Yes, I know that free-range musical creativity. It can occur, when half asleep and it does occur, when I am occupied with painting/color.
I believe, it is a state, that could be accessed by training "flow". That is when it happens and flow can be trained.
I also think, that the photographic memory, you speak of could be trained methodically. You do have it, basically. The rest is technique.
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Femaline
Special Interest: Beethoven