article_image_uploader.rb

class ArticleImageUploader < ImageUploader

  process :fix_exif_rotation
  process :strip
  process :convert => 'jpg'
  process :quality => 85 # Percentage from 0 - 100

  version :gallery_thumb do
    process :resize_to_fill => Settings.images.article_images.processing.gallery_thumb #44x44
  end

  version :gallery_large do
    process :resize_to_fill_if_larger => Settings.images.article_images.processing.gallery_large #604x300
  end

  version :side_bar do
    process :resize_to_fill => Settings.images.article_images.processing.side_bar      #140x106
  end

  version :large_lightbox do
    process :resize_to_limit => Settings.images.article_images.processing.large_lightbox  #1200x720
  end

  version :featured do
    process :resize_to_fill => Settings.images.article_images.processing.featured     #303x300
  end

  version :category_list_top do
    process :resize_to_fill => Settings.images.article_images.processing.category_list_top     #222x167
  end

  version :category_list_thumb do
    process :resize_to_fill => Settings.images.article_images.processing.category_list_thumb     #60x45
  end

end

carrierwave.rb

#config/initializers/carrierwave.rb
module CarrierWave
  module RMagick

    # Rotates the image based on the EXIF Orientation
    def fix_exif_rotation
      manipulate! do |img|
        img.auto_orient!
        img = yield(img) if block_given?
        img
      end
    end

    # Strips out all embedded information from the image
    def strip
      manipulate! do |img|
        img.strip!
        img = yield(img) if block_given?
        img
      end
    end

    # Reduces the quality of the image to the percentage given
    def quality(percentage)
      manipulate! do |img|
        img.write(current_path){ self.quality = percentage }
        img = yield(img) if block_given?
        img
      end
    end

    def resize_to_fill_if_larger(width, height, gravity=::Magick::CenterGravity)
      geometry = get_geometry
      if geometry.first>width && geometry.last > height
        manipulate! do |img|
          img.crop_resized!(width, height, gravity)
          img = yield(img) if block_given?
          img
        end
      end
    end

    def get_geometry
      img = ::Magick::Image::read(current_path).first
      geometry = [ img.columns, img.rows ]
    end

    module ClassMethods
      def resize_to_fill_if_larger(width, height, gravity=::Magick::CenterGravity)
        process :resize_to_fill_if_larger => [width, height]
      end
    end

  end
end

image_uploader.rb

class ImageUploader < CarrierWave::Uploader::Base

  # Include RMagick or ImageScience support:
  include CarrierWave::RMagick
  # include CarrierWave::MiniMagick
  # include CarrierWave::ImageScience

  # Including support for the asset pipeline
  # https://github.com/jnicklas/carrierwave/issues/493
  include Sprockets::Helpers::RailsHelper
  include Sprockets::Helpers::IsolatedHelper



  # Choose what kind of storage to use for this uploader:
  storage :file
  # storage :fog

  # Override the directory where uploaded files will be stored.
  # This is a sensible default for uploaders that are meant to be mounted:
  def store_dir
     "#{CarrierWave::Uploader::Base.store_dir}/#{model.class.to_s.underscore}/#{mounted_as}/#{model.id}"
  end

  # Provide a default URL as a default if there hasn't been a file uploaded:
  def default_url
      asset_path("defaults/#{model.class.to_s.underscore}/default#{'_' if version_name.present?}#{version_name}.jpg")
     #"/images/fallback/" + [version_name, "default.png"].compact.join('_')
  end

  # Process files as they are uploaded:
  # process :scale => [200, 300]
  #
  # def scale(width, height)
  #   # do something
  # end

  # Create different versions of your uploaded files:
  # version :thumb do
  #   process :scale => [50, 50]
  # end

  # Add a white list of extensions which are allowed to be uploaded.
  # For images you might use something like this:
   def extension_white_list
     %w(jpg jpeg gif png bmp)
   end

  # Override the filename of the uploaded files:
  # Avoid using model.id or version_name here, see uploader/store.rb for details.
  # def filename
  #   "something.jpg" if original_filename
  # end

end