Out of curiosity, I checked to see if Paint Shop Pro could do it, and it turns out it does it the right way. What you do is open up all 3 images within PSP. Copy the image with the pillows you want to keep and paste it as a new layer (ctrl-L) on top of the other rendered image. Now, select the new layer and from the Masks drop down menu, select New - From Image. From the Source Window drop down, choose the B&W mask image. Leave "Source Luminance" selected (Source luminance will allow you to mask using shades of gray to produce varying degrees of transparency. Any Non-Zero Value will make everything that's not black 100% visible. You could probably use this setting, actually, if you're trying to remove anti-aliasing). Hit OK. That's it. The image I included just shows the pillows masked over a white background since in low res I can't tell which pillows were supposed to be non-antialiased.