Digital image representation is perceptually uniform if a small perturbation of a component valuesuch as the digital code value used to represent red, green, blue, or luminanceproduces a change in light output at a display that is approximately equally perceptible across the range of that value. Most digital image coding systemsincluding sRGB (used in desktop graphics), BT.709 (used in high-definition television, HD), Adobe RGB (1998) (used in graphics arts), and DCI P3 RGB (used in digital cinema)represent colour component (pixel) values in a perceptually uniform manner. However, this behavior is not well documented and is often shrouded in confusion. This article surveys perceptual uniformity in digital imaging and attempts to clarify some widely misunderstood aspects of image coding. (c) 2013 Wiley Periodicals, Inc. Col Res Appl, 39, 6-15, 2014