Showing papers by "Gaurav Sharma published in 2001"

Digital Color Imaging

Abstract: 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.

Show-through cancellation in scans of duplex printed documents

Abstract: In scanning pages with double-sided printing, often the printing on the back-side shows through in the scan of the front-side because the paper is not completely opaque. This show-through is an undesirable artifact that one would like to remove. In this paper, the phenomenon of show-through is analyzed using first physical principles to obtain a simplified mathematical model. The model is linearized using suitable transformations and simplifying approximations. Based on the linearized model, an adaptive linear filtering scheme is developed for the electronic removal of show-through using scans of both sides of the document. Experimental results demonstrating the effectiveness of the method developed are presented.

A hierarchical image authentication watermark with improved localization and security

Abstract: Several fragile watermarking schemes presented in the literature are either vulnerable to vector quantization (VQ) counterfeiting attacks or sacrifice localization accuracy to improve security. Using a hierarchical structure, we propose a method that thwarts the VQ attack while sustaining the superior localization properties of blockwise independent watermarking methods. In particular, we propose dividing the image into blocks in a multi-level hierarchy and calculating block signatures in this hierarchy. While signatures of small blocks on the lowest level of the hierarchy ensure superior accuracy of tamper localization, higher level block signatures provide increasing resistance to VQ attacks. At the top level, a signature calculated using the whole image completely thwarts the counterfeiting attack. Moreover, "sliding window" searches through the hierarchy enable the verification of untampered regions after an image has been cropped.

Spectrum recovery from colorimetric data for color reproductions

Abstract: Colorimetric data can be readily computed from measured spectral data, however, as illustrated by metameric pairs, the mapping from spectral data to colorimetric values is many-to-one and therefore typically not invertible. In this paper, we investigate inversions of the spectrum-to-colorimetry mapping when the input is constrained to a single color reproduction medium. Under this constraint, accurate recovery of spectral data from colorimetric data is demonstrated for a number of different color reproduction processes. Applications of the spectrum reconstruction process are discussed and demonstrated through examples.

Analysis of feature-based geometry-invariant watermarking

Abstract: In this paper, we present an analysis of feature-based geometry invariant watermarking algorithms. A discussion of the requirements on each building block is followed by potential solutions to meet these requirements. Furthermore, we present theoretical and practical limitations of these solutions via examples. In particular, segmentation based feature point extractors and triangulation based elementary patch formations are evaluated.

Circadian and circannual rhythm of nonfatal pulmonary embolism

Abstract: in Japan. J Pediatr 1996;128:75–81. 9. Fugiware H, Hamashima Y. Pathology of the heart in Kawasaki disease. Pediatrics 1978;61:100–107. 10. Masuda H, Shozawa T, Naoe S, Tanaka N. The intercostal artery in Kawasaki disease. A pathologic 17 autopsy cases. Arch Pathol Lab Med 1986;110:1136– 1142. 11. Takahashi M, Shimada H, Billingham ME, Mason W, Miller JH. Electron microscopic findings of myocardial biopsy correlated with perfusion scan and coronary angiography in chronic Kawasaki syndrome: myocellular ischemia possibly due to microvasculopathy. In: Kato H, ed. Kawasaki Disease. Proceedings of the 5th International Kawasaki Disease Symposium, Fukuoka, Japan, May 22–25, 1995. The Netherlands: Elsevier Science BV, 1995:401–410. 12. Amano S, Hazama F, Hamashima Y. Pathology of Kawasaki disease. II. Distribution and incidence of vascular lesions. Jpn Circ J 1979;43:741–748. 13. Yoshida K, Yoshikawa J, Shakudo M, Akasaka T, Jyo Y, Takao S, Shiratori K, Koizumi K, Okumachi F, Kato H, Fukaya T. Color Doppler evaluation of valvular regurgitation in normal subjects. Circulation 1988;78:840–847. 14. Choong CY, Chir MBB, Abascal VM, Weyman J, Levine RA, Gentile F, Thomas JD, Weyman AE. Prevalence of valvular regurgitation by Doppler echocardiography in patients with structurally normal heart by two-dimensional echocardiography. Am Heart J 1989;117:636–642. 15. Thomson JDR, Allen J, Gibbs JL. Left sided valvar regurgitation in normal children and adolescents. Heart 2000;83:185–187. 16. Gidding SS. Late onset valvular dysfunction in Kawasaki disease. Prog Clin Biol Res 1987;250:305–309.

Systems and methods for halftoning multiple color separation layers by interlayer error diffusion

Abstract: Error diffusion halftoning systems and methods propagate the error both within a color layer and between the color layer being halftoned and subsequent color layers yet to be halftoned. Threshold array halftoning systems and methods diffuse error to subsequent color layers after a color layer has been halftoned using a threshold array. A color continuous tone image is separated into color layers. A plurality of weighting factors are selected that control how error is diffused to subsequent color layers as each color layer is halftoned. A first color layer is halftoned using error diffusion or threshold array halftoning. An error layer is generated from the first halftoned color layer and the first color layer. A modified second continuous tone color layer is generated based on at least one error layer and the corresponding weighting factor. That modified second continuous tone color layer is then halftoned and the process is repeated.

Comparative evaluation of color characterization and gamut of LCD versus CRTs

Abstract: Liquid-crystal-displays (LCDs) and cathode-ray-tubes (CRTs) are compared with regard to color-calibration and color gamut. Applicability of common display calibration models to LCDs and CRTs is experimentally tested. Color-calibration accuracy, ease of calibration, and achievable color gamut are evaluated for the displays. An offset, matrix, and tone-response correction model is found to be suitable for color calibration of LCDs for most applications. The model, however, results in larger calibration error for LCDs than for CRTs, and unlike CRTs a power law tone-response correction is unsuitable for LCDs. A very significant color variation is seen with change in viewing angle for the prototype LCD display employed in the study. The LCD display provides a significantly larger color gamut under typical viewing conditions than CRTs, primarily due to higher luminance.

Crop Weed Competition Study in Onion (Allium cepa L.) under Dry Temperate High Hills Condition of Himachal Pradesh

Abstract: Weed crop competition was studied to determine the critical period in onion (Allium cepa L.) during summer seasons of 1999 and 2000 at the Research Farm of H. P. K. V. Research Sub-Station, Lari (Lahaul and Spiti). Malva parvifora, Poa annua, Chenopodium album, Amaranthus sp., Anagalis arvensis and Melilotus indica were the dominant weed species associated with the crop. Among these M. pamiflora and P. annua were the most predominating weeds. Bulb yield loss increased with the increase in the duration of competition and maximum loss (594.7%) occurred due to full season competition. Significantly highest bulb yield and onion yield contributing characters were obtained in the plots remaining weed-free during the first 60 days after transplanting and resulted in 15.4 tons of onion bulb yield which indicated that the critical period of weed competition was found to be 60 days.

Influence of Resolution on Scanner Noise Perceptibility

Abstract: 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 noise component The system is analyzed to determine the perceived signal-to-noise ratio (SNR) as a function of the measured SNR The findings support the intuition that as resolution is increased a lower measured SNR is acceptable because the eye effectively averages over the pixels at the higher resolution Roughly speaking, the acceptable levels of measured SNR are inversely proportional to the resolution of the scanner The overall impact of increasing resolution in a scanner by changing the sensor while keeping the lamp and the optics fixed is also analyzed in the same framework The analysis indicates that if the signal-dependent component of the noise dominates, the perceived SNR does not degrade with increased resolution, but if signal-independent noise is also significant, the perceived SNR degrades with an increase in resolution

Show-Through Cancellation in Scans of

Abstract: In scanning pages with double-sided printing, often the printing on the back-side shows through in the scan of the front-side because the paper is not completely opaque. This show- through is an undesirable artifact that one would like to remove. In this paper, the phenomenon of show-through is analyzed using first physical principles to obtain a simplified mathematical model. The model is linearized using suitable transformations and simpli- fying approximations. Based on the linearized model, an adaptive linear filtering scheme is developed for the electronic removal of show-through using scans of both sides of the document. Experi- mental results demonstrating the effectiveness of the method de- veloped are presented. Index Terms—Adaptive filtering, restoration, scanning, show- through.