Reading under papyrus and paper using dynamic speckle

N. L. CAP; H. J. RABAL, ; M. TRIVI; L. BUFFARINI; E. E. GRUMEL

Pucon

Congreso; IX Reunión Iberoamericana de Óptica y XII Reunión Iberoamericana de Óptica, Láseres y Aplicaciones (RIAO/OPTILAS),; 2016

Red Iberoamericana de Optica

When paper is slightly heated its coherent images show dynamic speckle. This phenomenon is affected when paper is written, even in the non illuminated surface. Activity is lower in dark regions. This effect was first discovered and studied by other authors and the effect of multiple paper layers in the deterioration of read edges by us. A similar effect permits the detection of subsurface topography under drying paint.We explore the cooling of stacked strips of papyrus and paper tape after very slightly heating it with an incandescent lamp for one minute. Low power He Ne laser light is used for the illumination and stacks of images are registered by a CCD camera for digital processing.Dynamic speckle images of the surface diminish the activity during cooling. Activity is measured by using Tsallis non extensive q entropy for different q values. Plots of q entropy as a function of time show how activity diminishes during cooling to achieve a final equilibrium. They show an initial steep decrease in the first steps and a continuous evolution to equilibrium similar to that found in drying of paint. Experiment shows that few frames are required to estimate the activity. Inked regions both absorb and emit heat in a different proportion, thus permitting differential detection.We show experimental results obtained using different activity descriptors to their adding of a hidden word under a papyrus layer and the same covered by paper tape. Dark ink letters are clearly read in both cases. Also, we shoiw an example of a hidden word covered by a liquid paper? corrector fluid layer.