making a specific color transparent based on it's saturation

Here's what I'm trying to do...

I have a BMP file already created with a red background and a white anti-aliased object drawn over that background.

Basically I would like to substitute the degree of red showing for any pixel for a degree of transparency instead.

So where you see the red background, I'd like 100% transparent, where you see the red faded because of the anti-aliasing of the white object, to maybe 50% saturation, I'd like 50% transparency, etc, etc. In the end I'm looking for a ICO file, so I was looking to take the BMP to PNG then run it through an ICO program later.

Is this possible? I wasn't sure how to do this in Adobe.

"kirk" wrote in message

Here's what I'm trying to do...

I have a BMP file already created with a red background and a white anti-aliased object drawn over that background.

Basically I would like to substitute the degree of red showing for any pixel for a degree of transparency instead.

So where you see the red background, I'd like 100% transparent, where you see the red faded because of the anti-aliasing of the white object, to maybe 50% saturation, I'd like 50% transparency, etc, etc. In the end I'm looking for a ICO file, so I was looking to take the BMP to PNG then run it through an ICO program later.

Is this possible? I wasn't sure how to do this in Adobe.

K,

You can achieve transparency with a graduated mask.
Copy your background layer.(won't allow a mask otherwise) Go to the channels palette and ctrl+click on the blue channel if your image is primarily red.
This will load a selection from which you can make a mask. Go back to the layers palette with the selection still active and add a layer mask.
Switch off the background layer.
What was red in the image is now black on the mask and blocked, what is white on the mask is shown and the gray on the mask will allow the featering to show through.
TWK