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+/*
+ #
+ #  File        : pde_TschumperleDeriche2d.cpp
+ #                ( C++ source file )
+ #
+ #  Description : Implementation of the Tschumperle-Deriche's Regularization
+ #                PDE, for 2D multivalued images, as described in the articles below.
+ #                This file is a part of the CImg Library project.
+ #                ( http://cimg.eu )
+ #
+ #  (1) PDE-Based Regularization of Multivalued Images and Applications.
+ #               (D. Tschumperle). PhD Thesis. University of Nice-Sophia Antipolis, December 2002.
+ #  (2) Diffusion PDE's on Vector-valued Images : Local Approach and Geometric Viewpoint.
+ #               (D. Tschumperle and R. Deriche). IEEE Signal Processing Magazine, October 2002.
+ #  (3) Vector-Valued Image Regularization with PDE's : A Common Framework for Different Applications.
+ #               (D. Tschumperle and R. Deriche). CVPR'2003, Computer Vision and Pattern Recognition,
+ #                                                Madison, United States, June 2003.
+ #
+ #  This code can be used to perform image restoration, inpainting, magnification or flow visualization.
+ #
+ #  Copyright   : David Tschumperle
+ #                ( http://tschumperle.users.greyc.fr/ )
+ #
+ #  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
+#undef min
+#undef max
+
+// Main procedure
+//----------------
+int main(int argc,char **argv) {
+
+  // Read command line arguments
+  //-----------------------------
+  cimg_usage("Tschumperle-Deriche's flow for 2D Image Restoration, Inpainting, Magnification or Flow visualization");
+  const char *file_i  = cimg_option("-i",cimg_imagepath "milla.bmp","Input image");
+  const char *file_m  = cimg_option("-m",(char*)NULL,"Mask image (if Inpainting)");
+  const char *file_f  = cimg_option("-f",(char*)NULL,"Flow image (if Flow visualization)");
+  const char *file_o  = cimg_option("-o",(char*)NULL,"Output file");
+  const double zoom   = cimg_option("-zoom",1.0,"Image magnification");
+
+  const unsigned int nb_iter  = cimg_option("-iter",100000,"Number of iterations");
+  const double dt     = cimg_option("-dt",20.0,"Adapting time step");
+  const double alpha  = cimg_option("-alpha",0.0,"Gradient smoothing");
+  const double sigma  = cimg_option("-sigma",0.5,"Structure tensor smoothing");
+  const float a1      = cimg_option("-a1",0.5f,"Diffusion limiter along minimal variations");
+  const float a2      = cimg_option("-a2",0.9f,"Diffusion limiter along maximal variations");
+  const double noiseg = cimg_option("-ng",0.0,"Add gauss noise before aplying the algorithm");
+  const double noiseu = cimg_option("-nu",0.0,"Add uniform noise before applying the algorithm");
+  const double noises = cimg_option("-ns",0.0,"Add salt&pepper noise before applying the algorithm");
+  const bool stflag   = cimg_option("-stats",false,"Display image statistics at each iteration");
+  const unsigned int save = cimg_option("-save",0,"Iteration saving step");
+  const unsigned int visu = cimg_option("-visu",10,"Visualization step (0=no visualization)");
+  const unsigned int init = cimg_option("-init",3,"Inpainting initialization (0=black, 1=white, 2=noise, 3=unchanged)");
+  const unsigned int skip = cimg_option("-skip",1,"Step of image geometry computation");
+  bool view_t         = cimg_option("-d",false,"View tensor directions (useful for debug)");
+  double xdt = 0;
+
+  // Variable initialization
+  //-------------------------
+  CImg<> img, flow;
+  CImg<int> mask;
+
+  if (file_i) {
+    img = CImg<>(file_i).resize(-100,-100,1,-100);
+    if (file_m) mask = CImg<unsigned char>(file_m).resize(img.width(),img.height(),1,1);
+    else if (zoom>1) {
+      mask = CImg<int>(img.width(),img.height(),1,1,-1).
+        resize((int)(img.width()*zoom),(int)(img.height()*zoom),1,1,4) + 1;
+      img.resize((int)(img.width()*zoom),(int)(img.height()*zoom),1,-100,3);
+    }
+  } else {
+    if (file_f) {
+      flow = CImg<>(file_f);
+      img = CImg<>((int)(flow.width()*zoom),(int)(flow.height()*zoom),1,1,0).noise(100,2);
+      flow.resize(img.width(),img.height(),1,2,3);
+    } else
+      throw CImgException("You need to specify at least one input image (option -i), or one flow image (option -f)");
+  }
+  img.noise(noiseg,0).noise(noiseu,1).noise(noises,2);
+  float initial_min, initial_max = img.max_min(initial_min);
+  if (mask && init!=3)
+    cimg_forXYC(img,x,y,k) if (mask(x,y))
+      img(x,y,k) = (float)((init?
+                            (init==1?initial_max:((initial_max - initial_min)*cimg::rand())):
+                            initial_min));
+
+  CImgDisplay disp;
+  if (visu) disp.assign(img,"Iterated Image");
+  CImg<> G(img.width(),img.height(),1,3,0), T(G), veloc(img), val(2), vec(2,2);
+
+  // PDE main iteration loop
+  //-------------------------
+  for (unsigned int iter = 0; iter<nb_iter &&
+         (!disp || (!disp.is_closed() && !disp.is_keyQ() && !disp.is_keyESC())); ++iter) {
+    std::printf("\riter %u , xdt = %g               ",iter,xdt); std::fflush(stdout);
+    if (stflag) img.print();
+    if (disp && disp.is_keySPACE()) { view_t = !view_t; disp.set_key(); }
+
+    if (!(iter%skip)) {
+
+      // Compute the tensor field T, used to drive the diffusion
+      //---------------------------------------------------------
+
+      // When using PDE for flow visualization
+      if (flow) cimg_forXY(flow,x,y) {
+        const float
+          u = flow(x,y,0,0),
+          v = flow(x,y,0,1),
+          n = (float)std::sqrt((double)(u*u + v*v)),
+          nn = (n!=0)?n:1;
+        T(x,y,0) = u*u/nn;
+        T(x,y,1) = u*v/nn;
+        T(x,y,2) = v*v/nn;
+      } else {
+
+        // Compute structure tensor field G
+        CImgList<> grad = img.get_gradient();
+        if (alpha!=0) cimglist_for(grad,l) grad[l].blur((float)alpha);
+        G.fill(0);
+        cimg_forXYC(img,x,y,k) {
+          const float ix = grad[0](x,y,k), iy = grad[1](x,y,k);
+          G(x,y,0) += ix*ix;
+          G(x,y,1) += ix*iy;
+          G(x,y,2) += iy*iy;
+        }
+        if (sigma!=0) G.blur((float)sigma);
+
+        // When using PDE for image restoration, inpainting or zooming
+        T.fill(0);
+        if (!mask) cimg_forXY(G,x,y) {
+          G.get_tensor_at(x,y).symmetric_eigen(val,vec);
+          const float
+            l1 = (float)std::pow(1.0f + val[0] + val[1],-a1),
+            l2 = (float)std::pow(1.0f + val[0] + val[1],-a2),
+            ux = vec(1,0),
+            uy = vec(1,1);
+          T(x,y,0) = l1*ux*ux + l2*uy*uy;
+          T(x,y,1) = l1*ux*uy - l2*ux*uy;
+          T(x,y,2) = l1*uy*uy + l2*ux*ux;
+        }
+        else cimg_forXY(G,x,y) if (mask(x,y)) {
+          G.get_tensor_at(x,y).symmetric_eigen(val,vec);
+          const float
+            ux = vec(1,0),
+            uy = vec(1,1);
+          T(x,y,0) = ux*ux;
+          T(x,y,1) = ux*uy;
+          T(x,y,2) = uy*uy;
+        }
+      }
+    }
+
+    // Compute the PDE velocity and update the iterated image
+    //--------------------------------------------------------
+    CImg_3x3(I,float);
+    veloc.fill(0);
+    cimg_forC(img,k) cimg_for3x3(img,x,y,0,k,I,float) {
+      const float
+        a = T(x,y,0),
+        b = T(x,y,1),
+        c = T(x,y,2),
+        ixx = Inc + Ipc - 2*Icc,
+        iyy = Icn + Icp - 2*Icc,
+        ixy = 0.25f*(Ipp + Inn - Ipn - Inp);
+      veloc(x,y,k) = a*ixx + 2*b*ixy + c*iyy;
+    }
+    if (dt>0) {
+      float m, M = veloc.max_min(m);
+      xdt = dt/std::max(cimg::abs(m),cimg::abs(M));
+    } else xdt=-dt;
+    img+=veloc*xdt;
+    img.cut((float)initial_min,(float)initial_max);
+
+    // Display and save iterations
+    if (disp && !(iter%visu)) {
+      if (!view_t) img.display(disp);
+      else {
+        const unsigned char white[3] = {255,255,255};
+        CImg<unsigned char> visu = img.get_resize(disp.width(),disp.height()).normalize(0,255);
+        CImg<> isophotes(img.width(),img.height(),1,2,0);
+        cimg_forXY(img,x,y) if (!mask || mask(x,y)) {
+          T.get_tensor_at(x,y).symmetric_eigen(val,vec);
+          isophotes(x,y,0) = vec(0,0);
+          isophotes(x,y,1) = vec(0,1);
+        }
+        visu.draw_quiver(isophotes,white,0.5f,10,9,0).display(disp);
+      }
+    }
+    if (save && file_o && !(iter%save)) img.save(file_o,iter);
+    if (disp) disp.resize().display(img);
+  }
+
+  // Save result and exit.
+  if (file_o) img.save(file_o);
+  return 0;
+}