Apple weds high-res 5K visuals into its sleek, 5mm thin, mid 2017 27" iMac with Retina 5K Display. With a 5120 x 2880 screen resolution, this iMac provides 1 billion colors and 500 nits of brightness, which is 43% brighter than the previous model. The Retina 5K display also features a wider color gamut.