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ENH: Fix Parker weighting to not discard first and last projections #974

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ENH: Fix Parker weighting to not discard first and last projections #974

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23 changes: 23 additions & 0 deletions include/rtkParkerShortScanImageFilter.hxx
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Original file line number Diff line number Diff line change
Expand Up @@ -77,6 +77,29 @@ ParkerShortScanImageFilter<TInputImage, TOutputImage>::GenerateInputRequestedReg
m_Delta = 0.5 * (lastAngle - m_FirstAngle - itk::Math::pi);
m_Delta = m_Delta - 2 * itk::Math::pi * floor(m_Delta / (2 * itk::Math::pi)); // between -2*PI and 2*PI

// Extend the scan range by half a step so that the first and last projections get non-zero Parker weights.
if (nProj > 1)
{
// First angular step: gap from first to second projection in the short scan
auto itNext = itFirstAngle;
++itNext;
double firstStep = itNext->first - itFirstAngle->first;
if (firstStep < 0)
firstStep += 2 * itk::Math::pi;

// Last angular step: gap from second-to-last to last projection in the short scan
auto itPrev = itLastAngle;
--itPrev;
double lastStep = itLastAngle->first - itPrev->first;
if (lastStep < 0)
lastStep += 2 * itk::Math::pi;

double halfFirstStep = firstStep / 2;
double halfLastStep = lastStep / 2;
m_FirstAngle -= halfFirstStep;
m_Delta += (halfFirstStep + halfLastStep) / 2;
}

// Pre-compute the two corners of the projection images
typename TInputImage::IndexType id = this->GetInput()->GetLargestPossibleRegion().GetIndex();
typename TInputImage::SizeType sz = this->GetInput()->GetLargestPossibleRegion().GetSize();
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