vil/algo/vil_sobel_3x3.cxx

// This is core/vil/algo/vil_sobel_3x3.cxx
#include "vil_sobel_3x3.h"
//:
// \file
// \brief Apply gradient operator to 2D planes of data
// \author Tim Cootes

//: Compute gradients of single plane of 2D data using 3x3 Sobel filters
//  Computes both i and j gradients of an ni x nj plane of data
template <>
void
vil_sobel_3x3_1plane(const unsigned char * src,
                     std::ptrdiff_t s_istep,
                     std::ptrdiff_t s_jstep,
                     float * gi,
                     std::ptrdiff_t gi_istep,
                     std::ptrdiff_t gi_jstep,
                     float * gj,
                     std::ptrdiff_t gj_istep,
                     std::ptrdiff_t gj_jstep,
                     unsigned ni,
                     unsigned nj)
{
  const unsigned char * s_data = src;
  float * gi_data = gi;
  float * gj_data = gj;

  if (ni == 0 || nj == 0)
    return;
  if (ni == 1)
  {
    // Zero the elements in the column
    for (unsigned j = 0; j < nj; ++j)
    {
      *gi_data = 0;
      *gj_data = 0;
      gi_data += gi_jstep;
      gj_data += gj_jstep;
    }
    return;
  }
  if (nj == 1)
  {
    // Zero the elements in the column
    for (unsigned i = 0; i < ni; ++i)
    {
      *gi_data = 0;
      *gj_data = 0;
      gi_data += gi_istep;
      gj_data += gj_istep;
    }
    return;
  }

  // Compute relative grid positions
  //  o1 o2 o3
  //  o4    o5
  //  o6 o7 o8
  const std::ptrdiff_t o1 = s_jstep - s_istep;
  const std::ptrdiff_t o2 = s_jstep;
  const std::ptrdiff_t o3 = s_istep + s_jstep;
  const std::ptrdiff_t o4 = -s_istep;
  const std::ptrdiff_t o5 = s_istep;
  const std::ptrdiff_t o6 = -s_istep - s_jstep;
  const std::ptrdiff_t o7 = -s_jstep;
  const std::ptrdiff_t o8 = s_istep - s_jstep;

  const unsigned ni1 = ni - 1;
  const unsigned nj1 = nj - 1;

  s_data += s_istep + s_jstep;
  gi_data += gi_jstep;
  gj_data += gj_jstep;

  for (unsigned j = 1; j < nj1; ++j)
  {
    const unsigned char * s = s_data;
    float * pgi = gi_data;
    float * pgj = gj_data;

    // Zero the first elements in the rows
    *pgi = 0;
    pgi += gi_istep;
    *pgj = 0;
    pgj += gj_istep;

    for (unsigned i = 1; i < ni1; ++i)
    {
      // Compute gradient in i
      // Note: Multiply each element individually
      //      to ensure conversion to float before addition
      *pgi = (0.125f * s[o3] + 0.25f * s[o5] + 0.125f * s[o8]) - (0.125f * s[o1] + 0.25f * s[o4] + 0.125f * s[o6]);
      // Compute gradient in j
      *pgj = (0.125f * s[o1] + 0.25f * s[o2] + 0.125f * s[o3]) - (0.125f * s[o6] + 0.25f * s[o7] + 0.125f * s[o8]);

      s += s_istep;
      pgi += gi_istep;
      pgj += gj_istep;
    }

    // Zero the last elements in the rows
    *pgi = 0;
    *pgj = 0;

    // Move to next row
    s_data += s_jstep;
    gi_data += gi_jstep;
    gj_data += gj_jstep;
  }

  // Zero the first and last rows
  for (unsigned i = 0; i < ni; ++i)
  {
    *gi = 0;
    gi += gi_istep;
    *gj = 0;
    gj += gj_istep;
    *gi_data = 0;
    gi_data += gi_istep;
    *gj_data = 0;
    gj_data += gj_istep;
  }
}

//: Compute gradients of single plane of 2D data using 3x3 Sobel filters
//  Computes both i and j gradients of an ni x nj plane of data
template <>
void
vil_sobel_3x3_1plane(const unsigned char * src,
                     std::ptrdiff_t s_istep,
                     std::ptrdiff_t s_jstep,
                     double * gi,
                     std::ptrdiff_t gi_istep,
                     std::ptrdiff_t gi_jstep,
                     double * gj,
                     std::ptrdiff_t gj_istep,
                     std::ptrdiff_t gj_jstep,
                     unsigned ni,
                     unsigned nj)
{
  const unsigned char * s_data = src;
  double * gi_data = gi;
  double * gj_data = gj;

  if (ni == 0 || nj == 0)
    return;
  if (ni == 1)
  {
    // Zero the elements in the column
    for (unsigned j = 0; j < nj; ++j)
    {
      *gi_data = 0;
      *gj_data = 0;
      gi_data += gi_jstep;
      gj_data += gj_jstep;
    }
    return;
  }
  if (nj == 1)
  {
    // Zero the elements in the column
    for (unsigned i = 0; i < ni; ++i)
    {
      *gi_data = 0;
      *gj_data = 0;
      gi_data += gi_istep;
      gj_data += gj_istep;
    }
    return;
  }

  // Compute relative grid positions
  //  o1 o2 o3
  //  o4    o5
  //  o6 o7 o8
  const std::ptrdiff_t o1 = s_jstep - s_istep;
  const std::ptrdiff_t o2 = s_jstep;
  const std::ptrdiff_t o3 = s_istep + s_jstep;
  const std::ptrdiff_t o4 = -s_istep;
  const std::ptrdiff_t o5 = s_istep;
  const std::ptrdiff_t o6 = -s_istep - s_jstep;
  const std::ptrdiff_t o7 = -s_jstep;
  const std::ptrdiff_t o8 = s_istep - s_jstep;

  const unsigned ni1 = ni - 1;
  const unsigned nj1 = nj - 1;

  s_data += s_istep + s_jstep;
  gi_data += gi_jstep;
  gj_data += gj_jstep;

  for (unsigned j = 1; j < nj1; ++j)
  {
    const unsigned char * s = s_data;
    double * pgi = gi_data;
    double * pgj = gj_data;

    // Zero the first elements in the rows
    *pgi = 0;
    pgi += gi_istep;
    *pgj = 0;
    pgj += gj_istep;

    for (unsigned i = 1; i < ni1; ++i)
    {
      // Compute gradient in i
      // Note: Multiply each element individually
      //      to ensure conversion to double before addition
      *pgi = (0.125 * s[o3] + 0.25 * s[o5] + 0.125 * s[o8]) - (0.125 * s[o1] + 0.25 * s[o4] + 0.125 * s[o6]);
      // Compute gradient in j
      *pgj = (0.125 * s[o1] + 0.25 * s[o2] + 0.125 * s[o3]) - (0.125 * s[o6] + 0.25 * s[o7] + 0.125 * s[o8]);

      s += s_istep;
      pgi += gi_istep;
      pgj += gj_istep;
    }

    // Zero the last elements in the rows
    *pgi = 0;
    *pgj = 0;

    // Move to next row
    s_data += s_jstep;
    gi_data += gi_jstep;
    gj_data += gj_jstep;
  }

  // Zero the first and last rows
  for (unsigned i = 0; i < ni; ++i)
  {
    *gi = 0;
    gi += gi_istep;
    *gj = 0;
    gj += gj_istep;
    *gi_data = 0;
    gi_data += gi_istep;
    *gj_data = 0;
    gj_data += gj_istep;
  }
}

//: Compute gradients of single plane of 2D data using 3x3 Sobel filters
//  Computes both x and j gradients of an nx x nj plane of data
template <>
void
vil_sobel_3x3_1plane(const float * src,
                     std::ptrdiff_t s_istep,
                     std::ptrdiff_t s_jstep,
                     float * gi,
                     std::ptrdiff_t gi_istep,
                     std::ptrdiff_t gi_jstep,
                     float * gj,
                     std::ptrdiff_t gj_istep,
                     std::ptrdiff_t gj_jstep,
                     unsigned ni,
                     unsigned nj)
{
  const float * s_data = src;
  float * gi_data = gi;
  float * gj_data = gj;

  if (ni == 0 || nj == 0)
    return;
  if (ni == 1)
  {
    // Zero the elements in the column
    for (unsigned j = 0; j < nj; ++j)
    {
      *gi_data = 0;
      *gj_data = 0;
      gi_data += gi_jstep;
      gj_data += gj_jstep;
    }
    return;
  }
  if (nj == 1)
  {
    // Zero the elements in the column
    for (unsigned i = 0; i < ni; ++i)
    {
      *gi_data = 0;
      *gj_data = 0;
      gi_data += gi_istep;
      gj_data += gj_istep;
    }
    return;
  }

  // Compute relative grid positions
  //  o1 o2 o3
  //  o4    o5
  //  o6 o7 o8
  const std::ptrdiff_t o1 = s_jstep - s_istep;
  const std::ptrdiff_t o2 = s_jstep;
  const std::ptrdiff_t o3 = s_istep + s_jstep;
  const std::ptrdiff_t o4 = -s_istep;
  const std::ptrdiff_t o5 = s_istep;
  const std::ptrdiff_t o6 = -s_istep - s_jstep;
  const std::ptrdiff_t o7 = -s_jstep;
  const std::ptrdiff_t o8 = s_istep - s_jstep;

  const unsigned ni1 = ni - 1;
  const unsigned nj1 = nj - 1;

  s_data += s_istep + s_jstep;
  gi_data += gi_jstep;
  gj_data += gj_jstep;

  for (unsigned j = 1; j < nj1; ++j)
  {
    const float * s = s_data;
    float * pgi = gi_data;
    float * pgj = gj_data;

    // Zero the first elements in the rows
    *pgi = 0;
    pgi += gi_istep;
    *pgj = 0;
    pgj += gj_istep;

    for (unsigned i = 1; i < ni1; ++i)
    {
      // Compute gradient in i
      *pgi = 0.125f * (s[o3] + s[o8] - (s[o1] + s[o6])) + 0.25f * (s[o5] - s[o4]);
      // Compute gradient in j
      *pgj = 0.125f * (s[o1] + s[o3] - (s[o6] + s[o8])) + 0.25f * (s[o2] - s[o7]);

      s += s_istep;
      pgi += gi_istep;
      pgj += gj_istep;
    }

    // Zero the last elements in the rows
    *pgi = 0;
    *pgj = 0;

    // Move to next row
    s_data += s_jstep;
    gi_data += gi_jstep;
    gj_data += gj_jstep;
  }

  // Zero the first and last rows
  for (unsigned i = 0; i < ni; ++i)
  {
    *gi = 0;
    gi += gi_istep;
    *gj = 0;
    gj += gj_istep;
    *gi_data = 0;
    gi_data += gi_istep;
    *gj_data = 0;
    gj_data += gj_istep;
  }
}

//: Compute gradients of single plane of 2D data using 3x3 Sobel filters
//  Computes both x and j gradients of an nx x nj plane of data
template <>
void
vil_sobel_3x3_1plane(const double * src,
                     std::ptrdiff_t s_istep,
                     std::ptrdiff_t s_jstep,
                     double * gi,
                     std::ptrdiff_t gi_istep,
                     std::ptrdiff_t gi_jstep,
                     double * gj,
                     std::ptrdiff_t gj_istep,
                     std::ptrdiff_t gj_jstep,
                     unsigned ni,
                     unsigned nj)
{
  const double * s_data = src;
  double * gi_data = gi;
  double * gj_data = gj;

  if (ni == 0 || nj == 0)
    return;
  if (ni == 1)
  {
    // Zero the elements in the column
    for (unsigned j = 0; j < nj; ++j)
    {
      *gi_data = 0;
      *gj_data = 0;
      gi_data += gi_jstep;
      gj_data += gj_jstep;
    }
    return;
  }
  if (nj == 1)
  {
    // Zero the elements in the column
    for (unsigned i = 0; i < ni; ++i)
    {
      *gi_data = 0;
      *gj_data = 0;
      gi_data += gi_istep;
      gj_data += gj_istep;
    }
    return;
  }

  // Compute relative grid positions
  //  o1 o2 o3
  //  o4    o5
  //  o6 o7 o8
  const std::ptrdiff_t o1 = s_jstep - s_istep;
  const std::ptrdiff_t o2 = s_jstep;
  const std::ptrdiff_t o3 = s_istep + s_jstep;
  const std::ptrdiff_t o4 = -s_istep;
  const std::ptrdiff_t o5 = s_istep;
  const std::ptrdiff_t o6 = -s_istep - s_jstep;
  const std::ptrdiff_t o7 = -s_jstep;
  const std::ptrdiff_t o8 = s_istep - s_jstep;

  const unsigned ni1 = ni - 1;
  const unsigned nj1 = nj - 1;

  s_data += s_istep + s_jstep;
  gi_data += gi_jstep;
  gj_data += gj_jstep;

  for (unsigned j = 1; j < nj1; ++j)
  {
    const double * s = s_data;
    double * pgi = gi_data;
    double * pgj = gj_data;

    // Zero the first elements in the rows
    *pgi = 0;
    pgi += gi_istep;
    *pgj = 0;
    pgj += gj_istep;

    for (unsigned i = 1; i < ni1; ++i)
    {
      // Compute gradient in i
      *pgi = 0.125 * (s[o3] + s[o8] - (s[o1] + s[o6])) + 0.25 * (s[o5] - s[o4]);
      // Compute gradient in j
      *pgj = 0.125 * (s[o1] + s[o3] - (s[o6] + s[o8])) + 0.25 * (s[o2] - s[o7]);

      s += s_istep;
      pgi += gi_istep;
      pgj += gj_istep;
    }

    // Zero the last elements in the rows
    *pgi = 0;
    *pgj = 0;

    // Move to next row
    s_data += s_jstep;
    gi_data += gi_jstep;
    gj_data += gj_jstep;
  }

  // Zero the first and last rows
  for (unsigned i = 0; i < ni; ++i)
  {
    *gi = 0;
    gi += gi_istep;
    *gj = 0;
    gj += gj_istep;
    *gi_data = 0;
    gi_data += gi_istep;
    *gj_data = 0;
    gj_data += gj_istep;
  }
}