This study reports on research results in the field of powder mixing in a discontinuously operated charge mixer. The mixing time for a confidence interval can be determined from the mixing efficiency that characterizes the mixing of the participating solid components as a function of the mixing time. The mixing efficiency is determined here with the help of an image analysis method developed for these purposes. The particle fraction, that is interesting in terms of its distribution, is partially replaced for this purpose by a similarly behaving but optically well-identifiable tracer material. A dispersion coefficient can be obtained from the analysis of the mixing trial. The practical application of statistics on image analysis is described and discussed along with a description of the possibilities and limitations of the measurement method. The description of the procedure to determine the dispersion coefficient is built on that. Crown Copyright (C) 2009 Published by Elsevier Ltd. All rights reserved.