A signal processing method comprises: generating thinned data by thinning, in a checkerboard like manner, image data comprising a plurality of pixels that are arranged, as a square, in a row direction and in a column direction perpendicular to the row direction; generating a first square array by extracting odd-numbered lines from lines of the thinned data in the row direction and in the column direction, and generating a second square array by extracting even-numbered lines from the lines of the thinned data in the row direction and in the column direction; and performing an image compression process for each of the first square array and the second square array.