Evaluation of the areal material distribution of paper from its optical transmission image J. Takalo, J. Timonen, J. Sampo, S. Siltanen and M. Lassas Eur. Phys. J. Appl. Phys., 55 2 (2011) 20701 Published online: 11 August 2011 DOI: 10.1051/epjap/2011100366