I see your point, but by "using your imagination" I meant creating mental images of things and events described in the book, not just filling in the parts that are not described. In a way, you are following an author's instructions to create an image in your mind (at least by combining memories of things you have seen before) but you still have to do it yourself, no matter how detailed the instructions are. In a movie, images and events are there on the screen created for you, not inside your mind.

I believe there are big differences in how detailed and realistic images people can create in their minds. Because the computer game graphics are better than 20 years ago, there are now much more people who can feel like they really were in the game world than there used to be. For those who already could imagine the surroundings in detail themselves the advancement in graphics has been just eye candy.