Remove many seams at once (but don't use overlapping seams)

src/seam-carving.cpp

@@ -15,6 +15,9 @@
 bool silent;
 bool test_energy;
 
+int min(int a, int b) {
+  return a < b ? a : b;
+}
 
 /** e_1 energy */
 std::vector<unsigned char> energy_e1(unsigned char* source, int width, int height, int nbChannels) {
@@ -22,8 +25,8 @@ std::vector<unsigned char> energy_e1(unsigned char* source, int width, int heigh
 
   for (auto i=0; i < width*height; i++) { energy[i] = 0; }
 
-  for(auto i = 0 ; i < width ; ++i) {
+  for(auto i=0 ; i < width ; ++i) {
-    for(auto j = 0; j < height; ++j) {
+    for(auto j=0; j < height; ++j) {
       auto indexPixel = nbChannels*(width*j+i);
       auto indexPixel_up    = (j-1 > 0)      ? nbChannels*(width*(j-1)+i) : indexPixel;
       auto indexPixel_down  = (j+1 < height) ? nbChannels*(width*(j+1)+i) : indexPixel;
@@ -44,6 +47,69 @@ std::vector<unsigned char> energy_e1(unsigned char* source, int width, int heigh
   return energy;
 }
 
+std::vector<int> optimal_vertical_seams(std::vector<unsigned char> energy, int width, int height, int nbSeams) {
+  std::vector<unsigned char> dyn_energy(width*height);
+
+  //* Find an end of the minimal connected vertical/horizontal seam
+  for (auto i=1; i < height; i++) {
+    dyn_energy[width*i] = energy[width*i];
+  }
+
+  for (auto j=1; j < width; j++) {
+    for (auto i=0; i < height; i++) {
+      int bot_center = (i > 0) ? dyn_energy[width*(i-1)+j] : INT_MAX;
+      int bot_left = (i > 0 && j > 0) ? dyn_energy[width*(i-1)+(j-1)] : INT_MAX;
+      int bot_right = (i > 0 && j+1 < width) ? dyn_energy[width*(i-1)+(j+1)] : INT_MAX;
+
+
+      dyn_energy[width*i+j] = min(
+        bot_center,
+        min(
+          bot_left,
+          bot_right
+        )
+      ) + energy[width*i+j];
+    }
+  }
+
+  std::vector<int> result(height*nbSeams);
+
+  // To find the nbSeams largest points, we sort the pairs (dyn_energy[idx, height-1], idx)
+  std::vector<std::pair<int, int>> seamEnds(width);
+  for (auto j=0; j < width; j++) {
+    seamEnds[j] = {dyn_energy[(height-1)*width+j], j};
+  }
+  std::sort(seamEnds.begin(), seamEnds.end());
+  for (auto seam=0; seam < nbSeams; seam++) {
+    result[height*(seam+1)-1] = seamEnds[seam].second;
+  }
+
+  //* Backtracking to find the path
+  for (auto seam=0; seam < nbSeams; seam++) {
+    int min_idx = result[height*(seam+1)-1];
+    int min_val = dyn_energy[(height-1)*width+min_idx];
+
+    for (auto i=height-1; i > 0; i--) {
+      // We want to find either (bot_l, bot_c, bot_r) with dyn_energy[.] = min_val - energy[cur]
+      int objective_energy = min_val - energy[i*width+min_idx];
+      
+      if (dyn_energy[(i-1)+height*min_idx] == objective_energy) {
+        // min_idx does not change
+        min_val = dyn_energy[(i-1)+height*min_idx];
+      } else if (min_idx > 0 && dyn_energy[(i-1)+height*(min_idx-1)] == objective_energy) {
+        min_val = dyn_energy[(i-1)+height*(min_idx - 1)];
+      min_idx = min_idx - 1;
+    } else if (min_idx+1 < width && dyn_energy[(i-1)+height*(min_idx+1)] == objective_energy) {
+      min_val = dyn_energy[(i-1)+height*(min_idx + 1)];
+      min_idx = min_idx + 1;
+    }
+    result[height*seam+i-1] = min_idx;
+    }
+  }
+
+  return result;
+}
+
 
 int main(int argc, char **argv) {
   CLI::App app{"seam-carving"};
@@ -51,6 +117,8 @@ int main(int argc, char **argv) {
   app.add_option("-s,--source", sourceImage, "Source image")->required()->check(CLI::ExistingFile);;
   std::string outputImage= "output.png";
   app.add_option("-o,--output", outputImage, "Output image")->required();
+  int nbSeams = 1;
+  app.add_option("-n,--nb-seams", nbSeams, "Number of seams");
   silent = false;
   app.add_flag("--silent", silent, "No verbose messages");
   test_energy = false;
@@ -66,20 +134,69 @@ int main(int argc, char **argv) {
     exit(1);
   }
 
+  nbSeams = min(nbSeams, width);
   int outChannels = nbChannels;
+  int outHeight = height;
+  int outWidth = width;
   std::vector<unsigned char> output;
 
   if (test_energy) {
-    outChannels = 1;
+    //outChannels = 1;
-    output = energy_e1(source, width, height, nbChannels);
+    std::vector<unsigned char> energy = energy_e1(source, width, height, nbChannels);
+    std::vector<int> opt_seam = optimal_vertical_seams(energy, width, height, nbSeams);
+
+    std::vector<unsigned char> output2(width*height*3);
+    for (auto i=0; i < width*height; i++) {
+      output2[3*i] = energy[i];
+      output2[3*i+1] = energy[i];
+      output2[3*i+2] = energy[i];
+    }
+    for (auto seam=0; seam < nbSeams; seam++) {
+      for (auto i=0; i < height; i++) {
+        output2[3*(i*width+opt_seam[seam*height+i])] = 255;
+        output2[3*(i*width+opt_seam[seam*height+i])+1] = 0;
+        output2[3*(i*width+opt_seam[seam*height+i])+2] = 0;
+      }
+    }
+    output=output2;
   } else {
-    std::cout <<"Not implemented" << std::endl;
+    std::vector<unsigned char> energy = energy_e1(source, width, height, nbChannels);
-    exit(1);
+    std::vector<int> opt_seam = optimal_vertical_seams(energy, width, height, nbSeams);
+
+    std::vector<bool> blacklist(width*height);
+
+    for (auto k=0; k < width*height; k++) { blacklist[k] = false; }
+    for (auto seam=0; seam < nbSeams; seam++) {
+      bool overlap = false; // Check if 2 seams use similar pixels
+      for (auto i=0; i < height; i++) {
+        overlap = overlap || blacklist[i*width+opt_seam[seam*height+i]];
+      }
+      if (overlap) { nbSeams--; continue;}
+      for (auto i=0; i < height; i++) {
+        blacklist[i*width+opt_seam[seam*height+i]] = true;
+      }
+    }
+
+    outWidth = width-nbSeams; //! something is weird here
+
+    std::vector<unsigned char> output_l(outWidth*height*3);
+    for (auto i=0; i < height; i++) {
+      int cur_j = 0;
+      for (auto j=0; cur_j < outWidth && j < width; j++) {
+        if (!blacklist[i*width+j]) {
+          output_l[3*(i*outWidth+cur_j)] =   source[3*(i*width+j)];
+          output_l[3*(i*outWidth+cur_j)+1] = source[3*(i*width+j)+1];
+          output_l[3*(i*outWidth+cur_j)+2] = source[3*(i*width+j)+2];
+          cur_j++;
+        }
+      }
+    }
+    output = output_l;
   }
 
   //Final export
   if (!silent) std::cout<<"Exporting.."<<std::endl;
-  int errcode = stbi_write_png(outputImage.c_str(), width, height, outChannels, output.data(), outChannels*width);
+  int errcode = stbi_write_png(outputImage.c_str(), outWidth, outHeight, outChannels, output.data(), outChannels*outWidth);
   if (!errcode) {
     std::cout<<"Error while exporting the resulting image."<<std::endl;
     exit(errcode);