To calculate the energy used to generate a single pixel, for instance, you can't just add-up the energies from the three LED subpixels - red, green, blue (RGB). Previous estimates of power behavior were based on overly-simple assumptions. That's not at all straightforward because the way a phone's components draw power isn't a linear relationship: when you adjust screen brightness from 100% to 50%, for example, the power drawn by your OLED display isn't simply reduced by half. The researchers started by reexamining how power behavior is estimated.