics, unsigned int);
itkGetConstMacro(NumberOfPointSetMetrics, unsigned int);

/** Set metric i. It may be a SingleValuedCostFunction, instead of
* a ImageToImageMetric, but the first one should be an
Expand Down Expand Up @@ -453,6 +461,9 @@ class ITK_TEMPLATE_EXPORT CombinationImageToImageMetric : public AdvancedImageTo
private:
/** Store the metrics and the corresponding weights. */
unsigned int m_NumberOfMetrics{ 0 };
unsigned int m_NumberOfImageMetrics{ 0 };
unsigned int m_NumberOfTransformMetrics{ 0 };
unsigned int m_NumberOfPointSetMetrics{ 0 };
std::vector<SingleValuedCostFunctionPointer> m_Metrics{};
std::vector<double> m_MetricWeights{};
std::vector<double> m_MetricRelativeWeights{};
Expand Down
48 changes: 45 additions & 3 deletions ...Registrations/MultiMetricMultiResolutionRegistration/itkCombinationImageToImageMetric.hxx
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Expand Up @@ -160,6 +160,9 @@ CombinationImageToImageMetric<TFixedImage, TMovingImage>::PrintSelf(std::ostream

/** Add debugging information. */
os << "NumberOfMetrics: " << this->m_NumberOfMetrics << std::endl;
os << "NumberOfImageMetrics: " << this->m_NumberOfImageMetrics << std::endl;
os << "NumberOfTransformMetrics: " << this->m_NumberOfTransformMetrics << std::endl;
os << "NumberOfPointSetMetrics: " << this->m_NumberOfPointSetMetrics << std::endl;
for (unsigned int i = 0; i < this->m_NumberOfMetrics; ++i)
{
os << "Metric " << i << ":\n";
Expand Down Expand Up @@ -275,12 +278,51 @@ CombinationImageToImageMetric<TFixedImage, TMovingImage>::SetMetric(SingleValued
this->SetNumberOfMetrics(pos + 1);
}

if (metric != this->m_Metrics[pos])
SingleValuedCostFunctionPointer oldMetricPtr = this->m_Metrics[pos];
if (metric == oldMetricPtr)
{
this->m_Metrics[pos] = metric;
this->Modified();
return;
}

PointSetMetricType * testPtr1 = dynamic_cast<PointSetMetricType *>(metric);
TransformMetricType * testPtr2 = dynamic_cast<TransformMetricType *>(metric);

// Increase newly defined numberOfMetric counters
if (testPtr1)

@N-Dekker N-Dekker May 15, 2026

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I would make it:

if( dynamic_cast<PointSetMetricType *>(metric) )

And remove the local testPtr1 variable.

Similar for testPtr2, oldTestPtr1, oldTestPtr2. No show-stopper to me, though. Just a style thing.

{
this->m_NumberOfPointSetMetrics++;
}
else if (testPtr2)
{
this->m_NumberOfTransformMetrics++;
}
else
{
this->m_NumberOfImageMetrics++;
}

// if the metric has already been set, decrease the correct counter
if (oldMetricPtr != nullptr)
{
PointSetMetricType * oldTestPtr1 = dynamic_cast<PointSetMetricType *>(oldMetricPtr.GetPointer());
TransformMetricType * oldTestPtr2 = dynamic_cast<TransformMetricType *>(oldMetricPtr.GetPointer());
if (oldTestPtr1)
{
this->m_NumberOfPointSetMetrics--;
}
else if (oldTestPtr2)
{
this->m_NumberOfTransformMetrics--;
}
else
{
this->m_NumberOfImageMetrics--;
}
}

this->m_Metrics[pos] = metric;
this->Modified();

} // end SetMetric()


Expand Down
36 changes: 18 additions & 18 deletions ...etricMultiResolutionRegistration/itkMultiMetricMultiResolutionImageRegistrationMethod.hxx
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Expand Up @@ -565,44 +565,44 @@ MultiMetricMultiResolutionImageRegistrationMethod<TFixedImage, TMovingImage>::Ch
}

/** nrofmetrics >= nrofinterpolators >= nrofpyramids >= nofimages */
unsigned int nrOfMetrics = m_CombinationMetric->GetNumberOfMetrics();
if (this->GetNumberOfInterpolators() > nrOfMetrics)
unsigned int nrOfImageMetrics = this->GetCombinationMetric()->GetNumberOfImageMetrics();
if (this->GetNumberOfInterpolators() > nrOfImageMetrics)
{
itkExceptionMacro("NumberOfInterpolators can not exceed the NumberOfMetrics in the CombinationMetric!");
itkExceptionMacro("NumberOfInterpolators can not exceed the nrOfImageMetrics in the CombinationMetric!");
}
if (this->GetNumberOfFixedImagePyramids() > nrOfMetrics)
if (this->GetNumberOfFixedImagePyramids() > nrOfImageMetrics)
{
itkExceptionMacro("NumberOfFixedImagePyramids can not exceed the NumberOfMetrics in the CombinationMetric!");
itkExceptionMacro("NumberOfFixedImagePyramids can not exceed the nrOfImageMetrics in the CombinationMetric!");
}
if (this->GetNumberOfMovingImagePyramids() > nrOfMetrics)
if (this->GetNumberOfMovingImagePyramids() > nrOfImageMetrics)
{
itkExceptionMacro("NumberOfMovingImagePyramids can not exceed the NumberOfMetrics in the CombinationMetric!");
itkExceptionMacro("NumberOfMovingImagePyramids can not exceed the nrOfImageMetrics in the CombinationMetric!");
}
if (this->GetNumberOfMovingImagePyramids() > this->GetNumberOfInterpolators())
{
itkExceptionMacro("NumberOfMovingImagePyramids can not exceed the NumberOfInterpolators!");
}

/** For all components: ==nrofmetrics of ==1. */
if ((this->GetNumberOfInterpolators() != 1) && (this->GetNumberOfInterpolators() != nrOfMetrics))
/** For all components: ==nrOfImageMetrics of ==1. */
if ((this->GetNumberOfInterpolators() != 1) && (this->GetNumberOfInterpolators() != nrOfImageMetrics))
{
itkExceptionMacro("The NumberOfInterpolators should equal 1 or equal the NumberOfMetrics");
itkExceptionMacro("The NumberOfInterpolators should equal 1 or equal the nrOfImageMetrics");
}
if ((this->GetNumberOfFixedImagePyramids() != 1) && (this->GetNumberOfFixedImagePyramids() != nrOfMetrics))
if ((this->GetNumberOfFixedImagePyramids() != 1) && (this->GetNumberOfFixedImagePyramids() != nrOfImageMetrics))
{
itkExceptionMacro("The NumberOfFixedImagePyramids should equal 1 or equal the NumberOfMetrics");
itkExceptionMacro("The NumberOfFixedImagePyramids should equal 1 or equal the nrOfImageMetrics");
}
if ((this->GetNumberOfMovingImagePyramids() != 1) && (this->GetNumberOfMovingImagePyramids() != nrOfMetrics))
if ((this->GetNumberOfMovingImagePyramids() != 1) && (this->GetNumberOfMovingImagePyramids() != nrOfImageMetrics))
{
itkExceptionMacro("The NumberOfMovingImagePyramids should equal 1 or equal the NumberOfMetrics");
itkExceptionMacro("The NumberOfMovingImagePyramids should equal 1 or equal the nrOfImageMetrics");
}
if ((this->GetNumberOfFixedImages() != 1) && (this->GetNumberOfFixedImages() != nrOfMetrics))
if ((this->GetNumberOfFixedImages() != 1) && (this->GetNumberOfFixedImages() != nrOfImageMetrics))
{
itkExceptionMacro("The NumberOfFixedImages should equal 1 or equal the NumberOfMetrics");
itkExceptionMacro("The NumberOfFixedImages should equal 1 or equal the nrOfImageMetrics");
}
if ((this->GetNumberOfMovingImages() != 1) && (this->GetNumberOfMovingImages() != nrOfMetrics))
if ((this->GetNumberOfMovingImages() != 1) && (this->GetNumberOfMovingImages() != nrOfImageMetrics))
{
itkExceptionMacro("The NumberOfMovingImages should equal 1 or equal the NumberOfMetrics");
itkExceptionMacro("The NumberOfMovingImages should equal 1 or equal the nrOfImageMetrics");
Comment on lines -603 to +605

@N-Dekker N-Dekker Jun 18, 2026

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@stefanklein @mstaring Would this change (comparing the number of input images with the number of image metrics, instead of the total number of metrics) break legacy use cases that would use "dummy" images when they use multiple metrics?

If so, shall we still allow such legacy use cases, by relaxing this check?

}

} // end CheckOnInitialize()
Expand Down
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