An apparatus of approximating backlight spread is used in a display to estimate a backlight spread image corresponding to an image after backlight spreading of a plurality of backlight sources arranged in a matrix form. An equalizer receives backlight pulse width modulation signals of the backlight sources for performing an equalization operation and generating corresponding equalization signals. A backlight seed image constructor receives the equalization signals to establish a backlight seed image. A first calculation unit calculates positions corresponding to the backlight seed image based on a backlight spread image. A second calculation unit calculates coordinates of the backlight seed image corresponding to the positions. A distance calculator calculates distance differences between the positions and coordinates of the backlight seed image. A bilinear transformation unit performs a bilinear transformation on pixels of the backlight seed image and the distance differences so as to generate the backlight spread image.