1. An image forming method comprising the steps of: (a) forming a plurality of electrostatic latent images of a non-solid control patch having a non-solid pattern by converting image data having reference input densities different from each other; (b) detecting a patch potential of each of the plurality of electrostatic latent images; (c) calculating a single density value corresponding to a desired patch potential from the detected plurality of patch potentials; (d) detecting a density of each of the plurality of non-solid control patches which has been formed by an imagewise exposure according to the single density value of the reference input density obtained by the calculating step; and (e) forming an image by controlling an image forming condition in accordance with a detected density signal.