title: wpf bind property to resize bmp in hight dpi
body: <p>Having to display bitmap images - not vector at several user's dpi settings in a XBAP WPF application, I'd like to setup a dpiFactor global variable at startup, that will be calculated as a percentage of the original bitmSizeap: </p>
  
  <p>i.e. for 120 dpi I want both size of the image to be: newSize = originalSize * (100 - (120 - 96)) / 100
  which means multiply by 75% if the dpi is 125% of original.</p>
  
  <p>The dpiFactor have to be defined at startup, and then all measurement to be scaled down (or up) when page is launched.
  How can I express that in XAML perhaps with a bound property?  </p>