The article introduces digital image restoration to the reader who is just beginning in this field, and provides a review and analysis for the reader who may already be well-versed in image restoration. The perspective on the topic is one that comes primarily from work done in the field of signal processing. Thus, many of the techniques and works cited relate to classical signal processing approaches to estimation theory, filtering, and numerical analysis. In particular, the emphasis is placed primarily on digital image restoration algorithms that grow out of an area known as "regularized least squares" methods. It should be noted, however, that digital image restoration is a very broad field, as we discuss, and thus contains many other successful approaches that have been developed from different perspectives, such as optics, astronomy, and medical imaging, just to name a few. In the process of reviewing this topic, we address a number of very important issues in this field that are not typically discussed in the technical literature.

Digital Image Restoration

Developing light-harvesting materials with tunable emission colours has always been at the forefront of colour display technologies. The variation in materials composition, phase and structure can provide a useful tool for producing a wide range of emission colours, but controlling the colour gamut in a material with a fixed composition remains a daunting challenge. Here, we demonstrate a convenient, versatile approach to dynamically fine-tuning emission in the full colour range from a new class of core-shell upconversion nanocrystals by adjusting the pulse width of infrared laser beams. Our mechanistic investigations suggest that the unprecedented colour tunability from these nanocrystals is governed by a non-steady-state upconversion process. These findings provide keen insights into controlling energy transfer in out-of-equilibrium optical processes, while offering the possibility for the construction of true three-dimensional, full-colour display systems with high spatial resolution and locally addressable colour gamut.

Temporal full-colour tuning through non-steady-state upconversion

Defining Color. Describing Color. Measuring Color. Measuring Color Quality. Colorants. Producing Colors. Back to Principles. Appendix. Bibliography. Index.

Billmeyer and Saltzman's Principles of Color Technology

Developments in the theory of image reconstruction and restoration over the past 20 or 30 years are outlined. Particular attention is paid to common estimation structures and to practical problems not properly solved yet. The problem of image reconstruction and restoration is first formulated. Some of the current regularization approaches used to solve the problem are then described. The concepts of a priori information and compound criterion are introduced. A Bayesian interpretation of the regularization techniques is given which clarifies the role of the tuning parameters and indicates how they could be estimated. The practical aspects of computing the solution, first when the hyperparameters are known and second when they must be estimated, are then considered. Conclusions are drawn, and points that still need to be investigated are outlined. >

Image reconstruction and restoration: overview of common estimation structures and problems

Maps depict natural and human-induced changes on earth at a fine resolution for large areas and over long periods of time. In addition, maps—especially historical maps—are often the only information source about the earth as surveyed using geodetic techniques. In order to preserve these unique documents, increasing numbers of digital map archives have been established, driven by advances in software and hardware technologies. Since the early 1980s, researchers from a variety of disciplines, including computer science and geography, have been working on computational methods for the extraction and recognition of geographic features from archived images of maps (digital map processing). The typical result from map processing is geographic information that can be used in spatial and spatiotemporal analyses in a Geographic Information System environment, which benefits numerous research fields in the spatial, social, environmental, and health sciences. However, map processing literature is spread across a broad range of disciplines in which maps are included as a special type of image. This article presents an overview of existing map processing techniques, with the goal of bringing together the past and current research efforts in this interdisciplinary field, to characterize the advances that have been made, and to identify future research directions and opportunities.

A Survey of Digital Map Processing Techniques

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.

Digital Color Imaging

Accurate scanning of a color image, which is absolutely essential for good color reproduction, can ensure that all relevant information about the color stimulus of a signal is obtained. The set of scanning filters is hence an important component of a color reproduction system. In this paper we introduce a measure of the goodness of a set of color-scanning filters. This measure relates the space spanned by the scanning filters to the human visual subspace. The q factor of a single color-scanning filter is shown to be a particular case of the measure. Experimental results are presented to justify the appropriateness of the measure.

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Measure of goodness of a set of color-scanning filters

Blur identification by residual spectral matching

This paper presents measurements and analysis of the impedance of residential power-distribution circuits at frequencies from 5 to 20 kHz. These frequencies are used by systems such as distribution-line carriers which use the power distribution circuit as a communications medium. Residential impedances are determined by the distribution transformer secondary windings, entrance cables, house wiring, and electrical loads. Impedance measurements of these components and measurements at four residences are presented.

Impedance of the Residential Power-Distribution Circuit

A set theoretic approach for the spectral characterization of a color scanner is described These devices usually employ three channels to obtain a device dependent RGB (red, green, blue) im- age To display/print an image, the device dependent RGB values must be correctly transformed to the color space of the target de- vice To determine accurate and efficient transformations for a num- ber of devices, knowledge of the spectral sensitivity of the scanner is essential Direct measurement of the sensitivity requires a set of expensive narrow band reflectances and is often infeasible Meth- ods that estimate the spectral sensitivity based on measurements with typical reflectance samples are therefore of interest Due to the low dimensionality of the space of object reflectance spectra, this is a highly ill-conditioned problem As a result, conventional estimation techniques that fail to take a priori knowledge into account perform rather poorly on this problem A set theoretic approach that incorpo- rates available a priori knowledge into the estimation framework yields better results Results are presented for a simulated scanner characterization problem and for an actual characterization to dem- onstrate the increased accuracy compared with conventional methods © 1996 SPIE and IS&T

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H. Joel Trussell

Papers

Digital Color Imaging

Measure of goodness of a set of color-scanning filters

Blur identification by residual spectral matching

Impedance of the Residential Power-Distribution Circuit

Set theoretic estimation in color scanner characterization