An enhanced toner area coverage (ETAC) sensor may be calibrated to adjust for changes in LED intensity by determining a functional relationship between specular developed mass per unit area (DMA) values and diffuse readings obtained from the sensor. Specular and diffuse readings are obtained from an ETAC sensor that senses reflected light from toner patches generated with incrementally increasing densities on the photoreceptor belt. The specular readings in a particular range and their corresponding diffuse readings are selected for the calibration computations. Reflected ratios are computed from the specular readings and used to determine specular DMAs. The specular DMAs and selected diffuse readings define a set of points for which a functional relationship is determined.