Possible Duplicate:
Why are some pages in my PDF coming out bold?
I have problem with text on the page with a graph, it gets slightly thicker. The text on the next page without graph is normal.
Hopefully you are able to see the difference:

The culprit are these lines:
\begin{center}
\includegraphics[width=1.0\columnwidth]{times}
\end{center}
The problem is well described in here too: http://www.latex-community.org/forum/viewtopic.php?f=45&t=7533
If you don't want to follow a link then essentially, a possible answer from there:
"This is usually caused by alpha channels in included graphics.
Remove the alpha channel in the included graphics (something I cannot help you with)"
Additional question within an answer - how?
convert image.png -background white -flatten +matte image_new.png(taken from http://studio.imagemagick.org/pipermail/magick-users/2006-August/018215.html). – Jake Mar 24 '12 at 05:40convertanswer into the thread you linked and this thread can be closed then. – yo' Mar 24 '12 at 08:50