I’ve seen a few cases where reports exported or rendered to PDF have distorted charts and images. On past projects where I’ve seen this behavior, we’ve played with fonts and chart properties and have accidentally corrected the issue but without really getting to the core problem. A friend and industry associate, Dave DuVarney, researched the problem and figured it out. I’ve seen cases that were worse than this example. Here are before and after screen shots of a chart report rendered as a PDF:
Notice that the fonts on the X axis are dithered. As I said, this example isn’t extreme.
Now the corrected version:
Turns out that changing the background color of a chart changes the image scaling and corrects the problem. Follow his blog and the details here.