The least significant bits of respective count values of an H counter and a V counter are combined, to generate a timing signal defining a 2×2-size repeat block. A timing register including four registers each storing data which determines a color of each location within the repeat block is provided for each of input channels. A selector selects one of outputs of the timing registers based on the timing signal, and generates a signal designating a color of a pixel at a certain time for each of the input channels. A register storing black level correction data for each color is used in common by the input channels. For each of the input channels, an item of black level correction data at the certain time is selected based on the signal designating the color of the pixel at the certain time and input to a pre-processing circuit in each of the input channels.