There’re several steps to show an image on the screen. Display Driver IC is an indispensable semiconductor chip to operate each sub-pixels. DDI accepts a signal of an image from the CPU of the device and generates and controls the output signals. To put it simply, Display Driver IC commands the order to each sub-pixel on the panel how to operate.
Display Driver IC is composed of Gate IC, Source IC, and etc. When a certain amount of electricity is applied to TFT depending on the voltage differences between Gate IC and Source IC, TFT works as a switch to turn on/off each sub-pixels. The color of the display varies upon the on/off operation of each sub-pixels and the display generates an expected image on the screen eventually.