Problem with "Noise dissolve" filter Motion 1.0.1/ psd transparency

Question

Hello,
sorry for my english but i'm writing from france...
So, this is my problem. If you want, try the same thing and you will see something ugly :
this is an example (not real files that i'm working on) :
I import a photoshop file with two layers in Motion. Layer 1 is just a pink color. Layer 2 is a copy of small portion of Layer 1 ( so it's the same color : pink ). I make this copy with a progressive border/selection of 2px (soft edge of 2px).
In motion layer 1 is under layer 2. Of course layer 2 have a transparency, because it's just a copy of small portion of layer 1.
When you look at the image, you just see pink color ( in fact there's two layer of the same color ). This is before applying the "noise dissolve" filter.
I apply the "noise dissolve" filter on layer 2 to make this layer appear in 300 frames. At frame 0 layer 2 is hidden by effect, at frame 300 the effect reveal the layer 2 with animated pixels (this is the "noise dissolve" effect). Of course, once again you don't see layer 2 appear because it's the same color than layer 1.
BUT...
when layer 2 "appear", i can see a black (and ugly) border around the layer 2!
It seems that Motion make a soft border around a transparency object !
Maybe i don't understand something ? I try to change the settings of the alpha channel in the inspector when i'm selecting my imported image, but it doesn't change anything!
I try to make a progressive border/selection/soft edge of 0px ( it's like a hard edge i think ) on the layer 2 in photoshop. In Motion, it's better but i can see the black and ugly border again ( not so visible, but visible anyway).
Here is a capture of what i see with the effect applied (On left you have hard edge, on right soft edge.):
http://perso.wanadoo.fr/elzef/motion.jpg
I hope you understand what i mean...
Somebody know about this problem ?
Thank you
G5 2x2 Mac OS X (10.3.9) Motion 1.0.1
G4 MDD Dual 867 Mac OS X (10.3.9) and 9.2.2
G4 MDD Dual 867   Mac OS X (10.3.9)   and 9.2.2

Answer 1

Hi Patrick,
thank you,
i set layer 2's alpha to pre-multiplied:
at the begining it's seems to be OK,
but at the middle of the effect the noise appears as white pixels, then disappear when come to the end.
At the end the soft border is not visible ( that's waht i want for the end) but the hard edge still visible - not so visible whan it was black, but still here.
I try to set layer2 alpha to "behind". It seems to work with the soft edge but don't work with the hard edge.
I will try again with the images of my real project and try to not use hard edge, maybe it's gonna work.
Thank you very much
elzef (France)