I get these anomalies that I can't get rid of. It's some kind of grid that skews the rendered image. The only way to get rid of it that I've found is to change the camera to orthographic view. See attached images.
The file format of the saved image doesn't matter, the anomalies doesn't appear if I set the PPI down to 72. I use a PPI setting of 288, see this post why i use a PPI setting of 288 if you wonder why http://forums.autodesk.com/t5/Autodesk-Inventor-Pu