I've put together a photo collage as a single slide in PPT 2010 using a custom page size of 20"x16". When I save the slide as a jpeg, I use the Tools>Compress Pictures>Target output option to set the resolution to 220 ppi (which is also the default). This should yield a jpg with dimensions 4400x3520. Unfortunately, the resolution I get is 1920x1536, meaning that PPT saved the jpg at only 96 ppi.
How can I get PPT to produce a jpg of the appropriate dimensions?