Patent ID: 7884983

Claim:
An image formation method in which an optical diffraction structure forming layer is thermally transferred in a halftone dot state to a colored region on a transfer body to form an optical diffraction structure portion by heating with a thermal head, a transfer sheet where the optical diffraction structure forming layer in which an optical diffraction structure is formed is laminated on a base material sheet thereof, including: setting a gray-scale information as a value of printing energy to be applied to the thermal head; determining as halftone dot information, positions and sizes of the halftone dots constituting the optical diffraction structure portion which are diffused by an error diffusion method based on the printing energy to be applied to the thermal head so that an area of the halftone dot is smaller than 0.25 mm 2 and a dot area percent to the colored region ranges from 15% to 60%; and transferring the optical diffraction structure forming layer in the halftone dot state by controlling a thermal head operation based on the halftone dot information.