Apparatus generating gray scale voltage for organic light emitting diode display device and generating method thereof

An apparatus for generating gray scale voltage includes a brightness/color coordinate correction unit having a gamma table including data corresponding to an image displayed on a pixel unit of an OLED device at a first brightness level, and a gamma reference voltage look-up table including voltage values of red, green, and blue data corresponding to each gray scale and brightness values at the first brightness level in accordance with the gamma table, a gamma control signal output unit configured to output a gamma reference voltage control signal corresponding to a second brightness level in accordance with the gamma table and the gamma reference voltage look-up table, and a gamma correction circuit configured to receive the gamma reference voltage control signal, to generate gray scale voltages corresponding to the second brightness level, and to output the generated gray scale voltages to a data driver.