Also, how does the capacity for eidetic imagery correlate with ability to count visual objects? I can't instantaneously count more than about six things (e.g. marbles) at once or up to a dozen or so depending how they're arranged. If you asked an eidetic imager to imagine a bar code, and then asked them how many lines there were, would they be able to respond quickly?

Eidetic imagery seems to be more a matter of degree. If asked to imagine a table, I can tell you instantly the number of chairs around it, but I would fail the tiger test. So perhaps passing the tiger test has more to do fast counting than vivid imagining.