A signal processing device and an image display apparatus including the same are disclosed. The image display apparatus includes a display including an organic light emitting diode panel and a signal processor configured to control the display, wherein the signal processor is configured to perform luminance conversion based on a first luminance conversion pattern in the case in which the luminance level of an input image is greater a first level and to perform luminance conversion based on a second luminance conversion pattern having a higher luminance level than the first luminance conversion pattern in the case in which the luminance level of the input image is equal to or less than the first level, whereby low gray level expression of the organic light emitting diode panel is improved.