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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 itkGaussianOperator_h
#define itkGaussianOperator_h
#include "itkNeighborhoodOperator.h"
#include <cmath>
namespace itk
{
/**
* \class GaussianOperator
* \brief A NeighborhoodOperator whose coefficients are a one
* dimensional, discrete Gaussian kernel.
*
* GaussianOperator can be used to perform Gaussian blurring
* by taking its inner product with a Neighborhood
* (NeighborhoodIterator) that is swept across an image region.
* It is a directional operator. N successive applications
* oriented along each dimensional direction will effect separable,
* efficient, N-D Gaussian blurring of an image region.
*
* GaussianOperator takes two parameters:
*
* (1) The floating-point variance of the desired Gaussian function.
*
* (2) The "maximum error" allowed in the discrete Gaussian
* function. "Maximum error" is defined as the difference between the area
* under the discrete Gaussian curve and the area under the continuous
* Gaussian. Maximum error affects the Gaussian operator size. Care should
* be taken not to make this value too small relative to the variance
* lest the operator size become unreasonably large.
*
* References:
* The Gaussian kernel contained in this operator was described
* by Tony Lindeberg (Discrete Scale-Space Theory and the Scale-Space
* Primal Sketch. Dissertation. Royal Institute of Technology, Stockholm,
* Sweden. May 1991.).
*
* \note GaussianOperator does not have any user-declared "special member function",
* following the C++ Rule of Zero: the compiler will generate them if necessary.
*
* \sa NeighborhoodOperator
* \sa NeighborhoodIterator
* \sa Neighborhood
*
* \ingroup Operators
* \ingroup ITKCommon
*
* \sphinx
* \sphinxexample{Core/Common/CreateGaussianKernel,Create Gaussian Kernel}
* \endsphinx
*/
template <typename TPixel, unsigned int VDimension = 2, typename TAllocator = NeighborhoodAllocator<TPixel>>
class ITK_TEMPLATE_EXPORT GaussianOperator : public NeighborhoodOperator<TPixel, VDimension, TAllocator>
{
public:
/** Standard class type aliases. */
using Self = GaussianOperator;
using Superclass = NeighborhoodOperator<TPixel, VDimension, TAllocator>;
/** \see LightObject::GetNameOfClass() */
itkOverrideGetNameOfClassMacro(GaussianOperator);
/** Sets the desired variance of the Gaussian kernel. */
void
SetVariance(const double variance)
{
m_Variance = variance;
}
/** Sets the desired maximum error of the gaussian approximation. Maximum
* error is the difference between the area under the discrete Gaussian curve
* and the area under the continuous Gaussian. Maximum error affects the
* Gaussian operator size. The value must be between 0.0 and 1.0. */
void
SetMaximumError(const double max_error)
{
if (max_error >= 1 || max_error <= 0)
{
itkExceptionMacro("Maximum Error Must be in the range [ 0.0 , 1.0 ]");
}
m_MaximumError = max_error;
}
/** Returns the variance of the Gaussian (scale) for the operator. */
double
GetVariance()
{
return m_Variance;
}
/** Returns the maximum error of the gaussian approximation. Maximum error is
* the difference between the area under the discrete Gaussian curve and the
* area under the continuous Gaussian. Maximum error affects the Gaussian
* operator size. */
double
GetMaximumError()
{
return m_MaximumError;
}
/** Sets a limit for growth of the kernel. Small maximum error values with
* large variances will yield very large kernel sizes. This value can be
* used to truncate a kernel in such instances. A warning will be given on
* truncation of the kernel. */
void
SetMaximumKernelWidth(unsigned int n)
{
m_MaximumKernelWidth = n;
}
/** Returns the maximum allowed kernel width. */
unsigned int
GetMaximumKernelWidth() const
{
return m_MaximumKernelWidth;
}
void
PrintSelf(std::ostream & os, Indent indent) const override
{
Superclass::PrintSelf(os, indent);
os << indent << "Variance: " << m_Variance << std::endl;
os << indent << "MaximumError: " << m_MaximumError << std::endl;
os << indent << "MaximumKernelWidth: " << m_MaximumKernelWidth << std::endl;
}
/** Get the value of the debug flag.
* Mimics the itk::Object interface so that itkDebugMacro
* can be used in selective printouts from Gaussian kernel generation.*/
bool
GetDebug() const
{
return m_Debug;
}
/** Turn debugging output on. */
void
DebugOn() const
{
m_Debug = true;
}
/** Turn debugging output off. */
void
DebugOff() const
{
m_Debug = false;
}
/** Set the value of the debug flag. A non-zero value turns debugging on. */
void
SetDebug(bool debugFlag) const
{
m_Debug = debugFlag;
}
public:
/** Returns the value of the modified Bessel function I0(x) at a point x >= 0.
*/
double
ModifiedBesselI0(double);
/** Returns the value of the modified Bessel function I1(x) at a point x,
* x real. */
double
ModifiedBesselI1(double);
/** Returns the value of the modified Bessel function Ik(x) at a point x>=0,
* where k>=2. */
double
ModifiedBesselI(int, double);
protected:
/** Type alias support for coefficient vector type.*/
using typename Superclass::CoefficientVector;
/** Calculates operator coefficients. */
CoefficientVector
GenerateCoefficients() override;
/** Arranges coefficients spatially in the memory buffer. */
void
Fill(const CoefficientVector & coeff) override
{
this->FillCenteredDirectional(coeff);
}
private:
/** Desired variance of the discrete Gaussian function. */
double m_Variance{ 1 };
/** Difference between the areas under the curves of the continuous and
* discrete Gaussian functions. */
double m_MaximumError{ .01 };
/** Maximum kernel size allowed. This value is used to truncate a kernel
* that has grown too large. A warning is given when the specified maximum
* error causes the kernel to exceed this size. */
unsigned int m_MaximumKernelWidth{ 30 };
/** Enable/disable kernel generation debug warnings */
mutable bool m_Debug{ false };
};
} // namespace itk
#ifndef ITK_MANUAL_INSTANTIATION
# include "itkGaussianOperator.hxx"
#endif
#endif
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