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/*=========================================================================
Program: Insight Segmentation & Registration Toolkit
Module: $RCSfile: itkLinearInterpolateImageFunction.txx,v $
Language: C++
Date: $Date: 2008-01-06 23:12:49 $
Version: $Revision: 1.37 $
Copyright (c) Insight Software Consortium. All rights reserved.
See ITKCopyright.txt or http://www.itk.org/HTML/Copyright.htm for details.
This software is distributed WITHOUT ANY WARRANTY; without even
the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
PURPOSE. See the above copyright notices for more information.
=========================================================================*/
#ifndef __itkLinearInterpolateImageFunction_txx
#define __itkLinearInterpolateImageFunction_txx
// First, make sure that we include the configuration file.
// This line may be removed once the ThreadSafeTransform gets
// integrated into ITK.
#include "itkConfigure.h"
// Second, redirect to the optimized version if necessary
#if defined( ITK_USE_OPTIMIZED_REGISTRATION_METHODS ) && defined( LINEAR_INTERPOLATOR_FIXED )
#include "itkOptLinearInterpolateImageFunction.txx"
#else
#include "itkLinearInterpolateImageFunction.h"
#include "vnl/vnl_math.h"
namespace itk
{
/**
* Define the number of neighbors
*/
template<class TInputImage, class TCoordRep>
const unsigned long
LinearInterpolateImageFunction< TInputImage, TCoordRep >
::m_Neighbors = 1 << TInputImage::ImageDimension;
/**
* Constructor
*/
template<class TInputImage, class TCoordRep>
LinearInterpolateImageFunction< TInputImage, TCoordRep >
::LinearInterpolateImageFunction()
{
}
/**
* PrintSelf
*/
template<class TInputImage, class TCoordRep>
void
LinearInterpolateImageFunction< TInputImage, TCoordRep >
::PrintSelf(std::ostream& os, Indent indent) const
{
this->Superclass::PrintSelf(os,indent);
}
/**
* Evaluate at image index position
*/
template<class TInputImage, class TCoordRep>
typename LinearInterpolateImageFunction< TInputImage, TCoordRep >
::OutputType
LinearInterpolateImageFunction< TInputImage, TCoordRep >
::EvaluateAtContinuousIndex(
const ContinuousIndexType& index) const
{
unsigned int dim; // index over dimension
/**
* Compute base index = closet index below point
* Compute distance from point to base index
*/
signed long baseIndex[ImageDimension];
double distance[ImageDimension];
long tIndex;
for( dim = 0; dim < ImageDimension; dim++ )
{
// The following "if" block is equivalent to the following line without
// having to call floor.
// baseIndex[dim] = (long) vcl_floor(index[dim] );
if (index[dim] >= 0.0)
{
baseIndex[dim] = (long) index[dim];
}
else
{
tIndex = (long) index[dim];
if (double(tIndex) != index[dim])
{
tIndex--;
}
baseIndex[dim] = tIndex;
}
distance[dim] = index[dim] - double( baseIndex[dim] );
}
/**
* Interpolated value is the weighted sum of each of the surrounding
* neighbors. The weight for each neighbor is the fraction overlap
* of the neighbor pixel with respect to a pixel centered on point.
*/
RealType value = NumericTraits<RealType>::Zero;
RealType totalOverlap = NumericTraits<RealType>::Zero;
for( unsigned int counter = 0; counter < m_Neighbors; counter++ )
{
double overlap = 1.0; // fraction overlap
unsigned int upper = counter; // each bit indicates upper/lower neighbour
IndexType neighIndex;
// get neighbor index and overlap fraction
for( dim = 0; dim < ImageDimension; dim++ )
{
if ( upper & 1 )
{
neighIndex[dim] = baseIndex[dim] + 1;
overlap *= distance[dim];
}
else
{
neighIndex[dim] = baseIndex[dim];
overlap *= 1.0 - distance[dim];
}
upper >>= 1;
}
// get neighbor value only if overlap is not zero
if( overlap )
{
value += overlap * static_cast<RealType>( this->GetInputImage()->GetPixel( neighIndex ) );
totalOverlap += overlap;
}
if( totalOverlap == 1.0 )
{
// finished
break;
}
}
return ( static_cast<OutputType>( value ) );
}
} // end namespace itk
#endif
#endif
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