Keith Knox

Early Manuscripts Electronic Library

An image processing software package called Hoku is available to the public, free-of-charge, for use in recovering erased text from multispectral images of palimpsests. This software was developed by the author for his own use in recovering text, but has been built with an intuitive user interface that makes it suitable for non-technical users. It...

The spectral imaging techniques applied to the so-called “Syriac Galen palimpsest” in 2008-2010 are reported, including examples of results obtained. The imaging methods were adapted from those used on the Archimedes palimpsest during prior years, and are now comparatively elementary relative to methods that have been developed since. These recent...

It is no news to this audience that the past two decades or so have witnessed a dramatic improvement in the technologies of imaging, which have produced new tools for imaging and fostered new, and often unforeseen, applications of the these tools. Less obvious until recently, when newsworthy events have caught people's attention, is the threat to o...

Sparse representation of data has grown rapidly in signal processing. Herein we represent atmospheric turbulence point-spread-functions by training optimal redundant dictionaries from atmospheric turbulence data. Implications for blind-deconvolution of turbulent images are discussed.

Telescope images of astronomical objects and man-made satellites are frequently characterized by high dynamic range and low SNR. We consider the problem of how to enhance these images, with the aim of making them visually useful rather than radiometrically accurate. Standard contrast and histogram adjustment tends to strongly amplify noise in dark...

Intensity Interferometry is a form of imaging developed in the 1950's by Hanbury Brown and Twiss, which gave very early results for estimates of the diameters of stellar discs. It relies on the statistical properties of light to form an image by correlating the electronic signals measured independently and simultaneously at two or more separate col...

During his explorations of Africa, David Livingstone kept a diary and wrote letters about his experiences. Near the end of his travels, he ran out of paper and ink and began recording his thoughts on leftover newspaper with ink made from local seeds. These writings suffer from fading, from interference with the printed text and from bleed through o...

The Archimedes Palimpsest imaging team has developed a spectral imaging system and associated processing techniques for general use with palimpsests and other artifacts. It includes an illumination system of light-emitting diodes (LEDs) in 13 narrow bands from the near ultraviolet through the near infrared (Delta lambda <= 40nm), blue and infrared...

A spectral imaging system comprising a 39-Mpixel monochrome camera, LED-based narrowband illumination, and acquisition/control software has been designed for investigations of cultural heritage objects. Notable attributes of this system, referred to as EurekaVision, include: streamlined workflow, flexibility, provision of well-structured data and m...

A combination of x-ray fluorescence and image processing has been shown to recover text characters written in iron gall ink on parchment, even when obscured by gold paint. Several leaves of the Archimedes Palimpsest were imaged using rapid-scan, x-ray fluorescence imaging performed at the Stanford Synchrotron Radiation Lightsource of the SLAC Natio...

The rotation rates of asteroids can be determined by analyzing the periodic frequencies of time-varying photometric signatures from unresolved images of the asteroid. Due to the random nature of the asteroid, in terms of shape and albedo, a unique period can be determined. Because the various sides of an asteroid are different, the smallest repeat...

The Archimedes Palimpsest is a thousand-year old overwritten parchment manuscript, containing several treatises by Archimedes. Eight hundred years ago, it was erased, overwritten and bound into a prayer book. In the middle of the twentieth century, a few pages were painted over with forged Byzantine icons. Today, a team of imagers, scholars and con...

The Archimedes Palimpsest is a thousand-year old overwritten parchment manuscript, containing several treatises by Archimedes. Eight hundred years ago, it was erased, overwritten and bound into a prayer book. In the middle of the twentieth century, a few pages were painted over with forged Byzantine icons. Today, a team of imagers, scholars and con...

An analysis is presented of the periodic signal received from a rotating cylindrical regular polygon. All N faces of the polygon are assumed to be diffuse reflectors with the same reflectance. The closed-form solution shows that the modulation of the periodic signal falls off as the inverse of the cube of the number of faces.

Modern imaging techniques have been applied to ancient manuscripts to recover writings that are not visible to the naked eye. Over the years, many of these manuscripts have been damaged by the elements or even intentionally erased and re-used to record other information. To successfully recover text from such documents, it is important to under-sta...

In August 2002, the near-Earth Asteroid 2002 NY40, made its closest approach to the Earth. This provided an opportunity to study a near-Earth asteroid with a variety of instruments. Several of the telescopes at the Maui Space Surveillance System were trained at the asteroid and collected adaptive optics images, photometry and spectroscopy. Analysis...

When a pixel has saturated, its value has exceeded the dynamic range of the analog-to-digital converter. All that is recorded is that the value of the individual pixel exceeded the maximum value of the A/D converter. The actual value of the pixel is lost. There is one circumstance, however, in which the pixel value can be recovered, and that is whe...

A handwritten codex often included an inscription that listed facts about its publication, such as the names of the scribe and patron, date of publication, the city where the book was copied, etc. These facts obviously provide essential information to a historian studying the provenance of the codex. Unfortunately, this page was sometimes erased af...

Description: Modern imaging technologies may be applied to the problem of reading "missing" text in manuscripts with historical and cultural significance. This talk describes the various techniques used and results obtained for several documents that have been damaged or degraded by different mechanisms. Among the documents are the Archimedes Palim...

Multispectral imaging techniques are being applied to improve the readability of the text in a tenth-century manuscript that includes seven treatises of Archimedes. The manuscript was erased and overwritten about 200 years later with the text of a Christian prayer book. This talk reports on the results of the multispectral imaging techniques used o...

Many modifications to error diffusion have been proposed to improve the algorithm and to extend its application to print media and to color. In this article, we describe some of the lessons that have been learned in two areas of error-diffusion research: threshold modulation and error stability. Both of these areas are important in understanding ho...

Modern digital imaging techniques have been applied to the recovery of erased and overwritten writings on historical parchment manuscripts. In our work, we have found that images obtained under different illuminations can increase the contrast of erased or faded writings on parchment. This paper focuses on the use of ultraviolet illumination, which...

The perceptibility of scanner noise as a function of resolution is studied using a model for the human visual system and for the scanner noise. The visual system is modeled using a point-wise nonlinearity followed by a lightness contrast-sensitivity-function. The noise model incorporates a signal-dependent noise component and a signal-independent n...

Most present day color scanners, with red, green, and blue filters, are non-colorimetric. This means that their outputs cannot be linearly transformed into CIE tristimulus values for arbitrary input materials. On the other hand, by restricting oneself to a single class of inputs such as photographic, lithographic, or xerographic materials, very acc...

Invisible watermark images can be incorporated in printed halftone images using specially designed halftone screens. The watermark information is embedded into the image by varying the spatial correlation of the halftone texture. The halftone screen with embedded watermarks can be used exactly as a normal halftone screen, so there is no additional...

Invisible watermark images can be incorporated in printed halftone images using specially designed halftone screens. The watermark information is embedded into the image by varying the spatial correlation of the halftone texture. The halftone screen with embedded watermarks can be used exactly as a normal halftone screen, so there is no additional...

A method has been developed to induce symmetric edge enhancement in error diffusion with threshold modulation. The existing threshold modulation algorithm induces edge enhancement by subtracting a term proportional to the input image from the threshold. The edge enhancement that results in asymmetric due to the asymmetric shape of the error diffusi...

As we approach the new millennium, error diffusion is approaching the 25th anniversary of its invention. Because of its exceptionally high image quality, it continues to be a popular choice among digital halftoning algorithms. Over the last 24 years, many attempts have been made to modify and improve the algorithm - to eliminate unwanted textures a...

As we approach the new millenium, error diffusion is approaching the 25th anniversary of its invention. Because of its exceptionally high image quality, it continues to be a popular choice among digital halftoning algorithms. Over the last 24 years, many attempts have been made to modify and improve the algorithm - to eliminate unwanted textures an...

A method has been developed to hide one image inside another with little loss in image quality. If the second image is a logo or watermark, then this method may be used to protect the ownership rights of the first image and to guarantee the authenticity of the image. The two images to be combined may be either black & white or color continuous tone...

Advances in digital imaging technology have presented new opportunities for scholars to better study ancient texts through image clarification and enhancement, Textual material exists over a period of at least 5000 years, written on a great variety of material including leather, clay, stone, papyrus, copper and, of course, paper. Much of the knowle...

The authors explore the current use of modern image processing techniques to decipher ancient texts, and look toward future applications, including “discovering” original texts from overwritten documents.

A method will be shown to incorporate digital watermarks in printed halftone images using stochastic screens. The watermark is not visible to the eye and introduces no loss in image quality. Although it cannot be seen, the watermark can be extracted at a later time with post processing. Watermarks of high contrast are incorporated in the image by v...

Halftone calibration of a black and white printer is a known process that involves printing and measuring patches for many different halftone levels. It is a tedious process that has to be repeated for every halftone dot or algorithm to be used. A new calibration procedure is described that uses a halftone-independent characterization of the printe...

We describe a system which automatically annotates images with a set of prespecified keywords, based on supervised color classification of pixels intoNprespecified classes using simple pixelwise operations. The conditional distribution of the chrominance components of pixels belonging to each class is modeled by a two-dimensional Gaussian function,...

We present an approach to the annotation of natural scene images that used a simple color segmenter to indicate the presence of skin, sky and grass in an image. The results of the color based segmentation are then used to determine higher level description of images as 'People' or 'Outdoors'. The images are analyzed in a luminance-chrominance color...

Threshold modulation has been shown to produce strong effects in error diffusion images. In particular a threshold modulation that is proportional to the input image induces edge enhancement in the output error diffused image. In this paper, examples are shown for image- dependent threshold modulation incorporated into error diffusion implemented o...

Error diffusion has proven to be a very powerful method of producing binary images that are visually similar to the original grayscale images. It has become so popular that many attempts have been made to improve it. In this paper, two modifications to error diffusion, the serpentine raster and threshold modulation, are analyzed from a theoretical...

A theoretical analysis of threshold modulation in error diffusion is given. It is shown that spatial modulation of the threshold is mathematically identical to processing an equivalent input image with the standard error diffusion algorithm. The equivalent input is the sum of the original image with a high-pass-filtered version of the threshold spa...

This paper describes an under-compensated error diffusion algorithm that is intended for multi-level printing and copying. The new error diffusion algorithm is based on the fact that error calculations and feedback are less important in multi-level systems than in bi-level systems.

The concept of an error image is defined for the error diffusion algorithm. Ordinarily hidden from view, the error image is a visual representation of the internally generated errors from which the algorithm derives its name. In this paper, it is shown that the error image contains a linear component of the input image, which induces edge enhanceme...

Error diffusion is a popular algorithm for the binarization of continuous-tone images. A modification of the error-diffusion algorithm is shown that introduces an input-dependent threshold into the process. This modification establishes a fast and efficient way to increase or decrease edge enhancement in the algorithm.

A recently developed mathematical analysis of error diffusion by Weissbach et al. ¹ describes the output spectrum of the error diffusion algorithm in terms of a linear filter equation. Their analysis showed that the output spectrum is given by the sum of the input spectrum and a high-pass filtered error spectrum. This analysis has been extended to...

The error diffusion algorithm proposed by Floyd and Steinberg for the binarization of continuous tone input exhibits an inherent edge enhancement. An explanation for this enhancement is given and a way to increase or decrease the enhancement inside the error diffusion algorithm is demonstrated.

A technique has recently been proposed for processing astronomical photographs to remove the effects of turbulence. The method involves averaging over many short-exposure photographs of an object to reconstruct a diffraction-limited image of the object. A two-dimensional computer simulation of the reconstruction technique is presented. The results...

The theory underlying the technique proposed previously by Knox and Thompson (1974) for recovering near diffraction-limited images of arbitrarily shaped stellar objects degraded by atmospheric seeing is discussed. The proposed digital processing technique is intended for determining the phase of the object transform up to the diffraction limit of t...

The possibility is shown that the phase of an object transform can be determined from the autocorrelation of the image transform. The two together should give a diffraction-limited image of the object. A thereon based technique for the recovery of images from atmospherically degraded short-exposure photographs is proposed. Results from a one-dimens...

An explicit relation for exponential diffuser-transmittance power spectrum is derived in terms of the diffuser-surface statistics. Although closed-form solutions are not generally possible, some insight into the relations follows from expressions that are developed for zero-order energy and the mean-square spread of the spectrum. Known relations fo...

Short-exposure images of stars and other unresolved objects appear as speckle patterns that randomly move across the image. These random patterns and motion are induced by an accumulated random phase disturbance caused by the light traveling through the time-varying atmosphere. Larger phase disturbances are responsible for the random motion of the...

Time-resolved photometric measurements provide a means of constraining the attitude and/or shape of on-orbit objects that are too small or distant to be imaged by ground-based optical or radar facilities. At the most general level, a detailed inversion of photometric data to determine attitude and shape entails the solution of a multivariate numeri...

The Archimedes Palimpsest is a 10 th -century parchment manuscript that was erased in the 13 th century and overwritten with a Christian prayer book. The Walters Art Museum in Baltimore, MD, USA has supervised a ten-year collaboration by conservators, imaging scientists, and scholars to image and transcribe the original writings. This paper reports...