Disclosed is a signal processing device and an image display apparatus including the same. In the signal processing device and the image display apparatus according to the present disclosure, a High Dynamic Range (HDR) processor receives an image signal and adjust a luminance of the image signal, and a reduction unit configured to amplify the adjusted luminance of the image signal and increase a resolution of the grayscale of the image signal to generate an enhanced image signal, wherein the enhanced image signal provides an increased luminance and grayscale resolution of the image signal while maintaining high dynamic range within the displayed HDR image. Accordingly, expression of high grayscale of a received image may improve.