Image proportions

I regularly make backgrounds for PowerPoint, both in 4:3 and 16:9 depending on the screen in the room where I will be using PP.
In Magix P&GD (18) I set the page size to 16x9cm or 16x12 (for 4:3) and design my background. As per usual, I "store" elements I am not using in the grey area's not on the page. Sometimes the background is just a bit bigger than the page or imported png's or jpg's are not completely on the page (on purpose). When I export to JPG I choose the Page option (so that only what is actually on the page is exported) and 100 DPI.
When I use these backgrounds in PP, they are never quite the right size (proportion); there is always a small white margin on at least one side, usually on two, sometimes three sides. I have to manually adjust (stretch) the image by -0,1% or -0,2%. This is a pain.

My question is: why is a 4:3 (or 16:9) page size in P&GD not actually that propotion upon export? Or is this a (known) PP problem and not P&GD's problem at all? Or am I doing this wrong?

David

David, a page size in cm will get cropped to whole pixels as that all an image can be saved as.

There are 96 pixels to the inch and 2.54cm in the inch.
So 16x9cm is 604.72440945 x 340.15748031 pixels.

You, however are setting the dpi from 96 to 100, giving 629.92... x 354.33... px.

Instead, I would set the page to 640 x 360 (or 640 x 480), Export > Page keeping 96 dpi and in PP, scale down to 16cm across.
The resulting dpi would be 101.6. The dpi is irrelevant.

You enter 640px and will then se 6.67cm in the Custom Page Size in P&GD.

Acorn