FOURIER OPTIC CHARACTERIZATION OF PAPER SURFACES

We investigate the possibility of using a Fourier optic method for on- line determination of the quality of paper. A spatial light modulator is used for the incoherent to coherent image conversion that is necess ary since most paper types are opaque. Three different properties are studied, namely crepe frequency, periodicity and amplitude of wire mar ks and surface structure anisotropy, all of them important factors for controlling the production process. The experiments show that it is i ndeed possible to achieve good results in measurements down to an expo sure time of about 1/1000 s. (C) 1997 Society of Photo-Optical Instrum entation Engineers.