Add :write option to manipulate!. Issue #711.

lib/carrierwave/processing/rmagick.rb

@@ -238,6 +238,38 @@ def resize_and_pad(width, height, background=:transparent, gravity=::Magick::Cen
     # === Yields
     #
     # [Magick::Image] manipulations to perform
+    # [Integer] Frame index if the image contains multiple frames
+    # [Hash] options, see below
+    #
+    # === Options
+    #
+    # The options argument to this method is also yielded as the third
+    # block argument.
+    #
+    # Currently, the following options are defined:
+    #
+    # ==== :write
+    # A hash of assignments to be evaluated in the block given to the RMagick write call.
+    #
+    # An example:
+    # 
+    #      manipulate! do |img, index, options|
+    #        options[:write] = {
+    #          :quality => 50,
+    #          :depth => 8
+    #        }
+    #        img
+    #      end
+    #
+    # This will translate to the following RMagick::Image#write call: 
+    # 
+    #     image.write do |img|
+    #       self.quality = 50
+    #       self.depth = 8
+    #     end
+    #   
+    # ==== :format
+    # Specify the output format. If unset, the filename extension is used to determine the format. 
     #
     # === Raises
     #
@@ -251,7 +283,7 @@ def manipulate!(options={}, &block)
         list = ::Magick::ImageList.new
         image.each_with_index do |frame, index|
           processed_frame = if block_given?
-            yield *[frame, index].take(block.arity)
+            yield *[frame, index, options].take(block.arity)
           else
             frame
           end
@@ -260,14 +292,15 @@ def manipulate!(options={}, &block)
         block_given? ? list : list.append(true)
       else
         frame = image.first
-        frame = yield( *[frame, 0].take(block.arity) ) if block_given?
+        frame = yield( *[frame, 0, options].take(block.arity) ) if block_given?
         frame
       end
 
+      write_block = create_write_block(options[:write])
       if options[:format]
-        frames.write("#{options[:format]}:#{current_path}")
+        frames.write("#{options[:format]}:#{current_path}", &write_block)
       else
-        frames.write(current_path)
+        frames.write(current_path, &write_block)
       end
       destroy_image(frames)
     rescue ::Magick::ImageMagickError => e
@@ -276,6 +309,13 @@ def manipulate!(options={}, &block)
 
   private
 
+    def create_write_block(write_options)
+      return nil unless write_options
+      assignments = write_options.map { |k, v| "self.#{k} = #{v}" }
+      code = "lambda { |img| " + assignments.join(";") + "}"
+      eval code
+    end
+
     def destroy_image(image)
       image.destroy! if image.respond_to?(:destroy!)
     end

spec/processing/rmagick_spec.rb

@@ -73,6 +73,23 @@
     end
   end
 
+  describe "#manipulate!" do
+    it 'should support passing write options to RMagick' do
+      image = ::Magick::Image.read(file_path('landscape_copy.jpg'))
+      ::Magick::Image.stub(:read => image)
+      ::Magick::Image::Info.any_instance.should_receive(:quality=).with(50)
+      ::Magick::Image::Info.any_instance.should_receive(:depth=).with(8)
+
+      @instance.manipulate! do |img, index, options|
+        options[:write] = {
+          :quality => 50,
+          :depth => 8
+        }
+        img
+      end
+    end
+  end
+
   describe "test errors" do
     context "invalid image file" do
       before do