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Radiation Transport Simulation
Published in Harry E. Martz, Clint M. Logan, Daniel J. Schneberk, Peter J. Shull, X-Ray Imaging, 2016
Harry E. Martz, Clint M. Logan, Daniel J. Schneberk, Peter J. Shull
The scintillator in this flat-panel photodiode array detector system is only 1.4% of the electron density of the total detector assembly. So, about 99% of the photon interactions occurring in the flat-panel photodiode array detector take place somewhere other than in the scintillator. Further, the flat-panel mass is distributed over 37 mm thickness, causing scattered photons to deposit energy in the scintillator several centimeters from their original primary path. This causes an extreme form of blurring. In visible-light optics, the term veiling glare is applied to stray light at an image plane. This term has been adopted to describe a similar effect in image intensifiers (Seibert et al. 1985). Flat-panel photodiode array detectors have similar characteristics.
Optical Design and Aberrations
Published in Daniel Malacara-Hernández, Brian J. Thompson, Fundamentals and Basic Optical Instruments, 2017
Armando Gómez-Vieyra, Daniel Malacara-Hernández
Veiling glare occurs when object field point rays and rays from objects outside the geometrical field of view of the optical system strike a lens surface and are thereby scattered into the optical system. Veiling glare produces a diffuse background haze on the image plane, resulting primarily in a loss of overall image contrast.
Veiling glare
Published in Tom L. Williams, The Optical Transfer Function of Imaging Systems, 2018
There are several ways in which veiling glare is produced. The most common of these are as follows. Multiple reflections between the optical elements of a lens system; in this case some of the light passing through the optical system gets reflected back from each optical surface and then forward again by the surfaces that precede it in the normal light path. This is illustrated in figure 11.1. The light reflected onto the image plane in this way will usually be out of focus and will generate a background light level that reduces image contrast. Veiling glare from this source is reduced by putting antireflection coatings on the optical surfaces. The more efficient the coatings the less the reflected light and the lower the glare levels. Scatter from optical surfaces; some of the light incident on an optical surface will be scattered forward to the image plane to produce veiling glare. The scatter can be produced by poorly polished surfaces, by defects such as scratches, by the antireflection coatings on the surfaces and by dust and dirt. The production of glare by scatter is illustrated in figure 11.2Reflection from the detector in the image plane; most types of detector used in the image plane of an optical system (e.g. a photographic emulsion, or a CCD detector array) will reflect some of the incident light. A portion of this light will come back onto the detector as veiling glare, either by reflection from the optical surfaces or by reflection from the internal body of the device. This is illustrated in figure 11.3. To reduce this source of glare one needs to reduce the surface reflectivity of the detector and that of the body of the device as well as that of the optical surfaces. Reflections from mechanical parts of the imaging system and from edges of optical components; veiling glare in this case usually comes from reflection of light off the lens barrel, or off stops or iris diaphragms. It is also possible to get light reflected off the edges of lenses, mirrors or prisms. Figure 11.4 illustrates how veiling glare arises in such cases.
Single image veiling glare removal
Published in Journal of Modern Optics, 2018
Zheng Zhang, Huajun Feng, Zhihai Xu, Qi Li, Yueting Chen
Glare can be broadly classified into two categories: reflected glare and scattered glare. Reflected glare is caused by Fresnel reflections at the air-glass interface of the lens and can be further divided into aperture ghosting and lens flare. Aperture ghosting is the aperture-shaped ghost occurs along the direction of the direct light and lens flare is the bright surrounding of the light source. As shown in Figure 1, the second ray and the fourth ray results in the lens flare around the light source and the aperture ghosting along the lighting direction. Scattered glare, which is also named veiling glare, is caused due to the scattering of light in the lens. The third ray in Figure 1(b) presents the diffusion of light in the lens, which results in a foggy appearance in Figure 1(a). In general, the glare occurs quite close to the principal point of the lens, which means that the glare light projected on the sensor is out of focus and varies gently in space.