First pixel data of a pixel of interest is output from a first shift register, while second and third pixel data of neighboring pixels indicative of the same color are output from second and third shift registers, respectively. Differential data between estimated pixel data calculated from the second and third pixel data and the first pixel data is input to a comparator. A threshold value stored in a register is modulated by the estimated pixel data, and is input to the comparator as modulated threshold data. When the comparator judges that the differential data is greater than the modulated threshold data, a selector outputs the estimated pixel data as corrected pixel data.