streamtools/rescalers/lanczos.cpp

   1 #include "rescalers/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 rescaler");
  19
  20                 if(2 * a + 1 <= a)
  21                         throw std::runtime_error("Parameter alpha way too large in lanczos rescaler");
  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                         double x = point + 0.5 - (double)num / denum - 0.5 * width / twidth;
  41                         if(x < -1e-10 || x > 1e-10) {
  42                                 double xpi = x * pi;
  43                                 coeffs[count++] = a * sin(xpi) * sin(xpi / a) / ((xpi) * (xpi));
  44                         } else {
  45                                 coeffs[count++] = 1;
  46                         }
  47                 }
  48         }
  49
  50         void compute_coefficients_average(float* coeffs, position_t num, position_t denum, position_t width,
  51                 position_t twidth, unsigned& count, unsigned& base)
  52         {
  53                 signed lowbound, highbound, scan;
  54
  55                 lowbound = num;
  56                 highbound = num + width;
  57                 scan = lowbound - lowbound % denum;
  58
  59                 if((width + denum - 1) / denum > MAXCOEFFICIENTS)
  60                         throw std::runtime_error("Conversion would require more coefficients than supported");
  61
  62                 base = scan / denum;
  63                 *coeffs = (scan + denum) - lowbound;
  64                 count = 1;
  65                 scan = scan + denum;
  66                 while(scan < highbound) {
  67                         if(scan + denum > highbound)
  68                                 coeffs[count++] = highbound - scan;
  69                         else
  70                                 coeffs[count++] = denum;
  71
  72                         scan = scan + denum;
  73                 }
  74         }
  75
  76         simple_rescaler_linear_separable r_average("average", make_bound_method(compute_coefficients_average));
  77         simple_rescaler_linear_separable r_lanczos1("lanczos1", bind_last<void, int, float*, position_t, position_t,
  78                 position_t, position_t, unsigned&, unsigned&>(make_bound_method(compute_coefficients_lanczos), 1));
  79         simple_rescaler_linear_separable r_lanczos2("lanczos2", bind_last<void, int, float*, position_t, position_t,
  80                 position_t, position_t, unsigned&, unsigned&>(make_bound_method(compute_coefficients_lanczos), 2));
  81         simple_rescaler_linear_separable r_lanczos3("lanczos3", bind_last<void, int, float*, position_t, position_t,
  82                 position_t, position_t, unsigned&, unsigned&>(make_bound_method(compute_coefficients_lanczos), 3));
  83         simple_rescaler_linear_separable r_lanczos4("lanczos4", bind_last<void, int, float*, position_t, position_t,
  84                 position_t, position_t, unsigned&, unsigned&>(make_bound_method(compute_coefficients_lanczos), 4));
  85         simple_rescaler_linear_separable r_lanczos5("lanczos5", bind_last<void, int, float*, position_t, position_t,
  86                 position_t, position_t, unsigned&, unsigned&>(make_bound_method(compute_coefficients_lanczos), 5));
  87 }