Method for controlling density of image to be formed by image forming apparatus having developer and humidity sensors

An apparatus converts image data based on a conversion condition, forms an image using a developer, measures the developer, and measures humidity. The apparatus determines a first density of an image when a mode of the apparatus changes from a power saving mode in which the apparatus cannot form an image to a normal mode in which the apparatus can form an image, from values measured, based on a first determination condition, determines a second density of an image when the apparatus has formed images on a predetermined number of sheets in the normal mode, from values measured, based on a second determination condition that is different from the first determination condition, and generates the conversion condition based on the first density and the second density.