PURPOSE: To correct the reading error of respective resolved colors owing to various factors by calculating a point expansion function to represent the degradation of a read picture every respective color components based on the reading result of a color picture, calculating the changing quantity of a reference filter of the respective color components to compensate the degradation of the read picture and the filter of the respective color component and restoring the filter of the respective color component to correspond to respective picture elements.

CONSTITUTION: A line image sensor 111 color-separate a color picture on an original 101 into color components and reads, a point expansion function calculating means 121 calculates a point expansion function to represent the degradation of a read picture and a reference filter calculating means 131 calculates the coefficient of the filter of the respective color components to compensate the degradation of the read picture and outputs as the reference filter of the respective color components. Next, a changing quantity calculating means 132 calculates the filter of the respective color components to correspond to respective picture elements, calculates and outputs a changing quantity from the reference filter of the corresponding color component. A restoring means 141 of a correcting means 140 restores the filter of the repective color components to correspond to the respective picture elements from the changing quantity, the filter of the restored respective color components and the reading result of the color component are convolution-integrated by a correcting processing means 142 and the reading result with an error owing to respective kinds of factors removed can be obtained.