An image signal processor receives a Bayer image signal from an image sensor and converts the Bayer image signal into a normal image signal. The image signal processor includes a memory configured to store a table including reference brightness values and variation values according to the reference brightness values; a shot noise cancelation unit configured to calculate a reference brightness value of the Bayer image signal, select a variation value in the table of the memory according to the calculated reference brightness value, and perform shot noise cancelling on the Bayer image signal based on the selected variation value to generate a modified Bayer image signal; and an interpolation unit configured to generate the normal image signal by performing interpolation based on the modified Bayer image signal.