snapshot from rect XXX without card?

[RM]

So there I am, with my happy little stack making pictures
with rounded corners using the simplest code possible (take note of that
last bit people), and to obtain a snapshot of my graphic with rounded
corners with my picture inside it, and any ink effects I have to
do this sort of thing:

put the windowID of stack "CHOPPER" into CHOP
put the rect of graphic "g1" into REKT
export snapshot from rect REKT of window CHOP to file "stinkyCheese.png" 
as PNG

AND I end up with solid colour (the colour of the stack/card) outwith my 
rounded
edges . . .

'bummer' ( hey, look, Richmond learnt at least something other than
Hypercard while he was in the States)

I am unable to understand the Documentation on alphaData.

Richmond.