diff --git a/src/ray.ml b/src/ray.ml
new file mode 100644
index 00000000..8a392d1d
--- /dev/null
+++ b/src/ray.ml
@@ -0,0 +1,5 @@
+type ray = { origin: Vec3.vec3;
+             dir: Vec3.vec3 }
+
+let point_at_parameter r t =
+  Vec3.add r.origin (Vec3.mul t r.dir)
diff --git a/src/raytracer.ml b/src/raytracer.ml
index d30f8f0e..8990ad01 100644
--- a/src/raytracer.ml
+++ b/src/raytracer.ml
@@ -1,14 +1,10 @@
 open Core.Std
 open Printf
 open Vec3
-    
+open Ray
+
 type sphere = { center: Vec3.vec3;
                 radius: float }
-type ray = { origin: Vec3.vec3;
-             dir: Vec3.vec3 }
-
-let point_at_parameter r t =
-  add r.origin (mul t r.dir)
 
 let hit_sphere sphere ray =
   let oc = sub ray.origin sphere.center in
@@ -26,12 +22,46 @@ let get_color ray =
                 radius = 0.5 } in
   let t = (hit_sphere sphere ray) in
   if (t > 0.0)
-  then let n = unit_vector (sub (point_at_parameter ray t) sphere.center) in
+  then let n = unit_vector (sub (Ray.point_at_parameter ray t) sphere.center) in
     mul 0.5 (Vec3.of_floats (n.x +. 1., n.y +. 1., n.z +. 1.))
   else let unit_direction = unit_vector ray.dir in
     let t = 0.5 *. (unit_direction.y +. 1.0) in
     add (mul (1.0 -. t) {x= 1.0; y=1.0; z= 1.0}) (mul t {x= 0.5; y= 0.7; z= 1.0})
-          
+
+let write_to_file filename =
+  let nx = 200 in
+  let ny = 100 in
+  let oc = Out_channel.create filename in
+  fprintf oc "P3\n";
+  fprintf oc "%d\n" nx;
+  fprintf oc "%d\n"  ny;
+  fprintf oc "\n255\n";
+  let lower_left_corner = Vec3.of_floats (-2., -1., -1.) in
+  let horizontal = Vec3.of_floats (4., 0., 0.) in
+  let vertical = Vec3.of_floats (0., 2., 0.) in
+  let origin = Vec3.of_floats (0., 0., 0.) in
+  let color = ref {x=0.; y=0.; z=0.} in
+  for j = ny downto 1 do
+    for i = 0 to nx-1 do
+      let u = (Float.of_int i) /. (Float.of_int nx) in
+      let v = (Float.of_int j) /. (Float.of_int ny) in
+
+      let r = { origin = origin;
+                dir = Vec3.add lower_left_corner (Vec3.add (Vec3.mul u horizontal) (Vec3.mul v vertical)) } in
+      color := get_color r;
+
+      let {x=r; y=g; z=b} = !color in
+      let (ir, ig, ib) = (Int.of_float (r*.255.99),
+                          Int.of_float (g*.255.99),
+                          Int.of_float (b*.255.99)) in
+      fprintf oc "%d " ir;
+      fprintf oc "%d " ig;
+      fprintf oc "%d \n" ib;
+    done
+  done;
+  Out_channel.close oc;
+;;
+
 
 let main() =
   let nx = 200 in
@@ -67,4 +97,4 @@ let main() =
   done
 ;;
 
-main()
+(* main() *)