A measure is proposed to express the conformance between any pair of greyvalue curves. This may be used to compare a greyvalue curve against a standard. Such a measure may be used to quantify and compare various causes of non-conformance.
"Distances between greyvalue curves", Proc. SPIE 5372, Medical Imaging 2004: Image Perception, Observer Performance, and Technology Assessment, (4 May 2004); doi: 10.1117/12.544731; https://doi.org/10.1117/12.544731