diff --git a/src/seam-carving.cpp b/src/seam-carving.cpp
index c76485b..d233292 100644
--- a/src/seam-carving.cpp
+++ b/src/seam-carving.cpp
@@ -39,6 +39,7 @@ void export_image(const char* filename, const void* data, int width, int height,
 
 /** e_1 energy, energy is always normalized between 0 and 1 */
 std::vector<float> energy_e1(std::vector<unsigned char> source, int width, int height, int nbChannels) {
+  int nbColorChannels = nbChannels > 3 ? 3 : nbChannels; // nombre de canaux, excepté le alpha
   std::vector<float> energy(width*height);
 
   float max_energy = 0;
@@ -51,7 +52,7 @@ std::vector<float> energy_e1(std::vector<unsigned char> source, int width, int h
       auto indexPixel_right = (i+1 < width)  ? nbChannels*(width*j+(i+1)) : indexPixel;
     
       energy[width*j+i] = 0;
-      for (auto ch=0; ch < nbChannels; ch++) {
+      for (auto ch=0; ch < nbColorChannels; ch++) { // Le alpha n'est pas pris en compte dans l'énergie
         energy[width*j+i] += (
             fabs((float)source[indexPixel_up+ch] - source[indexPixel+ch])
             +fabs((float)source[indexPixel_down+ch] - source[indexPixel+ch])
@@ -160,12 +161,11 @@ std::vector<int> carving_step(const std::vector<unsigned char> source, std::vect
     int cur_j = 0;
     for (auto j=0; cur_j < dim_large-1 && j < dim_large; j++) {
       if (!blacklist[im_index(i, j)]) {
-        int out_pixelIndex = 3*(vertical ? ((width-1)*i + cur_j) : (width*cur_j + i));
-        int src_pixelIndex = 3*im_index(i, j);
+        int out_pixelIndex = nbChannels*(vertical ? ((width-1)*i + cur_j) : (width*cur_j + i));
+        int src_pixelIndex = nbChannels*im_index(i, j);
 
-        output[ out_pixelIndex ] = source[ src_pixelIndex ];
-        output[out_pixelIndex+1] = source[src_pixelIndex+1];
-        output[out_pixelIndex+2] = source[src_pixelIndex+2];
+        for (auto ch=0; ch < nbChannels; ch++)
+          output[out_pixelIndex+ch] = source[src_pixelIndex+ch];
         cur_j++;
       }
     }
@@ -175,17 +175,18 @@ std::vector<int> carving_step(const std::vector<unsigned char> source, std::vect
 
 
 void seam_carving(unsigned char* source, int width, int height, int nbChannels, const char* out_filename, int nbSeams, bool vertical, bool test_energy=false) {
+  int nbColorChannels = nbChannels > 3 ? 3 : nbChannels;
   int curWidth = width;
   int curHeight = height;
 
   int dim_large = vertical ? width : height;
   int dim_long  = vertical ? height : width;
 
-  std::vector<unsigned char> carve_output(width*height*3); // Receives at each step the newly carved image
+  std::vector<unsigned char> carve_output(width*height*nbChannels); // Receives at each step the newly carved image
   std::vector<unsigned char> source_img(width*height*nbChannels); // Contains at each step the carved image
   std::vector<bool> complete_blacklist(width*height); // Contains all removed pixels, for "test_energy"
   std::vector<float> ini_energy; // Contains the initial energy, only for "test_energy"
-  std::vector<unsigned char> test_energy_output(width*height*3); // Final output for "test_energy"
+  std::vector<unsigned char> test_energy_output(width*height*nbChannels); // Final output for "test_energy"
 
 
   for (auto i=0; i < width*height*nbChannels; i++) { source_img[i] = source[i]; }
@@ -196,12 +197,13 @@ void seam_carving(unsigned char* source, int width, int height, int nbChannels,
 
     //* Prepare final output
     for (auto k=0; k < width*height; k++) {
-      //output[3*k] = source_img[3*k]/3; //* Uncomment if you prefer to see darkened source image
-      //output[3*k+1] = source_img[3*k+1]/3;
-      //output[3*k+2] = source_img[3*k+2]/3;
-      test_energy_output[3*k] = ini_energy[k]*255;
-      test_energy_output[3*k+1] = ini_energy[k]*255;
-      test_energy_output[3*k+2] = ini_energy[k]*255;
+      //for (auto i=0; i < nbColorChannels; i++) //* Uncomment if you prefer to see darkened source image
+      //  output[nbChannels*k+i] = source_img[nbChannels*k+i]/nbChannels;
+      for (auto i=0; i < nbColorChannels; i++)
+        test_energy_output[nbChannels*k+i] = ini_energy[k]*255;
+
+      if (nbChannels==4)
+        test_energy_output[nbChannels*k+3] = source_img[nbChannels*k+3];
     }
   }
 
@@ -224,7 +226,7 @@ void seam_carving(unsigned char* source, int width, int height, int nbChannels,
         assert(cur_j == opt_seam[i]); // Else, j == width and cur_j is not in the source image..
   
         complete_blacklist[im_index(i, j)] = true;
-        test_energy_output[3*im_index(i, j)] = 255; // Set carved pixel to red
+        test_energy_output[nbChannels*im_index(i, j)] = 255; // Set carved pixel to red
       }
     }
     bar.increment();
@@ -261,10 +263,7 @@ int main(int argc, char **argv) {
   unsigned char *source = stbi_load(sourceImage.c_str(), &width, &height, &nbChannels, 0);
   nbSeams = min(nbSeams, width);
 
-  if (nbChannels < 3) { // TODO : really ?
-    std::cout<< "Input images must be RGB images."<<std::endl;
-    exit(1);
-  }
+  //std::cout << "channels: " << nbChannels << std::endl;
 
   seam_carving(source, width, height, nbChannels, outputImage.c_str(), nbSeams, vertical, test_energy=test_energy);