I've started to use Smart Objects and Filters in CS 5 but stumbled upon a problem today I don't know how to solve.

Let's say I open an image as object from ACR into Photoshop, generate a selection of a bird, save that selection and then select Smart Sharpen. It generates a "smart filter mask layer" which applies the sharpening to only the bird and which can be changed later, e.g. after resizing. So far so good.

Now, let's say I now want to do noise reduction on the background. So my thinking was that loading the original selection of the bird, inverting it and then choosing noise reduction from the filter menu would accomplish the same thing: namely that it would generate a new "smart filter mask layer" but which applies noise reduction only to the background. But no! It applies the noise reduction to the bird despite the background being selected. Huh??? In other words, it generates a new smart filter layer but it applies it to the original "smart filter mask layer".

Now, I can take the original object layer, copy it and rasterize it to convert it into a regular layer. On that layer I then can selectively apply noise reduction to the background. But here's the catch: now any changes to the smart sharpening filter on the original object layer don't show up.

I guess my question is: how do you generate two different "smart filter mask layers" on the original object layer which work on different parts of the image?

Thanks in advance. JR

PS: Sorry, I may be using the wrong terminology at times.