Does knowledge foster or destroy imagination?

I have noticed that very well educated people, specialists in one field are bound by its knowledge and information and when asked by someone about a novel thing in their field or profession, a concept, an idea, they deny discussing it. They have been given all the answers, they think, through their studies and knowledge. Also they are not eager to discuss other novelties in other fields. They are fortified in their field and feel consummate. This as a rule which of course has its exceptions.
Is knowledge a means, a prerequisite for imagination? If so to what extent?
Does knowledge help or destroy imagination? Is it an impediment towards it?