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/*
#
# File : edge_explorer2d.cpp
# ( C++ source file )
#
# Description : Real time edge detection while moving a ROI
# (rectangle of interest) over the original image.
# This file is a part of the CImg Library project.
# ( http://cimg.eu )
#
# Copyright : Orges Leka
# ( oleka(at)students.uni-mainz.de )
#
# License : CeCILL v2.0
# ( http://www.cecill.info/licences/Licence_CeCILL_V2-en.html )
#
# This software is governed by the CeCILL license under French law and
# abiding by the rules of distribution of free software. You can use,
# modify and/ or redistribute the software under the terms of the CeCILL
# license as circulated by CEA, CNRS and INRIA at the following URL
# "http://www.cecill.info".
#
# As a counterpart to the access to the source code and rights to copy,
# modify and redistribute granted by the license, users are provided only
# with a limited warranty and the software's author, the holder of the
# economic rights, and the successive licensors have only limited
# liability.
#
# In this respect, the user's attention is drawn to the risks associated
# with loading, using, modifying and/or developing or reproducing the
# software by the user in light of its specific status of free software,
# that may mean that it is complicated to manipulate, and that also
# therefore means that it is reserved for developers and experienced
# professionals having in-depth computer knowledge. Users are therefore
# encouraged to load and test the software's suitability as regards their
# requirements in conditions enabling the security of their systems and/or
# data to be ensured and, more generally, to use and operate it in the
# same conditions as regards security.
#
# The fact that you are presently reading this means that you have had
# knowledge of the CeCILL license and that you accept its terms.
#
*/
#include "CImg.h"
using namespace cimg_library;
#ifndef cimg_imagepath
#define cimg_imagepath "img/"
#endif
// Main procedure
//----------------
int main(int argc, char** argv) {
// Usage of the program displayed at the command line
cimg_usage("Real time edge detection with CImg. (c) Orges Leka");
// Read command line arguments
// With cimg_option we can get a new name for the image which is to be loaded from the command line.
const char* img_name = cimg_option("-i", cimg_imagepath "parrot.ppm","Input image.");
double
alpha = cimg_option("-a",1.0,"Blurring the gradient image."),
thresL = cimg_option("-tl",13.5,"Lower thresholding used in Hysteresis."),
thresH = cimg_option("-th",13.6,"Higher thresholding used in Hysteresis.");
const unsigned int
mode = cimg_option("-m",1,"Detection mode: 1 = Hysteresis, 2 = Gradient angle."),
factor = cimg_option("-s",80,"Half-size of edge-explorer window.");
cimg_help("\nAdditional notes : user can press following keys on main display window :\n"
" - Left arrow : Decrease alpha.\n"
" - Right arrow : Increase alpha.\n");
// Construct a new image called 'edge' of size (2*factor,2*factor)
// and of type 'unsigned char'.
CImg<unsigned char> edge(2*factor,2*factor);
CImgDisplay disp_edge(512,512,"Edge Explorer");
// Load the image with the name 'img_name' into the CImg 'img'.
// and create a display window 'disp' for the image 'img'.
const CImg<unsigned char> img = CImg<float>::get_load(img_name).norm().normalize(0,255);
CImgDisplay disp(img,"Original Image");
// Begin main interaction loop.
int x = 0, y = 0;
bool redraw = false;
while (!disp.is_closed() && !disp.is_keyQ() && !disp.is_keyESC()) {
disp.wait(100);
if (disp.button()&1) { alpha+=0.05; redraw = true; }
if (disp.button()&2) { alpha-=0.05; redraw = true; }
if (disp.wheel()) { alpha+=0.05*disp.wheel(); disp.set_wheel(); redraw = true; }
if (alpha<0) alpha = 0;
if (disp_edge.is_resized()) { disp_edge.resize(); redraw = true; }
if (disp_edge.is_closed()) disp_edge.show();
if (disp.is_resized()) disp.resize(disp);
if (disp.mouse_x()>=0) {
x = disp.mouse_x(); // Getting the current position of the mouse
y = disp.mouse_y(); //
redraw = true; // The image should be redrawn
}
if (redraw) {
disp_edge.set_title("Edge explorer (alpha=%g)",alpha);
const int
x0 = x - factor, y0 = y - factor, // These are the coordinates for the red rectangle
x1 = x + factor, y1 = y + factor; // to be drawn on the original image
const unsigned char
red[3] = { 255,0,0 }, //
black[3] = { 0,0,0 }; // Defining the colors we need for drawing
(+img).draw_rectangle(x0,y0,x1,y1,red,1.0f,0x55555555U).display(disp);
//^ We draw the red rectangle on the original window using 'draw_line'.
// Then we display the result via '.display(disp)' .
// Observe, that the color 'red' has to be of type 'const unsigned char',
// since the image 'img' is of type 'const CImg<unsigned char>'.
//'normalize' is used to get a greyscaled image.
CImg<> visu_bw = CImg<>(img).get_crop(x0,y0,x1,y1).get_norm().normalize(0,255).resize(-100,-100,1,2,2);
// get_crop(x0,y0,x1,y1) gets the rectangle we are interested in.
edge.fill(255); // Background color in the edge-detection window is white
// grad[0] is the gradient image of 'visu_bw' in x-direction.
// grad[1] is the gradient image of 'visu_bw' in y-direction.
CImgList<> grad(visu_bw.blur((float)alpha).normalize(0,255).get_gradient());
// To avoid unnecessary calculations in the image loops:
const double
pi = cimg::PI,
p8 = pi/8.0, p38 = 3.0*p8,
p58 = 5.0*p8, p78 = 7.0*p8;
cimg_forXY(visu_bw,s,t) {
// We take s,t instead of x,y, since x,y are already used.
// s corresponds to the x-ordinate of the pixel while t corresponds to the y-ordinate.
if ( 1 <= s && s <= visu_bw.width() - 1 && 1 <= t && t <=visu_bw.height() - 1) { // if - good points
double
Gs = grad[0](s,t), //
Gt = grad[1](s,t), // The actual pixel is (s,t)
Gst = cimg::abs(Gs) + cimg::abs(Gt), //
// ^-- For efficient computation we observe that |Gs|+ |Gt| ~=~ sqrt( Gs^2 + Gt^2)
Gr, Gur, Gu, Gul, Gl, Gdl, Gd, Gdr;
// ^-- right, up right, up, up left, left, down left, down, down right.
double theta = std::atan2(std::max(1e-8,Gt),Gs) + pi; // theta is from the interval [0,Pi]
switch(mode) {
case 1: // Hysterese is applied
if (Gst>=thresH) { edge.draw_point(s,t,black); }
else if (thresL <= Gst && Gst < thresH) {
// Neighbourhood of the actual pixel:
Gr = cimg::abs(grad[0](s + 1,t)) + cimg::abs(grad[1](s + 1,t)); // right
Gl = cimg::abs(grad[0](s - 1,t)) + cimg::abs(grad[1](s - 1,t)); // left
Gur = cimg::abs(grad[0](s + 1,t + 1)) + cimg::abs(grad[1](s + 1,t + 1)); // up right
Gdl = cimg::abs(grad[0](s - 1,t - 1)) + cimg::abs(grad[1](s - 1,t - 1)); // down left
Gu = cimg::abs(grad[0](s,t + 1)) + cimg::abs(grad[1](s,t + 1)); // up
Gd = cimg::abs(grad[0](s,t - 1)) + cimg::abs(grad[1](s,t - 1)); // down
Gul = cimg::abs(grad[0](s - 1,t + 1)) + cimg::abs(grad[1](s - 1,t + 1)); // up left
Gdr = cimg::abs(grad[0](s + 1,t - 1)) + cimg::abs(grad[1](s + 1,t - 1)); // down right
if (Gr>=thresH || Gur>=thresH || Gu>=thresH || Gul>=thresH
|| Gl>=thresH || Gdl >=thresH || Gu >=thresH || Gdr >=thresH) {
edge.draw_point(s,t,black);
}
};
break;
case 2: // Angle 'theta' of the gradient (Gs,Gt) at the point (s,t)
if(theta >= pi)theta-=pi;
//rounding theta:
if ((p8 < theta && theta <= p38 ) || (p78 < theta && theta <= pi)) {
// See (*) below for explanation of the vocabulary used.
// Direction-pixel is (s + 1,t) with corresponding gradient value Gr.
Gr = cimg::abs(grad[0](s + 1,t)) + cimg::abs(grad[1](s + 1,t)); // right
// Contra-direction-pixel is (s - 1,t) with corresponding gradient value Gl.
Gl = cimg::abs(grad[0](s - 1,t)) + cimg::abs(grad[1](s - 1,t)); // left
if (Gr < Gst && Gl < Gst) {
edge.draw_point(s,t,black);
}
}
else if ( p8 < theta && theta <= p38) {
// Direction-pixel is (s + 1,t + 1) with corresponding gradient value Gur.
Gur = cimg::abs(grad[0](s + 1,t + 1)) + cimg::abs(grad[1](s + 1,t + 1)); // up right
// Contra-direction-pixel is (s-1,t-1) with corresponding gradient value Gdl.
Gdl = cimg::abs(grad[0](s - 1,t - 1)) + cimg::abs(grad[1](s - 1,t - 1)); // down left
if (Gur < Gst && Gdl < Gst) {
edge.draw_point(s,t,black);
}
}
else if ( p38 < theta && theta <= p58) {
// Direction-pixel is (s,t + 1) with corresponding gradient value Gu.
Gu = cimg::abs(grad[0](s,t + 1)) + cimg::abs(grad[1](s,t + 1)); // up
// Contra-direction-pixel is (s,t - 1) with corresponding gradient value Gd.
Gd = cimg::abs(grad[0](s,t - 1)) + cimg::abs(grad[1](s,t - 1)); // down
if (Gu < Gst && Gd < Gst) {
edge.draw_point(s,t,black);
}
}
else if (p58 < theta && theta <= p78) {
// Direction-pixel is (s - 1,t + 1) with corresponding gradient value Gul.
Gul = cimg::abs(grad[0](s - 1,t + 1)) + cimg::abs(grad[1](s - 1,t + 1)); // up left
// Contra-direction-pixel is (s + 1,t - 1) with corresponding gradient value Gdr.
Gdr = cimg::abs(grad[0](s + 1,t - 1)) + cimg::abs(grad[1](s + 1,t - 1)); // down right
if (Gul < Gst && Gdr < Gst) {
edge.draw_point(s,t,black);
}
};
break;
} // switch
} // if good-points
} // cimg_forXY */
edge.display(disp_edge);
}// if redraw
} // while
return 0;
}
// (*) Comments to the vocabulary used:
// If (s,t) is the current pixel, and G=(Gs,Gt) is the gradient at (s,t),
// then the _direction_pixel_ of (s,t) shall be the one of the eight neighbour pixels
// of (s,t) in whose direction the gradient G shows.
// The _contra_direction_pixel is the pixel in the opposite direction in which the gradient G shows.
// The _corresponding_gradient_value_ of the pixel (x,y) with gradient G = (Gx,Gy)
// shall be |Gx| + |Gy| ~=~ sqrt(Gx^2 + Gy^2).
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