minimagick carrierwave round image (with white border)

carrierwave.rb

# config/initializers/carrierwave.rb

require 'mini_magick'

module CarrierWave
  module MiniMagick
    # round _square_ image
    def round
      manipulate! do |img|
        img.format 'png'

        width = img[:width]-2
        radius = width/2

        mask = ::MiniMagick::Image.open img.path
        mask.format 'png'

        mask.combine_options do |m|
          m.alpha 'transparent'
          m.background 'none'
          m.fill 'white'
          m.draw 'roundrectangle 1,1,%s,%s,%s,%s' % [width, width, radius, radius]
        end

        overlay = ::MiniMagick::Image.open img.path
        overlay.format 'png'

        overlay.combine_options do |o|
          o.alpha 'transparent'
          o.background 'none'
          o.fill 'none'
          o.stroke 'white'
          o.strokewidth 2
          o.draw 'roundrectangle 1,1,%s,%s,%s,%s' % [width, width, radius, radius]
        end

        masked = img.composite(mask, 'png') do |i|
          i.alpha "set"
          i.compose 'DstIn'
        end

        masked.composite(overlay, 'png') do |i|
          i.compose 'Over'
        end
      end
    end
  end
end

# somewhere in an uploader

varsion :email do
  process :round
end