d2/filter/sinc.h

   1 // Copyright 2004 David Hilvert <dhilvert@auricle.dyndns.org>,
   2 //                              <dhilvert@ugcs.caltech.edu>
   3
   4 /*  This file is part of the Anti-Lamenessing Engine.
   5
   6     The Anti-Lamenessing Engine is free software; you can redistribute it and/or modify
   7     it under the terms of the GNU General Public License as published by
   8     the Free Software Foundation; either version 2 of the License, or
   9     (at your option) any later version.
  10
  11     The Anti-Lamenessing Engine is distributed in the hope that it will be useful,
  12     but WITHOUT ANY WARRANTY; without even the implied warranty of
  13     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14     GNU General Public License for more details.
  15
  16     You should have received a copy of the GNU General Public License
  17     along with the Anti-Lamenessing Engine; if not, write to the Free Software
  18     Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  19 */
  20
  21 #ifndef __sinc_h__
  22 #define __sinc_h__
  23
  24 /*
  25  * A filtering class for the sinc function.
  26  *
  27  * Notes on Lanczos and Sinc by Dave Martindale et alia are available here:
  28  *
  29  *      http://www.binbooks.com/books/photo/i/l/57186AF8DE
  30  *      http://www.binbooks.com/books/photo/i/l/57186AE7E6&orig=1
  31  */
  32
  33 class sinc : public filter {
  34 public:
  35
  36         /*
  37          * Sinc filter.
  38          *
  39          * Width is infinite.
  40          */
  41         static double _sinc(ale_pos p) {
  42                 if (fabs(p) < 0.001)
  43                         return 1;
  44                 return sin(M_PI * p) / (M_PI * p);
  45         }
  46
  47         static double _sinc(point p) {
  48                 return _sinc(p[0]) * _sinc(p[1]);
  49         }
  50
  51         virtual int equals(const filter *f) const {
  52                 if (typeid(*f) == typeid(*this))
  53                         return 1;
  54                 return 0;
  55         }
  56
  57         /*
  58          * Size of filter support, in number of half-cycles to each side of the
  59          * filter center.
  60          */
  61         virtual ale_real support() const {
  62                 double zero = 0;
  63                 double infinity = 1 / zero;
  64                 assert (!isnan(infinity));
  65                 assert (1 < infinity);
  66                 return (ale_real) infinity;
  67         }
  68
  69         /*
  70          * Response of filter at point p
  71          */
  72         virtual ale_real response(point p) const {
  73                 return _sinc(p);
  74         }
  75 };
  76 #endif