Hey all-
Can anyone tell me how to remove the background color from an image?

I'm trying to get a picture of a t-shirt. I've got the shirt on a dress form in front of a black background and I want to take the background out, kind of like what they do in the movies where they use 'bluescreen' on the parts they want to remove.
I opened the photo in PS, chose the background color with the eyedropper, made a copy of the image in the layers window, but what's the final command? I tried extract etc, but nothing seems to be correct. Any suggestions? Thanks.
ps. I'm using PS 6.0