To prevent occurrence of density variation in a space frequency (approximately 50-100 lpi) which is caused by a difference between light quantities of light emitting points and can be visually observed on an image.

There is disclosed an optical writing method for performing optical writing by driving a light emitting means having the plurality of light emitting points according to a modulating signal based on an image signal. In an image processing process for generating the image signal, the inputted image data is processed by an error diffusion processing as a quasi-intermediate tone processing not having the periodicity in a sub-scanning direction. The image data inputted to an image processing section 122 from an image input section 121 is subjected to an emphasizing process by an MTF filter processing section 122a, and then is subjected to density controlling by a γ-correction processing section 122b. Next, the image data is subjected to the quasi-intermediate tone processing not having the periodicity in a sub-scanning direction so as to be matched with a characteristic of a printer by an error diffusion processing section 122c, and then the image data is transmitted to an image output section (an LD driving side) 129.