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While his approach is unlikely to be close to the true ink efficiency I give it points for a being a creative way of representing the relation.

I would guess they actually did this first (determine the area directly) so that they could judge how large to make their sample word. Their results look very nice and, notably, are scaled appropriately to a single ballpoint pen's worth of ink.

or maybe not. might have just turned out well!

Or draw them in memory and sum the pixels in (inverted) greyscale?