An Application of Multivariate Quality Control to Photographic Processing

Abstract There are a large number (p) of correlated variables to be controlled in a photographic process. Independent control charts for each would lead to a considerable misstatement of the Type I error for the system as a whole. The use of Hotelling's T may involve computational problems if the determinant is near zero. Since this would imply that the rank of the matrix is less than p, k < p linear combinations of the original variates are obtained by the method of principal components. These new variates are used both for short and long range control with some simplifications when the short range procedures are to be handled by production personnel.