4:3, 3:2 or 16:9?

I use Adobe Camera Raw 7.2 to do the crop as you can specify the aspect ratio you'd like.  ACR displays the image dimensions at the bottom of its window.

When you crop 3:2 to 16:9 you end up with an image which is 3776 x 2124, giving a total pixel count of 8,020,224.  That's about 10% less than what you'd get if you originally shot in 16:9.

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