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/*=========================================================================
*
* Copyright Insight Software Consortium
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0.txt
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
*=========================================================================*/
#include "itkHessianRecursiveGaussianImageFilter.h"
// This test creates an image varying as a 1D Gaussian in the X direction
// for different values of sigma, and checks the scale-space response of
// the xx component of the Hessian at the center of the Gaussian.
// If NormalizeAcrossScale works correctly, the filter should yield the
// same Hxx across different scales.
int itkHessianRecursiveGaussianFilterScaleSpaceTest(int, char* [] )
{
const unsigned int Dimension = 3;
typedef double PixelType;
typedef itk::Image<PixelType,Dimension> ImageType;
typedef itk::Index<Dimension> IndexType;
typedef itk::Size<Dimension> SizeType;
typedef itk::ImageRegion<Dimension> RegionType;
typedef ImageType::PointType PointType;
typedef ImageType::SpacingType SpacingType;
ImageType::Pointer inputImage = ImageType::New();
SizeType size;
size.Fill(21);
size[0] = 401;
IndexType start;
start.Fill(0);
RegionType region;
region.SetIndex(start);
region.SetSize(size);
PointType origin;
origin.Fill(-1.25);
origin[0] = -20.0;
SpacingType spacing;
spacing.Fill(0.1);
inputImage->SetOrigin(origin);
inputImage->SetSpacing(spacing);
inputImage->SetLargestPossibleRegion(region);
inputImage->SetBufferedRegion(region);
inputImage->SetRequestedRegion(region);
inputImage->Allocate();
typedef itk::ImageRegionIteratorWithIndex<ImageType> IteratorType;
const unsigned int numberOfScales = 4;
double scales[numberOfScales];
scales[0] = 1.0;
scales[1] = 2.0;
scales[2] = 3.0;
scales[3] = 5.0;
// changing the size of the object with the the size of the
// gaussian should produce the same results
for (unsigned int i=0; i<numberOfScales; i++)
{
IteratorType it(inputImage, inputImage->GetRequestedRegion());
PointType point;
double objectSize = scales[i];
// Fill the image with a 1D Gaussian along X with sigma equal to the current scale
// The Gaussian is not normalized, since it should have the same peak value across
// scales, only sigma should change
while(!it.IsAtEnd())
{
inputImage->TransformIndexToPhysicalPoint(it.GetIndex(),point);
double value = std::exp(-point[0]*point[0] / (2.0*objectSize*objectSize));
it.Set(value);
++it;
}
// Compute the hessian using NormalizeAcrossScale true
typedef itk::HessianRecursiveGaussianImageFilter<ImageType> FilterType;
typedef FilterType::OutputImageType HessianImageType;
FilterType::Pointer filter = FilterType::New();
filter->SetInput(inputImage);
filter->SetSigma(objectSize);
filter->SetNormalizeAcrossScale(true);
filter->Update();
HessianImageType::Pointer outputImage = filter->GetOutput();
// Get the value at the center of the image, the location of the peak of the Gaussian
PointType center;
center.Fill(0.0);
IndexType centerIndex;
outputImage->TransformPhysicalPointToIndex(center,centerIndex);
// Irrespective of the scale, the Hxx component should be the same
double centerHxx = outputImage->GetPixel(centerIndex)[0];
if (centerHxx > -0.3546 || centerHxx < -0.3547 )
{
std::cout << "center Hessian: " << outputImage->GetPixel(centerIndex) << std::endl;
return EXIT_FAILURE;
}
}
// maintaining the size of the object and gaussian, in physical
// size, should maintain the value, while the size of the image changes.
for (unsigned int i=0; i<numberOfScales; i++)
{
IteratorType it(inputImage, inputImage->GetRequestedRegion());
PointType point;
double objectSize = 5.0;
spacing.Fill(scales[i]/5.0);
inputImage->SetSpacing(spacing);
// Fill the image with a 1D Gaussian along X with sigma equal to
// the object size.
// The Gaussian is not normalized, since it should have the same peak value across
// scales, only sigma should change
while(!it.IsAtEnd())
{
inputImage->TransformIndexToPhysicalPoint(it.GetIndex(),point);
double value = std::exp(-point[0]*point[0] / (2.0*objectSize*objectSize));
it.Set(value);
++it;
}
// Compute the hessian using NormalizeAcrossScale true
typedef itk::HessianRecursiveGaussianImageFilter<ImageType> FilterType;
typedef FilterType::OutputImageType HessianImageType;
FilterType::Pointer filter = FilterType::New();
filter->SetInput(inputImage);
filter->SetSigma(objectSize);
filter->SetNormalizeAcrossScale(true);
filter->Update();
HessianImageType::Pointer outputImage = filter->GetOutput();
// Get the value at the center of the image, the location of the peak of the Gaussian
PointType center;
center.Fill(0.0);
IndexType centerIndex;
outputImage->TransformPhysicalPointToIndex(center,centerIndex);
// Irrespective of the scale, the Hxx component should be the same
double centerHxx = outputImage->GetPixel(centerIndex)[0];
if (centerHxx > -0.354 || centerHxx < -0.355 )
{
std::cout << "center Hessian: " << outputImage->GetPixel(centerIndex) << std::endl;
return EXIT_FAILURE;
}
}
return EXIT_SUCCESS;
}
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