a method of controlling image density in an electrophotographic copying machine includes operating a first detector to measure the density of a blank region on a photosensitive member , operating a second detector to measure the density of a reference toner image formed on a portion of the blank region , comparing the measured densities of the blank region and the reference toner image , and controlling the density of a developed image of an original in accordance with the results of the comparison . an apparatus in accordance with the invention includes a pair of optical density detecting sensors positioned in opposition to the photosensitive member and in juxtaposition to each other in the direction transverse to the direction of movement of the member .