Mask question (that I think I know the answer too and I hope I'm wrong)

Lets say I have a 300 x 300 image, and just for fun, lets say it’s a tic-tac-toe board. I have a mask that shows the upper left square.

Is the masked image still 300x300 and my center is in the center square (150x150) or is my center relative to the unmasked area?
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