vcl/inc/ResampleKernel.hxx

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  19
  20 #ifndef INCLUDED_VCL_RESAMPLEKERNEL_HXX
  21 #define INCLUDED_VCL_RESAMPLEKERNEL_HXX
  22
  23 #include <boost/math/special_functions/sinc.hpp>
  24
  25 namespace vcl {
  26
  27 // Resample kernels
  28
  29 class Kernel
  30 {
  31 public:
  32              Kernel() {}
  33     virtual ~Kernel() {}
  34
  35     virtual double  GetWidth() const = 0;
  36     virtual double  Calculate( double x ) const = 0;
  37 };
  38
  39 class Lanczos3Kernel final : public Kernel
  40 {
  41 public:
  42     Lanczos3Kernel() : Kernel () {}
  43
  44     virtual double  GetWidth() const override { return 3.0; }
  45     virtual double  Calculate (double x) const override
  46     {
  47         return (-3.0 <= x && x < 3.0) ? SincFilter(x) * SincFilter( x / 3.0 ) : 0.0;
  48     }
  49
  50     static double SincFilter(double x)
  51     {
  52         if (x == 0.0)
  53         {
  54             return 1.0;
  55         }
  56         x = x * M_PI;
  57         return boost::math::sinc_pi(x, SincPolicy());
  58     }
  59
  60 private:
  61     typedef boost::math::policies::policy<
  62         boost::math::policies::promote_double<false> > SincPolicy;
  63 };
  64
  65 class BicubicKernel final : public Kernel
  66 {
  67 public:
  68     BicubicKernel() : Kernel () {}
  69
  70 private:
  71     virtual double  GetWidth() const override { return 2.0; }
  72     virtual double  Calculate (double x) const override
  73     {
  74         if (x < 0.0)
  75         {
  76             x = -x;
  77         }
  78
  79         if (x <= 1.0)
  80         {
  81             return (1.5 * x - 2.5) * x * x + 1.0;
  82         }
  83         else if (x < 2.0)
  84         {
  85             return ((-0.5 * x + 2.5) * x - 4) * x + 2;
  86         }
  87         return 0.0;
  88     }
  89 };
  90
  91 class BilinearKernel final : public Kernel
  92 {
  93 public:
  94     BilinearKernel() : Kernel () {}
  95
  96 private:
  97     virtual double  GetWidth() const override { return 1.0; }
  98     virtual double  Calculate (double x) const override
  99     {
 100         if (x < 0.0)
 101         {
 102             x = -x;
 103         }
 104         if (x < 1.0)
 105         {
 106             return 1.0-x;
 107         }
 108         return 0.0;
 109     }
 110 };
 111
 112 } // namespace vcl
 113
 114 #endif // INCLUDED_VCL_RESAMPLEKERNEL_HXX
 115
 116 /* vim:set shiftwidth=4 softtabstop=4 expandtab: */