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         void compute_coefficients_lanczos(float* coeffs, position_t num, position_t denum, position_t width,
   9                 unsigned& count, unsigned& base, int a)
  10         {
  11                 signed lowbound, highbound, scan;
  12
  13                 if(num % denum == 0) {
  14                         coeffs[0] = 1;
  15                         count = 1;
  16                         base = num / denum;
  17                         return;
  18                 }
  19
  20                 if(a == 0)
  21                         throw std::runtime_error("Parameter alpha must be positive in lanczos resizer");
  22
  23                 if(2 * a + 1 <= a)
  24                         throw std::runtime_error("Parameter alpha way too large in lanczos resizer");
  25
  26                 if(2 * a + 1 > MAXCOEFFICIENTS)
  27                         throw std::runtime_error("Parameter alpha value would require more coefficients than supported");
  28
  29                 lowbound = num - a * denum;
  30                 highbound = num + a * denum;
  31                 if(lowbound < 0)
  32                         lowbound = 0;
  33                 if(highbound > width * denum)
  34                         highbound = width * denum - denum;
  35
  36                 scan = lowbound + (denum - lowbound % denum) % denum;
  37                 base = scan / denum;
  38                 count = 0;
  39                 while(scan <= highbound) {
  40                         float difference = (float)(num - scan) / denum;
  41                         if(num == scan)
  42                                 coeffs[count++] = 1;
  43                         else
  44                                 coeffs[count++] = a * sin(M_PI*difference) * sin(M_PI*difference/2) /
  45                                         (M_PI * M_PI * difference * difference);
  46
  47                         scan = scan + denum;
  48                 }
  49         }
  50
  51         void compute_coefficients_average(float* coeffs, position_t num, position_t denum, position_t width,
  52                 unsigned& count, unsigned& base)
  53         {
  54                 signed lowbound, highbound, scan;
  55
  56                 lowbound = num;
  57                 highbound = num + width;
  58                 scan = lowbound - lowbound % denum;
  59
  60                 if((width + denum - 1) / denum > MAXCOEFFICIENTS)
  61                         throw std::runtime_error("Conversion would require more coefficients than supported");
  62
  63                 base = scan / denum;
  64                 *coeffs = (scan + denum) - lowbound;
  65                 count = 1;
  66                 scan = scan + denum;
  67                 while(scan < highbound) {
  68                         if(scan + denum > highbound)
  69                                 coeffs[count++] = highbound - scan;
  70                         else
  71                                 coeffs[count++] = denum;
  72
  73                         scan = scan + denum;
  74                 }
  75         }
  76
  77         simple_resizer_linear_separable r_average("average", compute_coefficients_average);
  78         simple_resizer_linear_separable r_lanczos1("lanczos1", compute_coefficients_lanczos, 1);
  79         simple_resizer_linear_separable r_lanczos2("lanczos2", compute_coefficients_lanczos, 2);
  80         simple_resizer_linear_separable r_lanczos3("lanczos3", compute_coefficients_lanczos, 3);
  81         simple_resizer_linear_separable r_lanczos4("lanczos4", compute_coefficients_lanczos, 4);
  82         simple_resizer_linear_separable r_lanczos5("lanczos5", compute_coefficients_lanczos, 5);
  83 }