The way it works for me (I can't visualize like that), it's like I am writing a story. I can say I see a tiger, then think about it and write down more details but I am always consciously adding stuff to the tiger. If I want details about number of stripes, I need to think about it and then "write" it. Never do I see something I am not consciously forming.

Well, I did have a strange experience couple of nights ago. I was falling asleep and I saw something similar to a "movie" in my vision. It was a highly sped up simulator game I played, but it was quite vivid for me.