Consider sitting outside and looking at a flowering bush or tree. At first it's just a tree. Then you realize that there are flowers on it (they were always there, but you weren't attending to them before). After a little while you'll again suddenly realize that there are bees buzzing around the flowers, and a nest halfway up and a few feet from the center on the right. You, most likely, did not have all that in your head on your first glance at the tree. It was just a tree. This is how many mental images are formed.

If asked to imagine a person or object or scene it always starts off fuzzy for me until more details are prompted for (by myself or by the questioner). Someone kept bringing up Tony the Tiger in one of the recent discussions on this. For me, he starts as an image of the logo or just the face/head on the cereal box. If I continue to think of it, or am asked a question about it, more details will come to mind. I may even recall and imagine Tony walking around a scene, like from a commercial.

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.