Ubuntu系统一般自带ImageMagick，我们使用其中的convert做图片的格式转换，但是新安装的Ubuntu系统一般会将convert命令的权限默认设置成“none”，具体信息在/etc/ImageMagick-6/policy.xml 中

初始状态的权限如下：

  <!-- disable ghostscript format types -->
  <policy domain="coder" rights="none" pattern="PS" />
  <policy domain="coder" rights="none" pattern="EPS" />
  <policy domain="coder" rights="none" pattern="PDF" />
  <policy domain="coder" rights="none" pattern="XPS" />

我们看到rights后面的权限都是“none”，所以我们需要将其改为"read|write"，

  <!-- disable ghostscript format types -->
  <policy domain="coder" rights="read|write" pattern="PS" />
  <policy domain="coder" rights="read|write" pattern="EPS" />
  <policy domain="coder" rights="read|write" pattern="PDF" />  
  <policy domain="coder" rights="read|write" pattern="XPS" />

我们注意到这里的格式转换只有pdf格式，我们要讲eps转换为tif，png,或者jpg的话需要自己在这个.xml文件中添加对应的格式

  <!-- disable ghostscript format types -->
  <policy domain="coder" rights="read|write" pattern="PS" />
  <policy domain="coder" rights="read|write" pattern="EPS" />
  <policy domain="coder" rights="read|write" pattern="PDF" />
  <policy domain="coder" rights="read|write" pattern="TIF" />
  <policy domain="coder" rights="read|write" pattern="JPG" />
  <policy domain="coder" rights="read|write" pattern="PNG" />
  <policy domain="coder" rights="read|write" pattern="XPS" />