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/*=========================================================================
*
* Copyright NumFOCUS
*
* 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
*
* https://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.
*
*=========================================================================*/
#ifndef itkAnnulusOperator_hxx
#define itkAnnulusOperator_hxx
#include "itkMath.h"
#include "itkSphereSpatialFunction.h"
#include <memory> // For make_unique.
namespace itk
{
/** Create the operator */
template <typename TPixel, unsigned int TDimension, typename TAllocator>
void
AnnulusOperator<TPixel, TDimension, TAllocator>::CreateOperator()
{
CoefficientVector coefficients;
coefficients = this->GenerateCoefficients();
this->Fill(coefficients);
}
/** This function fills the coefficients into the corresponding
* neighborhood. */
template <typename TPixel, unsigned int TDimension, typename TAllocator>
void
AnnulusOperator<TPixel, TDimension, TAllocator>::Fill(const CoefficientVector & coeff)
{
const std::slice temp_slice(0, coeff.size(), 1);
typename Self::SliceIteratorType data(this, temp_slice);
auto it = coeff.begin();
// Copy the coefficients into the neighborhood
for (data = data.Begin(); data < data.End(); ++data, ++it)
{
*data = *it;
}
}
template <typename TPixel, unsigned int TDimension, typename TAllocator>
auto
AnnulusOperator<TPixel, TDimension, TAllocator>::GenerateCoefficients() -> CoefficientVector
{
// Determine the initial kernel values...
double interiorV, annulusV, exteriorV;
if (m_Normalize)
{
double bright = (m_BrightCenter ? 1.0 : -1.0);
// Initial values for a normalized kernel
interiorV = bright;
annulusV = -1.0 * bright;
exteriorV = 0.0;
}
else
{
// values for a specified kernel
interiorV = m_InteriorValue;
annulusV = m_AnnulusValue;
exteriorV = m_ExteriorValue;
}
// Compute the size of the kernel in pixels
SizeType r;
unsigned int i, j;
double outerRadius = m_InnerRadius + m_Thickness;
for (i = 0; i < TDimension; ++i)
{
r[i] = Math::Ceil<SizeValueType>(outerRadius / m_Spacing[i]);
}
this->SetRadius(r);
// Use a couple of sphere spatial functions...
using SphereType = SphereSpatialFunction<TDimension>;
auto innerS = SphereType::New();
auto outerS = SphereType::New();
innerS->SetRadius(m_InnerRadius);
outerS->SetRadius(m_InnerRadius + m_Thickness);
// Walk the neighborhood (this) and evaluate the sphere spatial
// functions
double sumNotExterior = 0.0;
double sumNotExteriorSq = 0.0;
unsigned int countNotExterior = 0;
const typename SizeType::SizeValueType w = this->Size();
const auto outside = std::make_unique<bool[]>(w);
CoefficientVector coeffP(w);
OffsetType offset;
typename SphereType::InputType point;
for (i = 0; i < w; ++i)
{
// get the offset from the center pixel
offset = this->GetOffset(i);
// convert to a position
for (j = 0; j < TDimension; ++j)
{
point[j] = m_Spacing[j] * offset[j];
}
// evaluate the spheres
const bool inInner = innerS->Evaluate(point);
const bool inOuter = outerS->Evaluate(point);
// set the coefficients
if (!inOuter)
{
// outside annulus
coeffP[i] = exteriorV;
outside[i] = true;
}
else if (!inInner)
{
// inside the outer circle but outside the inner circle
coeffP[i] = annulusV;
sumNotExterior += annulusV;
sumNotExteriorSq += (annulusV * annulusV);
++countNotExterior;
outside[i] = false;
}
else
{
// inside inner circle
coeffP[i] = interiorV;
sumNotExterior += interiorV;
sumNotExteriorSq += (interiorV * interiorV);
++countNotExterior;
outside[i] = false;
}
}
// Normalize the kernel if necessary
if (m_Normalize)
{
// Calculate the mean and standard deviation of kernel values NOT
// the exterior
auto num = static_cast<double>(countNotExterior);
double mean = sumNotExterior / num;
double var = (sumNotExteriorSq - (sumNotExterior * sumNotExterior / num)) / (num - 1.0);
double std = std::sqrt(var);
// convert std to a scaling factor k such that
//
// || (coeffP - mean) / k || = 1.0
//
double k = std * std::sqrt(num - 1.0);
// Run through the kernel again, shifting and normalizing the
// elements that are not exterior to the annulus. This forces the
// kernel to have mean zero and norm 1 AND forces the region
// outside the annulus to have no influence.
for (i = 0; i < w; ++i)
{
// normalize the coefficient if it is inside the outer circle
// (exterior to outer circle is already zero)
if (!outside[i])
{
coeffP[i] = (coeffP[i] - mean) / k;
}
}
}
return coeffP;
}
} // namespace itk
#endif
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