RF1CubicSpline.h

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#ifndef TIL_RECURSIVE_FILTER_CUBIC_SPLINE_H
#define TIL_RECURSIVE_FILTER_CUBIC_SPLINE_H

// includes from STL
#include <cmath>        // sqrt

// includes from TIL library
#include "til/til_common.h"
#include "til/rf1.h"


namespace til {

        // TODO: so far there is no choice in extrapolation. However recursive
        // filters propose a small choice. We could enable this choice, but then the
        // size of im might change! Might be a problem here...
        // Maybe a wrapper on an image class with templating on the shift might just
        // help, WindowedImage<TImage, x0,y0,z0,x1,y1,z1>?
        // We may also enable to be able to translate from the standard image extrapolation
        // classes. In this case I see yet another trait coming...
        template < typename TImage >
        void cubicSplineCoefficients(const TImage &im, TImage &coeffs)
        {
                typedef typename TImage::value_type value_type;
                const value_type z1 = ::sqrt(3.0) - 2;

                // Check that im and coeffs are allocated and have the same size
                similarityCheck(im, coeffs);

                RecursiveFilter<value_type, +1, 1> filter1;
                RecursiveFilter<value_type, -1, 1> filter2;

                filter1.setFilter(1, -z1);
                filter2.setFilter(-z1, -z1);

        
                for (ImageAxis axis = X_AXIS; axis <= Z_AXIS; ++axis)
                {
                        // Apply filter only if image is not flat in that direction
                        if (im.dim()[axis] > 1)
                        {
                                filterAlongAxis(im, coeffs, axis, filter1);
                                filterAlongAxis(im, coeffs, axis, filter2);
                        }
                }
        }
} // namespace

#endif