[swfmill] JPEG with alpha mask

[Måns Sewerin]

Hi!

I have a problem with creating JPEG compressed assets with a png  
mask. swfmill seems to drop the semi-transparent parts of a picture  
making them whole transparent. It is probably me creating the mask  
wrong, I use a grayscale image with a white component reflecting the  
alpha value of the real image:

transparent parts = 0 white
opaque parts = 255 white
semitransparent parts = 1-254 white depending on alpha value

is this the right approach?

best regards

/måns