1. A 3D image display device, comprising: a display device including a plurality of pixels and displaying each of a left-eye image and a right-eye image, wherein the display device inserts a black image between the left-eye image and the right-eye image such that the left-eye image is displayed for part of four frames and the black image is displayed for the remaining frames and the right-eye image is displayed for part of four other frames and the black image is displayed for the remaining other frames, wherein data representing an additional luminance is additionally applied to at least one of the left-eye image, the right-eye image, and the black image to display an image, wherein the 3D image display device further comprises a 3D image processor adding the data representing the additional luminance to image data for application to a frame, wherein the 3D image processor comprises: a gamma converter generating gamma-converted data from image data; a luminance improver improving the luminance of the gamma-converted data; and a luminance improvement rate provider, wherein the luminance improver comprises a luminance improvement data generator generating data having improved luminance depending on a luminance improvement rate provided from the luminance improvement rate provider, wherein the luminance improvement data generator generates data corresponding to a total of four frames through Equation 2 if a result of Equation 1 is true, and generates data corresponding to the total four frames through Equation 3 if the result is false: 
 L *(MBTR+1)<MDL  [Equation 1] 
 LN<=L *(MBTR+1) 
 LN+ 1<= L *(MBTR+1) 
 LN+ 2<=0  [Equation 2] 
 LN <=MDL 
 LN +1<=MDL 
 LN+ 2<={ L *(MBTR+1)−MDL}*2,  [Equation 3] wherein L represents luminance data inputted into the luminance improvement data generator, MBTR represents a max boost up threshold rate, MDL represents a maximum displayable luminance, and LN, LN+1, and LN+2 represent luminance data of an N frame, luminance data of an N+1 frame, and luminance data of an N+2 frame, respectively.