diff --git a/src/Output.cc b/src/Output.cc
index 81da024..e89ab7c 100644
--- a/src/Output.cc
+++ b/src/Output.cc
@@ -10,13 +10,13 @@ void Output::write() {
     for (unsigned int x = 0; x < width; ++x)
       fout << (char)(255.0f * red[y * width + x])
            << (char)(255.0f * green[y * width + x])
-           << (char)(255.0f * blue[y * width + x]);
+           << (char)(255.0f * blue[y * height + x]);
   fout.close();
 }
 
-float Output::r(int index) { return red.at(index); }
-float Output::g(int index) { return green.at(index); }
-float Output::b(int index) { return blue.at(index); }
+float Output::r(int index) const { return red.at(index); }
+float Output::g(int index) const { return green.at(index); }
+float Output::b(int index) const { return blue.at(index); }
 void Output::r(int index, float value) { red.at(index) = value; }
 void Output::g(int index, float value) { green.at(index) = value; }
 void Output::b(int index, float value) { blue.at(index) = value; }
diff --git a/src/Output.h b/src/Output.h
index d7b9af9..68f9350 100644
--- a/src/Output.h
+++ b/src/Output.h
@@ -27,11 +27,11 @@ private:
 
 public:
   void r(int, float);
-  float r(int);
+  float r(int) const;
   void g(int, float);
-  float g(int);
+  float g(int) const;
   void b(int, float);
-  float b(int);
+  float b(int) const;
 };
 
 #endif // !OUTPUT_H_