When a three-dimensional image viewed stereoscopically by superposition of a lenticular sheet is merely binarized and output, fringes are produced in the direction in which cylindrical lens elements repeat on the lenticular sheet, and therefore an appropriate stereoscopic image is not observed. Accordingly, a multiple viewpoint image sequence of the image of a subject is acquired, a three-dimensional stripe image is synthesized by the images of the image sequence, the stripe image is converted to a multivalued image by reducing the number of tones by the error diffusion method, the multivalued image is convened to a binary dot pattern by the density pattern method, and the dot pattern is formed on a recording medium. Any dot pattern of a prescribed plurality of dot patterns is selected in accordance with a pixel position in a direction perpendicular to the direction in which cylindrical lens elements repeat on the lenticular sheet, thereby obtaining a high-quality stereoscopic image in which the occurrence of fringes is reduced.