add -layers 'optimize' flag to animated gif convert cmds

lib/paperclip/thumbnail.rb

@@ -96,6 +96,7 @@ module Paperclip
       trans << "-auto-orient" if auto_orient
       trans << "-resize" << %["#{scale}"] unless scale.nil? || scale.empty?
       trans << "-crop" << %["#{crop}"] << "+repage" if crop
+      trans << "-layers \"optimize\"" if animated?
       trans
     end
 

test/thumbnail_test.rb

@@ -381,12 +381,16 @@ class ThumbnailTest < Test::Unit::TestCase
       should "create the 12 frames thumbnail when sent #make" do
         dst = @thumb.make
         cmd = %Q[identify -format "%wx%h" "#{dst.path}"]
-        assert_equal "50x50"*12, `#{cmd}`.chomp
+        assert_equal ("50x5050x5050x5050x5050x5050x49")*2, `#{cmd}`.chomp
       end
 
       should "use the -coalesce option" do
         assert_equal @thumb.transformation_command.first, "-coalesce"
       end
+
+      should "use the -layers 'optimize' option" do
+        assert_equal @thumb.transformation_command.last, '-layers "optimize"'
+      end
     end
 
     context "with omitted output format" do
@@ -397,12 +401,16 @@ class ThumbnailTest < Test::Unit::TestCase
       should "create the 12 frames thumbnail when sent #make" do
         dst = @thumb.make
         cmd = %Q[identify -format "%wx%h" "#{dst.path}"]
-        assert_equal "50x50"*12, `#{cmd}`.chomp
+        assert_equal ("50x5050x5050x5050x5050x5050x49")*2, `#{cmd}`.chomp
       end
 
       should "use the -coalesce option" do
         assert_equal @thumb.transformation_command.first, "-coalesce"
       end
+
+      should "use the -layers 'optimize' option" do
+        assert_equal @thumb.transformation_command.last, '-layers "optimize"'
+      end
     end
 
     context "with unidentified source format" do
@@ -414,12 +422,17 @@ class ThumbnailTest < Test::Unit::TestCase
       should "create the 12 frames thumbnail when sent #make" do
         dst = @thumb.make
         cmd = %Q[identify -format "%wx%h" "#{dst.path}"]
-        assert_equal "60x60"*12, `#{cmd}`.chomp
+        assert_equal "60x6059x5959x5959x5960x5959x5859x6059x5959x5959x5960x5959x58", `#{cmd}`.chomp
+
       end
 
       should "use the -coalesce option" do
         assert_equal @thumb.transformation_command.first, "-coalesce"
       end
+
+      should "use the -layers 'optimize' option" do
+        assert_equal @thumb.transformation_command.last, '-layers "optimize"'
+      end
     end
 
     context "with no source format" do
@@ -431,12 +444,16 @@ class ThumbnailTest < Test::Unit::TestCase
       should "create the 12 frames thumbnail when sent #make" do
         dst = @thumb.make
         cmd = %Q[identify -format "%wx%h" "#{dst.path}"]
-        assert_equal "70x70"*12, `#{cmd}`.chomp
+        assert_equal "70x7067x6867x6868x6769x6767x6768x6967x6867x6868x6769x6767x67", `#{cmd}`.chomp
       end
 
       should "use the -coalesce option" do
         assert_equal @thumb.transformation_command.first, "-coalesce"
       end
+
+      should "use the -layers 'optimize' option" do
+        assert_equal @thumb.transformation_command.last, '-layers "optimize"'
+      end
     end
 
     context "with animated option set to false" do