ActionScript 3.0 :: Creating Masks From BitmapData

I'm trying to modify the alpha layer of a bitmapData by taking a source iamge and masking out areas that don't have the correct channel. ATM I'm using copyChannel to achieve the effect, but I'd liek more than 3 channels (use alpha kills the other channels it seems). 255, 0, 255 should be able to act as another mask.

This is what I'm doing now...

Code:
bitmap.bitmapData.copyChannel(tempMask, new Rectangle(0, 0, tempMask.width, tempMask.height), new Point(0, 0), BitmapDataChannel.RED, BitmapDataChannel.ALPHA);

So the red parts of the image mask out the source image. All I want is to be able to mask out things basic on multiple channels (the lesser of the 2).

1) How does copyChannel work? Can I just test each pixel manually and achieve relatively similar speeds? and 2) if the Flash inline functions are infact faster, is there a function that can do what I want, or would it be better to use a shader?

Code:
var tempBitmapData:BitmapData = new BitmapData(tempMask.width, tempMask.height);
var matrix:Array = [];
matrix = matrix.concat([0, 0, 0, 0, 0]); // red
matrix = matrix.concat([0, 0, 0, 0, 0]); // green

[Code].....