Diffuse illumination source

Figure 8.1 Schematic representation of NIR chemical imaging instrument operating in diffuse reflectance mode. Radiation from the illumination source interacts with the sample. Light reflected off of the sample is focused onto a NIR sensitive 2D detector after passing through a solid-state tunable wavelength selection filter.

So far, we have mostly assumed that objects are directly illuminated by a light source. But what about shadows In real world scenes, one object may cast a shadow on another object. In this case, the area outside the shadow is directly illuminated, while the shadow area is diffusely illuminated by light that is reflected from other objects in the scene. Thus, for a natural scene containing shadows, we have at least two different illuminants, the light source and the illuminant of the shadow area. In Chapter 7, we have already seen a number of algorithms that can cope with an illuminant that varies smoothly over the image. A shadow, however, may have a sharp boundary. We discuss an algorithm for shadow removal in this chapter. 

As the reflected radiation is emitted from the sample in a random direction, diffusely reflected radiation can be separated from, potentially sensor-blinding, specular reflections. Common techniques are off-angle positioning of the sensor with respect to the position(s) of the illumination source(s) and the use of polarisation filters. Application restrictions apply to optically clear samples with little to no scattering centres, thin samples on an absorbing background and dark samples. In either of these cases, the intensity of radiation diffusely reflected off such samples is frequently insufficient for spectral analysis. While dark objectives remain a problem, thin and/or transparent samples can be measured in transmission or in transflectance. 

Iv) a light source to illuminate the three-phase contact region from behind. It should be equipped with a heat filter to prevent temperature fluctuations and, hence, convection. The light can be either diffuse or collimated, with different effects. Experience has shown that diffuse illumination (5delding a silhouette) is preferable for closed-circuit television (CCTV) imaging, whereas collimated light is suitable for telescope-type measurements. 

In backlighting, the bubble is illuminated by a diffuse light source from one side and its shadow is imaged with a high speed camera. After calibration the... 

In a typical UV-VIS diffuse/directional instrument, the source, generally a tungsten halogen lamp, is placed inside an integrating sphere. The diffuse illuminated sample is imaged onto a slit and then to a polychromator and diode array. By having two sets of sample holders, one with a wedge and one at 0°, both specular-included and specular-excluded measurements can be made. The 0° sample holder ensures that the sample is not illuminated at 0° incidence and is thus specular excluded. A typical accessory for diffuse/ directional measurement of reflectance is shown in Fig. 17. 

The illumination condition of the chart is not directly mentioned as part of the measurement procedure and condition described for the resolution requirement in ISO 16505 2015 but the requirement given under the same standard for sharpness evaluation states to illuminate the chart uniformly by a diffused light source of type D65 and same condition shall be applied. 

So far in this chapter we have considered mode excitation due to a single beam directed at a particular angle to the fiber axis. Let us now consider the effect on mode excitation when the illumination is composed of a family of beams which differ in their angles of incidence at the endface, e.g. the source of diffuse illumination depicted in Fig. 20-6(a). Such sources are known as (partially)... 

The partially diffuse source of Fig. 20-6(a) illuminates a single-mode fiber. We showed in Sections 20-7 and 20-12 that the fundamental mode is most efficiently excited by on-axis beams. Thus, it is intuitive that the more diffuse the source, i.e. the larger 0 , the lower the efficiency of the source in exciting the fundamental mode. To demonstrate this behavior quantitatively, we consider a source with a Gaussian intensity... 

If the quenching of fluorescence occurs at a diffusion-limited rate, then k(t) is given by the Smoluchowski expression [3] (19). Equation (35) is then equivalent to eqn. (31) providing t0 = 0. Pursuing this a little further, even if the illumination of the sample is with a constant intensity source,... 

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