1. An image forming method of exposing a surface of an image bearer with light according to an image pattern including an image portion and a non-image portion to form an electrostatic latent image corresponding to the image pattern, the image portion including a plurality of pixels, the method comprising: setting, among the pixels constituting the image portion, at least a first group of pixels existing at a boundary with respect to the non-image portion as a non-exposure pixel group, wherein, for each pixel in the non-exposure pixel group, a light power value is changed to zero from a predetermined light power value required for exposing the image portion; setting, among the pixels constituting the image portion, at least a second group of pixels existing at a boundary with respect to the non-exposure pixel group as a high power exposure pixel group where exposure is performed with light of a higher light power value than the predetermined light power value required for exposing the image portion; specifying, among the pixels constituting the image portion, a predetermined pixel as a target pixel; acquiring image identification information identifying a type of the image pattern from the pixels constituting the image portion; and specifying a light power value of the target pixel based on the image identification information.