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vigra/interpolating_accessor.hxx VIGRA

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00035 
00036 #ifndef VIGRA_INTERPOLATING_ACCESSOR_HXX
00037 #define VIGRA_INTERPOLATING_ACCESSOR_HXX
00038 
00039 
00040 #include "accessor.hxx"
00041 #include "diff2d.hxx"
00042 
00043 namespace vigra {
00044 
00045 /** \addtogroup DataAccessors
00046 */
00047 //@{
00048 
00049 /********************************************************/
00050 /*                                                      */
00051 /*            BilinearInterpolatingAccessor             */
00052 /*                                                      */
00053 /********************************************************/
00054 
00055 /** \brief Bilinear interpolation at non-integer positions.
00056 
00057     This accessor allows an image be accessed at arbitrary non-integer
00058     coordinates and performs an bi-linear interpolation to
00059     obtain a pixel value.
00060     It uses the given ACCESSOR (which is usually the
00061     accessor originally associated with the iterator)
00062     to access data.
00063 
00064     <b>\#include</b> <vigra/accessor.hxx>
00065     Namespace: vigra
00066 
00067     <b> Required Interface:</b>
00068 
00069     \code
00070     ITERATOR iter;
00071     ACCESSOR a;
00072     VALUETYPE destvalue;
00073     float s;
00074     int x, y;
00075 
00076     destvalue = s * a(iter, x, y) + s * a(iter, x, y);
00077 
00078     \endcode
00079 */
00080 template <class ACCESSOR, class VALUETYPE>
00081 class BilinearInterpolatingAccessor
00082 {
00083   public:
00084     /** the iterators' pixel type
00085     */
00086     typedef VALUETYPE value_type;
00087 
00088     /** init from given accessor
00089     */
00090     BilinearInterpolatingAccessor(ACCESSOR a)
00091     : a_(a)
00092     {}
00093 
00094     /** Interpolate the data item at a non-integer position.
00095         Ensure that no outside pixels are accessed if
00096         (x, y) is near the image border (as long as
00097         0 <= x <= width-1, 0 <= y <= height-1).
00098     */
00099     template <class ITERATOR>
00100     value_type operator()(ITERATOR const & i, float x, float y) const
00101     {
00102         int ix = int(x);
00103         int iy = int(y);
00104         float dx = x - ix;
00105         float dy = y - iy;
00106 
00107         value_type ret;
00108 
00109         // avoid dereferencing the iterator outside its range
00110         if(dx == 0.0)
00111         {
00112             if(dy == 0.0)
00113             {
00114                 ret = a_(i, Diff2D(ix, iy));
00115             }
00116             else
00117             {
00118                 ret = detail::RequiresExplicitCast<value_type>::cast(
00119                   (1.0 - dy) * a_(i, Diff2D(ix, iy)) +
00120                   dy * a_(i, Diff2D(ix, iy + 1)));
00121             }
00122         }
00123         else
00124         {
00125             if(dy == 0.0)
00126             {
00127                 ret = detail::RequiresExplicitCast<value_type>::cast(
00128                   (1.0 - dx) * a_(i, Diff2D(ix, iy)) +
00129                   dx * a_(i, Diff2D(ix + 1, iy)));
00130             }
00131             else
00132             {
00133                 ret = detail::RequiresExplicitCast<value_type>::cast(
00134                   (1.0 - dx) * (1.0 - dy) * a_(i, Diff2D(ix, iy)) +
00135                   dx * (1.0 - dy) * a_(i, Diff2D(ix + 1, iy)) +
00136                   (1.0 - dx) * dy * a_(i, Diff2D(ix, iy + 1)) +
00137                   dx * dy * a_(i, Diff2D(ix + 1, iy + 1)));
00138             }
00139         }
00140 
00141         return ret;
00142     }
00143 
00144     /** Interpolate the data item at a non-integer position.
00145         This function works as long as 0 <= x < width-1,
00146         0 <= y < height-1. It is slightly faster than <TT>operator()</TT>.
00147     */
00148     template <class ITERATOR>
00149     value_type unchecked(ITERATOR const & i, float x, float y) const
00150     {
00151         int ix = int(x);
00152         int iy = int(y);
00153         float dx = x - ix;
00154         float dy = y - iy;
00155         return detail::RequiresExplicitCast<value_type>::cast(
00156                (1.0 - dx) * (1.0 - dy) * a_(i, Diff2D(ix, iy)) +
00157                dx * (1.0 - dy) * a_(i, Diff2D(ix + 1, iy)) +
00158                (1.0 - dx) * dy * a_(i, Diff2D(ix, iy + 1)) +
00159                dx * dy * a_(i, Diff2D(ix + 1, iy + 1)));
00160     }
00161 
00162   private:
00163     ACCESSOR a_;
00164 };
00165 
00166 //@}
00167 
00168 } // namespace vigra
00169 
00170 #endif /* VIGRA_INTERPOLATING_ACCESSOR_HXX */

© Ullrich Köthe (ullrich.koethe@iwr.uni-heidelberg.de)
Heidelberg Collaboratory for Image Processing, University of Heidelberg, Germany

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