rails with Rmagick createing thumbnail image

gistfile1.rb

  #Create squre thumbnail from bytedata by RMagick
  def thumbnail(size=128)
   
    image = Magick::Image.from_blob(self.binary_contents).shift
    image_width = image.columns
    image_height  = image.rows
   
    if image_width > image_height
      crap_size = image_width -image_height  # 正方形にするため、カットするpixcel数
      thumbnail = image.crop(crap_size /2, 0, image_width - crap_size , image_height).resize(size, size)
    elsif(image_height > image_width)
      crap_size = image_height  - image_width
      thumbnail = image.crop(0, crap_size /2, image_width , image_height - crap_size).resize(size, size)
    else
      thumbnail = image.resize(size, size)
    end

    
  end