104 has an additional photodiode detector which collects only the diffusely reflected light component referred to as periphery detector 108 the advantage of the additional detector arrangement allows for separation of the specular light component from the total flux light component collected by the central detector specifically in operation the diffuse detector signal from the diffuse only detector 108 is subtracted from the total flux detector signal from central detector 106 which has both specular and diffuse light components thus the true specular signal can be determined this is based on the assumption that diffusely reflected light is evenly distributed over the whole sensor 104 one such sensor that operates in the above described fashion is previously described co pending u s patent application ser no 07 246 242 which was incorporated by reference it is noted that other arrangements of sensors will also work such as an array of small light detectors as provided by a charge coupled device ccd or the like as has been discussed in the background of the invention the prior densitometer calculations have not been responsive to both changing environmental conditions and differences between individual machines as you will recall for example dust conditions in and on the densitometer are a changing environmental.