streamtools/resizer-lanczos.cpp

   1 #include "resize-linear-separable.hpp"
   2 #include <stdint.h>
   3 #include <cmath>
   4 #include <stdexcept>
   5
   6 namespace
   7 {
   8         double pi = 3.1415926535897932384626;
   9
  10         //num / denum = x * swidth / twidth
  11         // swidth = n * twidth => x * n
  12         // twdith = n * swidth => x / n
  13
  14         void compute_coefficients_lanczos(float* coeffs, position_t num, position_t denum, position_t width,
  15                 position_t twidth, unsigned& count, unsigned& base, int a)
  16         {
  17                 if(a == 0)
  18                         throw std::runtime_error("Parameter alpha must be positive in lanczos resizer");
  19
  20                 if(2 * a + 1 <= a)
  21                         throw std::runtime_error("Parameter alpha way too large in lanczos resizer");
  22
  23                 if(2 * a + 1 > MAXCOEFFICIENTS)
  24                         throw std::runtime_error("Parameter alpha value would require more coefficients than "
  25                                 "supported");
  26
  27                 count = 0;
  28                 base = 0;
  29                 bool base_set = false;
  30                 position_t centralpoint = num / denum;
  31                 for(int i = -a + 1; i <= a; i++) {
  32                         position_t point = centralpoint + i;
  33
  34                         if(point < 0 || point >= width)
  35                                 continue;       //Out of range.
  36                         if(!base_set) {
  37                                 base_set = true;
  38                                 base = (unsigned)point;
  39                         }
  40                         if(num != centralpoint * denum) {
  41                                 double x = (double)num / denum - centralpoint;
  42                                 coeffs[count++] = a * sin(x * pi) * sin(x * pi / a) / ((x * pi) * (x * pi));
  43                         } else {
  44                                 coeffs[count++] = 1;
  45                         }
  46                 }
  47         }
  48
  49         void compute_coefficients_average(float* coeffs, position_t num, position_t denum, position_t width,
  50                 position_t twidth, unsigned& count, unsigned& base)
  51         {
  52                 signed lowbound, highbound, scan;
  53
  54                 lowbound = num;
  55                 highbound = num + width;
  56                 scan = lowbound - lowbound % denum;
  57
  58                 if((width + denum - 1) / denum > MAXCOEFFICIENTS)
  59                         throw std::runtime_error("Conversion would require more coefficients than supported");
  60
  61                 base = scan / denum;
  62                 *coeffs = (scan + denum) - lowbound;
  63                 count = 1;
  64                 scan = scan + denum;
  65                 while(scan < highbound) {
  66                         if(scan + denum > highbound)
  67                                 coeffs[count++] = highbound - scan;
  68                         else
  69                                 coeffs[count++] = denum;
  70
  71                         scan = scan + denum;
  72                 }
  73         }
  74
  75         simple_resizer_linear_separable r_average("average", compute_coefficients_average);
  76         simple_resizer_linear_separable r_lanczos1("lanczos1", compute_coefficients_lanczos, 1);
  77         simple_resizer_linear_separable r_lanczos2("lanczos2", compute_coefficients_lanczos, 2);
  78         simple_resizer_linear_separable r_lanczos3("lanczos3", compute_coefficients_lanczos, 3);
  79         simple_resizer_linear_separable r_lanczos4("lanczos4", compute_coefficients_lanczos, 4);
  80         simple_resizer_linear_separable r_lanczos5("lanczos5", compute_coefficients_lanczos, 5);
  81 }