Flatten animated gifs before converting format.

Based on @Andrekra solution.

Fixes #794

app/controllers/alchemy/pictures_controller.rb

@@ -49,13 +49,16 @@ def send_image(image, format)
       request.session_options[:skip] = true
       ALLOWED_IMAGE_TYPES.each do |type|
         format.send(type) do
+          options = []
           if type == 'jpeg'
             quality = params[:quality] || Config.get(:output_image_jpg_quality)
-            image = image.encode(type, "-quality #{quality}")
-          else
-            image = image.encode(type)
+            options << "-quality #{quality}"
           end
-          render text: image.data
+          # Flatten animated gifs, only if converting to a different format.
+          if type != "gif" && image.ext == 'gif'
+            options << "-flatten"
+          end
+          render text: image.encode(type, options.join(' ')).data
         end
       end
     end

spec/controllers/pictures_controller_spec.rb

@@ -235,6 +235,29 @@ module Alchemy
           end
         end
       end
+
+      context 'requesting an animated gif with different format' do
+        let(:image) do
+          fixture_file_upload(
+            File.expand_path('../../fixtures/animated.gif', __FILE__),
+            'image/gif'
+          )
+        end
+
+        let(:picture) { build_stubbed(:picture, image_file: image) }
+
+        before do
+          expect(image).to receive(:ext) { 'gif' }
+          expect(picture).to receive(:image_file) { image }
+          expect(Alchemy::Picture).to receive(:find) { picture }
+        end
+
+        it 'flattens the gif before converting the format.' do
+          expect(image).to receive(:encode).with('png', '-flatten') { double(data: '') }
+          alchemy_get :show, id: picture.id, name: picture.urlname,
+            format: 'png', sh: picture.security_token
+        end
+      end
     end
 
     describe '#thumbnail' do