streamtools/rescalers/bicubic.cpp

   1 #include "rescalers/linear-separable.hpp"
   2 #include <stdint.h>
   3 #include <cmath>
   4 #include <stdexcept>
   5
   6 namespace
   7 {
   8         void compute_coefficients_bicubic(float* coeffs, position_t num, position_t denum, position_t width,
   9                 position_t twidth, unsigned& count, unsigned& base)
  10         {
  11                 base = num / denum;
  12                 float t1 = (num % denum) / (float)denum;
  13                 float t2 = t1 * t1;
  14                 float t3 = t2 * t1;
  15                 count = 0;
  16                 /*
  17                 In matrix form, the equation is:
  18                                              / 0,  2,  0,  0 \ /a_-1\
  19                                              |-1,  0,  1,  0 | |a_0 |
  20                  p(t) = 0.5 * [1, t, t², t³] | 2, -5,  4, -1 | |a_1 |
  21                                              \-1,  3, -3,  1 / \a_2 /
  22                 Due to implicit muliplications, only the first part needs to be computed.
  23                 */
  24                 float c1 = t2 - 0.5 * (t1 + t3);
  25                 float c2 = 1 - 2.5 * t2 + 1.5 * t3;
  26                 float c3 = 0.5 * t1 + 2 * t2 - 1.5 * t3;
  27                 float c4 = 0.5 * (t3 - t2);
  28                 if(base == 0) {
  29                         coeffs[count++] = c2;
  30                         if(base < width - 1)    coeffs[count++] = c3;
  31                         if(base < width - 2)    coeffs[count++] = c4;
  32                 } else {
  33                         base--;
  34                         coeffs[count++] = c1;
  35                         coeffs[count++] = c2;
  36                         if(base < width - 2)    coeffs[count++] = c3;
  37                         if(base < width - 3)    coeffs[count++] = c4;
  38                 }
  39         }
  40
  41         simple_rescaler_linear_separable r_bicubic("bicubic", make_bound_method(compute_coefficients_bicubic));
  42 }