d2/filter/lanczos.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 3 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 __lanczos_h__
  22 #define __lanczos_h__
  23
  24 /*
  25  * A lanczos filter class.
  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 lanczos : public filter {
  34 private:
  35         ale_pos half_width;
  36
  37         /*
  38          * Lanczos function
  39          *
  40          * The lanczos function is the central lobe of the sinc function.
  41          */
  42         ale_real _lanczos(ale_pos p) const {
  43                 if (fabs(p) >= half_width)
  44                         return 0;
  45
  46                 return sinc::_sinc(p / half_width);
  47         }
  48
  49         ale_real _lanczos(point p) const {
  50                 return _lanczos(p[0]) * _lanczos(p[1]);
  51         }
  52
  53 public:
  54
  55         /*
  56          * Size of filter support, in number of half-cycles to each side of the
  57          * filter center.
  58          */
  59         ale_pos support() const {
  60                 return half_width;
  61         }
  62
  63         virtual int equals(const filter *f) const {
  64                 if (typeid(*f) == typeid(*this))
  65                         return ((lanczos *)f)->half_width == half_width;
  66                 return 0;
  67         }
  68
  69         /*
  70          * Response of filter at point p
  71          */
  72         virtual ale_real response(point p) const {
  73                 return _lanczos(p);
  74         }
  75
  76         lanczos(double half_width) {
  77                 this->half_width = half_width;
  78         }
  79
  80 };
  81 #endif