Patent ID: 7856189

Claim:
An image forming apparatus, comprising: an optical sensor configured to optically detect a density of a reference pattern image at intervals of printing a predetermined number of transfer sheets; a toner density sensor configured to detect a density of toner included in a two-component developer accommodated in a developing unit; a toner empty sensor configured to detect an almost empty state in a toner supplying unit; a storing unit configured to store an image area coverage of an output image; a determining unit configured to determine, when the toner empty sensor detects that the toner supplying unit is not in the almost empty state, whether a state of toner accommodated in the toner supplying unit is the almost empty state or an empty state or neither by comparing the density of the toner detected by the toner density sensor with a target toner density and, when the density of the toner detected is below the target toner density by a predetermined value, comparing an average image area coverage of a predetermined number of sheets with a reference value, wherein the determining unit determines that the toner is in the almost empty state or the empty state when the average image area coverage is not equal to or above a predetermined percentage of the reference value; and a controlling unit configured to control to continuously perform a toner state check when the image area coverage of the output image is greater than a predetermined image area coverage value and the density of the reference pattern image is greater than a predetermined density level, even after the toner density sensor detects a low density of toner and the determining unit determines the state of toner is the almost empty state or the empty state or neither, wherein: when the average image area coverage is equal to or above a predetermined percentage of the reference value, the determining unit determines whether density levels of two last patterns formed are equal to or lower than a predetermined density level, and the determining unit determines that the toner is in the almost empty state or the empty state when the determining unit determines that the density levels of the two last patterns formed are equal to or lower than the predetermined density level.