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vigra/interpolating_accessor.hxx

00001 /************************************************************************/
00002 /*                                                                      */
00003 /*               Copyright 1998-2002 by Ullrich Koethe                  */
00004 /*       Cognitive Systems Group, University of Hamburg, Germany        */
00005 /*                                                                      */
00006 /*    This file is part of the VIGRA computer vision library.           */
00007 /*    ( Version 1.6.0, Aug 13 2008 )                                    */
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00011 /*        ullrich.koethe@iwr.uni-heidelberg.de    or                    */
00012 /*        vigra@informatik.uni-hamburg.de                               */
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00025 /*    Software.                                                         */
00026 /*                                                                      */
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00037 
00038 #ifndef VIGRA_INTERPOLATING_ACCESSOR_HXX
00039 #define VIGRA_INTERPOLATING_ACCESSOR_HXX
00040 
00041 
00042 #include "accessor.hxx"
00043 #include "diff2d.hxx"
00044 
00045 namespace vigra {
00046 
00047 /** \addtogroup DataAccessors
00048 */
00049 //@{
00050 
00051 /********************************************************/
00052 /*                                                      */
00053 /*            BilinearInterpolatingAccessor             */
00054 /*                                                      */
00055 /********************************************************/
00056 
00057 /** \brief Bilinear interpolation at non-integer positions.
00058 
00059     This accessor allows an image be accessed at arbitrary non-integer
00060     coordinates and performs an bi-linear interpolation to
00061     obtain a pixel value.
00062     It uses the given ACCESSOR (which is usually the
00063     accessor originally associated with the iterator)
00064     to access data.
00065 
00066     <b>\#include</b> <<a href="accessor_8hxx-source.html">vigra/accessor.hxx</a>>
00067     Namespace: vigra
00068 
00069     <b> Required Interface:</b>
00070 
00071     \code
00072     ITERATOR iter;
00073     ACCESSOR a;
00074     VALUETYPE destvalue;
00075     float s;
00076     int x, y;
00077 
00078     destvalue = s * a(iter, x, y) + s * a(iter, x, y);
00079 
00080     \endcode
00081 */
00082 template <class ACCESSOR, class VALUETYPE>
00083 class BilinearInterpolatingAccessor
00084 {
00085   public:
00086     /** the iterators' pixel type
00087     */
00088     typedef VALUETYPE value_type;
00089 
00090     /** init from given accessor
00091     */
00092     BilinearInterpolatingAccessor(ACCESSOR a)
00093     : a_(a)
00094     {}
00095 
00096     /** Interpolate the data item at a non-integer position.
00097         Ensure that no outside pixels are accessed if
00098         (x, y) is near the image border (as long as
00099         0 <= x <= width-1, 0 <= y <= height-1).
00100     */
00101     template <class ITERATOR>
00102     value_type operator()(ITERATOR const & i, float x, float y) const
00103     {
00104         int ix = int(x);
00105         int iy = int(y);
00106         float dx = x - ix;
00107         float dy = y - iy;
00108 
00109         value_type ret;
00110 
00111         // avoid dereferencing the iterator outside its range
00112         if(dx == 0.0)
00113         {
00114             if(dy == 0.0)
00115             {
00116                 ret = a_(i, Diff2D(ix, iy));
00117             }
00118             else
00119             {
00120                 ret = detail::RequiresExplicitCast<value_type>::cast(
00121                   (1.0 - dy) * a_(i, Diff2D(ix, iy)) +
00122                   dy * a_(i, Diff2D(ix, iy + 1)));
00123             }
00124         }
00125         else
00126         {
00127             if(dy == 0.0)
00128             {
00129                 ret = detail::RequiresExplicitCast<value_type>::cast(
00130                   (1.0 - dx) * a_(i, Diff2D(ix, iy)) +
00131                   dx * a_(i, Diff2D(ix + 1, iy)));
00132             }
00133             else
00134             {
00135                 ret = detail::RequiresExplicitCast<value_type>::cast(
00136                   (1.0 - dx) * (1.0 - dy) * a_(i, Diff2D(ix, iy)) +
00137                   dx * (1.0 - dy) * a_(i, Diff2D(ix + 1, iy)) +
00138                   (1.0 - dx) * dy * a_(i, Diff2D(ix, iy + 1)) +
00139                   dx * dy * a_(i, Diff2D(ix + 1, iy + 1)));
00140             }
00141         }
00142 
00143         return ret;
00144     }
00145 
00146     /** Interpolate the data item at a non-integer position.
00147         This function works as long as 0 <= x < width-1,
00148         0 <= y < height-1. It is slightly faster than <TT>operator()</TT>.
00149     */
00150     template <class ITERATOR>
00151     value_type unchecked(ITERATOR const & i, float x, float y) const
00152     {
00153         int ix = int(x);
00154         int iy = int(y);
00155         float dx = x - ix;
00156         float dy = y - iy;
00157         return detail::RequiresExplicitCast<value_type>::cast(
00158                (1.0 - dx) * (1.0 - dy) * a_(i, Diff2D(ix, iy)) +
00159                dx * (1.0 - dy) * a_(i, Diff2D(ix + 1, iy)) +
00160                (1.0 - dx) * dy * a_(i, Diff2D(ix, iy + 1)) +
00161                dx * dy * a_(i, Diff2D(ix + 1, iy + 1)));
00162     }
00163 
00164   private:
00165     ACCESSOR a_;
00166 };
00167 
00168 //@}
00169 
00170 } // namespace vigra
00171 
00172 #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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