Apple weds high-res 4K visuals into its sleek, 5mm thin, mid 2017 21.5″ iMac with Retina 4K Display. With a 4096 x 2304 screen resolution, this iMac provides 1 billion colors and 500 nits of brightness, which is 43% brighter than the previous model. The Retina 4K display also features a wider color gamut. Using a P3-based color gamut, the Retina 4K display provides a larger color space that more equally represents red, green, and blue, as compared to standard sRGB displays. And with more available colors, the images will appear more vivid and reveal greater detail, with more balance and precision.