diff --git a/.gitignore b/.gitignore
index 4ee6b64..58aa30f 100644
--- a/.gitignore
+++ b/.gitignore
@@ -8,3 +8,5 @@
 /spec/reports/
 /tmp/
 /vendor
+.DS_Store
+/test/output/
diff --git a/lib/edge_detect.rb b/lib/edge_detect.rb
index 3604be2..7d07aea 100644
--- a/lib/edge_detect.rb
+++ b/lib/edge_detect.rb
@@ -8,3 +8,4 @@ require 'edge_detect/differ'
 require 'edge_detect/horizontal_differ'
 require 'edge_detect/vertical_differ'
 require 'edge_detect/edge_detector'
+require 'edge_detect/sobel_edge_detector'
diff --git a/lib/edge_detect/edge_detector.rb b/lib/edge_detect/edge_detector.rb
index 5f58b71..7af04dd 100644
--- a/lib/edge_detect/edge_detector.rb
+++ b/lib/edge_detect/edge_detector.rb
@@ -11,16 +11,19 @@ module EdgeDetect
     end
 
     def detect_edges
-      h_differ = HorizontalDiffer.new(self.image)
-      v_differ = VerticalDiffer.new(self.image)
+      image = ChunkyPNG::Image.new(@image.width, @image.height, ChunkyPNG::Color::TRANSPARENT)
+      h_diff = HorizontalDiffer.new(self.image)
+      v_diff = VerticalDiffer.new(self.image)
 
       self.image.width.times do |i|
         self.image.height.times do |j|
           
+          value = (h_diff[i, j] + v_diff[i, j]).abs
+          image[i, j] = ChunkyPNG::Color.rgb(value, value, value)
         end
       end
-
-    end
+      image
+    end   
 
   end
 
diff --git a/lib/edge_detect/gray_scaler.rb b/lib/edge_detect/gray_scaler.rb
index 7e5529a..a5ea450 100644
--- a/lib/edge_detect/gray_scaler.rb
+++ b/lib/edge_detect/gray_scaler.rb
@@ -6,7 +6,23 @@ module EdgeDetect
     end
 
     def [](x, y)
-      ChunkyPNG::Color.to_grayscale(@image[x, y])
+      begin
+        (ChunkyPNG::Color.to_grayscale(@image[x, y]) & 0x0000ff00) >> 8
+      rescue ChunkyPNG::OutOfBounds => e
+        0
+      end
+    end
+
+    def nearby(x, y, radius)
+      output = []
+      ((x - radius)..(x + radius)).each do |i|
+        row = []
+        ((y - radius)..(y + radius)).each do |j|
+          row << self[i, j] 
+        end
+        output << row
+      end
+      output
     end
 
   end
diff --git a/lib/edge_detect/sobel_edge_detector.rb b/lib/edge_detect/sobel_edge_detector.rb
new file mode 100644
index 0000000..a32f546
--- /dev/null
+++ b/lib/edge_detect/sobel_edge_detector.rb
@@ -0,0 +1,39 @@
+module EdgeDetect
+  class SobelEdgeDetector < EdgeDetector
+     def detect_edges
+      image = ChunkyPNG::Image.new(@image.width, @image.height, ChunkyPNG::Color::TRANSPARENT)
+      gray = GrayScaler.new(self.image)
+
+      self.image.width.times do |i|
+        self.image.height.times do |j|
+          v_x = (sobel_x * Matrix.columns(gray.nearby(i, j, 1))).sum
+          v_y = (sobel_y * Matrix.columns(gray.nearby(i, j, 1))).sum
+
+          # / 10 because otherwise it's too much noise
+          value = Math.sqrt(v_x ** 2 + v_y ** 2).to_i / 10
+          image[i, j] = ChunkyPNG::Color.rgb(value, value, value)
+        end
+      end
+      image
+    end
+
+    private
+
+      def sobel_x
+        @sobel_x ||= Matrix[
+          [1, 0, -1],
+          [2, 0, -2],
+          [1, 0, -1]
+        ]
+      end
+
+      def sobel_y
+        @sobel_y ||= Matrix[
+          [1,   2,  1],
+          [0,   0,  0],
+          [-1, -2, -1]
+        ]
+      end
+
+  end
+end
\ No newline at end of file
diff --git a/test/edge_detect/edge_detector_test.rb b/test/edge_detect/edge_detector_test.rb
index 827c090..239aecc 100644
--- a/test/edge_detect/edge_detector_test.rb
+++ b/test/edge_detect/edge_detector_test.rb
@@ -2,31 +2,35 @@ require 'test_helper'
 
 class EdgeDetectorTest < Minitest::Test
 
-  def setup
-    @vertical_line = create_vertical_line
-    @horizontal_line = create_horizontal_line
+
+  def test_vertical_line
+    input = File.expand_path('../../pictures/airplane.png', __FILE__)
+    image = ChunkyPNG::Image.from_file(input)
+
+    standard = EdgeDetector.new(image)
+    sobel  = SobelEdgeDetector.new(image)
+
+    output_standard = File.expand_path('../../output/airplane_standard.png', __FILE__)
+    output_sobel = File.expand_path('../../output/airplane_sobel.png', __FILE__)
+
+    standard.detect_edges.save(output_standard)
+    sobel.detect_edges.save(output_sobel)
   end
 
-  def test_a
-    edge = EdgeDetector.new(@vertical_line)
-    edge.detect_edges
+  def test_horizontal_line
+    input = File.expand_path('../../pictures/robot.png', __FILE__)
+    image = ChunkyPNG::Image.from_file(input)
+
+    standard = EdgeDetector.new(image)
+    sobel  = SobelEdgeDetector.new(image)
+
+    output_standard = File.expand_path('../../output/robot_standard.png', __FILE__)
+    output_sobel = File.expand_path('../../output/robot_sobel.png', __FILE__)
+
+    standard.detect_edges.save(output_standard)
+    sobel.detect_edges.save(output_sobel)
   end
 
-  private 
-  def create_horizontal_line
-    image = ChunkyPNG::Image.new(7, 3, ChunkyPNG::Color::TRANSPARENT)
-    (1..5).each do |i|
-      image[i, 1] = ChunkyPNG::Color('black')
-    end
-    image
-  end
 
-  def create_vertical_line
-    image = ChunkyPNG::Image.new(3, 7, ChunkyPNG::Color::TRANSPARENT)
-    (1..5).each do |i|
-      image[1, i] = ChunkyPNG::Color('black')
-    end
-    image
-  end
 
 end
\ No newline at end of file
diff --git a/test/pictures/airplane.png b/test/pictures/airplane.png
new file mode 100644
index 0000000..d6eca14
Binary files /dev/null and b/test/pictures/airplane.png differ
diff --git a/test/pictures/robot.png b/test/pictures/robot.png
new file mode 100644
index 0000000..c502347
Binary files /dev/null and b/test/pictures/robot.png differ