How to export to PNG with transparent background

Hi there,

I used the following line of code to export an mxd to PNG 8 bit (i am creating tiles)... BUT i cant seem to set the background to transparent (or No Color)... any clue as to what parameter i should use?!

I read on other forum threads that by setting the background color and transparent color to the same value should do the trick... it does not work in my case.

The data-frame background color is set to Hollow...


Any tips would be great :-)