  Several devices for substrate texture detection based on diffractive optics,
for paper, textiles and non-wovens have been proposed in the past for direct
inspection during the production processes. In spite of the presence of devices
totally based on image processing, the use of diffractive optics cannot be
considered surpassed for many reasons. Compared with image processing
procedures, it is less sensitive to vibrations and does not suffer from the
presence of ambient light. Based on transmitted light, it can give information
on changes in refractive indexes, thickness variation and surface conditions.
We study the use of optical Fourier spectrum to identify textures of polymer
films. As the power spectrum reveals, the texture is seldom homogeneous. Here
we report investigation on several substrates and on thin ink coatings on
substrate. Role of bulk and surface conditions is analysed.
