A method is provided for controlling an image processor to perform display of an image on a first display device in synchronization with short frames and to perform display of an image on a second display device in synchronization with long frames each of which has a time length longer than a time length of each short frame. According to the method, a synchronization signal acquisition process acquires a first synchronization signal synchronized with switching of the short frames. An estimation process estimates, each time the first synchronization signal is acquired, a generation position of a second synchronization signal synchronized with switching of the long frames within a 2-frame period corresponding to two short frames after the first synchronization signal is acquired. The image processor is provided with a drawing command instructing generation of an image to be displayed on the first display device or the second display device controllably in accordance with results of the estimating by the estimation process.