Ultraviolet solar-blind cameras are used for inspection and research within the High Voltage domain. The current research in the field is compared with each other, considering image processing and radiometry (energy). From this comparison and research experience, the aspects for the relation between optical and electrical energy are identified. These aspects include Ultraviolet camera selection, characterization, calibration, saturation and processing. Furthermore, the electrical aspects also highlighted are test configurations, partial discharge, atmospheric conditions and test standards. Practical examples are presented.
The technology for the measurement of colour rendering and colour quality is not new, but many parameters related to this issue are currently changing. A number of standard methods were developed and are used by different specialty areas of the lighting industry. CIE 13.3 has been the accepted standard implemented by many users and used for many years. Light-emitting Diode (LED) technology moves at a rapid pace and, as this lighting source finds wider acceptance, it appears that traditional colour-rendering measurement methods produce inconsistent results. Practical application of various types of LEDs yielded results that challenged conventional thinking regarding colour measurement of light sources. Recent studies have shown that the anatomy and physiology of the human eye is more complex than formerly accepted. Therefore, the development of updated measurement methodology also forces a fresh look at functioning and colour perception of the human eye, especially with regard to LEDs. This paper includes a short description of the history and need for the measurement of colour rendering. Some of the traditional measurement methods are presented and inadequacies are discussed. The latest discoveries regarding the functioning of the human eye and the perception of colour, especially when LEDs are used as light sources, are discussed. The unique properties of LEDs when used in practical applications such as luminaires are highlighted.
Most current lens distortion models use only a few terms of Brown's model, which assumes that the radial distortion
is dependant only on the distance from the distortion centre, and an additive tangential distortion can be
used to correct lens de-centering. This paper shows that the characterization of lens distortion can be improved
by over 79% compared to prevailing methods. This is achieved by using modern numerical optimization techniques
such as the Leapfrog algorithm, and sensitivity-normalized parameter scaling to reliably and repeatably
determine more terms for Brown's model. An additional novel feature introduced in this paper is to allow the
distortion to vary not only with polar distance but with the angle too. Two models for radially asymmetrical
distortion (i.e. distortion that is dependant on both polar angle and distance) are discussed, implemented and
contrasted to results obtained when no asymmetry is modelled. A sample of 32 cameras exhibiting extreme
barrel distortion (due to their 6.0mm focal lengths) is used to show that these new techniques can straighten
lines to within 7 hundredths of a pixel RMS over the entire image.
Inverse distortion is used to create an undistorted image from a distorted image. For each pixel in the undistorted
image it is required to determine which pixel in the distorted image should be used. However the process of
characterizing a lens using a model such as that of Brown, yields a non-invertible mapping from the distorted
domain to the undistorted domain. There are three current approaches to solving this: an approximation of the
inverse distortion is derived from a low-order version of Brown's model; an initial guess for the distorted position is
iteratively refined until it yields the desired undistorted pixel position; or a look-up table is generated to store the
mapping. Each approach requires one to sacrifice either accuracy, memory usage or processing time. This paper
shows that it is possible to have real-time, low memory, accurate inverse distortion correction. A novel method
based on the re-use of left-over distortion characterization data is combined with modern numerical optimization
techniques to fit a high-order version of Brown's model to characterize the inverse distortion. Experimental
results show that, for thirty-two 5mm lenses exhibiting extreme barrel distortion, inverse distortion can be
improved 25 fold to 0.013 pixels RMS over the image.
The simulation of infrared imagery forms an integral part of the design and evaluation of infrared systems. HWIL simulations require imagery at frame rates of 100Hz and above. The generation of real-time imagery used to be the domain of graphics super-computers and custom rendering hardware. We investigated the use of a new generation of personal computer graphics accelerators to generate real-time infrared imagery, using OpenGL as the graphics library. The hardware was a NVIDIA GeForce-based graphics accelerator running on a standard Pentium III computer. The graphics accelerator is limited to a color resolution of 8 bits per channel. A technique was investigated to artificially increase this resolution in order to increase the fidelity of the simulation. OpenGL was designed to render images in the visual band. The implementation of the simulation in OpenGL requires the mapping of spectrally variant entities such as atmospheric transmittance to single parameter equivalents. Various combinations of sensor spectral response, source radiance and atmospheric transmittance were investigated to determine the situations under which such a mapping is feasible. A combination of rendering images on the graphics card, and processing the resultant images on the personal computer was investigated to increase the rendering speed and the fidelity of the simulation.
Use of liquid crystal display technology for ocular prosthesis was recently proposed. Liquid crystal light valves are used for the purpose of light modulation to control pupil size proportional to incident light intensity. In the current study two different types of liquid crystal technology are tested for use in a prosthetic eye. The first type is the conventional twisted nematic (TN) cell. The second type of technology is a color dispersion system consisting of liquid crystal droplets in a polymer binder. Because of the principle of operation of the prosthetic device, in the off state the display should block light and appear black. This is easily achieved with TN cells. For the dispersed technology, a colored dispersed system using a black dichroic dye is used so that the display is black in the off state. The response of the two types of technology are measured and compared for ocular prosthesis. Factors such as photostability, battery life, alternate modes of operation, and the use of other types of liquid crystal display technology are also discussed.
For this research the spectral optical characteristics (diffuse spectral reflectance and transmittance) for a number of human teeth were measured in the 250 to 1500 nm region of the electromagnetic spectrum. From the reflectance and transmittance of the dental enamel the spectral absorptance and thus the attenuation coefficient can be determined. The optical characteristics of the human incisor/molar samples were measured with a Hitachi U3400 spectrophotometer and 60 mm (Phi) integrating sphere (IS) attachment, using a photomultiplier tube and PbS detectors. The characteristics of the IS attachment restricted the effective range of wavelengths that could be used to 250 - 1500 nm, which is also the wavelength range of interest. It is clear from the reflectance and transmittance characteristics of dental enamel that absorption is significantly higher in the UV and NIR regions than in the visible, with the attenuation coefficient the highest in the UV region from 250 to approximately 400 nm. The UV wavelengths may therefore prove to be extremely beneficial for laser dental procedures as a result of (1) better absorption, (2) simpler delivery systems than for CO<SUB>2</SUB>, (3) possible germicidal effects at approximately equals 250 nm, (4) higher optical resolution attainable, and (5) reduced stray reflections from the tooth surfaces.
Laser angioplasty as a method of removal of atherosclerotic plaque from arterial walls is still being developed as a reliable medical procedure. Problems encountered are thermal damage to surrounding tissue, perforation of the arterial wall, and identification of the atherosclerotic plaque that is to be removed. This study concentrates on the problem of distinguishing between the atherosclerotic and normal arterial tissue. Spectral optical characteristics, such as reflectance and fluorescence of the atherosclerotic tissue, could provide useful information to be implemented for identification purposes. The total reflected light (specular and diffuse reflectance plus fluorescence) of atherosclerotic arterial tissue and unaffected arterial tissue were measured between the wavelengths of 250 nm and 800 nm, using a double beam spectrophotometer, Hitachi U3400. The results show significant differences between the affected and unaffected aorta samples in the ultraviolet region, especially at the wavelengths 315 nm and 400 nm. These differences can be used as criteria to identify atherosclerotic plaque from normal arterial tissue. An instrument can be developed to be used with laser angioplasty. This instrument can combine the identification and ablation processes by using a 308 nm excimer laser, which emits light close enough to the 315 nm identification criteria and removes atherosclerotic plaque successfully.
Ocular prosthesis requires great skill in craftsmanship and technology to match the appearance of the natural eye for cosmetic reasons. All the effort and cost going into the prosthesis is neutralized by the effect of a fixed pupil size. The possibility of replacing the fixed pupil in the prosthetic eye with a light controlled liquid crystal light valve (LCLV), to match the pupil size of the healthy eye, is discussed.