How to access the dimensions of an image in the view using carrierwave and mini_magick

photo.rb

class Photo < ActiveRecord::Base
  mount_uploader :file, StillImageUploader

  def dimensions(version = nil)
    image ||= MiniMagick::Image.open(file.url(version))
    {width: image['width'], height: image['height']}
  end
end

# photo.dimensions
# => {:width=>545, :height=>300}
#
# photo.dimensions(:thumbnail)
# => {:width=>100, :height=>100}
#
# photo.dimensions[:width]
# => 545
#
# photo.dimensions[:height]
# => 300