Something less trivial. While all derpibooru arts average brightness is peaked at 99%-100%, top rated art average brightness is peaked at 80%. Also top half is slightly brighter than bottom. Actually this is not insight for artists, this is well-know rule that image top should have more space and lighter than bottom. Sorry, I can’t today make very clear illustrations, but
I have sacrificed non-safe images, because their fave count are less about brightness distribution and more about image plot, other “quality” thresholds for fave count and they are lesser part of images overall. Brightness is taken from image_intensities database table, value 85.425 is renormalized to 100%, top brightness is as ne+nw average, bttom brightness is taken as se+sw average