Poorvi L. Vora

Measure of goodness of a set of color-scanning filters

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.

Image capture: simulation of sensor responses from hyperspectral images

This paper describes the design and performance of an image capture simulator. The general model underlying the simulator assumes that the image capture device contains multiple classes of sensors with different spectral sensitivities and that each sensor responds in a known way to irradiance over most of its operating range. The input to the simulator is a set of narrow-band images of the scene taken with a custom-designed hyperspectral camera system. The parameters for the simulator are the number of sensor classes, the sensor spectral sensitivities, the noise statistics and number of quantization levels for each sensor class, the spatial arrangement of the sensors and the exposure duration. The output of the simulator is the raw image data that would have been acquired by the simulated image capture device. To test the simulator, we acquired images of the same scene both with the hyperspectral camera and with a calibrated Kodak DCS-200 digital color camera. We used the simulator to predict the DCS-200 output from the hyperspectral data. The agreement between simulated and acquired images validated the image capture response model and our simulator implementation. We believe the simulator will provide a useful tool for understanding the effect of varying the design parameters of an image capture device.

Mathematical methods for the design of color scanning filters

The problem of the design of color scanning filters is addressed in this paper. The problem is posed within the framework of the vector space approach to color systems. The measure of the goodness of a set of color scanning filters presented in earlier work is used as an optimization criterion to design color scanning filters modeled in terms of known, smooth, nonnegative functions. The best filters are then trimmed using the gradient of the mean square DeltaE(ab) error to obtain filters with a lower value of perceptual error. The results obtained demonstrate the utility of the method.

Protocols for watermark verification

In current digital watermarking schemes used to deter piracy of multimedia content, the owner typically reveals the watermark in the process of establishing piracy. Once revealed, a watermark can be removed. We eliminate this limitation by using cryptographic protocols to demonstrate the presence of a watermark without revealing it.

Remotegrity: design and use of an end-to-end verifiable remote voting system

We propose and implement a cryptographically end-to-end verifiable (E2E) remote voting system for absentee voters and report on its deployment in a binding municipal election in Takoma Park, Maryland. Remotegrity is a hybrid mail/internet extension to the Scantegrity in-person voting system, enabling secure, electronic return of vote-by-mail ballots. It provides voters with the ability to detect unauthorized modifications to their cast ballots made by either malicious client software, or a corrupt election authority--two threats not previously studied in combination. Not only can the voter detect such changes, they can prove it to a third party without giving up ballot secrecy.

Mathematical methods for the analysis of color scanning filters

The problem of the sensitivity analysis of color scanning filters is addressed in this paper. The second differential of the mean square DeltaE(ab) error provides a means of calculating the sensitivity of the mean square DeltaE(ab) error to filter fabrication errors. Tolerances on the allowable change in the mean square DeltaE(ab) error are used to define bounds on the filter fabrication errors at all wavelengths and at single wavelengths.

Distortion bounded authentication techniques

Authentication techniques provide a means of ensuring the integrity of a message. The recent proliferation of multimedia content has led to a need for developing authentication mechanisms. Although, authentication techniques have been studied for many decades, multimedia authentication poses some new challenges. Perhaps the key such challenge being the need to authenticate multimedia content as opposed to its representation. In this paper, we review some of the techniques proposed in the literature for multimedia content authentication. We then propose distortion bounded authentication techniques that give hard guarantees on the amount of distortion that will be tolerated before the multimedia object under consideration is deemed unauthentic. The basic idea behind distortion-bounded authentication is simple. Quantization is performed (in feature space) before authentication, thereby restricting image features in a known and deterministic manner. The same quantization is performed prior to verification. Distortions less than half the quantization step size will not affect the verification process and the content will be deemed authentic. The basic framework is simple and can be applied with many different techniques, distortion measures and feature sets. We give examples of distortion-bound authentication techniques using the L1 and L2 norms in pixel domain.

Comparison of primary and complementary color filters for CCD-based digital photography

This paper presents a comparison between primary (RGB) and complementary (CYMG) CCD color filters arrays, as applied to digital photography. Our analysis is based upon the measured spectral characteristics of the primary and complementary color versions of the Matsushita MN3776 CCD. The important role of the color correction matrix on the quality of the image is considered both in terms of noise and color saturation. Our calculations show that there is a tradeoff between color saturation and ISO speed, when complementary filters are used. Complementary color filters only gain an ISO speed advantage when the color saturation is low. When the color correction matrix is chosen to make the ISO speeds of the two filter systems equivalent, the well capacity of the complementary CCD must be significantly higher because of the higher overall transmission of its color filters. Our comparison includes ISO speed calculations and plots of the color gamut for primary and complementary color filters with various color correction matrices. We conclude that primary color filters are superior for digital photography.

Trade-offs between color saturation and noise sensitivity in image sensors

A color correction matrix is usually used to transform the raw color image obtained from color image sensors to adjust for factors such as variations in illumination and deviations of the actual filter characteristics from the ideal. Color correction matrices that have high condition numbers can greatly amplify noise, while it can be difficult to achieve good color saturation with low condition number matrices. Noise can be a significant problem for digital camera images which have limited bit-depth. We explore the trade-off between noise reduction and color saturation analytically, and using digital camera images. We present an orthonormality criterion to define optimality with respect to noise sensitivity and color saturation in the case of signal-independent, orthogonal sensor measurement noise in each color channel.

An Information-Theoretic Approach to Inference Attacks on Random Data Perturbation and a Related Privacy Measure

Random data perturbation (RDP) has been in use for several years in statistical databases and public surveys as a means of providing privacy to individuals while collecting information on groups, and has recently gained popularity as a privacy technique in data mining. This correspondence provides an information-theoretic framework for all inference attacks on RDP. The framework is used to demonstrate the existence of a tight asymptotic lower bound on the number of queries required per bit of entropy for all inference attacks with zero asymptotic error and bounded average power in the query sequence. A privacy measure based on security against inference attacks is proposed.