lib/simulacrum/diff/rmagick.rb in simulacrum-0.0.2 vs lib/simulacrum/diff/rmagick.rb in simulacrum-0.0.3

@@ -1,18 +1,29 @@
 require 'rmagick'
 require_relative '../diff'
 
 module Simulacrum
   class RmagicDiff < Simulacrum::Diff
+    def delta_percent
+      @delta * 100
+    end
+
     private
 
     def compare
-      a_image = Magick::Image.read(@a_path)
-      b_image = Magick::Image.read(@b_path)
-      @image, @delta = compare_images(a_image, b_image)
+      a = Magick::Image.read(@a_path)
+      b = Magick::Image.read(@b_path)
+      @image, @delta = compare_images(a, b)
     end
 
-    def compare_images(a_image, b_image)
-      a_image[0].compare_channel(b_image[0], Magick::MeanSquaredErrorMetric)
+    def compare_images(a, b)
+      # Calculate the Square Root Mean Squared Error for the comparison of the
+      # two images.
+      #
+      # Gets the color difference for each pixel, and square it, average all the
+      # squared differences, then return the square root.
+      #
+      # http://www.imagemagick.org/discourse-server/viewtopic.php?f=1&t=17284
+      a[0].compare_channel(b[0], Magick::MeanSquaredErrorMetric)
     end
   end
 end