Luminance Levels in Colour Transparencies and Reflexion Prints

The range of luminances perceivable in a projected transparency depends on the range of densities in the slide, the amount of flare in the projector and the amount of stray light on the screen. A survey has shown that a typical luminance range between whites and blacks in projected colour pictures is 2-1 log units. A similar survey for colour reflexion prints showed the range to be only 1-45 log units, because of the limited maximum density perceivable in typical viewing situations. The corresponding ranges of luminosities depend on the luminance levels and adaptation conditions involved. The implications of these facts for obtaining optimum quality in colour transparencies and reflexion prints are discussed.     

Color image sharpening inspired by human vision models

A method to sharpen digital color images that takes viewing conditions and human vision models into consideration is described. The method combines the Laplacian of Gaussian (LoG) operator with spatial filters that approximate the contrast sensitivity functions of human visual systems. The sharpening operation is introduced in the opponent color space, following the scheme proposed in the spatial extension of CIELAB (S-CIELAB). We deduce the modification of the original image necessary to obtain the spatially filtered image that approaches the perceived LoG-sharpened image for given viewing conditions. At short viewing distances, for which the spatial blurring is small, most fine edges and object contours are sharpened. At long distances, for which the spatial blurring is greater, only large figures are sharpened. Because of the smoothing Gaussian functions involved in the LoG operator, the proposed image sharpening does not tend to increase noise. When the sharpening operation is limited to the achromatic channel, the results are good. This is consistent with the high importance attached to the luminance channel in the spatial content of color images. Image sharpening based on only the Laplacian of the original is not sensitive to variations of viewing conditions, tends to increase noise, and suffers from its appearance deteriorating rather quickly with the depth of the sharpening operation.     

Characteristics of composite images in multiview imaging and integral photography

The compositions of images projected to a viewer's eyes from the various viewing regions of the viewing zone formed in one-dimensional integral photography (IP) and multiview imaging (MV) are identified. These compositions indicate that they are made up of pieces from different view images. Comparisons of the composite images with images composited at various regions of imaging space formed by camera arrays for multiview image acquisition reveal that the composite images do not involve any scene folding in the central viewing zone for either MV or IP. However, in the IP case, compositions from neighboring viewing regions aligned in the horizontal direction have reversed disparities, but in the viewing regions between the central and side viewing zones, no reversed disparities are expected. However, MV does exhibit them.     

Analytical estimation of solid angle subtended by complex well-resolved surfaces for infrared detection studies

The solid angle (Omega) subtended by the hot power-plant surfaces of a typical fighter aircraft, on the detector of an infrared (IR) guided missile, is analytically obtained. The use of the parallel rays projection method simplifies the incorporation of the effect of the optical blocking by engine surfaces, on Omega-subtended. This methodology enables the evaluation of the relative contribution of the IR signature from well-resolved distributed sources, and is important for imaging infrared detection studies. The complex 3D surface of a rear fuselage is projected onto an equivalent planar area normal to the viewing aspect, which would give the same Omega-subtended.     

Liquid-crystal-display-based touchable light field three-dimensional display using display-capture mapping calibration

An approach to achieving a light field three-dimensional (3D) display with a large viewing angular range based on spliced multi-LCDs is investigated. The light field reconstruction principle, LCD-based hardware configuration, and diffuser characteristics are analyzed. A point-to-point mapping calibration method is proposed to improve imaging performance, by using an image sensor to capture the coordinate distributions of the images on the LCD panel, projected onto the display space. By measuring the coordinate distributions, calibration is implemented considering both imaging aberration and geometrical inaccuracy of the whole system. The LCD-based experiment demonstrates that this method can achieve not only fast and precise calibration but also easy scalability, flexible depth, and angular range. A touchable floating 3D scene with correct occlusion, high image resolution, and a large continuous viewing angular range can be observed.     

Microscopic imaging through a turbid medium by use of annular objectives for angle gating

We report a new method for microscopic imaging of an object embedded in a turbid medium. The new method is based on the angle-gating mechanism achieved by the use of polarized annular objectives in the illumination and collection paths of a microscopic imaging system. A detailed experimental study is presented of the effects of the size of annular obstructions on image quality when turbid media, including polystyrene microspheres and milk suspensions, are imaged. Images of 22-mum polystyrene microspheres embedded in the turbid media show that misinterpretation can occur when circular objectives are used, because of the detection of mainly multiply scattered photons (i.e., diffusing photons). However, when annular objectives are employed, diffusing photons from a turbid medium can be efficiently suppressed; thus image contrast appears correctly, and image resolution is increased.     

Ion optics of ion microprobe instruments

A general survey of ion optical systems used in the formation of ion microprobes is presented. Various ion guns and their characteristics relevant in this context are reviewed. Probe forming systems in two forms, source imaging and Köhler illumination, are treated, and the limitations to minimum probe diameters due to image aberrations. A chapter on mass separation contains novel material on the combination of lenses with sector fields to give mass separation without energy dispersion. Beam deflectors and deflector/lens combinations are discussed. Finally, secondary signal collection is briefly touched upon.     

Multilayer coatings on glass for painting protection and optimized color rendering

Optical coatings offer a solution to the problem of damage to paintings, caused by ultraviolet and infrared radiation, by cutting radiation wavelengths outside the visible range. Simultaneously, these coatings can enhance an observer's viewing of the paintings by reducing the reflections from ordinary glass panes. All these functions should be performed by the same coating. The design of such a coating, as well as the evaluation of existing products, requires the definition of an appropriate merit function in which coating absorption, high transparency, and color rendering are combined.     

An illumination and highlights invariant colour model for image matching

Abstract

Colour can provide critical information for a variety of computer vision tasks such as image matching, object recognition and image retrieval. However, for it to be useful in practice, the colour model used to represent the intrinsic properties of the imaged objects must be insensitive of imaging conditions such as lighting geometry, illumination colour and highlights. In this paper, we present a colour model for image matching and object recognition that is invariant for illumination and highlights. The colour model is defined as the ratios of the colour differences between neighbouring pixels for each colour component. Based on the dichromatic reflection colour model, it is shown that the proposed colour model is invariant to lighting geometry, illumination colour, highlights and diffuse lighting. Experimental results show robust image matching using the proposed colour model on objects that are illuminated under different illumination colours and lighting geometry. The proposed colour model can be used as a prepossessing step for applications where limited or no constraints on the imaging process can be imposed.     

Bidirectional reflectance of dry and submerged Labsphere Spectralon plaque

We present the bidirectional reflectance of a Labsphere calibration plaque, both dry and submerged in water, at normal illumination. The measurements indicate that when submerged in water, the Labsphere calibration plaque has a higher reflectance value than when dry at viewing angles below 55 degrees . The results are presented in the form of a reflectance factor and are useful for calibrating underwater reflectance measurements.     

Optical design with parametrically defined aspheric surfaces

The standard aspheric surface definition has been used successfully to correct aberrations in a wide variety of systems. However, in some current applications a more general surface definition is needed. We present a more general approach that uses parametrically defined optical surfaces for the optical design of imaging and illumination systems.     

Spatial partially coherent imaging

We introduce the partial coherence response function for describing the behaviour of imaging systems under spatial partially coherent illumination in the centre and the diierence coordinates notation. It involves the impulse response of the system and the spatial coherence properties of the illumination. It is shown that this function is the image cross-spectral density for a Young's pair of pinholes attached at the object plane. Furthermore, the partial coherence response function and the partial coherence transfer function constitute a Fourier pair on which the Fourier representation of partially coherent imaging can be based.     

Development of a real-time stereo TEM

We have developed a real-time stereo transmission electron microscope (TEM) with tilting illumination. This system allows us to observe three-dimensional (3-D) images directly with a video-rate of 1/30 s. The system comprises two electrostatic deflectors. The first, included in the illumination system, is able to illuminate a specimen at two oblique stereoscopic angles (left and right of the optical axis) up to ±2.3 °. The second deflector, in the imaging system, is used to correct the image separation caused by defocusing of the tilted illumination. These deflectors are operated in synchronization with an NTSC video signal output from a CCD camera to record left projections on odd fields and right projections on even fields. The time series of stereo pairs is transferred to a 3-D display that enables viewing of the 3-D images without special glasses. Real-time observation of ZnO particles demonstrated that 3-D images were clear even while moving the specimen. We applied this system to observing dislocations in an Al thin film.     

Effect of partially coherent light on the subjective measurement of ocular astigmatism

Abstract

In this paper, we study the effect of meridional accommodation response of the eye, in the measurement of ocular astigmatism, using different targets (single slit, multiple slit and interference fringes) under different illumination conditions (white light, quasimonochromatic light and partially coherent light) in a subjective optometer. We have found that, under natural illumination conditions (incoherent white light), the accommodation of a subject viewing different orientations of a target varies in a manner that compensates for his or her ocular astigmatism. The compensation effect is minimum when interference fringes are used as targets. We also form interference images of different orientations, directly on the retina of the eye, using the meridional refraction properties of the eye and an optical field that has coherence only along specific meridians. Use of interference images formed directly on the retina yields values of cylinder that compares well with objective measurements obtained using an autorefractor.     

Feature-specific structured imaging

We present a feature-specific imaging system based on the use of structured light. Feature measurements are obtained by projecting spatially structured illumination onto an object and collecting all the reflected light onto a single photodetector. Principal component features are used to define the illumination patterns. The optimal linear minimum mean-square error (LMMSE) operator is used to generate object estimates from the measured features. We study the optimal allocation of illumination energy into each feature measurement in the presence of additive white Gaussian detector noise and optical blur. We demonstrate that this new imaging approach reduces imager complexity and provides improved image quality in high noise environments. Compared to the optimal LMMSE postprocessing of a conventional image, feature-specific structured imaging provides a 38% rms error reduction and requires 400 times fewer measurements for a noise standard deviation of sigma = 2 x 10(-3). Experimental results validate these theoretical predictions.     

Pilot study into optimisation of viewing conditions for electronically displayed images

The increased use of soft-copy reporting introduces new concerns over the effect of viewing conditions on the observer's ability to report images. Owing to their lower luminance, electronic display screens may be more susceptible to poor viewing conditions than conventional viewing boxes and there is the potential for images to be displayed in locations not optimised for viewing radiographs. In the present work, the effects of sub-optimal viewing conditions on the observer's performance for images on an electronic display device are investigated. A test object was used to produce a computed radiography image containing a wide range of grey levels. The image was scored under quasi-ideal and sub-optimal conditions and the effect of changing the viewing conditions on the observer's performance determined. Basic photometric quantities were used to characterise the viewing conditions and the degradation in observer performance related to these quantities. The presence of structured reflection had a significant effect on the observer's ability to discern low-contrast objects. The study demonstrates the need for adequate viewing conditions especially when images are displayed on low luminance devices in sub-optimal conditions.     

Blockchain technology for enhancing swift-trust,collaboration and resilience within a humanitarian supply chain setting

There has been tremendous interest in blockchain technology (BT) (also known as distributed ledger technology) around the globe and across sectors. Following significant success in the financial sector, other sectors, such as humanitarian sector, have started deploying BT at various levels. Although the use of BT in the humanitarian sector is in its infancy, donors and government agencies are increasingly calling for building BT-enabled swift-trust (ST) and more collaborative relationships among various humanitarian actors in order to improve the transparency and traceability of disaster relief materials, information exchanges and flow of funds in disaster relief supply chains. Our study, which is informed by organisational information processing theory and relational view, proposes a theoretical model to understand how BT can influence operational supply chain transparency (OSTC) and ST among actors engaged in disaster relief operations. Our model also shows how BT-enabled ST can further improve collaboration (CO) among actors engaged in disaster relief operations and enhance supply chain resilience (SCR). We formulated and tested six research hypotheses, using data gathered from international non-governmental organisations with the help of the Coordinator for Humanitarian Affairs (OCHA) database. We received 256 usable responses using a pre-tested survey-based instrument designed for key informants. Our results confirm that our six hypotheses were supported. Our study offers significant and valid contributions to the literature on ST, CO and SCR and BT/distributed ledger technology. We have also noted the limitations of our study and have offered future research directions.     

Development of speckle shearing interferometer error analysis as an aperture function of wavefront divergence

Increasing the confidence in whole-field speckle-based optical metrology transducers requires a detailed understanding of the error sources of the respective instruments. The analysis of error contributions to the optical phase output of a Michelson-based speckle shearing interferometer have been modelled. Specific attention has been paid to the effect of the aperture at the image plane, with respect to collimated and non-collimated object illumination. This modelling presents an advance on a previous modelled analytical relationship, which includes partial displacement derivative terms and components as a function of illumination geometries and, importantly, aperture effects. The work has identified a phase error contribution due to the aperture function of between 0.15% and 1.48%, dependent on the object distance, when considering a planar object undergoing predominantly surface to normal deformation.     

Scanning and surface alignment considerations in chemical imaging with desorption electrospray mass spectrometry

The effects of surface scanning mode (raster vs unidirectional scanning) and the constancy of spray tip-to-surface and atmospheric sampling interface capillary-to-surface distances on chemical image quality using desorption electrospray ionization mass spectrometry were investigated. Unidirectional scanning was found to provide a spatially and a quantitatively more precise chemical image of the surface as compared to raster scanning. Maintaining constant spray tip-to-surface and atmospheric sampling interface capillary-to-surface distances during an imaging experiment was found to also be critical. An automation process was implemented using a custom image analysis software (HandsFree Surface Analysis) to keep these distances constant during the surface sampling experiment. Improved chemical image quality afforded through this software control was illustrated by imaging printed objects on normal copy paper.