dlib C++ Library - hough_transform.h

// Copyright (C) 2014 Davis E. King (davis@dlib.net)
// License: Boost Software License See LICENSE.txt for the full license.
#ifndef DLIB_HOUGH_tRANSFORM_Hh_
#define DLIB_HOUGH_tRANSFORM_Hh_
#include "hough_transform_abstract.h"
#include "../image_processing/generic_image.h"
#include "../geometry.h"
#include "../algs.h"
#include "assign_image.h"
#include <limits>
namespace dlib
{
// ----------------------------------------------------------------------------------------
 class hough_transform
 {
 public:
 explicit hough_transform (
 unsigned long size_
 ) : _size(size_) 
 {
 DLIB_CASSERT(size_ > 0,
 "\t hough_transform::hough_transform(size_)"
 << "\n\t Invalid arguments given to this function."
 );
 even_size = _size - (_size%2);
 const point cent = center(rectangle(0,0,size_-1,size_-1));
 xcos_theta.set_size(size_, size_);
 ysin_theta.set_size(size_, size_);
 std::vector<double> cos_theta(size_), sin_theta(size_);
 const double scale = 1<<16;
 for (unsigned long t = 0; t < size_; ++t)
 {
 double theta = t*pi/even_size;
 cos_theta[t] = scale*std::cos(theta)/sqrt_2;
 sin_theta[t] = scale*std::sin(theta)/sqrt_2;
 }
 const double offset = scale*even_size/4.0 + 0.5;
 for (unsigned long c = 0; c < size_; ++c)
 {
 const long x = c - cent.x();
 for (unsigned long t = 0; t < size_; ++t)
 xcos_theta(c,t) = static_cast<int32>(x*cos_theta[t] + offset);
 }
 for (unsigned long r = 0; r < size_; ++r)
 {
 const long y = r - cent.y();
 for (unsigned long t = 0; t < size_; ++t)
 ysin_theta(r,t) = static_cast<int32>(y*sin_theta[t] + offset);
 }
 }
 inline unsigned long size(
 ) const { return _size; }
 long nr(
 ) const { return _size; }
 long nc(
 ) const { return _size; }
 std::pair<dpoint, dpoint> get_line (
 const dpoint& p
 ) const
 {
 DLIB_ASSERT(rectangle(0,0,size()-1,size()-1).contains(p) == true,
 "\t pair<dpoint,dpoint> hough_transform::get_line(dpoint)"
 << "\n\t Invalid arguments given to this function."
 << "\n\t p: " << p 
 << "\n\t size(): " << size()
 );
 // First we compute the radius measured in pixels from the center and the theta
 // angle in radians.
 double theta, radius;
 get_line_properties(p, theta, radius);
 theta *= pi/180;
 // now make a line segment on the line.
 const rectangle box = get_rect(*this);
 const dpoint cent = center(box);
 dpoint v1 = cent + dpoint(size()+1000,0) + dpoint(0,radius);
 dpoint v2 = cent - dpoint(size()+1000,0) + dpoint(0,radius);
 dpoint p1 = rotate_point(cent, v1, theta);
 dpoint p2 = rotate_point(cent, v2, theta);
 clip_line_to_rectangle(box, p1, p2);
 return std::make_pair(p1,p2);
 }
 double get_line_angle_in_degrees (
 const dpoint& p 
 ) const
 {
 double angle, radius;
 get_line_properties(p, angle, radius);
 return angle;
 }
 void get_line_properties (
 const dpoint& p,
 double& angle_in_degrees,
 double& radius
 ) const
 {
 const dpoint cent = center(get_rect(*this));
 double theta = p.x()-cent.x();
 radius = p.y()-cent.y();
 angle_in_degrees = 180*theta/even_size;
 radius = radius*sqrt_2 + 0.5;
 }
 template <
 typename image_type
 >
 point get_best_hough_point (
 const point& p,
 const image_type& himg_
 )
 {
 const const_image_view<image_type> himg(himg_);
 DLIB_ASSERT(himg.nr() == size() && himg.nc() == size() &&
 rectangle(0,0,size()-1,size()-1).contains(p) == true,
 "\t point hough_transform::get_best_hough_point()"
 << "\n\t Invalid arguments given to this function."
 << "\n\t himg.nr(): " << himg.nr()
 << "\n\t himg.nc(): " << himg.nc()
 << "\n\t size(): " << size()
 << "\n\t p: " << p 
 );
 typedef typename image_traits<image_type>::pixel_type pixel_type;
 COMPILE_TIME_ASSERT(pixel_traits<pixel_type>::grayscale == true);
 pixel_type best_val = std::numeric_limits<pixel_type>::min();
 point best_point;
 const long max_n8 = (himg.nc()/8)*8;
 const long max_n4 = (himg.nc()/4)*4;
 const long r = p.y();
 const long c = p.x();
 const int32* ysin = &ysin_theta(r,0);
 const int32* xcos = &xcos_theta(c,0);
 long t = 0;
 while(t < max_n8)
 {
 long rr0 = (*xcos++ + *ysin++)>>16;
 long rr1 = (*xcos++ + *ysin++)>>16;
 long rr2 = (*xcos++ + *ysin++)>>16;
 long rr3 = (*xcos++ + *ysin++)>>16;
 long rr4 = (*xcos++ + *ysin++)>>16;
 long rr5 = (*xcos++ + *ysin++)>>16;
 long rr6 = (*xcos++ + *ysin++)>>16;
 long rr7 = (*xcos++ + *ysin++)>>16;
 if (himg[rr0][t++] > best_val)
 {
 best_val = himg[rr0][t-1];
 best_point.x() = t-1;
 best_point.y() = rr0;
 }
 if (himg[rr1][t++] > best_val)
 {
 best_val = himg[rr1][t-1];
 best_point.x() = t-1;
 best_point.y() = rr1;
 }
 if (himg[rr2][t++] > best_val)
 {
 best_val = himg[rr2][t-1];
 best_point.x() = t-1;
 best_point.y() = rr2;
 }
 if (himg[rr3][t++] > best_val)
 {
 best_val = himg[rr3][t-1];
 best_point.x() = t-1;
 best_point.y() = rr3;
 }
 if (himg[rr4][t++] > best_val)
 {
 best_val = himg[rr4][t-1];
 best_point.x() = t-1;
 best_point.y() = rr4;
 }
 if (himg[rr5][t++] > best_val)
 {
 best_val = himg[rr5][t-1];
 best_point.x() = t-1;
 best_point.y() = rr5;
 }
 if (himg[rr6][t++] > best_val)
 {
 best_val = himg[rr6][t-1];
 best_point.x() = t-1;
 best_point.y() = rr6;
 }
 if (himg[rr7][t++] > best_val)
 {
 best_val = himg[rr7][t-1];
 best_point.x() = t-1;
 best_point.y() = rr7;
 }
 }
 while(t < max_n4)
 {
 long rr0 = (*xcos++ + *ysin++)>>16;
 long rr1 = (*xcos++ + *ysin++)>>16;
 long rr2 = (*xcos++ + *ysin++)>>16;
 long rr3 = (*xcos++ + *ysin++)>>16;
 if (himg[rr0][t++] > best_val)
 {
 best_val = himg[rr0][t-1];
 best_point.x() = t-1;
 best_point.y() = rr0;
 }
 if (himg[rr1][t++] > best_val)
 {
 best_val = himg[rr1][t-1];
 best_point.x() = t-1;
 best_point.y() = rr1;
 }
 if (himg[rr2][t++] > best_val)
 {
 best_val = himg[rr2][t-1];
 best_point.x() = t-1;
 best_point.y() = rr2;
 }
 if (himg[rr3][t++] > best_val)
 {
 best_val = himg[rr3][t-1];
 best_point.x() = t-1;
 best_point.y() = rr3;
 }
 }
 while(t < himg.nc())
 {
 long rr0 = (*xcos++ + *ysin++)>>16;
 if (himg[rr0][t++] > best_val)
 {
 best_val = himg[rr0][t-1];
 best_point.x() = t-1;
 best_point.y() = rr0;
 }
 }
 return best_point;
 }
 template <
 typename in_image_type,
 typename out_image_type
 >
 void operator() (
 const in_image_type& img_,
 const rectangle& box,
 out_image_type& himg_
 ) const
 {
 typedef typename image_traits<in_image_type>::pixel_type in_pixel_type;
 typedef typename image_traits<out_image_type>::pixel_type out_pixel_type;
 DLIB_CASSERT(box.width() == size() && box.height() == size(),
 "\t void hough_transform::operator()"
 << "\n\t Invalid arguments given to this function."
 << "\n\t box.width(): " << box.width()
 << "\n\t box.height(): " << box.height()
 << "\n\t size(): " << size()
 );
 COMPILE_TIME_ASSERT(pixel_traits<in_pixel_type>::grayscale == true);
 COMPILE_TIME_ASSERT(pixel_traits<out_pixel_type>::grayscale == true);
 const_image_view<in_image_type> img(img_);
 image_view<out_image_type> himg(himg_);
 himg.set_size(size(), size());
 assign_all_pixels(himg, 0);
 auto record_hit = [&](const point& hough_point, const point& /*img_point*/, const in_pixel_type& val)
 {
 himg[hough_point.y()][hough_point.x()] += val;
 };
 perform_generic_hough_transform(img_, box, record_hit);
 }
 template <
 typename in_image_type,
 typename out_image_type
 >
 void operator() (
 const in_image_type& img_,
 out_image_type& himg_
 ) const
 {
 rectangle box(0,0, num_columns(img_)-1, num_rows(img_)-1);
 (*this)(img_, box, himg_);
 }
 template <
 typename in_image_type
 >
 std::vector<std::vector<point>> find_pixels_voting_for_lines (
 const in_image_type& img,
 const rectangle& box,
 const std::vector<point>& hough_points,
 const unsigned long angle_window_size = 1,
 const unsigned long radius_window_size = 1
 ) const
 {
 typedef typename image_traits<in_image_type>::pixel_type in_pixel_type;
 DLIB_CASSERT(angle_window_size >= 1);
 DLIB_CASSERT(radius_window_size >= 1);
 DLIB_CASSERT(box.width() == size() && box.height() == size(),
 "\t std::vector<std::vector<point>> hough_transform::find_pixels_voting_for_lines()"
 << "\n\t Invalid arguments given to this function."
 << "\n\t box.width(): " << box.width()
 << "\n\t box.height(): " << box.height()
 << "\n\t size(): " << size()
 );
#ifdef ENABLE_ASSERTS
 for (auto& p : hough_points)
 DLIB_CASSERT(get_rect(*this).contains(p), 
 "You gave a hough_points that isn't actually in the Hough space of this object."
 << "\n\t get_rect(*this): "<< get_rect(*this) 
 << "\n\t p: "<< p 
 );
#endif
 std::vector<std::vector<point>> constituent_points(hough_points.size());
 // make a map that lets us look up in constant time if a hough point is in the
 // constituent_points output and if so where.
 matrix<uint32> hmap(size(),size());
 hmap = hough_points.size();
 for (size_t i = 0; i < hough_points.size(); ++i)
 {
 rectangle area = centered_rect(hough_points[i],angle_window_size,radius_window_size).intersect(get_rect(hmap));
 for (long r = area.top(); r <= area.bottom(); ++r)
 {
 for (long c = area.left(); c <= area.right(); ++c)
 {
 hmap(r,c) = i;
 }
 }
 }
 // record that this image point voted for this Hough point
 auto record_hit = [&](const point& hough_point, const point& img_point, in_pixel_type)
 {
 auto idx = hmap(hough_point.y(), hough_point.x());
 if (idx < constituent_points.size())
 {
 // don't add img_point if it's already in the list.
 if (constituent_points[idx].size() == 0 || constituent_points[idx].back() != img_point)
 constituent_points[idx].push_back(img_point);
 }
 };
 perform_generic_hough_transform(img, box, record_hit);
 return constituent_points;
 }
 template <
 typename in_image_type
 >
 std::vector<std::vector<point>> find_pixels_voting_for_lines (
 const in_image_type& img,
 const std::vector<point>& hough_points,
 const unsigned long angle_window_size = 1,
 const unsigned long radius_window_size = 1
 ) const
 {
 rectangle box(0,0, num_columns(img)-1, num_rows(img)-1);
 return find_pixels_voting_for_lines(img, box, hough_points, angle_window_size, radius_window_size);
 }
 template <
 typename image_type,
 typename thresh_type
 >
 std::vector<point> find_strong_hough_points(
 const image_type& himg_,
 const thresh_type hough_count_threshold,
 const double angle_nms_thresh,
 const double radius_nms_thresh
 )
 {
 const_image_view<image_type> himg(himg_);
 DLIB_CASSERT(himg.nr() == size());
 DLIB_CASSERT(himg.nc() == size());
 DLIB_CASSERT(angle_nms_thresh >= 0)
 DLIB_CASSERT(radius_nms_thresh >= 0)
 std::vector<std::pair<double,point>> initial_lines;
 for (long r = 0; r < himg.nr(); ++r)
 {
 for (long c = 0; c < himg.nc(); ++c)
 {
 if (himg[r][c] >= hough_count_threshold)
 initial_lines.emplace_back(himg[r][c], point(c,r));
 }
 }
 std::vector<point> final_lines;
 std::vector<std::pair<double,double>> final_angle_and_radius;
 // Now do non-max suppression. First, sort the initial_lines so the best lines come first.
 std::sort(initial_lines.rbegin(), initial_lines.rend(), 
 [](const std::pair<double,point>& a, const std::pair<double,point>& b){ return a.first<b.first;});
 for (auto& r : initial_lines)
 {
 double angle, radius;
 get_line_properties(r.second, angle, radius);
 // check if anything in final_lines is too close to r.second. If
 // something is found then discard r.second.
 auto too_close = false;
 for (auto& ref : final_angle_and_radius)
 {
 auto& ref_angle = ref.first;
 auto& ref_radius = ref.second;
 // We need to check for wrap around in angle since, for instance, a
 // line with angle and radius of 90 and 10 is the same line as one with
 // angle -90 and radius -10.
 if ((std::abs(ref_angle - angle) < angle_nms_thresh && std::abs(ref_radius-radius) < radius_nms_thresh) ||
 (180 - std::abs(ref_angle - angle) < angle_nms_thresh && std::abs(ref_radius+radius) < radius_nms_thresh))
 {
 too_close = true;
 break;
 }
 }
 if (!too_close)
 {
 final_lines.emplace_back(r.second);
 final_angle_and_radius.emplace_back(angle, radius);
 }
 }
 return final_lines;
 }
 template <
 typename in_image_type,
 typename record_hit_function_type
 >
 void perform_generic_hough_transform (
 const in_image_type& img_,
 const rectangle& box,
 record_hit_function_type record_hit
 ) const
 {
 typedef typename image_traits<in_image_type>::pixel_type in_pixel_type;
 DLIB_ASSERT(box.width() == size() && box.height() == size(),
 "\t void hough_transform::perform_generic_hough_transform()"
 << "\n\t Invalid arguments given to this function."
 << "\n\t box.width(): " << box.width()
 << "\n\t box.height(): " << box.height()
 << "\n\t size(): " << size()
 );
 COMPILE_TIME_ASSERT(pixel_traits<in_pixel_type>::grayscale == true);
 const_image_view<in_image_type> img(img_);
 const rectangle area = box.intersect(get_rect(img));
 const long max_n8 = (size()/8)*8;
 const long max_n4 = (size()/4)*4;
 for (long r = area.top(); r <= area.bottom(); ++r)
 {
 const int32* ysin_base = &ysin_theta(r-box.top(),0);
 for (long c = area.left(); c <= area.right(); ++c)
 {
 const auto val = img[r][c];
 if (val != 0)
 {
 /*
 // The code in this comment is equivalent to the more complex but
 // faster code below. We keep this simple version of the Hough
 // transform implementation here just to document what it's doing
 // more clearly.
 const point cent = center(box);
 const long x = c - cent.x();
 const long y = r - cent.y();
 for (long t = 0; t < size(); ++t)
 {
 double theta = t*pi/even_size;
 double radius = (x*std::cos(theta) + y*std::sin(theta))/sqrt_2 + even_size/2 + 0.5;
 long rr = static_cast<long>(radius);
 record_hit(point(t,rr), point(c,r), val);
 }
 continue;
 */
 // Run the speed optimized version of the code in the above
 // comment.
 const int32* ysin = ysin_base;
 const int32* xcos = &xcos_theta(c-box.left(),0);
 long t = 0;
 while(t < max_n8)
 {
 long rr0 = (*xcos++ + *ysin++)>>16;
 long rr1 = (*xcos++ + *ysin++)>>16;
 long rr2 = (*xcos++ + *ysin++)>>16;
 long rr3 = (*xcos++ + *ysin++)>>16;
 long rr4 = (*xcos++ + *ysin++)>>16;
 long rr5 = (*xcos++ + *ysin++)>>16;
 long rr6 = (*xcos++ + *ysin++)>>16;
 long rr7 = (*xcos++ + *ysin++)>>16;
 record_hit(point(t++,rr0), point(c,r), val);
 record_hit(point(t++,rr1), point(c,r), val);
 record_hit(point(t++,rr2), point(c,r), val);
 record_hit(point(t++,rr3), point(c,r), val);
 record_hit(point(t++,rr4), point(c,r), val);
 record_hit(point(t++,rr5), point(c,r), val);
 record_hit(point(t++,rr6), point(c,r), val);
 record_hit(point(t++,rr7), point(c,r), val);
 }
 while(t < max_n4)
 {
 long rr0 = (*xcos++ + *ysin++)>>16;
 long rr1 = (*xcos++ + *ysin++)>>16;
 long rr2 = (*xcos++ + *ysin++)>>16;
 long rr3 = (*xcos++ + *ysin++)>>16;
 record_hit(point(t++,rr0), point(c,r), val);
 record_hit(point(t++,rr1), point(c,r), val);
 record_hit(point(t++,rr2), point(c,r), val);
 record_hit(point(t++,rr3), point(c,r), val);
 }
 while(t < (long)size())
 {
 long rr0 = (*xcos++ + *ysin++)>>16;
 record_hit(point(t++,rr0), point(c,r), val);
 }
 }
 }
 }
 }
 template <
 typename in_image_type,
 typename record_hit_function_type
 >
 void perform_generic_hough_transform (
 const in_image_type& img_,
 record_hit_function_type record_hit
 ) const
 {
 rectangle box(0,0, num_columns(img_)-1, num_rows(img_)-1);
 perform_generic_hough_transform(img_, box, record_hit);
 }
 
 private:
 unsigned long _size;
 unsigned long even_size; // equal to _size if _size is even, otherwise equal to _size-1.
 matrix<int32> xcos_theta, ysin_theta;
 };
}
#endif // DLIB_HOUGH_tRANSFORM_Hh_