A method of determining pixel luminance includes determining a smoothing reference line between a display region and a non-display region in a display panel, determining a boundary pixel, through which the smoothing reference line passes, among pixels included in the display region, dividing the boundary pixel into a first pixel region in the display region and a second pixel region in the non-display region based on the smoothing reference line, calculating a smoothing rate corresponding to a ratio of an area of the first pixel region to a total area of the boundary pixel, and determining dimming luminance of the boundary pixel based on the smoothing rate.