title: Changing file type Paperclip
body: <p>I have an existing Paperclip setup that converts all uploaded images to JPG's. However, I've noticed that PNG's and GIF's uploaded and converted to JPG's end up with a strange colors and some kind of in-versing effect. I know JPG's don't support transparency, but I've recently found the need to accept PNG's and GIF's and not convert them to JPG...</p>
  
  <p>My current config:</p>
  
  <pre><code>has_attached_file :icon,
                    :styles =&gt; { :featured =&gt; ["330x90&gt;", :jpg], :thumb =&gt; ["48x48&gt;", :jpg] },
                    :convert_options =&gt; { :all =&gt; "-quality 95" },
                    :path =&gt; "media/nation_apps/content_sources/:id/icon_:style.:extension"
  </code></pre>
  
  <p>When I removed the :jpg key it broke all existing uploads. How can I change my paperclip setup to not force JPG conversion but still work with all of my previously uploaded attachments?</p>
  
  <p>Any help would be much appreciated! </p>