There is disclosed an image post-processing method for adjusting glossiness of a fixed toner image. The method includes a glossiness control step and a temperature control step. The glossiness control step is a step of, to a toner image formed of a toner containing a light absorbing compound and fixed to a recording medium, emitting glossiness control light so as to reduce or increase glossiness of the toner image. The temperature control step is a step of heating the toner image immediately before the light is emitted to the toner image such that the toner image has a surface temperature which is at least 20° C. lower than a softening temperature of the toner. The glossiness control light has a maximum emission wavelength in a wavelength range in which the compound absorbs light and is made to at least reduce the glossiness of the toner image.