I have a bunch of interviews which were shot against a black drape with a blue tint. Sadly the camera we used was not good enough to defocus the background so it doesn't look as good as I had hoped.
Can I use AEX to defocus those areas of the picture which have a blue tint? I tried it by duplicating the layer, applying a lens blur effect to the bottom layer, and then chroma keying the top layer over it, using blue as the key, but as you might expect the subject's edges don't key very well.
Any other suggestions?
Try Effect --> Channel --> Shift Channel to extract the blues as a greyscale map (set the other channels to Full Off), then use Levels, Curves etc. to manipulate the thresholds. You should then be able to feed the result into Lensblur and similar tool. You could also try Channel Combiner to transform to another colorspace and perhaps extract more useful info this way...