回形针调整大小以适合矩形框

Question

我有一个矩形图像，例如30x800像素

如何使用回形针对其进行缩放以将宽高比保持为100x100像素的图像，边框填充空白区域？

示例：http://www.imagemagick.org/Usage/thumbnails/pad_extent.gif

Answer 1

  has_attached_file :image, :styles => { :thumb => "100x100>" }, 
    :convert_options => {:thumb => "-gravity center -extent 100x100"}

或者没有白色背景

  has_attached_file :image, :styles => { :thumb => "100x100>" }, 
    :convert_options => {:thumb => "-background red -gravity center -extent 100x100"}