1. An image processing apparatus comprising: an input device configured to receive a stroke input given by a user; and a display controller configured to control a displaying of a modified stroke, wherein the modified stroke is synthesized based on characteristic parameters of the received stroke input, characteristic parameters of a reference stroke that has been matched to the received stroke input, and a correction coefficient that has been set based on the user, wherein the characteristic parameters of the received stroke input comprise coordinate values of representative points along the received stroke input, and the characteristic parameters of the reference stroke comprise respective coordinate values of representative points along the reference stroke, and wherein the characteristic parameters of the reference stroke are normalized according to the characteristic parameters of the received stroke input.