PDF thumbnail problem

[Scooby08]

I'm just wondering if anybody has run into this problem, and what they did to fix it..

 

The problem is that when I upload a PDF and it then creates a thumbnail of the first page, which is fine, but some of the text ends up having black blocks around it, sort of like it's highlighted and it shows up in the thumbnails.. Has anybody ran across this problem before??

 

Here is the line I have that creates the thumbnail:

 

exec("/usr/local/bin/convert $supplied_dir/$new_file_name'[0]' -thumbnail '75x100' $supplied_dir/.thumbs/viewer_75x100_$new_file_name_image");

 

Perhaps there is something I am doing incorrectly here..