1. A control method for an electrophotographic apparatus comprising the steps of: forming first and second toner images having first and second different respective densities on a photoconductive member; sensing the first and second densities; dividing a first predetermined function of the first density by a second predetermined function of the second density to obtain a ratio; comparing the ratio with a first predetermined value; controlling a predetermined operation of the electrophotographic apparatus which affects image density in accordance with whether the ratio is above or below the first predetermined value; the first and second toner images being formed adjacent to each other on the photoconductive member and sensed while the photoconductive member is being moved; and detecting a transition between the first and second toner images by comparing the first and second densities with a second predetermined value which is intermediate between possible ranges of the first and second densities; the first and second predetermined functions comprising average value of the first and second densities over first and second respective predetermined lengths of time.