Brake pistons

I am not a brake man so please forgive me if this question is silly.

I got my two front and one rear disc brake calipers off and tore them down to what you see in the pic.

I assume the piston is supposed to slide easily, but it is a real bugger on all of the calipers to get the piston to move at all.

Is the piston supposed to slide right out? I don't want to be yanking on it all evening only to find out it needs some special trick to get that sucker out.

The bike did sit for a while, just FYI. The front calipers don't look near as bad or rusty as this one, and I do have a spare rear caliper.

Thanks.

Okay nevermind, I looked in the previous posts and found the answer.
My bad.

Dave...I'm assuming that You read that compessed air will assist You in removing the pistons...BE CAREFUL!!
Put a rag in between the edge of the piston,and the opposite side of the caliper(to absorb the impact)...the piston MAY come out quite abruptly!...KEEP YOUR HANDS CLEAR!
Good luck,Bud.