Digital Color Imaging

This paper surveys current technology and research in the area of digital color imaging. In order to establish the background and lay down terminology, fundamental concepts of color perception and measurement are first presented us-ing vector-space notation and terminology. Present-day color recording and reproduction systems are reviewed along with the common mathematical models used for representing these devices. Algorithms for processing color images for display and communication are surveyed, and a forecast of research trends is attempted. An extensive bibliography is provided

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

Evaluation of the color image and video processing chain and visual quality management for consumer systems

With the advent of novel digital display technologies, color processing is increasingly becoming a key aspect in consumer video applications. Today’s state-of-the-art displays require sophisticated color and image reproduction techniques in order to achieve larger screen size, higher luminance and higher resolution than ever before. However, from color science perspective, there are clearly opportunities for improvement in the color reproduction capabilities of various emerging and conventional display technologies. This research seeks to identify potential areas for improvement in color processing in a video processing chain. As part of this research, various processes involved in a typical video processing chain in consumer video applications were reviewed. Several published color and contrast enhancement algorithms were evaluated, and a novel algorithm was developed to enhance color and contrast in images and videos in an effective and coordinated manner. Further, a psychophysical technique was developed and implemented for performing visual evaluation of color image and consumer video quality. Based on the performance analysis and visual experiments involving various algorithms, guidelines were proposed for the development of an effective color and contrast enhancement method for images and video applications. It is hoped that the knowledge gained from this research will help build a better understanding of color processing and color quality management methods in consumer video

High dynamic range display systems

High contrast ratio (CR) enables a display system to faithfully reproduce the real objects. However, achieving high contrast, especially high ambient contrast (ACR), is a challenging task. In this dissertation, two display systems with high CR are discussed: high ACR augmented reality (AR) display and high dynamic range (HDR) display. For an AR display, we improved its ACR by incorporating a tunable transmittance liquid crystal (LC) film. The film has high tunable transmittance range, fast response time, and is fail-safe. To reduce the weight and size of a display system, we proposed a functional reflective polarizer, which can also help people with color vision deficiency. As for the HDR display, we improved all three aspects of the hardware requirements: contrast ratio, color gamut and bit-depth. By stacking two liquid crystal display (LCD) panels together, we have achieved CR over one million to one, 14-bit depth with 5V operation voltage, and pixel-by-pixel local dimming. To widen color gamut, both photoluminescent and electroluminescent quantum dots (QDs) have been investigated. Our analysis shows that with QD approach, it is possible to achieve over 90% of the Rec. 2020 color gamut for a HDR display. Another goal of an HDR display is to achieve the 12-bit perceptual quantizer (PQ) curve covering from 0 to 10,000 nits. Our experimental results indicate that this is difficult with a single LCD panel because of the sluggish response time. To overcome this challenge, we proposed a method to drive the light emitting diode (LED) backlight and the LCD panel simultaneously. Besides relatively fast response time, this approach can also mitigate the imaging noise. Finally yet importantly, we improved the display pipeline by using a HDR gamut mapping approach to display HDR contents adaptively based on display specifications. A psychophysical experiment was conducted to determine the display requirements

Color transformation modeling for printed images using interpolation based on barycentric coordinates

This document is a report on the research of a potentially superior method of color image transformation for producing rapid and accurate printed color output from a digitized color image. The primary objective is to reduce the complexities, inaccuracies, objectionable artifacts, and processing time common to current methods of color modeling. A new method of vector-corrected mathematical modeling combined with improved color space interpolation is studied. This achievement allows for rapid automatic closed-loop color-match calibration between image capture and output devices. Currently, digital image creation or manipulation systems rely on image proof printing which is slow and often of poor color fidelity or proprietary. The ideal system would provide optimum color reproduction fidelity and rapid proof printing at a low cost. Existing systems often rely on mathematical models for image con version for printing. These models are usually a bottleneck in the proofing process and are not accurate enough for many applica tions. Increasing their accuracy rapidly increases processing time to the point of impracticality well before graphic arts quality levels are achieved. A common solution to this problem in larger systems is a massive and tediously generated color look-up table based on actual measured print samples. This method is costly and does not readily accommodate printing process changes such as paper grade or ink color. Attempts to reduce the size of these look-up tables and the large quantity of required sample measurements have been disappointing. In this thesis, new methods will be reported which should allow practical small-system color proof printing with excellent color fidelity and rapid processing. By eliminating common problems associated with color space interpolation, these new methods make closed-loop control practical with a relatively small quantity of sample measurements which can be automatically printed, scanned, and incorporated into conversion processes

Signal detection using pseudocolor scales

Historically, gray scale has been the standard method of displaying univariate medical images. A few color scales have been proposed and evaluated, but have had little acceptance by radiologists. It is possible that carefully desired scales might give lesion detection performance that equals gray scale and improves performance of other tasks. We investigated 13 display scales including the physically linear gray scale, the popular rainbow scale and the other 1 1 perceptually linearized scales. One was the hot body (heated object) scale and the other 10 were spiral trajectories in the CIELAB uniform color space. The experiments were performed using signals added to white noise and a statistically defined (lumpy) background. In general, the best performance was obtained using the gray scale and the hot body scale. Performance for the rainbow scale was very poor ( about 30% of gray scale performance)

Color coding for a facsimile system.

Thesis. 1975. Ph.D.--Massachusetts Institute of Technology. Dept. of Electrical Engineering and Computer Science.Vita.Includes bibliographical references.Ph.D

Computer mediated colour fidelity and communication

Developments in technology have meant that computercontrolled imaging devices are becoming more powerful and more affordable. Despite their increasing prevalence, computer-aided design and desktop publishing software has failed to keep pace, leading to disappointing colour reproduction across different devices. Although there has been a recent drive to incorporate colour management functionality into modern computer systems, in general this is limited in scope and fails to properly consider the way in which colours are perceived. Furthermore, differences in viewing conditions or representation severely impede the communication of colour between groups of users. The approach proposed here is to provide WYSIWYG colour across a range of imaging devices through a combination of existing device characterisation and colour appearance modeling techniques. In addition, to further facilitate colour communication, various common colour notation systems are defined by a series of mathematical mappings. This enables both the implementation of computer-based colour atlases (which have a number of practical advantages over physical specifiers) and also the interrelation of colour represented in hitherto incompatible notations. Together with the proposed solution, details are given of a computer system which has been implemented. The system was used by textile designers for a real task. Prior to undertaking this work, designers were interviewed in order to ascertain where colour played an important role in their work and where it was found to be a problem. A summary of the findings of these interviews together with a survey of existing approaches to the problems of colour fidelity and communication in colour computer systems are also given. As background to this work, the topics of colour science and colour imaging are introduced