An apparatus outputs an image signal for each frame, divides a frame into sub-frames, acquires a first signal of high frequency components and a second signal of low frequency components of a sub-frame, and generates a third signal by multiplying the second signal by K. If a fourth signal obtained by adding the third signal to the first signal falls within a predetermined range, the apparatus outputs the third signal, whereas if the fourth signal includes a portion exceeding the range, the apparatus outputs a signal obtained by correcting the third signal. The apparatus also generates a composition signal of the output signal and the first signal and a fifth signal by multiplying the third signal by a correction amount y of the third signal. As a sub-frame of interest, either the composition signal or the fifth signal is output.