title: Find Color percentage in a Image through GraphicsMagic
body: <p>So all my images are pdf and tiff and saved in database. I want to accept images which has only light color like signature in red/blue but no colorful logo or things like that.
  I was able to get somewhere closer throw Imagemagick.</p>
  <p>In order to increase speed of a conversion, and avoid bugs, I'd like to convert the following ImageMagick command to a GraphicsMagick command.</p>
  <pre><code>   convert filename.pdf -colorspace HSI -channel g +channel -format &quot;%[fx:mean.g]&quot; info:
  </code></pre>
  <p>I noticed that we don't have similar mean function in graphicsmagick. But Can we do something similar through graphics magick? TIA.</p>