Page 39 [39]
OCR
CHARISM A I 7 a — Pigment-binder effects It has been established that the luminescence of materials, such as organic binders or colorants found in painted surfaces are generally severely affected by the presence of absorbing non-fluorescing materials, such as inorganic pigments.“*° The effect, also known as the “pigment-binder interaction”, is represented schematically in Figure 1-24, which shows pigment particles (black ovals) homogeneously dispersed in a binding medium (light and dark grey circles). The luminescence produced by the organic binding medium by radiation entering the painted surface, can be: (a) Emitted without further modification; (b) Absorbed and re-emitted by binder particles; (c) Interact with the surrounding pigmented particles and undergo scattering and absorption phenomena. & Fee “= e e 2 @ 9 e = e. e Figure 1-24. Schematic model for the propagation of luminescence from the organic binding medium in a paint layer. Luminescence can: (a) be emitted without further modification; (b) be absorbed and re-emitted by binder particles; or (c) interact with the surrounding pigmented particles and undergo scattering and absorption phenomena.? As a result the true emissions, corresponding to the presence of materials which exhibit luminescent properties as in Figure 1-24(a), will be compromised by emissions arising from the interactions among luminescent materials and surrounding non-fluorescent materials, as in Figure 1-24 (b-c). The luminescence captured in the image will be a superposition of all these emissions, leading to an inaccurate record of the luminescence properties of the Surface. Post-processing methodologies can be applied in order to decouple the various contributions to the luminescence recorded in the image. The correction uses a mathematical model based on the Kulbelka-Munk theory “®’*’’“® and essentially consists of dividing the luminescence image by a function (y), which expresses the extent to which the pigment particles absorb the radiation emitted by the luminescent materials (see Appendix 1 and references therein for more detail). Version No. 1.0 31 Date : 14/10/2013
