回形针调整大小以适应一个矩形框

Question

我具有例如矩形图像30x800像素

如何可以与回形针缩放它保持与边框填充空区域的纵横比为100×100像素的图像？

一个例子：​​

Answer 1

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

还是有不白色背景

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