Data-efficient methods applied to general spectral image capture

Commercialization of spectral imaging for color reproduction will require low bandwidth but highly accurate spectral image acquisition systems. Self-adapting systems are proposed as potential solutions. Such systems perform spectral content analysis on an encountered scene, reacting to the analysis by configuring efficient high quality spectral reconstruction. An experiment is reported comparing scene-derived spectral estimation transforms to static global transforms in multi-channel imaging simulations. For noisefree simulations, the adaptive approach showed clear benefit in terms of colorimetric and spectral statistics. When noise was added, the adaptive method continued to be superior in terms of spectral evaluations, but colorimetric degradation for the adaptive approach exceeded that of the static. This provided additional evidence that spectral reconstruction methods should reference psychometrics as an integral part of spectral error management

Spectral imaging of human portraits and image quality

This dissertation addresses the problem of capturing spectral images for human portraits and evaluating image quality of spectral images. A new spectral imaging approach is proposed in this dissertation for spectral images of human portraits. Thorough statistical analysis is performed for spectral reflectances from various races and different face parts. A spectral imaging system has been designed and calibrated for human portraits. The calibrated imaging system has the ability to represent not only the facial skin but also the spectra of lips, eyes and hair from various races as well. The generated spectral images can be applied to color-imaging system design and analysis. To evaluate the image quality of spectral imaging systems, a visual psychophysical image quality experiment has been performed in this dissertation. The spectral images were simulated based on real spectral imaging system. Meaningful image quality results have been obtained for spectral images generated from different spectral imaging systems. To bridge the gap between the physical measures and subjective visual perceptions of image quality, four image distortion factors were defined. Image quality metrics were obtained and evaluated based statistical analysis and multiple analysis. The image quality metrics have high correlation with subjective assessment for image quality. The image quality contribution of the distortion factors were evaluated. As an extension of the work other researchers in MCSL have initiated, this dissertation research will, working with other researchers in MCSL, put effort to build a publicly accessible database of spectral images, Lippmann2000

Comparison of the accuracy of various transformations from multi-band images to reflectance spectra

This report provides a comparative study of the spectral and colorimetric accuracy of various transformations from multi-band digital signals to spectral reflectance. The multiband channels were obtained by multi-channel visible-spectral imaging (MVSI) using a monochrome CCD and two different filtering systems. In the first system we used a liquid-crystal tunable filter (LCTF) capturing 31 narrow-band channels. We also used a filter wheel with a set of 6 glass filters imaging with and without an extra Wratten absorption filter giving a total of 12 channels. Four different mathematical methods were tested to derive reflectance spectra from digital signals: pseudo-inverse, eigenvector analysis, modified-discrete sine transformation (MDST) and non-negative least squares (NNLS). We also considered two different approaches to sampling the digital signals; in one approach we averaged the digital counts

Validation of a Method to Estimate Skin Spectral Reflectance Using a Digital Camera.

The accurate measurement of skin color and skin spectral reflectance is becoming increasingly desirable due to its application across several domains, including medical, cosmetics, graphic arts, automation, and social science fields. While there exist robust ways to accurately measure color and spectral reflectance, these methods typically require the use of specialized instruments which are often expensive, invasive, and require expert training. Therefore, it would clearly be advantageous to develop methods that can extract accurate colorimetric and spectral data from readily-available, inexpensive digital RGB cameras. Such methodology involves overcoming several fundamental obstacles due to the limitations of RGB camera data. The current paper reviews the importance of accurate skin color and skin spectral reflectance to several domains. The paper continues by describing an existing methodology (i.e., ColourWorker) that overcomes the limitations inherent in using RGB camera data to estimate spectral reflectance. Finally, the paper presents two experiments that test the validity of ColourWorker in estimating skin spectral reflectance. Experiment 1 compares the ground-truth skin spectral reflectance data obtained from a spectroradiometer (taken from the face of volunteers at rest) to spectral reflectance data estimated from an RGB camera using ColourWorker. Experiment 2 compares the ground-truth skin spectral reflectance data obtained from a spectroradiometer (taken from the hand of volunteers with changing physiological states) to spectral reflectance data estimated from an RGB camera using ColourWorker. The results show good performance in ColourWorker’s ability to estimate skin spectral reflectance, and suggest that performance can be improved with careful consideration of reference spectra

Navigating the roadblocks to spectral color reproduction: data-efficient multi-channel imaging and spectral color management

Commercialization of spectral imaging for color reproduction will require the identification and traversal of roadblocks to its success. Among the drawbacks associated with spectral reproduction is a tremendous increase in data capture bandwidth and processing throughput. Methods are proposed for attenuating these increases with data-efficient methods based on adaptive multi-channel visible-spectrum capture and with low-dimensional approaches to spectral color management. First, concepts of adaptive spectral capture are explored. Current spectral imaging approaches require tens of camera channels although previous research has shown that five to nine channels can be sufficient for scenes limited to pre-characterized spectra. New camera systems are proposed and evaluated that incorporate adaptive features reducing capture demands to a similar few channels with the advantage that a priori information about expected scenes is not needed at the time of system design. Second, proposals are made to address problems arising from the significant increase in dimensionality within the image processing stage of a spectral image workflow. An Interim Connection Space (ICS) is proposed as a reduced dimensionality bottleneck in the processing workflow allowing support of spectral color management. In combination these investigations into data-efficient approaches improve two critical points in the spectral reproduction workflow: capture and processing. The progress reported here should help the color reproduction community appreciate that the route to data-efficient multi-channel visible spectrum imaging is passable and can be considered for many imaging modalities

Spectral modeling of a six-color inkjet printer

After customizing an Epson Stylus Photo 1200 by adding a continuous-feed ink system and a cyan, magenta, yellow, black, orange and green ink set, a series of research tasks were carried out to build a full spectral model of the printers output. First, various forward printer models were tested using the fifteen two color combinations of the printer. Yule- Nielsen-spectral-Neugebauer (YNSN) was selected as the forward model and its accuracy tested throughout the colorant space. It was found to be highly accurate, performing as well as a more complex local, cellular version. Next, the performance of nonlinear optimization-routine algorithms were evaluated for their ability to efficiently invert the YNSN model. A quasi-Newton based algorithm designed by Davidon, Fletcher and Powell (DFP) was found to give the best performance when combined with starting values produced from the non-negative least squares fit of single-constant Kubelka- Munk. The accuracy of the inverse model was tested and different optimization objective functions were evaluated. A multistage objective function based on minimizing spectral RMS error and then colorimetric error was found to give highly accurate matches with low metameric potential. Finally, the relationship between the number of printing inks and the ability to eliminate metamerism was explored

Every shade is a light

Künstler_innen stehen zwei grundlegenden Problemen gegenüber, wenn sie die Tonwerte einer natürlichen Szene in ein Gemälde übersetzen wollen. Zuerst müssen sie mit dem Phänomen der Helligkeitskonstanz umgehen, also der Tatsache dass wir Tonwerte nicht objektiv wahrnehmen, sondern diese von unserem visuellen System interpretiert werden, und zweitens müssen sie die den hohen Tonwertumfang komprimieren, sodass dieser auf der Leinwand, dargestellt werden kann. Wenn Künstler_innen eine natürliche Szene abbilden wollen, müssen sie ein Bild schaffen, das dem Bild der natürlichen Szene auf der Netzhaut nahe kommt, damit uns das Bild korrekt erscheint. In Bezug auf Helligkeiten müssen sie die Wirkung der Helligkeitskonstanz unterbinden, entweder, indem sie auf frühe Verarbeitungsstufen des Perzepts zugreifen können, oder indem sie ihre eigenen wahrnemungsgebundenen Fehler in einem zweiten Schritt zu korrigieren vermögen. Tatsächlich ist bekannt, dass Künstler_innen bessere Wahrnehmungsfähigkeiten haben, z.B. schnitten sie besser bei einem Formkonstanz-Test ab (Cohen & Jones, 2008). Wenn Künstler_innen tatsächlich die Wirkung der Helligkeitskonstanz über Prozesse der Wahrnehmung abwenden können, so sollten sie besser darin sein, Helligkeiten objektiv zu beurteilen. Um diese Annahme zu testen, nahmen Testpersonen an einer Aufgabe teil, in welcher sie Helligkeiten beurteilen sollten. Sie mussten entscheiden, welcher von zwei Stimuli einen größeren Unterschied zeigte: einer, der einen tatsächlichem Kontrast beinhaltete oder einer, welcher lediglich die Illusion eines Kontrasts bot. Die Höhe der jeweiligen echten oder illusiorischen Kontraste variierte. Nicht-Künstler_innen (n=11) und Künstler_innen (n=11) zeigten keinen Unterschied in ihren Fähigkeiten der Beurteilung von Helligkeiten. Zusätzlich zeigte sich kein Zusammenhang zwischen der künstlerischen Erfahrung und der Fähigkeit zur Helligkeitenbewertung. Die Ergebnisse weisen nicht daraufhin, dass Künstler_innen die Helligkeitenkonstanz durch spezielle Wahrnehmungsprozesse überwinden können. In einer zweiten Studie präsentiere ich die Strategien zur Helligkeitenkomprimierung einer Gruppe von Maler_innen (n=10). Alle diese Strategien fußen in der selben natürlichen Szene, welche unter den selben Lichtverhältnissen gemalt wurde. Ich zeige ein Modell, welches die umfassenden Helligkeitskomprimierungs- Strategien eines Malers oder einer Malerin veranschaulicht – der “artist’s look-up table” (Graham, 2009). Dieser scheint grundlegende stilistische Komponenten 81 erfassen zu können. Unterscheidliche “artist’s look-up tables” scheinen sich systematisch über verschiedene Techniken hinweg zu unterscheiden (z.B. Aquarell oder Tusche). In dem Maße wie manche Maler_innen oder Gruppen von Gemälden durch eine gewisse Helligkeiten-Komprimierungs-Strategie beschreibbar sind, ist der “artist’s look-up table” ein nützliches Werkzeug in der Stilforschung oder auch in Autor_innenschaftsdebatten.Artists face two major problems when they render luminances from a natural scene onto a painting. First, they have to overcome lightness constancy, i.e. the fact that we don´t perceive luminances objectively but rather “interpret” them, and second, they must compress the high dynamic range luminances so that they fit on the restricted range the canvas presents. When artists render a natural scene, they must create an image, which is close to the retinal image of the scene in order to appear correct to us. In terms of luminances, they must therefore undo lightness constancy, either by accessing early visual processing stages, or by correcting their own perceptual errors in a second step. Indeed we find evidence for better perceptual abilities in artists, like better performance on a shape constancy task (Cohen & Jones, 2008). If artists were able to overcome lightness constancy perceptually, they should also be better at judging luminances objectively. To test this assumption, subjects were involved in a luminance judgment test. They had to choose whether real contrast stimuli or illusory contrast stimuli at varying contrast levels showed greater luminance difference. Non-artists (n=11) and artists (n=11) showed no difference in their luminance judgmental abilities; furthermore, artistic expertise was not correlated to luminance judgmental abilities, suggesting that artists when painting, cannot undo lightness constancy through more accurate perceptual processes. In a second study I present a group of painter´s (n=10) luminance compression strategies, all originating in the same natural scene, which was painted under the same lighting conditions. I show a model that visualizes a given artist´s global luminance compression strategy — the “artist’s look-up table” – which seems to reflect fundamental stylistic components (Graham, 2009). The different “Artist’s look-up tables” appear to vary systematically across different techniques (such as aquarelle or ink painting). To the degree that certain luminance compression strategies are also a fundamental property of a given painter or grouping of paintings, the “Artist’s look-up table” can be a helpful tool in authorship debates and in stylometry

QUEST Hierarchy for Hyperspectral Face Recognition

Face recognition is an attractive biometric due to the ease in which photographs of the human face can be acquired and processed. The non-intrusive ability of many surveillance systems permits face recognition applications to be used in a myriad of environments. Despite decades of impressive research in this area, face recognition still struggles with variations in illumination, pose and expression not to mention the larger challenge of willful circumvention. The integration of supporting contextual information in a fusion hierarchy known as QUalia Exploitation of Sensor Technology (QUEST) is a novel approach for hyperspectral face recognition that results in performance advantages and a robustness not seen in leading face recognition methodologies. This research demonstrates a method for the exploitation of hyperspectral imagery and the intelligent processing of contextual layers of spatial, spectral, and temporal information. This approach illustrates the benefit of integrating spatial and spectral domains of imagery for the automatic extraction and integration of novel soft features (biometric). The establishment of the QUEST methodology for face recognition results in an engineering advantage in both performance and efficiency compared to leading and classical face recognition techniques. An interactive environment for the testing and expansion of this recognition framework is also provided

The influence of the skin colour on the perceived attributes

Skin colour data are important for many applications such as medical, imaging, cosmetics. The present study was aimed to collect a comprehensive skin colour database, and to study the impact of the skin colour on the variety of facial impression attributes. Although many researchers and engineers have collected skin data，few of them studied the skin colours to measure the same locations on a large number of subjects from different ethnic groups using the same colour measuring instruments. As for studying the impact of the skin colour on the visual perceptions, many studies investigated the impact of the skin colour on the attractiveness, health and youth. Limited previous studies investigated the impact of the skin colour on the other impression attributes. The present study was divided into two experiments, Experiments 1 and 2. Experiment 1 was to accumulate the skin colour database, named the Leeds Liverpool skin colour (LLSC). It included skin colours of 188 people from four ethnic groups (Caucasian, Oriental, South Asian and African) and both genders. Three colour measuring methods were used to accumulate the skin colour of each subject’s 10 locations including facial locations (forehead, cheekbone, cheek, nose tip, chin and neck) and body locations (the back of the hand, inner forearm, outer forearm and fingertip). The colour measuring methods included a tele-spectroradiometer (TSR), a spectrophotometer (SP) and a set of skin colour chart used as a visual aid. Also, a characterised digital camera controlled by an imaging system was used to collect facial images. Before the data collection, the short-term repeatability of different settings of the TSR and the SP on measuring human skin colour in vivo was determined. And this was used to settle the measurement protocols of the two instruments. The LLSC database was later used to investigate the skin colour distribution between ethnic groups, between genders, between measuring methods. A skin whiteness and blackness scales based on the CIELAB L* and Cab* scales in CIELAB was developed by referencing the vividness and depth formulae, which was developed by Berns (2000). It was found that these scales and CIELAB hue angle can describe well the property of skin colour of each ethnic group. Experiment 2 was to investigate the impact of the skin colour on the facial impression attributes. Based on the LLSC database, the gamut of skin colour was defined. Twenty-three attributes used to describe facial skin colours were accumulated. They were classified into two groups (appearance and impression). Two experiments were carried out on a monitor to understand the impact of the skin colour on the perceived facial impression attributes. The first experiment (Experiment 2.1) was to study the relationship between different attributes by 10 observers. The results showed that only four dimensions were required to describe skin facial colours, which were named Likeable, Sociable, Feminine and Youth. The health was also selected because the traditional Chinese medicine has interested in it. The second experiment (Experiment 2.2) was to scale facial images selected from two ethnic groups and both genders by using these five impression attributes by 24 Chinese observers. The experimental results showed that there were systematic patterns between the impression attributes and the whiteness and hue angle scales. There are some differences between these images for each impression. The ethnic group had an impact on the judgement, but the difference between the Oriental and Caucasian female images was limited. Finally, mathematical models were successfully developed to predict the impressions from the skin whiteness and hue angle data

Cornell University remote sensing program

Aircraft and satellite remote sensing technology were applied in the following areas: (1) evaluation of proposed fly ash disposal sites; (2) development of priorities for drainage improvements; (3) state park analysis for rehabilitation and development; (4) watershed study for water quality planning; and (5) assistance project-landfill site selection. Results are briefly summarized. Other projects conducted include: (1) assessment of vineyard-related problems; (2) LANDSAT analysis for pheasant range management; (3) photo-historic evaluation of Revolutionary War sites; and (4) thermal analysis of building insulation. The objectives, expected benefits and actions, and status of these projects are described