ITK Registration Optimization/Testing And Backward Forward Compatibility

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Backward Forward Compatibility

This page describes the testing framework used for verifying the backward/forward compatibility of the optimized classes developed in this project with the standard classes currently in ITK.

Compatibility

Backward Compatibility
A modified class is backward compatible with a given version "V", when applications that used the version "V" of the class, can adopt the new modified version of the class without having to change their source code to compile it, and by arriving to identical results when using the class at run-time.
Forward Compatibility
A modified class is forward compatible with a given version "V", when interactions based on the old API of the class are safely translated to the new API of the class.

Testing

The ONLY way to tell for sure if a class is backward/forward compatible is to have a test for it.

In order to verify the backward/forward compatibility of the optimized classes a testing framework was put in place. This framework generates tests based on combinations of the following components

  • Transforms
    • Translation
    • Rigid (2D/3D)
    • Affine
    • BSplineDeformable
  • Metrics
    • MeanSquares
    • MutualInformation
    • MattesMutualInformation
  • Interpolators
    • NearestNeighbor
    • Linear
    • BSpline

These component were mixed in their optimized and non-optimized (standard) versions, in order to create regression tests comparing the result of the non-optimized versions with the results of the optimized versions.

Since this is a combinatorial problem, the source code of the tests was generated using CMake macros, that combines the components in different ways and prepares their corresponding initializations.

The choice of optimizers was mostly driven by the Transform, according to the following table:

Transform Optimizer
Translation RegularStepGradientDescent
Rigid2D RegularStepGradientDescent
Rigid3D VersorRigid3DTransform
Affine RegularStepGradientDescent
BSplineDeformable LBFGSB

However, inconsistencies in the current API of some metrics and some optimizers induced the following variations

MeanSquares MutualInformation MattesMutualInformation
Translation RegularStepGradientDescent RegularStepGradientDescent RegularStepGradientDescent
Rigid2D RegularStepGradientDescent RegularStepGradientDescent RegularStepGradientDescent
Rigid3D VersorRigid3DTransform VersorRigid3DTransform VersorRigid3DTransform
Affine RegularStepGradientDescent RegularStepGradientDescent RegularStepGradientDescent
BSplineDeformable LBFGSB RegularStepGradientDescent LBFGSB