a 'sharp' image/picture/photograph [=an image/picture/photograph in which the small details can be clearly seen]
a 'sharp' break from tradition [=a sudden change from the traditional way of doing things]
A 'sharp-eyed' [='perceptive'] reader will notice the book's repeating themes.
(..) Damn it. Rachel! Open up! It's your sister. I have to talk to you. Hi, Amy. You're not Rachel. Still sharp as a tack! Um, Charlie, this is Rachel's sister, Amy. Amy, this is Charlie. Hi, nice to meet you/ Hi And you are? Ross. (..)2003 TvShow: Friends Title: The One Where Rachel's Sister Babysits Season: 10 Episode 5