An organic light emitting display device includes a display panel having pixels and a display panel driver driving the display panel. Each of the pixels includes an organic light emitting diode, and the display panel driver selects one of the pixels, determines a reference grayscale value, compares a grayscale value, and determines the selected pixel as a low grayscale pixel when the grayscale value is lower than the reference grayscale value and higher than a black grayscale value. Some of the low grayscale pixels display the black grayscale value when there are more than one neighboring low grayscale pixels. The reference grayscale value is determined based on a reference grayscale variable, and the reference grayscale variable includes at least one of a temperature of the display panel, a time period when the selected pixel emits light, and a wavelength of light emitted by the selected pixel.