I've bought Scott Kelby's book "The Photoshop book for digital photographers, ISBN 0-7357-1236-0. I applied one of the technique he suggested: using the Lab color mode and then move to grayscale. What do you think about it?
Following Neige advice I tried to limit to one broom. The thing is that clearing the background should have been done at the time of the picture. Since they were a lot of broom around mickey to isolate one was difficult. But I should have more control of DOF.