The caveat to that would be best illustrated by the example of doing a close-up of someone's eyes. Whatever is in the shot would need to be 720 x 540 but a normal head is a lot bigger than just the eyes. Therefore the head texture would have to be proportionally bigger. In other words if you zoomed in and showed one third of the face in a close up, you'd probably need the head texture to be at least 1620 pixels in height. If the texture itself was a full-body texture then everything would need to be proportionally bigger.

Before they made me they broke the mold!
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