model.rb

      def file_path
        # -- I changed this line from: --
        # "#{directory_path}/#{id}.#{self.class.image_storage_format}"
        "#{directory_path}/#{id}.#{self.server_format}"
      end

        def pre_save
          if @uploaded_image
            # perform preprocessing
            perform_preprocess_operation
            
            # Convert to storage format
        
            # -- I removed this line: --
            # @uploaded_image.format = self.class.image_storage_format.to_s.upcase
            # -- and replaced it with: --
            @uploaded_image.format = self.server_format
            
            # Write image data to the DB field
            if self.class.db_store?
              self.image_file_data = @uploaded_image.to_blob
            end
          end
        end