In the control method of the signal processing apparatus of the present embodiment, the portion at which a predetermined number of pixel values exceeding a first threshold value is continuous is specified as floating data of continuous image data indicated by pixel values output from a plurality of continuous light-shielded pixels. Reference data indicating a reference of a specific color is output, which is obtained by using a rest of image data, which is the continuous image data from which the floating data is removed, and alternative image data having pixel values not exceeding the first threshold value, which is used in place of the floating data.