When an ILS is connected to the system, there are two calibration values needed to transform the pixel values into proportional reflectance. Proportional reflectance means that if the pixel is at half range (128 out of 255), the reflectance of the object in the field of view is 50% for the band in question. During factory calibration, an object of known reflectance is photographed with ILS values from a typical sunny day, and a fixed exposure. Upon review, the pixel value will be too high or too low compared to the reflectance. A scale factor is determined by dividing the expected value by the actual value. This scaling factor is applied to the fixed exposure used in order to produce an "ILS calibration Exposure". This is the exposure value at which the band in question will produce proportional pixel values for reflectance, when the downwelling radiation for the band is as measured by the ILS during Calibration. The ILS value measured is saved as the "ILS Cal Value".

Usually, the ILS value reported during a mission is different from the ILS Cal Value. The exposure will also be different based on the complex conditions in the field of view. To get a pixel value proportional to reflectance, The pixel must be scaled up or down based on the ratio of the new ILS value to the ILS Calibration Value. Then the pixel must be scaled to reflect the ratio between the ILS Calibration Exposure, and the exposure used to capture the image.

The result of these tranformations will produce images that appear a little dark, since most subjects are less than 50% reflective, but in 16-bit save mode there is more than enough digitizing range to allow accurate calculations based on the results. 16 bit file save format should always be used for images that are adjusted for ILS sensing.