When I read, I definitely visualise everything as if it's really happening. I have clear silhouettes of what the characters look like and I imagine vividly what the environments are.

Something I've recognised however is that my imagination when reading tends to follow a blueprint of my own memory so to speak. As in most of what I'm imagining in my mind is all in the same style visually as to what I am familiar with in my daily life. It's hard to imagine a completely foreign concept on the spot.

Like if I asked you to imagine a book in your mind right now, the image you get will likely be similar to books you have recently read or books you are familar with visually. If I asked you to imagine a completely new book that you've never seen before, it'l be very difficult. It's like trying to imagine a musical melody you've never heard before.