Expanding Dimensionality in Cinema Color: Impacting Observer Metamerism through Multiprimary Display

Television and cinema display are both trending towards greater ranges and saturation of reproduced colors made possible by near-monochromatic RGB illumination technologies. Through current broadcast and digital cinema standards work, system designs employing laser light sources, narrow-band LED, quantum dots and others are being actively endorsed in promotion of Wide Color Gamut (WCG). Despite artistic benefits brought to creative content producers, spectrally selective excitations of naturally different human color response functions exacerbate variability of observer experience. An exaggerated variation in color-sensing is explicitly counter to the exhaustive controls and calibrations employed in modern motion picture pipelines. Further, singular standard observer summaries of human color vision such as found in the CIE’s 1931 and 1964 color matching functions and used extensively in motion picture color management are deficient in recognizing expected human vision variability. Many researchers have confirmed the magnitude of observer metamerism in color matching in both uniform colors and imagery but few have shown explicit color management with an aim of minimized difference in observer perception variability. This research shows that not only can observer metamerism influences be quantitatively predicted and confirmed psychophysically but that intentionally engineered multiprimary displays employing more than three primaries can offer increased color gamut with drastically improved consistency of experience. To this end, a seven-channel prototype display has been constructed based on observer metamerism models and color difference indices derived from the latest color vision demographic research. This display has been further proven in forced-choice paired comparison tests to deliver superior color matching to reference stimuli versus both contemporary standard RGB cinema projection and recently ratified standard laser projection across a large population of color-normal observers

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

An Investigation of Soft Proof to Print Agreement under Bright Surround

Color quality is a vital concern in the printing industry. The ability of an LCD monitor to accurately and consistently predict the color of a printed work is often in doubt. According to Chung (2005), color reproduction technology is different for soft proofing and hard proofing which could lead a layman to believe that the two technologies may not produce the same result. Nevertheless, it is still possible for both reproduction technologies to achieve a metameric match which gives the same perceived color sensation between display and print. ISO/CD 14681 provides guidelines for creating the conditions required to perform soft proofing. This standard builds on ISO 12646 requirements for monitors and introduces a new softproofing environment (lightbooth with integrated monitor) to better meet the needs of industrial users. The ISO 14681 integrated viewing environment removes one important obstacle to achieving print to softproof match, i.e., the problem of simultaneous color contrast inherent in using a dim monitor surround with a bright paper viewing condition for soft proofing. Thus, the first objective of this research was to assess print to softproof visual match in the ISO 14681 integrated viewing environment. Nevertheless, even in this environment, inconsistency between paper white and monitor white remains as the next major obstacle to achieving consistent print to softproof match. Thus, a second objective of this research is to develop a methodology for matching the monitor\u27s white point to the white point of the paper viewed in an ISO 14681 integrated viewing environment. The methodology for fulfilling these objectives began with the creation of the hardware/software environment required to support experimentation. This environment consisted of a 24-inch EIZO CG242W display conforming to ISO 12646 and an integrated viewing environment conforming to the P2 specification in ISO 3664:2009. Two ISO 12647-2 conformed press sheets were prepared and became the reference for the experiment. The researcher next developed a methodology for matching the monitor white point to the white point of the paper under the P2 viewing condition. Finally, a panel of observers was used to compare print to softproof match for four display conditions in a paired comparison experiment. The results of the experiment were highly encouraging. The mismatch between monitor and paper white points, as measured by the sum of the differences in R, G, and B counts between the monitor and the paper, was reduced by nearly 90%. In addition, the paired comparison experiment demonstrated that the use of a custom monitor white point and optimized monitor gamma outperformed the use of standard D65 and D50 white points with the same optimized gamma at a .05 level of significance

Evaluation and improvement of the workflow of digital imaging of fine art reproduction in museums

Fine arts refer to a broad spectrum of art formats, ie~painting, calligraphy, photography, architecture, and so forth. Fine art reproductions are to create surrogates of the original artwork that are able to faithfully deliver the aesthetics and feelings of the original. Traditionally, reproductions of fine art are made in the form of catalogs, postcards or books by museums, libraries, archives, and so on (hereafter called museums for simplicity). With the widespread adoption of digital archiving in museums, more and more artwork is reproduced to be viewed on a display. For example, artwork collections are made available through museum websites and Google Art Project for art lovers to view on their own displays. In the thesis, we study the fine art reproduction of paintings in the form of soft copy viewed on displays by answering four questions: (1) what is the impact of the viewing condition and original on image quality evaluation? (2) can image quality be improved by avoiding visual editing in current workflows of fine art reproduction? (3) can lightweight spectral imaging be used for fine art reproduction? and (4) what is the performance of spectral reproductions compared with reproductions by current workflows? We started with evaluating the perceived image quality of fine art reproduction created by representative museums in the United States under controlled and uncontrolled environments with and without the presence of the original artwork. The experimental results suggest that the image quality is highly correlated with the color accuracy of the reproduction only when the original is present and the reproduction is evaluated on a characterized display. We then examined the workflows to create these reproductions, and found that current workflows rely heavily on visual editing and retouching (global and local color adjustments on the digital reproduction) to improve the color accuracy of the reproduction. Visual editing and retouching can be both time-consuming and subjective in nature (depending on experts\u27 own experience and understanding of the artwork) lowering the efficiency of artwork digitization considerably. We therefore propose to improve the workflow of fine art reproduction by (1) automating the process of visual editing and retouching in current workflows based on RGB acquisition systems and by (2) recovering the spectral reflectance of the painting with off-the-shelf equipment under commonly available lighting conditions. Finally, we studied the perceived image quality of reproductions created by current three-channel (RGB) workflows with those by spectral imaging and those based on an exemplar-based method

A Physiological and Psychometric Evaluation of Human Subconscious Visual Response and Its Application in Health Promoting Lighting.

Subconscious vision is a recent focus of the vision science community, brought on by the discovery of a previously unknown photoreceptor in the retina dedicated to driving non-image-forming responses, intrinsically photosensitive retinal ganglion cells (ipRGCs). In addition to accepting inputs from rod and cone photoreceptors, ipRGCs contain their own photopigment, melanopsin, and are considered true photoreceptors. ipRGCs drive various non-image-forming photoresponses, including circadian photoentrainment, melatonin suppression, and pupil constriction. In order to understand more about ipRGC function in humans, we studied its sensitivity to light stimuli in the evening and day. First, we measured the sensitivity threshold of melatonin suppression at night. Using a protocol that enhances data precision, we have found the threshold for human melatonin suppression to be two orders of magnitude lower than previously reported. This finding has far-reaching implications since there is mounting evidence that nocturnal activation of the circadian system can be harmful. Paradoxically, ipRGCs are understimulated during the day. Optimizing daytime non-image-forming photostimulation has health benefits, such as increased alertness, faster reaction times, better sleep quality, and treatment of depression. In order to enhance ipRGC excitation, we aimed to circumvent adaptation (i.e. desensitization) of the photoresponse by using flickering instead of steady light. We find that properly timed flickering light enhances pupillary light reflex significantly when compared to steady light with 9-fold more energy density. Employing our findings, a new form of LED light is proposed to enhance subconscious visual responses at a typical indoor illuminance level. Using the silent substitution technique, a melanopsin-selective flicker is introduced into the light. A linear optimization algorithm is used to maximize the contrast of the subconscious, melanopsin-based response function while keeping conscious, cone-driven responses to the pulsing light fixed. Additional boundary conditions utilizing test color samples as an environmental mimic are introduced to limit the amount of perceived color change in a simulated environment. Two examples of lights are given to illustrate potential applications for general illumination and therapeutic purposes. For the lighting and electronics industry, we hope our study of subconscious-stimulative thresholds at night will better inform their design guidelines for health conscious products.PhDMacromolecular Science and EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/133226/1/garenv_1.pd

The Effects of Multi-channel Visible Spectrum Imaging on Perceived Spatial Image Quality and Color Reproduction Accuracy

Two paired-comparison psychophysical experiments were performed. The stimuli consisted of six image types resultingfrom several multispectral image-capture and reconstruction techniques. A seventh image type, color-managed images from a high-end consumer camera, was also included in thefirst experiment to compare the accuracy of commercial RGB imaging. The images were evaluated under simulated daylight (6800K) and incandescent (2700K) illumination. The first experiment evaluated color reproduction accuracy. Under simulated daylight, the subjects judged all of the images to have the same color accuracy, except the consumer camera image which was significantly worse. Under incandescent illumination, all the images, including the consumer camera, had equivalent performance. The second experiment evaluated image quality. The results of this experiment were highly target dependent. A subsequent image registration experiment showed that the results of the image quality experiment were affected by image registration to some degree. An analysis of the color reproduction accuracy and image quality experiments combined showed that the consumer camera image type was preferred the least over all. The most preferred image types were the thirty-one-channel image type and both six-channel image types created using RGB filters along with a Wratten filter, with eigenvector analysis and pseudo-inverse transformations

Filter Selection for Spectral Estimation Using a Trichrmatic Camera

Current imaging practices are based on exploiting metamerism to record and reproduce images. As a result, the data obtained in these images are dependent on the viewing conditions and the observer. While these methods produce acceptable results for day to day use, they often do not exhibit the type of accuracy and control required for scientific purposes such as art conservation. As a solution, many research institutions are now advocating the use of multispectral imaging to record the objects fundamental spectral properties to remove the data\u27s dependency on the observer and viewing environment. The research described in this thesis involved determining if a trichromatic camera and readily available filters can be used for spectral estimation purposes. The Pixel Physics TerraPix camera system was characterized, its response to a target and 105 Kodak Wratten Filters under tungsten illumination was simulated, and spectral reflectance estimations were generated. The top filter candidates were chosen based on their simulated performance. These filters were then used in an imaging experiment designed to approximate conditions that would be found in an art gallery or other place where copy work is performed. The results of the imaging experiment were compared with the simulation, and shortcomings of the model were identified. The results of the experiment show that a camera model can be used as a guiding tool to make filter selections for spectral estimation

Accurate Colour Reproduction of Human Face using 3D Printing Technology

The colour of the face is one of the most significant factors in appearance and perception of an individual. With the rapid development of colour 3D printing technology and 3D imaging acquisition techniques, it is possible to achieve skin colour reproduction with the application of colour management. However, due to the complicated skin structure with uneven and non-uniform surface, it is challenging to obtain accurate skin colour appearance and reproduce it faithfully using 3D colour printers. The aim of this study was to improve the colour reproduction accuracy of the human face using 3D printing technology. A workflow of 3D colour image reproduction was developed, including 3D colour image acquisition, 3D model manipulation, colour management, colour 3D printing, postprocessing and colour reproduction evaluation. Most importantly, the colour characterisation methods for the 3D imaging system and the colour 3D printer were comprehensively investigated for achieving higher accuracy

Evaluation and optimal design of spectral sensitivities for digital color imaging

The quality of an image captured by color imaging system primarily depends on three factors: sensor spectral sensitivity, illumination and scene. While illumination is very important to be known, the sensitivity characteristics is critical to the success of imaging applications, and is necessary to be optimally designed under practical constraints. The ultimate image quality is judged subjectively by human visual system. This dissertation addresses the evaluation and optimal design of spectral sensitivity functions for digital color imaging devices. Color imaging fundamentals and device characterization are discussed in the first place. For the evaluation of spectral sensitivity functions, this dissertation concentrates on the consideration of imaging noise characteristics. Both signal-independent and signal-dependent noises form an imaging noise model and noises will be propagated while signal is processed. A new colorimetric quality metric, unified measure of goodness (UMG), which addresses color accuracy and noise performance simultaneously, is introduced and compared with other available quality metrics. Through comparison, UMG is designated as a primary evaluation metric. On the optimal design of spectral sensitivity functions, three generic approaches, optimization through enumeration evaluation, optimization of parameterized functions, and optimization of additional channel, are analyzed in the case of the filter fabrication process is unknown. Otherwise a hierarchical design approach is introduced, which emphasizes the use of the primary metric but the initial optimization results are refined through the application of multiple secondary metrics. Finally the validity of UMG as a primary metric and the hierarchical approach are experimentally tested and verified