There may be another way of interpreting Hume on this matter.
According to him, every simple idea arises from a sense impression. So, even if I replace in my mind’s eye the tan color of the salad bowl with blue, the idea of the blue color was ultimately sensed some time in the past and is now merely being remembered.
Hume then may be saying that the bowl being recalled truly produces the most forceful and vivid image in the mind; while the more the imagination rearranges the simple parts (color, shape, smell, etc.) in novel ways, the less clear the resulting complex idea becomes in comparison with the idea of the original thing. How interesting.
Thus, the force and vivacity of the idea of a new mousetrap still to be built in the mind of its inventor are bound to be weaker than the force and vivacity of the same idea in mind of a consumer who bought the mousetrap after it’d been produced, carefully inspected and tested it, and, having put it away, is indulging in recalling its form.
This may or may not be plausible; I am not sure.